IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME...

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IDAHO DEPARTMENT OF FISH AND GAME FISHERY MANAGEMENT ANNUAL REPORT Virgil Moore, Director October 2018 IDFG 18-103 PANHANDLE REGION 2015 Rob Ryan, Regional Fishery Biologist Carson Watkins, Regional Fishery Biologist Andy Dux, Regional Fishery Manager Kenneth Bouwens, Regional Fishery Biologist Dan Kaus, Fishery Technician Elizabeth Ng, University of Idaho

Transcript of IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME...

Page 1: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

IDAHO DEPARTMENT OF FISH AND GAME FISHERY MANAGEMENT ANNUAL REPORT

Virgil Moore, Director

October 2018 IDFG 18-103

PANHANDLE REGION 2015

Rob Ryan, Regional Fishery Biologist Carson Watkins, Regional Fishery Biologist

Andy Dux, Regional Fishery Manager Kenneth Bouwens, Regional Fishery Biologist

Dan Kaus, Fishery Technician Elizabeth Ng, University of Idaho

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TABLE OF CONTENTS

POPULATION CHARACTERISTICS AND EXPLOITATION OF LARGEMOUTH BASS IN NORTH IDAHO LAKES .................................................................................................... 1

ABSTRACT ................................................................................................................................. 1 INTRODUCTION ........................................................................................................................ 2 OBJECTIVES ............................................................................................................................. 3 STUDY AREA ............................................................................................................................. 3 METHODS .................................................................................................................................. 4

Fish Sampling and Hard Structure Processing ......................................................................... 4 Data analysis ........................................................................................................................... 4

RESULTS ................................................................................................................................... 5 DISCUSSION.............................................................................................................................. 6 MANAGEMENT RECOMMENDATIONS ..................................................................................... 7 BULL TROUT REDD COUNTS ................................................................................................. 14 ABSTRACT ............................................................................................................................... 14 INTRODUCTION ...................................................................................................................... 15 STUDY SITES .......................................................................................................................... 15 METHODS ................................................................................................................................ 15 RESULTS AND DISCUSSION .................................................................................................. 15

Pend Oreille Core Area .......................................................................................................... 15 Priest Lake Core Area ............................................................................................................ 16 St Joe Core Area ................................................................................................................... 16 North Fork Clearwater Core Area (Little North Fork Clearwater River) ................................... 16 Kootenai River Core Area ...................................................................................................... 16

MANAGEMENT RECOMMENDATIONS ................................................................................... 17 PRIEST LAKE FISHERY INVESTIGATIONS ............................................................................ 23 ABSTRACT ............................................................................................................................... 23 INTRODUCTION ...................................................................................................................... 24 METHODS ................................................................................................................................ 24

Kokanee Monitoring ............................................................................................................... 24 RESULTS ................................................................................................................................. 26

Kokanee Monitoring ............................................................................................................... 26 Discussion ................................................................................................................................ 26

Kokanee Monitoring ............................................................................................................... 26 RECOMMENDATIONS ............................................................................................................. 27 UPPER PRIEST LAKE – LAKE TROUT MANAGEMENT ......................................................... 33 ABSTRACT ............................................................................................................................... 33 INTRODUCTION ...................................................................................................................... 34 OBJECTIVES ........................................................................................................................... 34 STUDY SITE ............................................................................................................................. 34 METHODS ................................................................................................................................ 35 RESULTS ................................................................................................................................. 36

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DISCUSSION............................................................................................................................ 36 RECOMMENDATIONS ............................................................................................................. 37 AN EVALUATION OF BAROTRAUMA-RELATED MORTALITY ON HOOK-AND-LINE

CAUGHT LAKE TROUT ...................................................................................................... 41 ABSTRACT ............................................................................................................................... 41 INTRODUCTION ...................................................................................................................... 42 METHODS ................................................................................................................................ 42 RESULTS ................................................................................................................................. 43 DISCUSSION............................................................................................................................ 44 RECOMMENDATIONS ............................................................................................................. 46 HUGHES MEADOW FISHERIES INVENTORY ........................................................................ 52 ABSTRACT ............................................................................................................................... 52 INTRODUCTION ...................................................................................................................... 53 METHODS ................................................................................................................................ 53 RESULTS ................................................................................................................................. 54 DISCUSSION............................................................................................................................ 54 RECOMMENDATIONS ............................................................................................................. 55 HAYDEN AND PRIEST LAKE MYSID SURVEYS ..................................................................... 58 ABSTRACT ............................................................................................................................... 58 INTRODUCTION ...................................................................................................................... 59 METHODS ................................................................................................................................ 59 RESULTS ................................................................................................................................. 59 DISCUSSION............................................................................................................................ 60 RECOMMENDATIONS ............................................................................................................. 60 SPOKANE BASIN WILD TROUT MONITORING ...................................................................... 64 ABSTRACT ............................................................................................................................... 64 INTRODUCTION ...................................................................................................................... 65 OBJECTIVES ........................................................................................................................... 66 STUDY AREA ........................................................................................................................... 66 METHODS ................................................................................................................................ 66 RESULTS ................................................................................................................................. 67

North Fork Coeur d’Alene River ............................................................................................. 67 St. Joe River .......................................................................................................................... 68

DISCUSSION............................................................................................................................ 68 MANAGEMENT RECOMMENDATIONS ................................................................................... 70 LITTLE NORTH FORK CLEARWATER RIVER FISHERY EVALUATION ................................. 78 ABSTRACT ............................................................................................................................... 78 INTRODUCTION ...................................................................................................................... 79 OBJECTIVES ........................................................................................................................... 79 STUDY AREA ........................................................................................................................... 79 METHODS ................................................................................................................................ 80

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Fish Assemblage Monitoring .................................................................................................. 80 Exploitation and Harvest Patterns of Wild Trout ..................................................................... 81

RESULTS ................................................................................................................................. 81 Fish Assemblage Monitoring .................................................................................................. 81 Exploitation and Harvest Patterns of Wild Trout ..................................................................... 82

DISCUSSION............................................................................................................................ 82 MANAGEMENT RECOMMENDATIONS ................................................................................... 83 LAKE COEUR D’ALENE CHINOOK SALMON EVALUATIONS ................................................ 87 ABSTRACT ............................................................................................................................... 87 INTRODUCTION ...................................................................................................................... 88 OBJECTIVES ........................................................................................................................... 90 STUDY AREA ........................................................................................................................... 90 METHODS ................................................................................................................................ 90

Spawner abundance .............................................................................................................. 90 Performance of supplemental Chinook Salmon...................................................................... 91

RESULTS ................................................................................................................................. 91 DISCUSSION............................................................................................................................ 91 MANAGEMENT RECOMMENDATIONS ................................................................................... 93 LAKE COEUR D’ALENE AND SPIRIT LAKE KOKANEE EVALUATIONS ................................ 97 ABSTRACT ............................................................................................................................... 97 INTRODUCTION ...................................................................................................................... 98 OBJECTIVES ........................................................................................................................... 99 STUDY AREA ........................................................................................................................... 99

Lake Coeur d’Alene ............................................................................................................... 99 Spirit Lake .............................................................................................................................. 99

METHODS .............................................................................................................................. 100 Fish sampling and hard structure processing ....................................................................... 100 Data Analysis ....................................................................................................................... 101

RESULTS ............................................................................................................................... 101 Lake Coeur d’Alene ............................................................................................................. 101

Population monitoring ........................................................................................................ 101 Spawner assessment ........................................................................................................ 102

Spirit Lake ............................................................................................................................ 102 Population monitoring ........................................................................................................ 102

DISCUSSION.......................................................................................................................... 102 Lake Coeur d’Alene ............................................................................................................. 102 Spirit Lake ............................................................................................................................ 103

MANAGEMENT RECOMMENDATIONS ................................................................................. 103 Windy Bay Northern Pike Management .................................................................................. 117 ABSTRACT ............................................................................................................................. 117 INTRODUCTION .................................................................................................................... 118 OBJECTIVES ......................................................................................................................... 120 STUDY AREA ......................................................................................................................... 120

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METHODS .............................................................................................................................. 120 RESULTS ............................................................................................................................... 121 DISCUSSION.......................................................................................................................... 122 MANAGEMENT RECOMMENDATIONS ................................................................................. 123 NORTHERN PIKE ANGLER EXPLOITATION ........................................................................ 129 ABSTRACT ............................................................................................................................. 129 INTRODUCTION .................................................................................................................... 130 OBJECTIVE ............................................................................................................................ 130 METHODS .............................................................................................................................. 130 RESULTS ............................................................................................................................... 131 DISCUSSION.......................................................................................................................... 132 MANAGEMENT RECOMMENDATIONS ................................................................................. 133 HATCHERY TROUT STOCKING EVALUATIONS .................................................................. 138 ABSTRACT ............................................................................................................................. 138 INTRODUCTION .................................................................................................................... 139 OBJECTIVEs .......................................................................................................................... 140 METHODS .............................................................................................................................. 140

Fingerling Trout Evaluations................................................................................................. 140 Catchable Rainbow Trout Evaluations ................................................................................. 142

RESULTS ............................................................................................................................... 142 Hayden Lake ........................................................................................................................ 142 Cocolalla Lake ..................................................................................................................... 142 Avondale Lake ..................................................................................................................... 143 Freeman Lake ...................................................................................................................... 143 Crystal Lake ......................................................................................................................... 143

DISCUSSION.......................................................................................................................... 144 Hayden Lake ........................................................................................................................ 144 Cocolalla Lake ..................................................................................................................... 144 Avondale Lake ..................................................................................................................... 145 Freeman Lake ...................................................................................................................... 145 Crystal Lake ......................................................................................................................... 146

RECOMMENDATIONs ........................................................................................................... 146 REGIONAL LOWLAND LAKE INVESTIGATIONS .................................................................. 153 ABSTRACT ............................................................................................................................. 153

Brush Lake ........................................................................................................................... 153 McArthur Lake...................................................................................................................... 153 Avondale Lake ..................................................................................................................... 154

INTRODUCTION .................................................................................................................... 155 Brush Lake ........................................................................................................................... 155 McArthur Lake...................................................................................................................... 155 Avondale Lake ..................................................................................................................... 156

METHODS .............................................................................................................................. 156 RESULTS ............................................................................................................................... 157

Brush Lake ........................................................................................................................... 157

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McArthur Lake...................................................................................................................... 158 Avondale Lake ..................................................................................................................... 159

DISCUSSION.......................................................................................................................... 159 Brush Lake ........................................................................................................................... 159 McArthur Lake...................................................................................................................... 161 Avondale Lake ..................................................................................................................... 161

RECOMMENDATIONS ........................................................................................................... 161 ALPINE LAKE FISHERY EVALUATIONS ............................................................................... 177 ABSTRACT ............................................................................................................................. 177 INTRODUCTION .................................................................................................................... 178 OBJECTIVES ......................................................................................................................... 179 STUDY AREA ......................................................................................................................... 180 METHODS .............................................................................................................................. 180 RESULTS ............................................................................................................................... 181 DISCUSSION.......................................................................................................................... 182 MANAGEMENT RECOMMENDATIONS ................................................................................. 183 LITERATURE CITED .............................................................................................................. 193

LIST OF TABLES

Table 1. Sample size (n), mean catch-per-unit-effort (CPUE = fish/minute of electrofishing), total length (mm; Minimum–Maximum [Min–Max]) statistics, proportional size distribution (PSD), total annual mortality (A), recruitment coefficient of determination (RCD), recruitment variability index (RVI), and annual angler exploitation (µ) for Largemouth Bass populations sampled from lakes in northern Idaho (2014–2015). Numbers in parentheses represent one standard error of the mean. ................................... 8

Table 2. Fishes sampled from lakes in north Idaho as part of Largemouth Bass population assessment during 2014–2015. Taxa indicated include Brown Bullhead (BBH), Black Crappie (BCR), Bluegill (BLG), Brook Trout (BKT), Channel Catfish (CAT), Green Sunfish (GSN), Largemouth Bass (LMB), Longnose Sucker (LNS), Largescale Sucker (LSS), Northern Pike (NPK), Pumpkinseed (PKS), Rainbow Trout (RBT), Smallmouth Bass (SMB), Tench (TNC), Westslope Cutthroat Trout (WCT), and Yellow Perch (YLP). ......... 9

Table 3. Bull Trout redd counts by year from tributaries of Lake Pend Oreille, Clark Fork River, and Pend Oreille River, Idaho. ......................................................... 18

Table 4. Bull Trout redd counts by year from the Upper Priest River, Idaho and selected tributaries between 1993 and 2015. Redd surveys were not completed on all stream reaches in all years between 1993 and 2004. As such, averaged redd counts for surveys completed between these years may include fewer completed counts. ................................................................ 19

Table 5. Bull Trout redd counts by year from the St. Joe River, Idaho and selected tributaries. Redd surveys were not completed on all stream reaches in all years between 1992 and 2003. As such, averaged redd counts for

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surveys completed between these years may include fewer completed counts. ............................................................................................................... 20

Table 6. Bull Trout redd counts by year for index stream reaches in the Little North Fork Clearwater River, Idaho (2000–2015). ....................................................... 22

Table 7. Bull Trout redd counts by year from the selected tributaries of the Kootenai River, Idaho. ....................................................................................... 22

Table 8. Hydroacoustic survey results for kokanee from Priest Lake, Idaho on August 11, 2015. ................................................................................................ 28

Table 9. Kokanee spawner counts at three standard locations on Priest Lake, Idaho in 2015. .................................................................................................... 29

Table 10. Upper Priest Lake 2015 gill net effort and Lake Trout (LKT) catch by gill net mesh size. Total length ranges of Lake Trout caught were reported by associated gill net mesh sizes. ........................................................................... 38

Table 11. Covariates included in initial model selection process to estimate the probability of post-release mortality for Lake Trout captured in Priest Lake in 2015. Two covariates (fizz and barotrauma) were included in all models evaluated. Corresponding biological hypothesis is also included for each effect considered................................................................................................ 47

Table 12. Parameter estimates and standard errors (log-odds scale) from the top logistic regression model evaluating the probability that Lake Trout would escape from the net pen. Covariates are total length (TL; mm) and a variable indicating if the fish was fizzed. ............................................................. 48

Table 13. Results of model selection process to estimate post-release mortality of Lake Trout. Only models with substantial support (∆AICc < 2) are given. All models contain main effects for barotrauma condition (Baro) and an indicator variable for treatment by fizzing (Fizz). Other covariates are listed and included: catch time (CT), handling time (HT), total length (TL), and capture gear (Gear; jig or trolling). The value K describes the number of estimated variables in each model. ................................................................ 48

Table 14. Parameter estimates and standard errors (log-odds scale) for logistic regression models evaluating the probability of post-release mortality for Lake Trout. All models included a three-level indicator variable for barotrauma condition and a two-level variable indicating if a fish was fizzed. Other covariates included catch time (CT; min), handling time (HT; hr), and an indicator variable for method of capture (Troll). Model number corresponds to Table 13. ................................................................................... 49

Table 15. Estimated probability of post-release angling mortality of Lake Trout held in a large net pen. Probabilities and lower (LCB) and upper (UCB) 95% confidence bounds were estimated using the top model (see Table 3). ............. 50

Table 16. Locations of sites sampled during 2015 surveys of Bench Creek and the Hughes Fork. Waypoints represent the approximate uppermost points of each survey section. Section length and average wetted width at the time of sampling are listed for each survey section. ................................................... 56

Table 17. Bench Creek and Hughes Fork 2015 survey results by site and species. Total catch references all fish caught. Only fish ≥ 75 mm were included in estimates of abundance (Est N). ........................................................................ 56

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Table 18. Densities of mysids (per m2) collected from Hayden Lake on June 18, 2015. Densities were listed by location (UTM, zone 11, WGS84) and life stage (young-of-year [YOY], immature and adults). ........................................... 61

Table 19. Densities of mysids (per m2) collected from Priest Lake on June 17, 2015. Densities were listed by location (UTM, zone 11, WGS84) and life stage (young-of-year [YOY], immature and adults). ..................................................... 61

Table 20. Location, description of index reaches, and number of Chinook Salmon redds counted during surveys from the most recent five years. Surveys are conducted in the Coeur d’Alene River and St. Joe River. Reaches include only those with long time series information used to index Chinook Salmon redd abundance. ..................................................................... 94

Table 21. Estimated abundance of kokanee made by midwater trawl in Lake Coeur d’Alene, Idaho, from 1979–2014. ..................................................................... 104

Table 22. Estimated abundance of kokanee made by midwater trawl in Spirit Lake, Idaho, from 1981–2014. ................................................................................... 105

Table 23. Weekly catch information for Northern Pike management in Windy Bay including sampling time period, gill net set type, and catch statistics. Recapture information includes the year of during which recaptured Northern Pike were initially translocated in parentheses. ................................. 124

Table 24. Parameters used to estimate angler exploitation (µ) of Northern Pike on Hayden and Killarney lakes in northern Idaho. ................................................. 134

Table 25. Date, time (hours), and sampling locations (UTM) for Hayden Lake and Cocolalla Lake gill net surveys completed during 2015. ................................... 147

Table 26. History of Rainbow Trout stocking in Hayden Lake, Idaho from 2011 to 2014. ................................................................................................................ 147

Table 27. Table 3. History of Westslope Cutthroat Trout and Rainbow Trout stocking in Cocolalla Lake, Idaho from 2011 to 2014. ...................................... 148

Table 28. Species, minimum and maximum total length (TL), catch (n), and catch rate (CPUE) from a Hayden Lake gill net survey completed during April, 2015. ................................................................................................................ 148

Table 29. Species, minimum and maximum total length (TL), catch (n), and catch rate (CPUE) from a Cocolalla Lake gill net survey completed during April, 2015. ................................................................................................................ 149

Table 30. Annual ZPR and ZQI indices and density estimates estimated from zooplankton sampling in Hayden and Cocolalla lakes. ..................................... 149

Table 31. Sample locations by date and method for lowland lakes surveyed in 2015. ..... 163 Table 32. Descriptive statistics for fish sampled from Brush Lake in June 2015.

Statistics summarized include catch, proportion of catch by number and biomass, minimum and maximum total length (TL), and catch rates (CPUE; 80% confidence intervals) by gear type. .............................................. 164

Table 33. Descriptive statistics for fish sampled from McArthur Lake in June 2015. Statistics summarized include catch, proportion of catch by number and biomass, minimum and maximum total length (TL), and catch rates (CPUE; 80% confidence intervals) by gear type. .............................................. 164

Table 34. Descriptive statistics for fish sampled from Avondale Lake in June 2015. Statistics summarized include catch, proportion of catch by number and

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biomass, minimum and maximum total length (TL), and catch rates (CPUE; 80% confidence intervals) by gear type. .............................................. 165

Table 35. Summary of lowland lake survey metrics from past and present surveys of Brush Lake, Idaho. Metrics include percent of catch by number (% #), percent of catch by weight (% Wt), proportional stock density (PSD), relative stock density of preferred size fish (RSD-P), relative weight range (Wr Range), relative weight at 200 mm (Wr 200), and total length-at-age (TL @ 3, TL @ 6). ............................................................................................ 165

Table 36. Summary of species proportions in samples from past and present surveys of McArthur Lake, Idaho. ..................................................................... 166

Table 37. Sample year and physical characteristics of alpine lakes sampled in the Panhandle Region, Idaho (2014–2015). Alpine lakes are organized by parent drainage. ............................................................................................... 184

Table 38. Sample size (n), mean catch-per-unit-effort (CPUE = fish/gill net night), total length (mm; Minimum–Maximum [Min–Max]) statistics, weight (g; Minimum–Maximum [Min–Max]) statistics, and relative weight (Wr) for Brook Trout populations sampled from alpine lakes in the Panhandle Region, Idaho (2014–2015). Numbers in parentheses represent one standard error about the mean. ........................................................................ 185

Table 39. Mean length-at-age (mm; [SD]) and von Bertalanffy growth model equation (VBGM) for Brook Trout sampled from alpine lakes in the Panhandle Region, Idaho (2015). .................................................................... 186

LIST OF FIGURES

Figure 1. Length-frequency distributions for Largemouth Bass sampled from northern Idaho lakes (2014–2015). .................................................................... 10

Figure 2 Estimates of Studentized residuals from catch curve regressions for Largemouth Bass sampled from northern Idaho lakes (2014–2015). Positive residuals represent strong year-classes and negative residuals represent weak year-classes.............................................................................. 11

Figure 3. Age-structure distribution of Largemouth Bass sampled from North Idaho lakes with weighted catch curve regressions estimating mortality and recruitment variability for Largemouth Bass sampled from northern Idaho lakes (2014–2015). Closed circles represent age-classes to which the regression model was fitted. Open circles represent age classes that were not fully-recruited to the gear and not included the model. ......................... 12

Figure 4. Mean length-at-age for Largemouth Bass sampled from northern Idaho lakes (2014–2015). Error bars represent one standard error about the mean. ................................................................................................................. 13

Figure 5. Standard transects on Priest Lake, Idaho used in hydroacoustic surveys of kokanee abundance. ...................................................................................... 30

Figure 6. Distribution of target strengths detected in an August 2015 hydroacoutic survey of Priest Lake, Idaho. .............................................................................. 31

Figure 7. Kokanee adult spawner counts at five standard locations on Priest Lake, Idaho between 2001 and 2015. Additionally, length of male kokanee spawners sampled at the mouth of Hunt Creek each year is shown................... 31

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Figure 8. Kokanee density estimates from hydroacoustic surveys completed during 2012 to 2015 in Priest Lake, Idaho. .................................................................... 32

Figure 9. Water temperature profile measured in association with our August 2015 hydroacoustic survey of Priest Lake, Idaho. ....................................................... 32

Figure 10. Average daily Lake Trout catch rates (Lake Trout/box) and 80% confidence intervals by year from combined standard gill net mesh sizes (51 mm, 64 mm, and 76 mm) fished in Upper Priest Lake, Idaho from 2010 to 2015. ..................................................................................................... 39

Figure 11. Average daily Lake Trout catch rate (Lake Trout/box) and 80% confidence intervals by mesh size from standardized gill nets fished in Upper Priest Lake, Idaho in 2014 and 2015. ...................................................... 39

Figure 12. Size structure of Lake Trout sampled in Upper Priest Lake, Idaho during 2015. .................................................................................................................. 40

Figure 13. Average daily Bull Trout catch rate (Bull Trout/box) and 80% confidence intervals for all mesh sizes fished in Upper Priest Lake, Idaho from 2007 to 2015. Confidence intervals were only estimated for years in which gill net mesh size and effort were standardized. ...................................................... 40

Figure 14. Results of post hoc logistic regression model evaluating the probability of Lake Trout escape from the net pen enclosure after being held for 20 or 21 days. The model included covariates for total length and fizzing (red, not fizzed; blue, fizzed). Mean probabilities are given by solid lines; shaded bands indicate 95% confidence intervals. Tick marks along the horizontal axis indicate individual observations. ................................................. 50

Figure 15. Results of the top logistic regression model evaluating the probability of post-release angling mortality for Lake Trout held in a large enclosure for 20-21 days. The model included covariates for barotrauma condition (mild, moderate, severe) and fizzing (red, not fizzed; blue, fizzed). .................... 51

Figure 16. Bench Creek and Hughes Fork survey locations sampled in 2015. .................... 57 Figure 17. Length distribution by life stage of mysid shrimp sampled from random

locations in Hayden Lake, Idaho on June 18, 2015. ........................................... 62 Figure 18. Length distribution of Mysis shrimp collected from random locations in

Priest Lake, Idaho on June 17, 2015. ................................................................. 62 Figure 19. Estimated density (per m2) of immature and adult mysid shrimp from

Hayden and Priest lakes in 2010, 2013, 2014, and 2015. Error bars represent 80% confidence intervals. No survey was completed on Priest Lake in 2010. ..................................................................................................... 63

Figure 20. Location of 44 index reaches sampled using snorkeling in the Coeur d’Alene River, Idaho during July 26–31, 2015. ................................................... 71

Figure 21. Location of 35 index reaches sampled using snorkeling in the St. Joe River, Idaho during August 3–6, 2015. ............................................................... 72

Figure 22. Mean density of Westslope Cutthroat Trout observed during snorkeling in the North Fork of the Coeur d’Alene River and Little North Fork of the Coeur d’Alene River (1973–2015). ..................................................................... 73

Figure 23. Mean density of Westslope Cutthroat Trout larger than 300 mm TL observed during snorkeling in the North Fork of the Coeur d’Alene River and Little North Fork of the Coeur d’Alene River (1973–2015). .......................... 73

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Figure 24. Mean density of Rainbow Trout observed during snorkeling in the North Fork of the Coeur d’Alene River and Little North Fork of the Coeur d’Alene River (1973–2015). ............................................................................... 74

Figure 25. Mean density of Mountain Whitefish observed during snorkeling in the North Fork of the Coeur d’Alene River and Little North Fork of the Coeur d’Alene River (1973–2015). ............................................................................... 74

Figure 26. Mean density of Westslope Cutthroat Trout observed during snorkeling in the St. Joe River (1969–2015). .......................................................................... 75

Figure 27. Mean density of Westslope Cutthroat Trout larger than 300 mm TL observed during snorkeling in the St. Joe River (1969–2015). ........................... 75

Figure 28. Mean density of Rainbow Trout observed during snorkeling in the St. Joe River (1969–2015). ............................................................................................ 76

Figure 29. Mean density of Mountain Whitefish observed during snorkeling in the St. Joe River (1969–2015)....................................................................................... 76

Figure 30. Length-frequency distributions of Westslope Cutthroat Trout observed during snorkeling in the North Fork Coeur d’Alene River (includes Little North Fork Coeur d’Alene River and Teepee Creek) and St. Joe River (2015). ............................................................................................................... 77

Figure 31. Location of 48 index reaches sampled using snorkeling in the Little North Fork Clearwater River, Idaho (2015). ................................................................. 84

Figure 32. Mean total density of Westslope Cutthroat Trout and mean density of Westslope Cutthroat Trout ≥ 305 mm TL observed by snorkeling in the Little North Fork Clearwater River, Idaho (1997–2015). ..................................... 84

Figure 33. Length-frequency distribution of salmonid species observed by snorkeling in the Little North Fork Clearwater River, Idaho (2015)....................................... 85

Figure 34. Length-frequency distribution of Westslope Cutthroat Trout tagged to evaluate angler exploitation in the Little North Fork Clearwater River, Idaho (2015). ..................................................................................................... 85

Figure 35. Estimated annual angler exploitation of Westslope Cutthroat Trout in the Little North Fork Clearwater River (1997–2015). ................................................ 86

Figure 36. Location of Lake Coeur d’Alene, Idaho. The black dot represents the location of the adult trap and where juvenile hatchery Chinook Salmon were released. ................................................................................................... 95

Figure 37. Number of Chinook Salmon redds counted during sampling of index reaches in the Coeur d’Alene River and St. Joe River from 1990–2015. ............ 96

Figure 38. Approximate location of historical trawling transects used to estimate abundance of kokanee in Lake Coeur d’Alene. ................................................ 106

Figure 39. Approximate location of historical trawling transects used to estimate abundance of kokanee in Spirit Lake, Idaho. .................................................... 107

Figure 40. Length-frequency distribution for kokanee sampled using a modified-midwater trawl from Lake Coeur d’Alene, Idaho (July 16–17, 2015). ................ 108

Figure 41. Age-frequency distribution for kokanee sampled using a modified-midwater trawl from Lake Coeur d’Alene, Idaho (July 16–17, 2015). ................ 109

Figure 42. Mean length-at-age of kokanee sampled from Lake Coeur d’Alene and Spirit Lake, Idaho (July 14, 2015). .................................................................... 110

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Figure 43. Relationship between total length and body condition of kokanee sampled from Lake Coeur d’Alene, Idaho (July 16–17, 2015). ....................................... 111

Figure 44. Length-frequency distribution for male and female kokanee sampled from Lake Coeur d’Alene, Idaho (December 2, 2015). ............................................. 112

Figure 45. Mean total length of mature male and female kokanee sampled near Higgens Point in Lake Coeur d’Alene Idaho (1954–2015). Horizontal lines indicate the upper and lower limit of the adult length management objective (250–280 mm). .................................................................................. 113

Figure 46. Length-frequency distribution for kokanee sampled using a modified-midwater trawl from Spirit Lake, Idaho (July 14, 2015). .................................... 114

Figure 47. Age-frequency distribution for kokanee sampled using a modified-midwater trawl from Spirit Lake, Idaho (July 14, 2015). .................................... 115

Figure 48. Relationship between total length and body condition of kokanee sampled from Spirit Lake, Idaho (July 14, 2015). ............................................................ 116

Figure 49. Map of the Lake Coeur d’Alene system in North Idaho. Capture and translocation areas are indicated by bold text. ................................................. 125

Figure 50. Relationship between catch-per-unit-effort and cumulative catch of Northern Pike sampled in Windy Bay, Lake Coeur d’Alene (2015). Estimated abundance of Northern Pike in Windy Bay was 327.72. .................. 126

Figure 51. Length frequency distribution of all Northern Pike captured in Windy Bay (top panel), Northern Pike that were translocated to Cougar Bay (middle panel), and translocated Northern Pike caught by anglers (bottom panel; 2015). .............................................................................................................. 127

Figure 52. Tag returns of translocated Northern Pike caught by anglers during 2015 (based on capture date). .................................................................................. 128

Figure 53. Length distribution of Northern Pike tagged in Hayden Lake in 2014. .............. 135 Figure 54. Length distribution of Northern Pike tagged in Hayden Lake in 2015. .............. 135 Figure 55. Length distribution of Northern Pike tagged in Killarney Lake in 2015. ............. 136 Figure 56. Mean length-at-age (± one standard deviation) for Northern Pike sampled

from Hayden Lake in 2015. .............................................................................. 136 Figure 57. Mean length-at-age (± one standard deviation) for Northern Pike sampled

from Killarney Lake in 2015. ............................................................................. 137 Figure 58. Length-at-age for Northern Pike sampled from Killarney Lake in 2015.

The dashed line demonstrates a divergent pattern of growth observed within the sampled population. ......................................................................... 137

Figure 59. Number of Rainbow Trout stocked from 1942 to 2015 in Hayden Lake, Idaho. ............................................................................................................... 150

Figure 60. Number of Rainbow Trout stocked from 1951 to 2015in Cocolalla Lake, Idaho. ............................................................................................................... 150

Figure 61. Number of Westslope Cutthroat Trout stocked from 1957 to 2015 in Cocolalla Lake, Idaho. ..................................................................................... 151

Figure 62. Temperature (C) and DO (mg/L) profiles of Hayden and Cocolalla lakes measured in August 2015. ............................................................................... 152

Figure 63. Size structure of Bluegill, Largemouth Bass, and Rainbow Trout sampled via boat electrofishing, gill nets, and trap nets from Brush Lake in June 2015. ................................................................................................................ 167

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Figure 64. Mean (± one standard deviation) length-at-age for Bluegill and Largemouth Bass sampled from Brush Lake in June 2015. ............................. 168

Figure 65. Bluegill (> 80 mm) and Largemouth Bass (>150 mm) condition as indexed by relative weight (Wr) for fish sampled from Brush Lake in June 2015. ........... 169

Figure 66. Age-frequency for Largemouth Bass and Bluegill sampled from Brush Lake in June 2015. ........................................................................................... 169

Figure 67. Temperature and dissolved oxygen profiles of Brush Lake on August 4, 2015. ................................................................................................................ 170

Figure 68. Size Structure of Rainbow Trout, Largemouth Bass, and Yellow Perch sampled via boat electrofishing, gill nets, and trap nets from McArthur Lake in June 2015. ........................................................................................... 171

Figure 69. Age-frequency of Yellow Perch and Largemouth Bass sampled from McArthur Lake in June 2015. ........................................................................... 172

Figure 70. Mean (± SD) length-at-age for Largemouth Bass and Yellow Perch sampled from McArthur Lake in June 2015. ..................................................... 172

Figure 71. Size structure of Yellow Perch, Bluegill, and Largemouth Bass sampled using floating and sinking gill nets and boat electrofishing from Avondale Lake in June 2011 and 2015. ........................................................................... 173

Figure 72. Bluegill (≥ 80 mm), Largemouth Bass (≥150 mm), and Yellow Perch (≥ 130 mm) condition as indexed by relative weight (Wr) for fish sampled from Avondale Lake in June 2015. ................................................................... 174

Figure 73. Age-frequency of Largemouth Bass sampled from Avondale Lake in June 2015. ................................................................................................................ 175

Figure 74. Mean (± one standard deviation) length-at-age for Largemouth Bass sampled from Avondale Lake in June 2015...................................................... 175

Figure 75. Temperature and dissolved oxygen profiles of Avondale Lake on September 11, 2015.3 ..................................................................................... 176

Figure 76. Length-frequency distributions for Brook Trout sampled from alpine lakes in the Kootenai River Drainage (2014–2015). .................................................. 187

Figure 77. Length-frequency distributions for Brook Trout sampled from alpine lakes in the Pend Oreille River Drainage (2014–2015). ............................................. 188

Figure 78. Length-frequency distributions for Brook Trout sampled from alpine lakes in the Spokane River Drainage (2014–2015). .................................................. 189

Figure 79. Length-weight relationship for Brook Trout sampled from alpine lakes in the Panhandle Region (2014–2015)................................................................. 190

Figure 80. Weighted catch-curve regressions used to estimate total annual mortality (A), instantaneous mortality (Z), and recruitment variability (RCD) for Brook Trout populations sampled from alpine lakes in the Panhandle Region (2015). ................................................................................................. 191

Figure 81. Mean lengths-at-age of Brook Trout sampled from alpine lakes in the Panhandle Region (2015). ............................................................................... 192

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POPULATION CHARACTERISTICS AND EXPLOITATION OF LARGEMOUTH BASS IN NORTH IDAHO LAKES

ABSTRACT

Largemouth Bass Micropterus salmoides is an important sportfish species throughout the state of Idaho and select populations are managed for quality angling opportunities. Largely due to the close proximity to several large cities, lowland lakes in the Panhandle Region support very popular recreational fisheries, with considerable effort targeting Largemouth Bass. We assessed Largemouth Bass population characteristics and exploitation during the spring of 2014 and 2015 to describe several regionally-important Largemouth Bass populations. More specifically, we sought to evaluate population size structure, somatic growth, total annual mortality, recruitment variability, and angler exploitation. A total of 1,379 Largemouth Bass was sampled from the study lakes throughout the duration of this study. Annual angler exploitation varied from 0–51.6%, which was higher on average than exploitation estimates obtained in recent history from other popular Largemouth Bass fisheries in the Panhandle Region. Recruitment stability varied among lakes, with Round Lake showing the most stable recruitment (RCD = 0.90) and Kelso Lake exhibiting the least stable recruitment (RCD = 0.41). Total annual mortality averaged 28.4% and varied from 18.9–31.6%. In general, water bodies managed under quality Largemouth Bass regulations (i.e., two fish daily bag; none < 16 in) did not exhibit lower angler exploitation or improved population characteristics relative to lakes managed under general rules. Author:

Carson Watkins Regional Fisheries Biologist

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INTRODUCTION

Understanding the status and trends of fish population demographics (e.g., age structure, longevity) and dynamics (i.e., growth, recruitment, mortality) is central to fisheries management (Ricker 1975; Allen and Hightower 2010). Population dynamics are of particular importance to fisheries biologists because rate functions work concomitantly to directly regulate the number and size of fish available in a fishery. Estimates of all three dynamic rate functions are commonly used in combination to evaluate management activities (e.g., harvest regulations, habitat enhancement) and formulate management objectives.

Recruitment is considered the most important, yet most variable, rate function regulating

fish population abundance and assemblage structure (Ricker 1975; Gulland 1982). As such, understanding patterns in year-class strength and recruitment provides valuable insight on how management actions may influence various metrics (e.g., size structure, catch rates). Mortality can provide valuable insight on trends in fish populations, and can reflect changes in habitat, biological interactions, and exploitation (Swain et al. 2007). Collectively, recruitment and mortality act to determine the number of fish existing within a population.

While population assessments may estimate all rate functions, understanding somatic growth can be particularly insightful for understanding the ecology and management of a given species. Growth is a unique population parameter because it integrates various environmental (e.g., climate, nutrient availability, physical habitat), biological (e.g., inter- and intra-specific competition), and genetic elements. Furthermore, growth is of particular importance because it indirectly regulates the other rate functions such as recruitment and mortality (Quist and Spiegel 2012). All life history events (e.g., maturation, migration) and ontogenetic shifts (e.g., gape size) throughout a fish’s life occur as a function of growth (Olson 1996). Therefore, growth is not only related to size structure, but also survival and reproduction; thus, knowledge of fish growth is critical for formulating sound fishery management plans.

Black basses Micropterus spp. represent a group of important freshwater sportfishes across most of their range and are commonly managed to provide quality recreational angling opportunities (Allen et al. 2008). Of the black basses, Largemouth Bass Micropterus salmoides have been introduced to many systems throughout North America because of their popularity among anglers. While select Largemouth Bass fisheries are managed for catch-and-release angling opportunities (Cline et al. 2012), natural resource agencies typically allow limited harvest opportunity (Eder 1984). As such, considerable research has been dedicated to understanding the population dynamics and biology of Largemouth Bass to satisfy a diversity of values among the angling public.

A greater interest in improving Largemouth Bass angling has increased the availability of region-specific information on the species, particularly in North America (Dean et al. 1991; Beamesderfer and North 1995; Garvey et al. 2003). However, intensive management of warmwater sportfish does not have as rich of a history in the Pacific Northwest compared to other parts of the United States, making stock-specific datasets limited. Development of management plans is further complicated by the fact that population dynamics of Largemouth Bass in the Pacific Northwest are vastly different than populations where regulations have been evaluated such as Florida (Allen et al. 2008; Allen and Pine 2011), Texas (Bonds et al. 2008), and Wisconsin (Schnell 2014). These shortfalls, combined with increased interest in bass angling, have prompted agencies to better understand Largemouth Bass populations in places outside of their native distribution, such as Idaho (Dillon 1990).

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In Idaho, many Largemouth Bass populations are managed for quality angling. Idaho’s statewide fisheries management plan describes a quality Largemouth Bass fishery as being one where anglers are likely to experience high catch rates relative to similar waters and likely to catch larger fish (i.e., > 406 mm) in waters with special regulations (IDFG 2013). Currently, the most restricted quality Largemouth Bass fisheries in Idaho are managed to provide limited harvest opportunity and no waters are managed exclusively for catch-and-release.

Several lakes in the Idaho Panhandle are managed as quality Largemouth Bass fisheries and support considerable angler effort. Despite their regional importance, relatively little is known about exploitation patterns, population characteristics, and potential factors influencing Largemouth Bass around the Panhandle Region. Several of these Largemouth Bass populations are managed under special regulations (two fish daily bag limit; none under 406 mm) in systems that have historically produced some of the best Largemouth Bass angling in the Panhandle Region. Previous creel surveys in Hayden Lake have shown that Largemouth Bass angling comprises around 10% of the total annual angling effort (Davis et al. 1995; Hardy et al. 2013), but that figure is presumably much higher for other lowland lakes with less fish diversity. While catch rates of Largemouth Bass have typically been good in many of the region’s lowland lakes, exploitation has remained relatively low (~ 12%; Liter et al. 2003). However, anglers have noted declines in size structure and catch rates of quality Largemouth Bass in some waters. Therefore, this study was conducted to assess the Largemouth Bass populations in waters with outdated information and provide a basis for the variation in angler exploitation, population characteristics, and growth patterns around the Panhandle Region.

OBJECTIVES

1. Estimate angler exploitation of Largemouth Bass in northern Idaho lakes.

2. Estimate dynamic rate functions (i.e., growth, recruitment, mortality) and population characteristics (i.e., relative abundance, size structure) of Largemouth Bass in northern Idaho lakes.

STUDY AREA

Lakes included in this study are natural oligotrophic water bodies located in Kootenai, Bonner, and Boundary counties in the Idaho Panhandle. The study sites vary in surface area from approximately 22–1,821 ha and 6–54 m in maximum depth (Bellatty 1990). Shoreline characteristics vary substantially with around 15–85% of the shoreline of each study lake being either residentially or agriculturally developed (Wersal et al. 2010). The lakes support mixed fisheries for both warmwater and coldwater fish species. A complete list of species sampled during this study can be found in Table 2.

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METHODS

Fish Sampling and Hard Structure Processing

Largemouth Bass were sampled from northern Idaho lakes during April–June of 2014 and 2015 when they are known to occupy shallow water habitat during their spawning period (Winter 1977; Schnell 2014). The shoreline of each lake was measured and segmented into 400-m long sampling units using ArcGIS Version 10.1 (Esri, Redlands, California, USA). The upper and lower terminus of each segment was georeferenced and a simple random sampling design was used to allocate sampling effort among segments. Nighttime boat-mounted electrofishing was used to capture Largemouth Bass. Previous studies have shown that electrofishing is an effective sampling technique used to sample Largemouth Bass and is commonly used by natural resource agencies (Hall 1986; Ebbers 1987; Hill and Willis 1994). Electrofishing equipment consisted of a Smith-Root model VVP-15b electrofisher (Smith-Root, Inc., Vancouver, Washington, USA). Electrofishing power was standardized to 3,000 W based on ambient water conductivity and temperature (Miranda 2009). Two netters collected fish from the bow of the boat during sampling. Electrofishing effort consisted of a single, 600 s pass allocated to each segment proceeding in a clockwise direction around the lake. Upon completion of a sampling segment, each Largemouth Bass was measured to the nearest millimeter (total length). The first and second dorsal spines were removed from 10 individuals per 1-cm length group for each lake, if present. Largemouth Bass were tagged using a non-reward FD-94 T-bar anchor tags (76 mm; Floy Tag Inc., Seattle, Washington, USA) near the posterior end of the dorsal fin to evaluate angler exploitation. Only stock-length and larger or 406-mm and larger individuals were tagged in waters with or without a quality minimum length limit, respectively. All tags were uniquely-numbered and possessed the telephone number for the IDFG’s “Tag! You’re It!” reporting hotline. Exploitation of Largemouth Bass was estimated using the non-reward tag reporting estimator described by Meyer et al. (2012) incorporating estimates of tag loss and tagging mortality.

Dorsal spines were allowed to air dry and subsequently mounted in epoxy using 2 mL microcentrifuge tubes following Koch and Quist (2007). Cross sections (0.9 mm thick) were cut near the base of each dorsal spine just distal to the articulating process using an Isomet low-speed saw (Buehler Inc., Lake Bluff, Illinois, USA). Resulting dorsal spine cross-sections were viewed using a dissecting microscope with transmitted light and an image analysis system (Image ProPlus; Media Cybernetics, Silver Springs, Maryland, USA). Annuli were enumerated on all structures by a single reader. Knowledge of biological information for each fish was unknown during the age estimation process to avoid bias.

Data analysis

Catch-per-unit-effort (CPUE) was estimated as the number of fish sampled per electrofishing segment (i.e., each 600 s pass). Exploitation (µ) was estimated as the number of fish harvested by anglers (obtained from tag return information) divided by the number of fish tagged, after one year at-large. We assumed a 39% reporting rate, 13% tag-loss, and 3.0% tagging mortality based on work conducted by Meyer et al. (2012).

Proportional size distribution (PSD) was used to summarize length-frequency

distributions (Gablehouse 1984; Neumann et al. 2012) and describe size structure. Proportional size distribution was calculated as

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PSD = (a / b) × 100,

where a is the number of fish greater than or equal to the minimum quality length (300 mm) and b is the number of fish greater than or equal to the minimum stock length (200 mm) (Neumann et al. 2012).

Age structure of Largemouth Bass was estimated with an age-length key (Isermann and Knight 2005; Quist et al. 2012). Total annual mortality (A) was estimated using a weighted catch curve (Miranda and Bettoli 2007). Largemouth Bass appeared to be fully-recruited to the sampling gear at either age-2 or 3, so A was only estimated for fish older than 2–4 years of age depending on age-at-recruitment. Age structure information was used to describe patterns in recruitment, and those patterns were described using several techniques. Recruitment was first indexed using the residual technique described by Maceina (1997) where residual estimates derived from a catch curve regression represent relative year-class strength (i.e., positive residuals equal strong year-classes, negative residuals equal weak year-classes). Secondly, recruitment was indexed using the recruitment variability index (RVI; Guy and Willis 1995) and was calculated as

RVI = [SN / (NM + NP)] – NM / NP, where SN is the summation of the cumulative relative frequencies across year-classes included in the sample, NM is the number of year-classes missing from the sample (year-classes beyond the oldest year-class in the sample are excluded), and NP is the number of year-classes present in the sample (NP must be greater than NM). Recruitment variability index values vary from -1 to 1, with values close to 1 representing stable recruitment. Development of the RVI was partially based on catch curve analysis because fish populations with stable recruitment will exhibit a steady decline in abundance as age increases. Lastly, the recruitment coefficient of determination (RCD; Isermann et al. 2002) was also used to explain stability in recruitment. The RCD is simply the coefficient of determination (R2) value that results from a catch curve regression. Indices of recruitment are often useful for comparing among water bodies and provide a general idea of recruitment stability over multiple years. Age-based information was also used to estimate somatic growth. Growth was summarized by plotting mean length-at-age at capture and associated variance estimates.

RESULTS

A total of 1,379 Largemouth Bass was sampled throughout the duration of this study. Anglers had reported 45 tags as of June 1, 2016. Of those, 13 were harvested and 32 were released. We estimated corrected annual exploitation rates varying from 0–44.4% (Table 1). Relative abundance was only slightly variable (mean CPUE = 5.88 fish/segment; SE = 1.77; Table 1). Mean total length of Largemouth Bass varied from 195.6–293.6 mm (Table 1; Figure 1) and PSD estimates varied considerably from 10–57 (Table 1). For lakes with minimum length limits (i.e., Chase, Robinson, and Hayden lakes), between 3–15% of stock-length and larger fish met or exceeded the 406 mm minimum length limit.

Age structure was used to provide insight on population mortality and recruitment patterns. Among lakes, longevity varied from 7–19 years (Figure 3). Largemouth Bass recruited to electrofishing between age-1 and age-4, and catch curve regressions were fitted to age classes along the descending limb of log linearized age-frequency distributions (Figure 3). We estimated total annual mortality rates varying from 18.9–43.8% (Table 1). Recruitment patterns

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showed some variability among years for all study lakes (Table 1; Figure 2), but year-class strength has shown consistent patterns for most lakes (Figure 2). Missing year-classes were only observed in Chase and Kelso lakes, and recruitment failure occurred during the same consecutive years in both systems. In general, recruitment patterns appeared to follow similar patterns among study lakes with strong and weak year-classes usually occurring simultaneously in the same years.

Largemouth Bass reached preferred length (304 mm) in 4–5 years and quality length (380 mm) in 6–8 years (Figure 4). Largemouth Bass require an average of eight years to reach the 406 mm minimum length limit in Chase, Robinson, and Hayden lakes, meaning that long-lived individuals may be available for harvest for around 1–4 years. Growth rates were highest for ages 1–4, and growth trajectory thereafter tended to vary among lakes (Figure 4).

DISCUSSION

Largemouth Bass remain the most popular resident sportfish species in Idaho following trout species (IDFG 2013). Largemouth Bass can be found in all seven IDFG regions where they support popular fisheries, both consumptive and non-consumptive. Northern Idaho lakes produce some of the finest Largemouth Bass angling in Idaho and these fisheries are highly accessible due to their close proximity to major population centers. For these reasons, Largemouth Bass fisheries in northern Idaho lakes are very popular and fisheries management is a high priority.

Our basic observations remain consistent with other studies in the Panhandle Region

that have assessed Largemouth Bass population dynamics (Hardy 2008; Fredericks and Horner 1995). Largemouth Bass are slow-growing in the Pacific Northwest (Beamesderfer and North 1995; Rieman 1987; Dillon 1990) and our study lakes are no exception. On average, Largemouth Bass require eight years to recruit to the harvestable portion of the fisheries with length-based rules. We observed longevity of around 12 years on average, which agrees with estimated longevity for wild bass at similar latitudes. As such, we are confident in our maximum age estimates for Largemouth Bass in our study lakes, thus reinforcing the utility of these methods for future age-based evaluations of angling rules.

Size structure of Largemouth Bass varied considerably, with the highest PSD values

occurring in Upper Twin, Lower Twin, Spirit, Fernan, and Hayden lakes. Exploitation was also highly variable and did not show a strong relationship with PSD in lakes without minimum length limits. Although it is often proposed that harvest has potential to alter Largemouth Bass size structure (Dean et al. 1991; Allen et al. 2008), we did not observe that pattern in our study. Angler exploitation was as low as zero in Chase, Kelso, Lower Twin, Robinson, and Spirit lakes, and as high as 44.4% in Round Lake. In general, we found that accessibility and proximity to town influenced the rate of angler exploitation. For instance, lakes with popular littoral fisheries (e.g., Hayden and Fernan lakes) and lakes with good bank access and developed camping (e.g., Kelso and Round lakes) tended to have the highest angler exploitation rates. Angler exploitation was not well-correlated with abundance or growth in any of our study rates. It is more likely that abundance and growth are regulated by variation in environmental and fish assemblage differences among our study lakes (Allen and Hightower 2010).

One of the most interesting patterns that emerged through this study was the

consistency of A and recruitment among our study lakes. Total annual mortality varied only slightly among most study sites, with the exception of Robinson Lake. Total annual mortality

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averaged 30.4% and was consistent with estimates of A from other parts of the Panhandle Region (i.e., Chain Lakes; Rieman 1987). Recruitment estimated in our study showed higher variability than previous population assessments in other parts of the Panhandle Region (Liter et al. 2009); however, recruitment patterns were consistent among study sites. For example, year-class strength showed high corroboration among strong and weak cohorts. In addition, year-class failure occurred during the same years in both Chase and Kelso lakes. We hypothesize that patterns in year-class strength are likely influenced by regional environmental patterns that have the potential to similarly affect multiple water bodies. Although environmental conditions cannot be influenced from a management perspective, understanding of how weather and climate influence Largemouth Bass recruitment can inform fishery managers how factors other than harvest that may be driving bass abundance and size structure. .

Largemouth Bass populations support abundant angling opportunity and are an

important component of many lentic fish assemblages in the Panhandle Region. Our evaluation of several populations demonstrates that population characteristics are minimally influenced by angler exploitation, and that harvest is an important part of many Largemouth Bass fisheries throughout the region. While this is not true for all lakes included in this study, the diversity of angling opportunities maintained by a variety of different fishing rules is important for supporting the interests of many angler contingents. The IDFG manages many waters in the Panhandle Region for quality Largemouth Bass angling and our results suggest that objective is being met for many water bodies, even those under general rule management. Exceptions to this are Chase and Robinson lakes, which have relatively poor population size structure despite special rules. In comparison to Hayden Lake, which is also managed under special quality bass angling rules, angler exploitation does not appear to be a relevant concern in Chase and Robinson Lakes. It is likely that these populations are limited by habitat conditions rather than angler harvest. For waters such as Round Lake, high angler exploitation appears to influence longevity and maximum length, with both metrics likely being reduced by high harvest. Managers could consider rule alterations on Round Lake that may reduce fishing mortality, and consider removal of special rules on Chase and Robinson lakes. In general, the majority of water bodies in this study are managed under general angling rules to support consumptive fisheries for Largemouth Bass and other warmwater fish species. It is unlikely that harvest significantly influences size structure and angler catch rates in many of these lakes (i.e., Lower and Upper Twin, Fernan, Spirit lakes); however, exploitation should be monitored to assess changes in angler behavior. Future changes to angler behavior relative to Largemouth Bass harvest could potentially alter the population structure of Largemouth Bass populations in lakes managed with generally rules, and motivate public desire to managed said populations more conservatively.

MANAGEMENT RECOMMENDATIONS

1. Remove 16" minimum length limit in Chase and Robinson lakes.

2. Increase minimum length limit on Hayden Lake to 20”.

3. Maintain general rules on remaining lakes.

4. Perform periodic sampling to assess changes to Largemouth Bass populations throughout Panhandle Region.

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Table 1. Sample size (n), mean catch-per-unit-effort (CPUE = fish/minute of electrofishing), total length (mm; Minimum–Maximum [Min–Max]) statistics, proportional size distribution (PSD), total annual mortality (A), recruitment coefficient of determination (RCD), recruitment variability index (RVI), and annual angler exploitation (µ) for Largemouth Bass populations sampled from lakes in northern Idaho (2014–2015). Numbers in parentheses represent one standard error of the mean.

Total length Water body n CPUE Mean Min–Max PSD A RCD RVI µ Chase Lake1 101 1.5 (0.3) 243.3 (8.0) 112–520 26 28.2 0.65 0.53 0.0 Fernan Lake2 202 2.5 (0.4) 264.9 (6.3) 65–560 43 -- -- -- 22.1 Hayden Lake1 184 0.5 (0.2) 293.6 (5.7) 95–505 43 31.1 0.83 0.73 15.3 Kelso Lake2 129 2.1 (0.3) 226.8 (7.4) 73–568 10 30.9 0.41 0.60 0.0 Lower Twin Lake2 106 1.5 (0.2) 195.6 (6.6) 94–404 46 -- -- -- 0.0 Robinson Lake1 84 1.4 (0.2) 260.7 (7.1) 64–548 15 18.9 0.70 0.60 0.0 Round Lake2 93 1.8 (0.7) 227.5 (8.4) 55–402 37 43.8 0.90 0.75 44.4 Spirit Lake2 238 1.3 (0.2) 198.2 (6.8) 62–523 51 29.8 0.61 0.74 0.0 Upper Twin Lake2 242 2.4 (0.5) 202.9 (5.7) 87–560 57 -- -- -- 13.8

1 Six bass, only two LMB, LMB 16” min 2 General rules, 6 bass, no size restrictions

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Table 2. Fishes sampled from lakes in north Idaho as part of Largemouth Bass population assessment during 2014–2015. Taxa indicated include Brown Bullhead (BBH), Black Crappie (BCR), Bluegill (BLG), Brook Trout (BKT), Channel Catfish (CAT), Green Sunfish (GSN), Largemouth Bass (LMB), Longnose Sucker (LNS), Largescale Sucker (LSS), Northern Pike (NPK), Pumpkinseed (PKS), Rainbow Trout (RBT), Smallmouth Bass (SMB), Tench (TNC), Westslope Cutthroat Trout (WCT), and Yellow Perch (YLP).

Water body BBH BCR BLG BKT CAT GSN LMB LNS LSS NPK PKS RBT SMB TNC WCT YLP Chase Lake X X X X X Fernan Lake X X X X X X X X X X X Hayden Lake X X X X X X X X X Kelso Lake X X X X X X X X Lower Twin Lake X X X X X X X X

Robinson Lake X X X X X X X X Round Lake X X X X X X X X X X Spirit Lake X X X X X X X X X Upper Twin Lake X X X X X X X

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Figure 1. Length-frequency distributions for Largemouth Bass sampled from northern

Idaho lakes (2014–2015).

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Figure 2 Estimates of Studentized residuals from catch curve regressions for Largemouth

Bass sampled from northern Idaho lakes (2014–2015). Positive residuals represent strong year-classes and negative residuals represent weak year-classes.

Chase Lake

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Figure 3. Age-structure distribution of Largemouth Bass sampled from North Idaho lakes

with weighted catch curve regressions estimating mortality and recruitment variability for Largemouth Bass sampled from northern Idaho lakes (2014–2015). Closed circles represent age-classes to which the regression model was fitted. Open circles represent age classes that were not fully-recruited to the gear and not included the model.

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Figure 4. Mean length-at-age for Largemouth Bass sampled from northern Idaho lakes

(2014–2015). Error bars represent one standard error about the mean.

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BULL TROUT REDD COUNTS

ABSTRACT

In 2015, we counted Bull Trout redds as an index of adult abundance in each of the major drainages in northern Idaho’s Panhandle Region. Bull Trout redd surveys detected a total of 656 redds, including; 553 in the Pend Oreille drainage, 54 redds in the Upper Priest Lake drainage, 11 in the St. Joe drainage, 37 in the Little North Fork Clearwater drainage, and one in the Kootenai River drainage. Redd count totals from 2015 represented both increases and decreases relative to averages of count totals from the previous ten year period, but did not reflect dramatic shifts in total counts in any core area. Authors: Rob Ryan Regional Fisheries Biologist Ken Bouwens Regional Fisheries Biologist Carson Watkins Regional Fisheries Biologist T.J. Ross Fisheries Research Biologist

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INTRODUCTION

Bull Trout Salvelinus confluentus were listed by the U.S. Fish and Wildlife Service (USFWS) as a threatened species under the endangered species act in 1999. Idaho Department Fish and Game (IDFG) personnel, along with employees of other state and federal agencies, annually count Bull Trout redds in some of the core recovery areas to monitor long-term trends of these populations. Redd counts allow for evaluation of the status of the populations in these areas and to help in directing future management and recovery activities.

STUDY SITES

Bull Trout redds were counted in headwater streams within the Priest River, Pend Oreille Lake, Kootenai River, and St. Joe River drainages where Bull Trout were known to spawn. These watersheds make up all or part of four different core areas that occur in the IDFG Panhandle Region. The boundaries of the Kootenai River core area extends outside of the Panhandle Region so our counts represent only a small portion of the population in these core areas.

METHODS

We counted Bull Trout redds in selected tributaries of the Priest Lake, Priest River, Pend Oreille Lake, Kootenai River, and St. Joe River where Bull Trout were known or believed to occur. We summarized counts by basins or core area. Redd counts in the Middle Fork (MF) East River and Uleda Creek (tributaries of Priest River) were combined with the Pend Oreille Lake Core Area in 2003 when these Bull Trout were documented to spend their adult life in Pend Oreille Lake (Dupont et al. 2009).

We located redds visually by walking along annually monitored sections within each

tributary. Bull Trout redds were defined as areas of clean gravels at least 0.3 x 0.6 m in size with gravels of at least 76.2 mm in diameter having been moved by the fish, and with a mound of loose gravel downstream from a depression (Pratt 1984). In areas where one redd was superimposed over another redd, each distinct depression was counted as one redd. Redd surveys were conducted during the standardized time periods (late September/ October). In some surveys redd locations were recorded on maps and/or recorded by global positioning system (GPS).

We compared Bull Trout redd count totals by core area to prior count years to assess

dramatic shifts in redd abundance. Total redd counts were compared to average counts from the previous ten years of sampling. Comparisons were generally qualitative references to increases or declines relative to previous count averages.

RESULTS AND DISCUSSION

Pend Oreille Core Area

We completed the Pend Oreille core area redd counts between October 7 and 20, 2015. A total of 553 Bull Trout redds were counted among all surveyed streams (Table 3). Six index streams counted consistently since 1983 accounted for 297 of the total redds. Due to inclement weather and high flows, redds were not counted in two index streams (Lightning Creek and

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Grouse Creek). Overall counts were below the previous ten-year averages for total and index counts of 753 and 461, respectively.

Priest Lake Core Area

We completed the Priest River core area redd counts on September 29, 2015. We counted 54 Bull Trout redds between seven standard (defined in 2013) stream reaches surveyed in the core area (Table 4). Overall counts declined from the previous year, but were above the previous ten-year average for combined counts of 38 redds.

St Joe Core Area

St Joe River core area redd counts were completed on October 3, 2015. We surveyed Index streams (i.e., Wisdom Creek, Medicine Creek, and mainstem St. Joe River [between Heller Creek and St. Joe Lake]) that have consistent monitoring data. We counted a total of 11 Bull Trout redds among four index reaches in the core area (Table 5). We counted four redds in Medicine Creek and seven redds in the St. Joe River between Medicine Creek and St. Joe Lake. Total redds observed in 2015 represented a decline from previous years and from the ten year average for index streams.

The number of streams surveyed per year in the St Joe River core area has varied

considerably over time. Interpretation of total count values should be done cautiously. We recommend focusing future efforts primarily on index streams to better understand trends in redd abundance.

North Fork Clearwater Core Area (Little North Fork Clearwater River)

Little North Fork Clearwater River redd counts were completed on Ocotber 4, 2015. We surveyed index streams (i.e., Lund Creek, Little Lost Lake Creek, Lost Lake Creek, and mainstem Little North Fork Clearwater River [between USFS rd 1268 crossing and Fish Lake]) that have consistent monitoring data. We counted a total of 37 Bull Trout redds among the four index reaches (Table 6). Our survey results represent a slight decline in redd abundance

The number of redds counted during the 2015 survey is 18% below the long-term mean

and 48% below the 10-year mean. We recommend continued monitoring with a primary focus on index streams to better understand trends in redd abundance over time.

Kootenai River Core Area

Kootenai River core area redd counts were completed on Idaho tributary streams in October 2015. A single Bull Trout redd was observed in the Callahan Creek drainage in Idaho (Table 7). Bull Trout redd surveys were not conducted in Boulder Creek, Idaho in 2015. Boulder Creek is on a three-year rotation and will be surveyed again in 2016. Additional Bull Trout redd surveys were completed within Montana tributaries to the Kootenai River, but were not reported here. Idaho Bull Trout surveys continue to represent a small proportion of the total redds observed in the Kootenai system.

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MANAGEMENT RECOMMENDATIONS

1. Continue to monitor Bull Trout spawning escapement using redd surveys. 2. Continue to balance the frequency and location of surveys with the availability of time

and intended use of collected data.

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Table 3. Bull Trout redd counts by year from tributaries of Lake Pend Oreille, Clark Fork River, and Pend Oreille River, Idaho. STREAM (*Index) 1983-2005 Avg. 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Clark Fork R. 7 3 2 0 1 0 0 - - - - Lightning Cr. 11 9 3 10 11 0 20 1 1 4 11 E.F. Lightning Cr.* 51 51 34 38 85 26 64 11 26 22 17 Savage Cr. 8 25 0 8 5 6 1 - 5 6 5 Char Cr. 11 20 1 5 1 4 9 0 4 2 0 Porcupine Cr. 10 8 8 8 15 11 13 2 4 15 0 Wellington Cr. 8 29 9 10 4 7 6 5 5 11 8 Rattle Cr. 22 21 2 24 62 43 65 59 8 63 5 Morris Cr. 2 16 0 6 6 9 0 0 3 14 0 Johnson Cr.* 20 28 32 40 47 57 54 54 50 21 5 Twin Cr. 9 11 0 4 0 0 1 - - - - Strong Cr. 1 - - 7 6 2 11 3 47 17 0 Trestle Cr.* 248 395 145 183 279 188 178 187 133 159 117 Granite Cr. 48 166 104 52 106 75 129 68 217 115 68 Sullivan Springs 15 28 17 7 2 9 11 4 11 4 0 N. Gold Cr.* 30 30 28 17 28 28 6 3 28 25 41 S. Gold Cr.* 123 235 179 73 107 130 56 110 106 88 69 W. Gold Cr. NA 4 0 7 5 4 0 8 29 10 3 M.F. East R. 20 71 34 36 25 22 28 28 25 51 51 Uleda Cr. 4 7 2 7 16 6 9 24 14 26 11 N.F. East R. 1 0 - 0 - 0 - - - - - Pack R. 24 44 16 11 4 0 1 7 6 1 35 Grouse Cr.* 39 55 38 31 51 27 116 69 12 54 48 Caribou Cr. NA - - - - - 37 6 47 9 57 Hellroaring Cr. NA - - - - - - 3 - - 2 Total 6 index streams 508 794 456 382 597 456 474 434 355 369 297 Total of all streams 654 1256 654 584 866 654 815 652 781 717 553

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Table 4. Bull Trout redd counts by year from the Upper Priest River, Idaho and selected tributaries between 1993 and 2015. Redd surveys were not completed on all stream reaches in all years between 1993 and 2004. As such, averaged redd counts for surveys completed between these years may include fewer completed counts.

Stream Transect Length (km) Avg. 1993 -2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Upper Priest River Falls to Rock Cr. 12.5 12 13 21 5 14 5 17 10 36 34 58 25

Rock Cr. to Lime Cr. 1.6 2 0 1 0 0 2 4 1 0 7 8 12

Lime Cr. to Snow Cr. 4.2 7 3 4 1 5 10 3 1 3 6 9 13

Snow Cr. to Hughes Cr. 11.0 4 10 0 1 2 4 0 7 2 2 0 1

Hughes Cr. to Priest Lk 2.3 0 -- -- -- -- -- 0 0 0 -- -- --

Rock Cr. Mouth to F.S. trail 308 0.8 < 1 0 0 0 0 0 1 0 0 -- -- --

Lime Cr. Mouth upstream 1.2 km 1.2 < 1 0 0 0 0 0 0 0 0 -- -- --

Cedar Cr. Mouth upstream 3.4 km 3.4 < 1 0 0 0 0 0 0 0 0 -- -- --

Ruby Cr. Mouth to waterfall 3.4 0 0 -- 0 0 0 0 -- -- -- -- --

Hughes Cr. Trail 311 to trail 312 2.5 1 0 0 0 0 0 0 0 0 -- -- --

F.S. road 622 to Trail 311 4.0 1 1 1 0 0 5 0 7 5 0 3 0

F.S. road 622 to mouth 7.1 2 1 1 0 0 3 11 3 2 1 2 3

Bench Cr. Mouth upstream 1.1 km 1.1 < 1 0 0 0 0 0 0 0 0 -- -- --

Jackson Cr. Mouth to F.S. trail 311 1.8 0 0 1 0 0 0 0 0 0 -- -- --

Gold Cr. Mouth to Culvert 3.7 3 1 0 0 1 5 6 2 4 3 1 0

Boulder Cr. Mouth to waterfall 2.3 0 0 -- 0 0 0 0 -- 0 -- -- --

Trapper Cr. Mouth upstream 5.0 km upstream from East Fork 5.0 2 0 -- 0 0 0 0 -- 0 -- -- --

Caribou Cr. Mouth to old road crossing 2.6 < 1 -- -- -- -- -- 0 -- -- -- -- --

All stream reaches combined 70.5 31 29 29 7 22 34 42 31 52 53 81 54 Only those stream reaches counted during 1985-86 23.8 14 6 6 1 6 23 20 13 14 -- 15 16

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Table 5. Bull Trout redd counts by year from the St. Joe River, Idaho and selected tributaries. Redd surveys were not completed on all stream reaches in all years between 1992 and 2003. As such, averaged redd counts for surveys completed between these years may include fewer completed counts.

Stream Name Avg 1992 - 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Aspen Cr. 0 -- -- -- -- -- -- -- -- -- -- Bacon Cr. 0 -- -- -- 0 -- -- 0 -- 0 -- Bad Bear Cr. 0 -- -- -- -- -- -- -- -- -- -- Bean Cr. 7 -- -- -- 1 -- -- 1 0 -- -- North Fork Bean Creek -- -- -- -- -- -- -- 19 8 0 -- Unnamed tributary to N.Fk. Bean -- -- -- -- -- -- --

3 -- --

Beaver Cr. <1 0 0 0 0 3 -- 0 -- -- -- Bluff Cr.- East Fork 0 -- -- -- -- -- -- -- -- -- -- California Cr. 1 0 0 0 2 -- -- 0 -- -- -- Cascade Creek -- -- -- -- -- -- -- 2 -- -- -- Copper Cr. 0 -- 0 0 -- -- -- -- -- -- -- Entente Cr. <1 -- -- -- -- -- -- -- -- -- -- Fly Cr. <1 -- 0 2 1 0 -- 0 -- -- -- Gold Cr. Lower mile 0 -- -- -- -- -- -- -- -- -- -- Gold Cr. Middle 0 -- -- -- -- -- -- -- -- -- -- Gold Cr. Upper 1 -- -- -- -- -- -- -- -- -- -- Gold Cr. All 1 -- -- -- -- -- -- -- -- -- -- Heller Cr. <1 5 0 0 3 9 5 5 -- 0 -- Indian Cr. 0 -- -- -- -- -- -- -- -- -- -- Medicine Cr.* 32 71 55 71 41 48 35 20 20 17 4 Mill Cr. -- -- -- -- -- -- -- 9 6 -- -- Mosquito Cr. 1 -- -- -- -- -- -- -- -- -- -- My Cr. -- -- -- -- -- -- -- 0 -- -- -- Pole -- -- -- -- -- -- -- 0 -- -- -- Quartz Cr. 0 -- -- -- -- -- -- -- -- -- -- Red Ives Cr. <1 0 1 1 -- 2 4 0 -- -- -- Ruby Cr. 3 -- -- -- -- -- -- 0 -- 0 -- Sherlock Cr. 1 0 0 3 -- 1 -- 2 -- 0 -- Simmons Cr. - Lower 0 -- -- 1 0 -- -- -- -- -- -- Simmons Cr. - NF to Three Lakes 3 0 -- -- 0 -- -- -- -- -- -- Simmons Cr. - Three Lakes to Rd 1278 2 0 -- -- 0 -- -- -- -- -- -- Simmons Cr. - Rd 1278 to Washout <1 -- -- -- 0 -- -- -- -- -- --

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Table 5 (continued)

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Stream Name Avg 1992 - 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Simmons Cr. - Upstream of Washout 0 -- -- -- 0 -- -- -- -- -- -- Simmons Cr. - East Fork 0 -- -- -- 0 -- -- -- -- -- -- St. Joe River - below Tento Creek 0 -- -- -- -- -- -- -- -- -- -- St. Joe River - Spruce Tree CG to St. J. Lodge 0 -- -- -- -- -- -- -- -- -- -- St. Joe River - St. Joe Lodge to Broken Leg 4 -- -- -- -- -- -- -- -- -- -- St. Joe River - Broken Leg Cr upstream 0 -- -- -- -- -- -- -- -- -- -- St. Joe River - Bean to Heller Cr. 0 -- -- -- -- -- -- -- -- -- -- St. Joe River - Heller to St. Joe Lake* 9 0 6 8 1 5 7 4 1 0 7 Three Lakes Creek 0 -- -- -- -- -- -- -- -- -- -- Timber Cr. <1 -- -- -- -- -- -- -- -- -- -- Tinear Cr. -- -- -- -- -- -- -- 2 5 -- -- Wampus cr 0 -- -- -- -- -- -- -- -- -- -- Washout cr. 1 -- -- -- -- -- -- -- -- -- -- Wisdom Cr* 7 12 32 27 8 1 1 5 1 0 0 Yankee Bar <1 3 0 0 -- -- -- -- -- -- -- Total - Index Streams* 48 83 93 106 50 54 43 29 22 17 11 Total - All Streams 73 91 94 113 57 69 52 69 44 17 11 Number of streams counted 26 11 11 12 15 8 5 18 8 8 3 * Index streams

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Table 6. Bull Trout redd counts by year for index stream reaches in the Little North Fork Clearwater River, Idaho (2000–2015). Stream 2000 2001 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2015 Buck Creek -- -- -- -- 5 -- -- -- -- -- -- -- -- -- Canyon Creek -- -- -- -- 0 -- -- -- -- -- -- -- -- -- Butte Creek -- -- 5 0 -- -- -- -- -- -- -- -- -- -- Rutledge Creek -- -- -- -- 1 1 6 0 -- -- -- -- -- -- Rocky Run Creek -- -- -- 5 1 3 21 13 8 -- 8 10 1 -- Lund Creek 1 13 5 7 8 5 19 7 30 22 11 6 1 3 Little Lost Lake Creek 3 1 -- 6 7 16 1 38 36 14 5 19 1 1 Lost Lake Creek 1 -- -- 0 -- 1 -- 10 13 8 9 7 6 1 Little North Fork Clearwater River

1268 Bridge to Lund Cr. -- -- 17 6 13 8 16 18 20 13 3 6 19 18 Lund Cr. to Lost Lake Cr. 8 3 12 7 7 5 8 16 21 9 11 9 11 13 Lost Lake Cr. to headwaters 5 1 -- 5 6 5 11 13 8 20 14 7 6 1 All stream reaches surveyed in 2003 18 18 39 36 48 44 82 115 136 86 61 64 45 37

Table 7. Bull Trout redd counts by year from the selected tributaries of the Kootenai River, Idaho.

Stream Length (km) Avg 2002-2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

IDAHO

North Callahan Creek 3.3 21 10 29 3 17 10 9 2 6 9 7 1

South Callahan Creek 4.3 7 5 4 0 0 0 1 0 0 2 0 0 Boulder Creek 1.8 1 1 0 0 0 0 0 0 0 0 -- -- Idaho Total 9.4 28 16 33 3 17 10 10 2 6 11 7 1

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PRIEST LAKE FISHERY INVESTIGATIONS

ABSTRACT

In 2015, we investigated Priest Lake kokanee abundance in an effort to describe population trends. We conducted a lakewide mobile hydroacoustic survey to estimate kokanee abundance. We also monitored kokanee spawner abundance in Priest Lake by counting mature adults at five standard areas. Estimated Priest Lake kokanee density was 25 fry/ha and 8 ages1-4 kokanee/ha. We counted a total of 6,117 kokanee spawners along five standard shoreline areas of Priest Lake. The combined observations from our acoustic survey and shoreline spawner counts suggested kokanee abundance declined from the increased abundances observed since 2011. Author: Rob Ryan Regional Fishery Biologist

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INTRODUCTION

Priest Lake is located in Idaho’s panhandle approximately 28 km south of the Canadian border. Surface area of the lake is 9,446 ha with 8,190 ha of open water habitat greater than 12 m deep. Historically, Priest Lake provided fisheries for Bull Trout Salvelinus confluentus, Westslope Cutthroat Trout Oncorhynchus clarkii lewisi, and Mountain Whitefish Prosopium williamsoni. Introductions of kokanee Oncorhynchus nerka, Lake Trout Salvelinus namaycush, Largemouth Bass Micropterus salmoides, Smallmouth Bass Micropterus dolomieu, and Yellow Perch Perca flavescens created additional fishing opportunities that are present today (Liter et al. 2009, Watkins et al. in review). The Priest Lake fishery is significant with an estimated $5.9 million spent by anglers fishing the lake in 2011 (IDFG, unpublished data).

Priest Lake fisheries management has changed significantly since the early 1900’s. Bull

Trout and Westslope Cutthroat Trout were once the primary target of anglers, but have been regulated under “no harvest” fishing rules since the late 1980’s due to perceived declines in abundance. Kokanee also once offered the primary fishery in the lake and a significant harvest opportunity. However, kokanee abundance declined through the 1970’s and 80’s resulting in fishery closure. Kokanee densities in the lake remain low, but a harvest fishery was re-established in 2011 and has gained considerable interest among anglers (Fredericks et al. 2013). Lake Trout, once less common in the catch, provided a trophy opportunity prior to kokanee collapse. However, increased Lake Trout abundance between the 1970’s and 90’s led to shifting management objectives and the current yield fishery (IDFG 2013). Recently, Smallmouth Bass were unintentionally established in Priest Lake and have gained angler interest. Mysis shrimp Mysis diluviana were introduced to Priest Lake in the 1960’s and are assumed to have positively influenced Lake Trout and negatively influenced other once–abundant fish species (i.e., kokanee, Bull Trout, Westslope Cutthroat Trout; IDFG 2013).

Current fishery management objectives for Priest Lake are independent of Upper Priest

Lake, a 566 hectare lake north of Priest Lake. However, observations of fish movements through the Thorofare, approximately 3 km of flowing water connecting the two lakes, clearly demonstrate the fish communities within the lakes are not entirely independent (Fredericks and Venard 2001). Current management priorities include a focus on native species in Upper Priest Lake, and a focus on mixed species including Lake Trout, kokanee, and Westslope Cutthroat Trout in Priest Lake. Due to the interaction between these connected water bodies, independent management of these fisheries may be in conflict and create challenges for maintaining quality fisheries in either lake. In addition, Priest Lake anglers are currently divided between interests in Lake Trout and enhancement of other species (i.e., Westslope Cutthroat Trout, kokanee; IDFG 2013). To address these issues the Idaho Department of Fish and Game Fisheries Management Plan (2013-2018) indicates a better understanding of the fish communities in this system is necessary to guide future management direction (IDFG 2013). Consistent with this objective, we investigated Priest Lake kokanee abundance during 2015 to describe current population trends.

METHODS

Kokanee Monitoring

We conducted a lakewide mobile hydroacoustic survey on Priest Lake to estimate kokanee abundance on the night of August 11, 2015. We used a Simrad EK60 split-beam, scientific echosounder with a 120 kHz transducer to estimate kokanee abundance. Ping rate

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was set at 0.3 to 0.51 seconds per ping. A pole-mounted transducer was located 0.52 m below the surface, off the port side of the boat, and pointed downward. The echosounder was calibrated prior to the survey using a 23 mm copper calibration sphere to set the gain and to adjust for signal attenuation to the sides of the acoustic axis. Prior to our survey, we measured a water temperature profile to calibrate signal speed and as a reference of the expected zone of occupancy for kokanee. Water temperatures were measured at one meter intervals from the surface to 15 meters using a YSI 85-50 dissolved oxygen and temperature meter (YSI Incorporated). Mean water temperature for water depths between zero and ten meters was used in system calibration. We used Simrad ER60 software (Simrad Yachting) to determine and input the calibration settings.

We used standardized transects to complete the survey (Maiolie et al. 2013). We

followed a uniformly spaced, zigzag pattern of 15 transects stretching from shoreline to shoreline (Figure 5). The zigzag pattern was used to maximize the number of transects that could be completed in one night. The pattern followed the general rule of using a triangular design (zigzags) when the transect length was less than twice the transect spacing (Simmonds and MacLennan 2005). The starting point of the first transect at the northern end of the lake was originally chosen at random. Boat speed was approximately 2.4 m/s.

Kokanee abundance was determined using echo integration techniques. Echoview

software version 5.4 (Echoview Software Pty Ltd) was used to view and analyze the collected data. A box was drawn around the kokanee layer on each of the echograms and integrated to obtain the nautical area scattering coefficient (NASC) and analyzed to obtain the mean target strength of all returned echoes. This integration accounted for fish that were too close together to detect as a single target (MacLennan and Simmonds 1992). Densities were then calculated by the equation:

Density (fish/ha) = (NASC /4π10TS/10) 0.00292 where: NASC is the total backscattering in m2/nautical mile2, and TS is the mean target strength in dB for the area sampled.

Kokanee density was estimated directly from the echograms. All fish in the observed pelagic fish layer were identified as kokanee if target strengths of the observed fish were within the expected size range. Size ranges were based on Love’s equation, which describes the relationship between target strength and fish length (Love 1971). A total kokanee density for all fish was calculated by echo integration. Next, a virtual echogram was built from the corrected target strengths. We then multiplied the total kokanee density estimate on each transect by the proportion of small targets (-60 dB and -45 dB) to estimate the density of kokanee fry. The proportion of large targets (-44 dB to -30 dB) was used to estimate density of kokanee age classes one to four.

We calculated kokanee abundance by multiplying estimated densities by the area of pelagic usable habitat in Priest Lake. Priest Lake has been estimated to contain 8,190 ha of pelagic habitat usable by kokanee (Maiolie et al. 2013). Eighty-percent confidence intervals were calculated for the estimates of fry and older age classes of kokanee. Error bounds calculated for arithmetic mean densities utilized a Student’s T distribution. The entire lake was considered to be one section, without stratification by area.

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We also monitored kokanee spawner abundance in Priest Lake on November 5, 2015. Spawning kokanee were observed and counted at five standard nearshore areas, including Copper Bay, Hunt Creek, Cavanaugh Bay, Indian Creek, and Huckleberry Bay. We collected a sample of spawning kokanee adjacent to the mouth of Hunt Creek using monofilament gill nets to obtain size, sex, and age class information. One gillnet was set for 15 minutes. The monofilament gillnet was 46 m long with variable mesh panels from 1.9 mm to 6.4 mm bar mesh. We estimated mature kokanee ages by examining freshly removed whole otoliths under a dissecting microscope. Sexes were determined by examining the fish’s external characteristics and gonads.

RESULTS

Kokanee Monitoring

Estimated Priest Lake kokanee density in August 2015 was 25 fry/ha (± 12.7, 80% C.I.;Table 8) and 8 age-1 to age-4 kokanee/ha (± 2.5, 80% C.I.;Table 8). Expanded densities estimates were 205,923 kokanee fry and 61,636 kokanee ages 1-4.

Target strengths observed during the hydroacoustic surveys showed a bimodal distribution that we used to parse out kokanee fry from older age classes (Figure 6). Based on the bimodal distribution, we split kokanee fry from older age classes at -44.0 dB.

We counted a total of 6,117 kokanee spawners along five shoreline areas of Priest Lake in 2015 (Table 9). Counts included 1,885 at Copper Bay, 2,550 at Hunt Creek, 1,155 at Cavanaugh Bay, 520 at Indian Creek, and 7 at Huckleberry Bay. Counts were lower than observed since 2011 (Figure 7). Spawning adult kokanee collected near Hunt Creek varied in length from 356 mm to 445 mm and averaged 400 mm (n = 13) and 374 mm (n = 3), for males and females, respectively. All mature adults collected were estimated to be three years of age.

DISCUSSION

Kokanee Monitoring

Kokanee density estimates continued to reflect a low density population in Priest Lake. Our density estimates represented a decline from 2014 levels, but within the observed variability of individual estimates (Figure 8; Fredericks et al. 2013, Maoilie et al. 2013, and Ryan et al. 2014, Watkins et al. in review). Priest Lake kokanee spawner counts also declined relative to counts completed between 2011 through 2014 (Figure 7; Fredericks et al. 2013, Maoilie et al. 2013, Ryan et al. 2014, Watkins et al. in review). In 2015, we observed about 50% fewer spawners than in the previous year. Average length of kokanee spawners increased marginally from recent years (Figure 8), and fish size continued to indicative of a low density population. The combined observations from our acoustic survey and shoreline spawner counts, although not definitive, suggested kokanee abundance declined from the increased abundances observed since 2011.

Shoreline spawner counts continued to be a crude approximation of the total number of

mature kokanee. In 2015, we observed numerous constructed redds in areas with few adult kokanee. In addition, we received miscellaneous reports of large numbers of kokanee in count areas prior to our survey, yet fish were not abundant during our survey. As such, shoreline

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spawner counts were interpreted as general trend information to be used in combination with acoustic surveys to detect notable changes in kokanee abundance.

One of the primary limitations of our current monitoring efforts continued to be a lack of

age-specific abundance information. The absence of age-specific abundance data limited our ability to investigate kokanee survival and, more specifically, identify potential survival bottlenecks at a particular life stage. We recommend continuing standard monitoring efforts that enable population trend monitoring, but that additional effort to describe population age-specific abundance also be incorporated.

RECOMMENDATIONS

1. Utilize hydroacoustic surveys as a tool for monitoring Priest Lake kokanee abundance in low density conditions.

2. Consider additional methods for describing population structure (e.g., suspended gill nets)

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Table 8. Hydroacoustic survey results for kokanee from Priest Lake, Idaho on August 11, 2015. Transect Single Targets NASC Mean TS Total Density (fish/ha) % Fry Fry Density (#/ha) % Ages 1-4 Age 1-4 Density (#/ha)

1 2 1.86 -38.89 3 0.50 2 0.50 2 2 3 3.83 -37.92 6 0.33 2 0.67 4 3 10 10.51 -40.11 25 0.70 18 0.30 8 4 13 15.71 -39.09 30 0.54 16 0.46 14 5 10 8.21 -38.92 15 0.60 9 0.40 6 6 12 10.86 -39.32 22 0.83 18 0.17 4 7 14 14.22 -36.97 16 0.79 13 0.21 4 8 13 5.44 -42.80 24 0.62 15 0.38 9 9 29 26.43 -35.73 23 0.66 15 0.34 8 10 26 9.12 -44.31 57 0.85 48 0.15 9 11 27 56.93 -37.46 74 0.63 46 0.37 6 12 15 65.49 -34.75 45 0.33 15 0.67 30 13 17 25.20 -34.62 17 0.35 6 0.65 11 14 0 -- -- 0 0 0 0 0 15 13 4.33 -51.87 155 1.00 155 0.00 0 Mean 34 25 8

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Table 9. Kokanee spawner counts at three standard locations on Priest Lake, Idaho in 2015. Location 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015* Copper Bay 588 549 1,237 1,584 906 1,288 308 223 400 37 750 7,995 1,070 1,960 1,885 Cavanaugh Bay 523 921 933 1,673 916 972 463 346 550 331 1,340 3,135 2,295 838 1,155 Huckleberry Bay 200 49 38 359 120 43 38 0 37 18 90 665 340 525 7 Indian Creek Bay 222 0 0 441 58 0 40 27 15 49 1,050 830 1,270 2,750 520

Hunt Creek Mouth 232 306 624 2,060 2,961 842 1,296 884 1,635 1,410 16,103 14,570 26,770 7,530 2,550

Total 1,765 1,825 2,832 6,117 4,961 3,145 2,145 1,480 2,637 1,845 19,333 27,195 31,745 13,603 6,117 * We counted an additional 15 fish at Grandview * Wind/snow during the survey created difficult viewing conditions * Evidence of spawning in areas with few fish observed - appeared to be late in the spawning period

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Transect Location

1 48o 44.105 N x 1160 51.216 W 48o 42.752 N x 1160 50.490 W 2 48o 42.752 N x 1160 50.490 W 48o 41.685 N x 1160 51.965 W 3 48o 41.685 N x 1160 51.965 W 48o 40.469 N x 1160 50.052 W 4 48o 40.469 N x 1160 50.052 W 48o 39.509 N x 1160 52.258 W 5 48o 39.509 N x 1160 52.258 W 48o 38.042 N x 1160 51.267 W 6 48o 38.042 N x 1160 51.267 W 48o 37.034 N x 1160 53.687 W 7 48o 37.034 N x 1160 53.687 W 48o 36.185 N x 1160 51.942 W 8 48o 36.185 N x 1160 51.942 W 48o 34.963 N x 1160 53.804 W 9 48o 34.963 N x 1160 53.804 W 48o 34.112 N x 1160 51.784 W 10 48o 34.112 N x 1160 51.784 W 48o 33.288 N x 1160 49.723 W 11 48o 33.288 N x 1160 49.723 W 48o 32.423 N x 1160 51.475 W 12 48o 32.423 N x 1160 51.475 W 48o 31.535 N x 1160 53.247 W 13 48o 31.535 N x 1160 53.247 W 48o 30.357 N x 1160 52.023 W 14 48o 30.357 N x 1160 52.023 W 48o 29.169 N x 1160 50.815 W 15 48o 36.208 N x 1160 51.323 W 48o 35.115 N x 1160 50.215 W

Figure 5. Standard transects on Priest Lake, Idaho used in hydroacoustic surveys of

kokanee abundance.

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Figure 6. Distribution of target strengths detected in an August 2015 hydroacoutic survey

of Priest Lake, Idaho.

Figure 7. Kokanee adult spawner counts at five standard locations on Priest Lake, Idaho

between 2001 and 2015. Additionally, length of male kokanee spawners sampled at the mouth of Hunt Creek each year is shown.

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Figure 8. Kokanee density estimates from hydroacoustic surveys completed during 2012 to

2015 in Priest Lake, Idaho.

Figure 9. Water temperature profile measured in association with our August 2015

hydroacoustic survey of Priest Lake, Idaho.

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UPPER PRIEST LAKE – LAKE TROUT MANAGEMENT

ABSTRACT

Upper Priest Lake is currently managed for the conservation of native species. In support of this objective, removal of non-native Lake Trout has occurred since 1998. In 2015, gill nets were used to remove 1,657 Lake Trout during a two-week period from May 11 to May 22, 2015. Average daily catch rate from standardized gill net mesh sizes was 7.9 fish/box (± 2.4, 80% C.I.), a decrease from 2014. Lake Trout length varied from 197 mm to 912 mm. Bull Trout catch rate (0.17/box) was above average for the previous eight-year period. Results indicate that the removal strategy being implemented is effectively keeping the Lake Trout population from increasing and likely benefitting native fish populations. Author: Rob Ryan Regional Fishery Biologist

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INTRODUCTION

Native fishes, including Bull Trout Salvelinus confluentus and Westslope Cutthroat Trout Oncorhynchus clarkii lewisi, played an important role in the history of Priest Lake and Upper Priest Lake fishing. Historically, Bull Trout provided a harvest-oriented trophy fishery in Priest and Upper Priest lakes (Bjornn 1957). However, harvest opportunities were discontinued in 1984 following declines in Bull Trout abundance. Although the influence of fishing mortality on the population was removed, a positive population response did not occur (Mauser et al. 1988). Today, the Bull Trout population in Upper Priest Lake is considered severely depressed while the population in Priest Lake is considered functionally lost (DuPont et al. 2007). Native Westslope Cutthroat Trout were also historically abundant in Priest Lake and Upper Priest lakes and provided the primary fishery in both lakes prior to the 1950’s (Mauser et al. 1988). Westslope Cutthroat Trout harvest was closed in 1988, also following a decline in abundance. Overharvest, interspecific competition, predation, and degradation of spawning habitat were all believed to contribute to the decline of native fish in this system.

Although multiple factors have likely influenced the abundance of native fishes in Priest

and Upper Priest lakes, increasing Lake Trout Salvelinus namaycush abundance was believed to be the primary cause of population-scale changes in native fish communities. Lake Trout, where introduced as a non-native sport fish, are often linked to negative responses in other native and non-native species through predation and/or competition (Martinez et al. 2009). In Upper Priest Lake, Lake Trout did not become well-established until the late 1990’s (Fredericks 1999). By 1998, Lake Trout abundance in Upper Priest Lake was estimated to be 859 fish (Fredericks 1999). Fishery managers were concerned that the establishment of Lake Trout posed a threat to native fish communities in Upper Priest Lake, particularly if the population continued to grow.

Native fish conservation has been an ongoing management focus on Upper Priest Lake.

In an effort to reduce the potential impacts of Lake Trout on native fish populations in Upper Priest Lake, the Idaho Department of Fish and Game (IDFG) began a Lake Trout removal program in 1998. Gill nets have been used annually to remove Lake Trout and reduce their abundance in the lake. These management efforts have removed between 150 and 5,000 Lake Trout annually from Upper Priest Lake (Fredericks et al. 2013). In 2015, we continued Lake Trout reduction efforts in Upper Priest Lake with the intent of benefiting native fish species.

OBJECTIVES

Conserve native fish populations in Upper Priest Lake by reducing Lake Trout abundance.

STUDY SITE

Upper Priest Lake is located approximately 21 kilometers (km) south of the Idaho-British Columbia border in the northwest corner of the Idaho Panhandle. It is a glacial lake that has roughly 13 km of shoreline, a surface area of 566 hectares (ha), a maximum depth of approximately 31 meters (m) and a maximum surface temperature of approximately 21 °C. The lake is bathtub-shaped with steep shoreline slopes and a flat bottom. Upper Priest and Priest lakes are held at 743 m elevation from the end of spring runoff until mid-October, which is controlled by a low-head dam located at the outlet of Priest Lake. Upper Priest Lake is connected to Priest Lake by a channel known as the Thorofare. This channel is roughly 3.2 km

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long, 70 m wide and 1.5-3 m deep at summer pool. At low pool, water depth in the Thorofare outlet is < 0.15 m and prohibits most boat traffic.

METHODS

We completed Lake Trout removal in Upper Priest Lake between May 11 and May 22, 2015. Hickey Brothers Research, LLC was contracted to provide equipment and labor for completion of the netting project. An 11 m commercial gill net boat was used to complete sampling efforts. Funding for completion of the Lake Trout removal effort was provided by the United States Fish and Wildlife Service (USFWS) and Kalispel Tribe, with in-kind contributions from IDFG.

We used monofilament-sinking gill nets to capture and remove Lake Trout from Upper

Priest Lake. Individual gill net dimensions were 91 m by 2.7 m. Multiple nets were tied together end-to-end to create a single net gang. Collectively, the net gang was comprised of a range of mesh sizes. Standardized mesh sizes (stretch-measure) were 45 mm, 51 mm, 64 mm, 76 mm, 89 mm, 102 mm, 114 mm, and 127 mm (Table 1). Fishing effort was measured in units defined as net boxes. Boxes were used to transport nets onboard the boat, and each box of net was equivalent to approximately 273 m, or three 91-m nets. Daily effort was split between morning and afternoon sets. The combined effort per day was 30 boxes of gill net. A total of 240 boxes of gill net were placed over ten days. Both morning and afternoon sets were made on each day, except the first and last days of each work week during which sets occurred during only one time period. The combined total effort for the first and last day of each work week was 30 boxes of net. Typically 18 boxes of net were set in the morning and 12 boxes of net were set in the afternoon. The combined effort by mesh size was consistent within morning and afternoon sets, respectively. The time between net placement and initiating net lifting varied from two to five hours for all sets. Gill nets were set throughout Upper Priest Lake over the course of the sampling period at depths varying from 10 m to 31 m. Placement of nets in and around the primary inlets and outlet of Upper Priest Lake was avoided to reduce bycatch of Bull Trout and Westslope Cutthroat Trout.

Relative abundance of Lake Trout in Upper Priest Lake was measured as average daily catch per unit of effort (CPUE) or fish per net box per day for catch associated with 51 mm, 64 mm, and 76 mm mesh sizes. These mesh sizes were selected as standards because they represented the longest time series of mesh sizes fished during Upper Priest Lake removal efforts. We compared these standardized catch rates to prior years in an attempt to evaluate trends in abundance. We only used data from 2010 to 2017 because catch by mesh was not recorded prior to 2010. We calculated 80% confidence bounds around estimates of average daily catch rate and used those bounds to infer differences in catch rate between years. We also evaluated change in size structure of the Lake Trout catch using catch rate from individual gill net mesh sizes. Lake Trout length was found to generally increase with gill net mesh size (Ryan et al. 2014), suggesting mesh-specific catch rates provide a relative measure of size-specific abundance. We compared mesh-specific catch rates from 2014 and 2015. Prior to 2014, a standard set of mesh sizes was not used and limited comparisons with prior years.

All Lake Trout caught during netting efforts were measured for total length (mm) and

examined for marks from past capture events. A portion of the Lake Trout catch greater than 400 mm were cleaned, packed on ice, and distributed to local food banks. Remaining Lake Trout were dispatched and returned to the lake. A portion of the catch was also used as study

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fish for an ongoing research project on Lake Trout movements in the system (Personal communication, Derek Entz, Eastern Washington University).

Bycatch of non-target species associated with the removal effort was generally noted

and fish were released if alive, though not all individuals were recorded. However, all Bull Trout were measured for total length and a condition score was assigned to each fish. Bull Trout condition was ranked from zero to three, with zero representing mortality and three representing excellent condition. We reported Bull Trout catch rate as the average of daily catch per unit of effort or fish per net box per day among all mesh sizes and compared catch rates from 2007 to 2015. Variance around catch rate estimates was described using 80% confidence bounds. Confidence bounds were only estimated for years during which standardized gill net effort and mesh were used (i.e. 2014-2015).

RESULTS

We removed 1,657 Lake Trout during the seven-day effort. Average daily catch rate from standardized mesh sizes was 7.9 fish/box (± 2.4, 80% C.I.), a 63% decrease from 2014 (Figure 10; Watkins et al. in review). Mesh specific catch rates also declined relative to 2014 in all mesh sizes except 102 mm and 114 mm (Figure 11; Watkins et al. in review). The largest declines in catch rates were observed in 51 mm and 64 mm meshes with reductions of 60% and 70%, respectively.

Total lengths of Lake Trout varied by mesh size (Figure 12). Lake Trout length varied

from 197 mm to 912 mm (Table 10). In general, fish length increased with increased gill net mesh size. Small mesh sizes (45 mm, 51 mm, and 64 mm) represented the highest catch rates and accounted for 77% of the total catch.

Incidentally caught species included Bull Trout, kokanee Oncorhynchus nerka,

Longnose Sucker Catostomus catostomus, Largescale Sucker C. macrocheilus, Mountain Whitefish Prosopium williamsoni, Northern Pikeminnow Ptychocheilus oregonensis, Peamouth Mylocheilus caurinus, and Westslope Cutthroat Trout. We caught 45 Bull Trout, representing an average daily catch rate of 0.17 fish per box of net. Observed catch rate was above the average for the previous eight-year period (0.13 Bull Trout per box; Figure 13). Bull Trout varied from 222 mm to 822 mm and averaged 350 mm.

DISCUSSION

In 2015, Lake Trout catch rates in Upper Priest Lake removal efforts represented a significant decline from rates observed between 2010 and 2014 (Figure 10). In past years, catch rates in standardized gill net mesh sizes have been relatively stable. In contrast, the reduction in catch rate that occurred during 2015 was considerably larger. Prior to 2015, it was difficult to conclude that Lake Trout removal efforts were leading to lower catch rates (and assumed lower Lake Trout abundance). The more substantial catch rate decline in 2015 may indicate that removal efforts are beginning to produce a population decline.

Although removal efforts likely play an important role in observed catch rates, other

factors may also influence Upper Priest Lake Lake Trout abundance. As an example, Lake Trout immigration from and emigration to Priest Lake may have influenced Upper Priest Lake abundance. Movement of Lake Trout between the lakes is known to occur and may be

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influenced seasonally by water conditions (Fredericks and Venard 2001). In 2015, water conditions throughout the watershed were atypical and characterized by a below average water year (e.g. low precipitation), and seasonally warmer water temperatures during the spring months.

Bull Trout catch rates in Upper Priest Lake continued an increasing trend observed since

2007 in concert with Lake Trout removal efforts (Figure 13), which may correspond to an increase in abundance. Bull Trout redd counts in the Upper Priest River also demonstrated a similar trend (see Panhandle Bull Trout Redd Count Summary in this report).The apparent positive response of Bull Trout provides evidence that incidental bycatch is not negatively influencing the population. And, though somewhat speculative, our data suggest that Lake Trout removals in Upper Priest Lake are benefitting Bull Trout.

RECOMMENDATIONS

1. Continue annual gillnetting at existing levels on Upper Priest Lake to remove Lake Trout to conserve native fishes.

2. Continue application of standardized gear types and effort quantities during Upper

Priest Lake netting to allow for inference relative to changes in the Lake Trout population and impacts of removal efforts

3. Periodically monitor of Westslope Cutthroat Trout abundance in Upper Priest Lake

and tributaries to further assess the influence of Lake Trout removal efforts on the conservation of native fishes

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Table 10. Upper Priest Lake 2015 gill net effort and Lake Trout (LKT) catch by gill net mesh size. Total length ranges of Lake Trout caught were reported by associated gill net mesh sizes.

Mesh Effort (ft) % of Effort LKT Caught Min TL Max TL 45 mm 43,200 20% 449 197 813 51 mm 43,200 20% 432 240 805 64 mm 43,200 20% 399 259 826 76 mm 14,400 7% 127 283 773 89 mm 14,400 7% 88 212 796 102 mm 28,800 13% 114 220 912 114 mm 14,400 7% 33 400 881 127 mm 14,400 7% 15 215 875

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Figure 10. Average daily Lake Trout catch rates (Lake Trout/box) and 80% confidence

intervals by year from combined standard gill net mesh sizes (51 mm, 64 mm, and 76 mm) fished in Upper Priest Lake, Idaho from 2010 to 2015.

Figure 11. Average daily Lake Trout catch rate (Lake Trout/box) and 80% confidence

intervals by mesh size from standardized gill nets fished in Upper Priest Lake, Idaho in 2014 and 2015.

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Figure 12. Size structure of Lake Trout sampled in Upper Priest Lake, Idaho during 2015.

Figure 13. Average daily Bull Trout catch rate (Bull Trout/box) and 80% confidence intervals

for all mesh sizes fished in Upper Priest Lake, Idaho from 2007 to 2015. Confidence intervals were only estimated for years in which gill net mesh size and effort were standardized.

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AN EVALUATION OF BAROTRAUMA-RELATED MORTALITY ON HOOK-AND-LINE CAUGHT LAKE TROUT

ABSTRACT

We investigated the probability of barotrauma-related mortality to better understand the impact of angling on the Lake Trout Salvenlinus namaycush population in Priest Lake, Idaho. With an interest in describing potential methods for mitigating barotrauma-related mortality, we also evaluated the benefit of “fizzing” or releasing pressure in the gas bladder of Lake Trout pre-release. Twenty anglers caught Lake Trout by hook-and-line on May 5 and 6, 2016 from Priest Lake. Barotrauma condition was assessed for each fish, and a subsample of fish was fizzed prior to release. All Lake Trout were released into in a large multifilament mesh holding pen (6.1 x 6.1 x 30.5 m) to assess levels of post-release mortality over a 20 to 21 day period. Probability of post-release mortality was evaluated using logistic regression models. A total of 196 Lake Trout were captured. Overall mortality rate was 30%. The top model describing Lake Trout mortality included covariates for barotrauma condition and fizzing and the interaction between barotrauma condition and fizzing. The estimated probability of mortality varied from 0.04 for fish with mild barotrauma to 0.84 for fish with severe barotrauma that were not fizzed. Overall, fizzing tended to reduce the probability of mortality for fish affected by barotrauma, but was more effective for fish with severe barotrauma. Our results combined with knowledge from previous studies suggested barotrauma-related mortality had the potential to negatively impact the Lake Trout population in Priest Lake, but the influence of post-release mortality on a population scale under current conditions is likely minimal. Authors:

Rob Ryan Idaho Department of Fish and Game Elizabeth Ng University of Idaho

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INTRODUCTION

Mortality associated with barotrauma is a concern in recreational fisheries where catch-and-release of deep-dwelling fishes occurs (Wilde 2009). Lake Trout Salvelinus namaycush commonly occur and are caught by anglers in deep water areas. Although, Lake Trout are physostomus fish that and have the capability regulating gas pressure in the swim bladder (Loftus et al. 1988), evidence of barotrauma-related mortality in Lake Trout rapidly brought to the surface from depth exists (Ng et al. 2015).

Catch-and-release of Lake Trout is common among anglers fishing on Priest Lake, Idaho (Watkins et al. in review). Anecdotal observations from Priest Lake anglers provide numerous accounts of barotrauma (i.e., expanded gas bladders) occurring in Lake Trout. The combination of these factors suggests unaccounted fishing-related mortality of Lake Trout may occur. Estimates of angler exploitation on Priest Lake Trout are low (μ = 13.6%; Ng 2015), but fail to account for delayed mortality of Lake Trout impacted by barotrauma. As such, fisheries managers may currently underestimate the influence fishing-related mortality has on annual survival rates.

We investigated the probability of barotrauma-related mortality to better understand the impact of angling on the Lake Trout population in Priest Lake. With an interest in describing potential methods for mitigating barotrauma-related mortality, we also evaluated the benefit of “fizzing” or releasing pressure in the gas bladder of Lake Trout pre-release.

METHODS

Twenty anglers caught Lake Trout by hook-and-line on May 5 and 6, 2015 from Priest Lake, Idaho. A variety of angling techniques were used, but were generally categorized as vertical jigging or trolling. Angling gear consisted of artificial lures tipped with natural bait. Anglers were dispersed on the lake and fished from boats. However, the study collection area was restricted to the central portion of Priest Lake in an effort to reduce fish transport duration.

Upon capture, Lake Trout were placed in a holding tank. These tanks varied in

dimension, but generally were in the form of either an onboard livewell or cooler. Water was periodically refreshed in each holding tank and bubblers were used to maintain oxygen levels. Surface water temperature of Priest Lake was not monitored during our study, but was generally cool and consistent with conditions for early May.

Anglers recorded information on each Lake Trout captured. Recorded information

included approximated catch location, water depth, angling method, time caught, time to retrieve, physical hooking location, and barotrauma condition. Hooking location was categorized by mouth, gills, esophagus, or other external location. Barotrauma condition was also categorized as mild - swimming upright with no abdominal distention; moderate - visibly bloated with some difficulty swimming upright; or severe - rigid body being unable to swim upright and or visible bleeding in the eyes as described in Ng et al. 2015. Anglers tagged each fish at the base of the dorsal fin with a uniquely numbered T-bar anchor tag used to identify individual fish.

All Lake Trout were held in a large multifilament mesh holding pen (6.1 x 6.1 x 30.5 m) to assess post-release mortality. We transferred Lake Trout from angler boats to the holding pen using a transport boat. In transport, fish were held in a holding tank with oxygen emitted through an oxygen stone. Lake Trout transfer occurred periodically throughout each day as anglers

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caught fish. Length of time fish were held by angler boats and the transport boat was recorded for each fish. Fish condition was assessed for each fish prior to release in the holding pen. Condition factors included trauma (mild - no or little physical damage; moderate - torn maxilla, eye damage, significant hooking tears; severe - heavy bleeding, torn gill filaments), a second evaluation of barotrauma (criteria previously described) and direct mortality resulting from angling or holding. A subsample of fish moderately or severely impacted by barotrauma was treated to release air bladder pressure (fizzed) prior to release. Fish were fizzed by inserting a 20 gauge hypodermic needle in the air bladder from a point below the lateral line and just posterior to the trailing edge of the left pectoral fin when held against the body of the fish. We randomly selected the first fish to fizz and then alternated between treatment and non-treatment fish. Fish were held in the holding pen for 20 or 21 days. We periodically observed the holding pen over that period and removed floating dead fish from the net.

Probability of post-release mortality was evaluated using logistic regression models. Severity of barotrauma (e.g., mild, moderate, and severe) and treatment by fizzing (e.g., not fizzed and fizzed) were included in all models. Additionally, based on previous field observations and literature review, we identified five covariates that we hypothesized would affect post-release mortality rate (Table 11). We also identified a priori six two-way interactions and one three-way interaction of interest (Table 11). Models incorporating combinations of these parameters were fit using the MuMIn package in R (Barton 2015; R Core Team 2015). Akaike’s Information Criterion, corrected for small sample sizes (AICc), was used to evaluate candidate models, and models with ∆AICc < 2 were considered to have a substantial level of support (Burnham and Anderson 2002; Richards 2005). We qualitatively evaluated parameter estimates for covariates in all of the top models, and then restricted hypothesis tests for the effect of fizzing to the model with the lowest AICc value.

RESULTS

During the two days of fish collection, a total of 196 Lake Trout were captured by 20 different anglers fishing from 10 different boats. Fifty-four percent of Lake Trout were captured by anglers using jigs and 46% of Lake Trout were captured by trolling. Average time spent catching each fish was 1.9 min (SD, 1.0 min). Only two fish had moderate hooking trauma; all other fish (99%) had mild hooking trauma. Most Lake Trout were hooked in the mouth (94%), no fish were hooked in the esophagus, 4% were hooked in the gills, and 3% were hooked elsewhere externally. Total length of fish captured varied from 290 to 890 mm (470 ± 85 mm). Capture depth varied from 12 to 63 m (mean ± SD: 46 ± 10 m), and barotrauma condition scores were approximately uniform in distribution (33% mild, 31% moderate, 36% severe). Holding time from capture to release into the holding pen varied from 0.2 to 2.8 h (1.1 ± 0.5 h).

Of the 132 Lake Trout with moderate or severe barotrauma, 64 were fizzed before they

were placed into the holding pen. After fish were held for 20 or 21 days, the overall mortality rate was 30%, excluding 44 fish that were missing. A previous study found no evidence of cannibalism in the holding pen, but suggested that fish length and condition (i.e., floating at the surface) were associated with higher probability of escape from a holding pen of the same construction (Ng et al. 2015). Therefore, we used a post hoc logistic regression to identify factors associated with higher probability of escape. Covariates evaluated included fish length, barotrauma condition, treatment with fizzing, interaction between barotrauma condition and fizzing, and the interaction between barotrauma and length. Fish size was found to be the most important factor, followed by whether the fish had been fizzed (Table 12; Figure 14). Smaller fish and fish that had not been fizzed tended to have higher probability of escape.

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After excluding the 44 missing fish and any fish with incomplete information, 147 fish

remained to evaluate post release mortality. Model selection indicated that there were five models with substantial support (Table 13). In addition to covariates for barotrauma condition and fizzing, which were included in all models, the top models also indicated that time catching, holding time, and fish length were important in determining probability of post-release mortality. Interactions between holding time and fizzing and between holding time and barotrauma condition were also important, indicating potentially complex effects of holding conditions. Although estimated effects for most of these covariates were consistent with hypotheses, effect sizes were small relative to standard errors (Table 14). For example, longer catch times tended to be associated with lower probabilities of mortality, but were generally not statistically significant. This could be due to low variability in catch times by anglers in the study.

In addition to the effects of barotrauma condition and fizzing, the top model (i.e., model

with the lowest AICc) also included the interaction between barotrauma condition and fizzing. The probability of mortality varied from 0.04 for fish with mild barotrauma to 0.84 for fish with severe barotrauma that were not fizzed (Table 15; Figure 15). Overall, fizzing tended to reduce the probability of mortality for fish affected by barotrauma, but was more effective for fish with severe barotrauma. Fizzing reduced the probability of mortality by 0.57 (P< 0.01) for severely affected fish, but only reduced probability of mortality by 0.13 (P = 0.33) for moderately affect fish.

DISCUSSION

Our results, combined with knowledge from previous studies, suggest barotrauma related mortality has potential to negatively impact the survival of angler-released Lake trout in Priest Lake. We found the probability of post-release mortality was high, especially for Lake Trout experiencing severe barotrauma. Release rate of Lake Trout in the Priest Lake fishery was estimated to be substantial, at approximately one third of the fish caught annually (Watkins et al. in review). Thus, post-release mortality could be significant on a population scale if angler effort is sufficiently high. However, current levels of angler effort and associated annual exploitation (13.6%) on Lake Trout were estimated to be low (Watkins et al. in review; Ng 2015). A recent estimate of instantaneous mortality for Priest Lake Lake Trout was also low (Z = 0.108; Ng 2015). Together these factors suggest that the additive influence of post-release mortality under current conditions was likely minimal on a population scale. As such, we do not recommend any specific management actions to address angler behaviors or reduce fishing mortality on Lake Trout. We do suggest consideration should be given to the potential influence of post-release mortality on Lake Trout if angler effort and catch should increase above current levels.

Angler behavior likely influences how fish are harvested and released and subsequently

how post-release mortality may impact the population. Our estimate of post-release mortality for Lake trout assumed anglers released fish irrespective of barotrauma condition. In reality, angler behavior and the decision to harvest fish in a recreational fishery may be influenced by a variety of factors (Hunt et al. 2002). Although no evaluation of fish condition was completed by Hunt et al. (2002), we speculated barotrauma condition could influence release rates. Specifically, fish presumed by an angler to be in poor condition as a result of expanded air bladders may be harvested more frequently. We did not measure this type of behavior in our study or in previous angler surveys on Priest Lake, but general comments from anglers encountered reflected that this type of behavior occurs on some level. If post-release mortality of Priest Lake Lake Trout

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becomes a concern we recommend further evaluation of angler behavior and its influence on harvest of Lake Trout be considered.

Depth at which a fish was caught was not identified to be a significant covariate in

describing the probability of mortality of caught and released Lake Trout in our study. However, we did not effectively incorporate the influence of depth in our evaluation. We anticipated depth at which a fish was caught could influence the occurrence and perhaps the severity of barotrauma. Initially, anglers in this study were directed to fish within two depth strata, shallow (< 15 m) and deep (> 15 m). However, poor catch rates within the shallow depth zone resulted in a small sample size and precluded stratification by depth. Lake Trout in this study were caught primarily below 30 m. The influence of depth on decompression-related mortality of caught and released fishes was found to be irrelevant in some studies (Loftus et al. 1988), but others suggested the type and level of injury related to barotrauma varied by depth for deep-dwelling fishes (Rummer and Bennet 2005, Bartholomew and Bohnsack 2005). Despite our limited ability to evaluate the influence of capture depth, we suspect that depths where fish were caught are fairly representative of what typically occurs in the Priest Lake fishery.

The top model in this study suggested fizzing of Lake Trout exhibiting signs of expanded

gas bladders promoted post-release survival. Our results were generally in opposition to Wilde (2009) who compiled and compared studies on post-release survival of vented or fizzed fishes. In that comparison, fizzing did not benefit post-release survival in most studies. The factors specifically affecting the positive influence of fizzing in our study were not clear, but we speculated that several factors contributed. We did not find in the literature a study where Lake Trout were the focal species of a study incorporating fizzing in evaluation of post-release survival. Although, it seems unlikely the benefits of fizzing would be species-specific, difference among species may exist. Loftus et al. (1988) suggested Lake Trout were less likely to be impacted by decompression as a physostomus fish. Fizzing was not a factor evaluated in that study. In contrast, Ng et al. (2015) found barotrauma was clearly influential in longer term post-release survival of Lake Trout in Priest Lake. Our study also evaluated post-release survival over a relatively long time period and, as such, may have detected benefits that were not evident in shorter duration studies. Finally, the condition of fizzed fish may influence the overall benefit. We observed a gradient of mortality probabilities relative to observed barotrauma condition. Although it is difficult to compare barotrauma condition among studies post hoc, it is possible the level of gas bladder inflation in fish released in our study was more severe than observed in other studies. Although, we found evidence fizzing may reduce post-release mortality of Lake Trout experiencing barotrauma, we do not recommend anglers be required to fizz Lake Trout prior to release. We found the act of fizzing required fairly specific knowledge of anatomy to place a fizzing needle accurately. This type of knowledge may be difficult to disseminate to the general angling public. In addition, as previously indicated our understanding of current population vital rates suggested angler related mortality is not currently a concern relative to sustaining a fishable population of Lake Trout.

Approximately 33% of the fish placed in the net pen were not present at the end of our

study. We observed fish escape the net pen by floating or swimming through larger mesh covering the surface of the net pen suggesting fish absent from the net pen at the end of the study were escapees. Our post hoc evaluation suggested smaller un-fizzed Lake Trout were more likely to be absent from our net pen at the end of the study. The reduction in short or un-fizzed Lake Trout may have biased our interpretation of the influence of fish length and or fizzing on post release survival. Although bias in our estimate may have occurred, we argue it likely impacted effect size and not the direction of the estimates. In all top models incorporating total length, the probability of post-release mortality was negatively related to length. We

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hypothesize that freely swimming fish able to swim through the upper net pen were likely in good condition and more likely to survive, supporting our interpretation of the models. In contrast, fizzing was negatively related to post-release mortality. Under severe barotrauma, heavily bloated Lake Trout were unable to regulate buoyancy and observed floating at the surface. We hypothesized, a Lake Trout unable to rectify buoyancy was in poor condition and generally more likely to die, also supporting our interpretation of the models.

RECOMMENDATIONS

1. Consider the potential influence of post-release mortality on Lake Trout abundance if Priest Lake angler effort and Lake Trout catch increase.

2. Evaluate angler harvest behavior and its influence on post-release mortality of Lake

Trout if angler related mortality becomes a concern

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Table 11. Covariates included in initial model selection process to estimate the probability of post-release mortality for Lake Trout captured in Priest Lake in 2015. Two covariates (fizz and barotrauma) were included in all models evaluated. Corresponding biological hypothesis is also included for each effect considered.

Covariate Shorthand Hypothesis Main effects Fizz Fizz Fizzing reduces mortality rate

Barotrauma Baro Mortality rate increases with barotrauma severity Fish length TL Mortality rate varies with fish length Gear Gear Mortality rate varies by gear type Capture depth Depth Mortality rate increases with capture depth Catch time CT Mortality rate decreases with catch time Holding time HT Mortality rate increases with holding time

Two-way interactions TL×Baro Mortality due to barotrauma varies across length Baro×Fizz Mortality rate decreases more with fizzing for severely affected fish TL×Fizz Fizzing is more helpful for fish of different lengths Baro×HT Mortality rate increases more with barotrauma and holding time HT×Fizz Fizzing is less effective for fish that have longer holding times Three-way interaction TL×Fizz×Baro Effect of fizzing varies across length and barotrauma conditions

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Table 12. Parameter estimates and standard errors (log-odds scale) from the top logistic regression model evaluating the probability that Lake Trout would escape from the net pen. Covariates are total length (TL; mm) and a variable indicating if the fish was fizzed.

Parameter Estimate SE Intercept 4.427 1.353 TL -0.012 0.003 Fizzed -0.546 0.420

Table 13. Results of model selection process to estimate post-release mortality of Lake

Trout. Only models with substantial support (∆AICc < 2) are given. All models contain main effects for barotrauma condition (Baro) and an indicator variable for treatment by fizzing (Fizz). Other covariates are listed and included: catch time (CT), handling time (HT), total length (TL), and capture gear (Gear; jig or trolling). The value K describes the number of estimated variables in each model.

Model name K AICc ∆AICc

1 Baro x Fizz 5 138 0 2 CT + HT + Baro x Fizz + Fizz x HT 8 138.1 0.06 3 HT + Baro x Fizz + Fizz x HT 7 138.4 0.4 4 CT + Baro x Fizz 6 138.4 0.41 5 TL + Baro x Fizz 6 139.5 1.51 6 HT + Baro x Fizz + Baro x HT 8 139.5 1.51 7 CT + HT + Baro x Fizz + Baro x HT 9 139.6 1.59 8 Gear + Baro x Fizz 6 139.7 1.71 9 CT + HT + TL + Baro x Fizz + Baro x HT 9 139.8 1.74 10 Gear + HT + Baro x Fizz + Fizz x HT 8 139.8 1.75 11 Baro + Fizz (base model; no interaction) 4 139.8 1.8 12 CT + TL + Baro x Fizz 7 139.9 1.88

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Table 14. Parameter estimates and standard errors (log-odds scale) for logistic regression models evaluating the probability of post-release mortality for Lake Trout. All models included a three-level indicator variable for barotrauma condition and a two-level variable indicating if a fish was fizzed. Other covariates included catch time (CT; min), handling time (HT; hr), and an indicator variable for method of capture (Troll). Model number corresponds to Table 13.

Model 1 2 3 4 5 6 Parameter Estimate SE Estimate SE Estimate SE Estimate SE Estimate SE Estimate SE Intercept -3.07 0.72 -1.47 1.05 -2.11 0.98 -2.42 0.85 -1.87 1.62 -1.35 1.57 Baro (moderate) 2.37 0.84 2.45 0.87 2.34 0.85 2.42 0.85 2.39 0.85 1.59 1.81 Baro (severe) 4.73 0.91 5.01 0.96 4.74 0.92 4.89 0.93 4.75 0.91 1.98 1.77 Fizzed -2.64 0.67 -5.13 1.43 -4.88 1.39 -2.63 0.68 -2.65 0.67 -2.93 0.74 Baro:Fizzed 1.95 0.97 2.1 1.01 2 1 2.01 0.98 1.97 0.98 2.3 1.03 CT -- -- -1.47 1.05 -- -- -0.4 0.31 -- -- -- -- HT -- -- -0.51 0.33 -0.89 0.69 -- -- -- -- -1.76 1.71 HT:Fizzed -- -- 2.14 1.03 1.94 1 -- -- -- -- -- -- HT:Baro (moderate) -- -- -- -- -- -- -- -- -- -- 0.85 1.89 HT:Baro (severe) -- -- -- -- -- -- -- -- -- -- 2.84 1.85 TL -- -- -- -- -- -- -- -- -0.25 0.32 -- -- Troll -- -- -- -- -- -- -- -- -- -- -- -- Model 7 8 9 10 11 12 Parameter Estimate SE Estimate SE Estimate SE Estimate SE Estimate SE Estimate SE Intercept -0.89 1.58 -2.93 0.75 -0.4 1.75 -1.91 1 -3.07 0.72 -1.14 1.72 Baro (moderate) 1.79 1.81 2.36 0.84 2.5 0.87 2.32 0.85 2.73 0.82 2.48 0.86 Baro (severe) 2.23 1.77 4.73 0.91 5.08 0.97 4.77 0.93 4.22 0.84 4.96 0.94 Fizzed -2.99 0.75 -2.64 0.67 -5.12 1.44 -5.04 1.42 -1.85 0.49 -2.65 0.68 Baro:Fizzed 2.43 1.05 1.94 0.98 2.13 1.01 2.02 1 -- -- 2.03 0.99 CT -0.48 0.34 -- -- -0.53 0.33 -- -- -- -- -0.41 0.31 HT -1.49 1.69 -- -- -0.71 0.71 -0.9 0.69 -- -- -- -- HT:Fizzed -- -- -- -- 2.11 1.04 2.06 1.01 -- -- -- -- HT:Baro (moderate) 0.74 1.87 -- -- -- -- -- -- -- -- -- -- HT:Baro (severe) 2.84 1.83 -- -- -- -- -- -- -- -- -- -- TL -- -- -- -- -0.24 0.32 -- -- -- -- -0.27 0.32

Troll -- -- -0.3 0.45 -- -- -0.44 0.47 -- -- -- --

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Table 15. Estimated probability of post-release angling mortality of Lake Trout held in a large net pen. Probabilities and lower (LCB) and upper (UCB) 95% confidence bounds were estimated using the top model (see Table 3).

Barotrauma condition Fizzed Estimate LCB UCB Mild — 0.044 0.008 0.131 Moderate No 0.333 0.169 0.532 Moderate Yes 0.200 0.067 0.405 Severe No 0.840 0.667 0.947 Severe Yes 0.273 0.142 0.438

Figure 14. Results of post hoc logistic regression model evaluating the probability of Lake Trout escape from the net pen enclosure after being held for 20 or 21 days. The model included covariates for total length and fizzing (red, not fizzed; blue, fizzed). Mean probabilities are given by solid lines; shaded bands indicate 95% confidence intervals. Tick marks along the horizontal axis indicate individual observations.

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Figure 15. Results of the top logistic regression model evaluating the probability of post-

release angling mortality for Lake Trout held in a large enclosure for 20-21 days. The model included covariates for barotrauma condition (mild, moderate, severe) and fizzing (red, not fizzed; blue, fizzed).

0.00

0.25

0.50

0.75

Mild Moderate SevereBarotrauma condition

Pro

babi

lity

of m

orta

lity

Fizz

Fizzed: 0

Fizzed: 1

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HUGHES MEADOW FISHERIES INVENTORY

ABSTRACT

Bench Creek and the Hughes Fork were surveyed in July, 2015 to identify fish species presence, abundance, and distribution in waters associated with Hughes Meadow, an area of proposed channel restoration in the Upper Priest River drainage. We collected fish using backpack electrofishing equipment at strategically selected sites in each stream. We estimated abundance at each survey site using depletion sampling methods for closed populations. We detected Westslope Cutthroat Trout and Brook Trout at all sites. A single Bull Trout was detected at the uppermost Hughes Fork site. Westslope Cutthroat Trout dominated in Bench Creek samples, while Brook Trout dominated Hughes Fork samples. Our results provided a baseline for evaluating changes in fish communities associated with proposed Hughes Fork restoration activities. Author: Rob Ryan Regional Fisheries Biologist

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INTRODUCTION

Hughes Meadow is a natural meadow located along the Hughes Fork, a tributary of the Upper Priest River in the Selkirk Mountains of northern Idaho. Hughes Meadow was once a complex meadow system. However, a long history of development, including channelization of the Hughes Fork, has created a much simpler and less effective meadow complex (personal communication, Jill Cobb, USFS Hydrologist). In an effort to restore natural function of Hughes Meadow and the Hughes Fork, a restoration of the meadow was proposed. Proposed restoration actions primarily center on reconstruction of the historic Hughes Fork channel as a means of benefiting both meadow function and the fish community.

Native salmonids of the Hughes Fork include Westslope Cutthroat Trout Oncorhynchus

clarkii lewisi, Bull Trout Salvelinus confluentus, and Mountain Whitefish Prosopium williamsoni. These species remain present throughout the basin, but with reduced abundance and distribution (Dupont et al. 2004). Brook Trout, introduced widely in the 1960’s through the 1980’s (IDFG, unpublished data), were known to be present in the Hughes Fork system (Dupont et al. 2004). Non-native species introduction, habitat alteration, and overharvest have been suggested causes of declines in native fish communities in the Priest River Basin (Bjornn 1957, Mauser 1986, Mauser et al. 1988).

In 2015, we conducted fisheries surveys in streams associated with Hughes Meadow,

including Bench Creek and the Hughes Fork. The objective of these surveys was to identify fish species presence, abundance, and distribution. This information will provide a baseline for evaluating changes in fish communities associated with proposed Hughes Fork restoration activities and improve our general understanding of fisheries in the Panhandle Region.

METHODS

Survey sites within sampled streams were pre-selected strategically to describe the fish community throughout the Hughes Meadow reach of Hughes Creek and within the lower reaches of Bench Creek (Figure 1). Three sites were selected on the Hughes Fork and two on Bench Creek. Hughes Fork sites were selected to describe upper, middle, and lower reaches of the stream through the Hughes Meadows area. Bench Creek sites were located at approximately 500 m intervals upstream from the confluence with the Hughes Fork. The volume of each sample site was described by measuring reach length and width using a 100 m measure tape. Stream width was measured at eight intervals through the sample reach. Reach volumes were used to estimate fish densities at each site.

We collected fish using a Smith-Root backpack electrofishing unit and pulsed DC

settings, typically at 600-800 volts, 40-50Hz, and 2-5 M.S. Two netters captured fish. Collected fish were identified to species and measured (total length; mm). To estimate abundance of tributary fish populations we used multi-pass removals (Zippin 1958). Abundance estimates only included fish >75mm (total length; TL) due to sampling efficiency considerations. Sample sections were approximately 100 m in length. We closed sample sections using block nets at the downstream end of each survey section to prevent escapement during downstream electrofishing passes. Multi-pass samples were completed with sequential passes until captures of an individual pass were approximately 20% or less than the total capture by species of the first pass. Two or three passes were completed at each site. We derived abundance estimates

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and associated 80% confidence intervals for two and three pass samples using calculations for removal estimates in closed populations (Hayes et. al 2007). We reported the total catch on the first pass as the population estimate when all individuals of a particular species were captured on the first pass. In cases where lower confidence bounds were less than the total number of fish captured, the total number of fish captured was reported as the lower bound. We reported density estimates as the number per 100 m2.

RESULTS

We surveyed selected sites on the Hughes Fork and Bench Creek between July 13 and July 16, 2015. Water was present and an electrofishing survey was completed at all sections visited (Table 16). We detected Westslope Cutthroat Trout and Brook Trout at all sites surveyed (Table 17). We also collected a single Bull Trout at Site 3, the upper most site, on the Hughes Fork. Westslope Cutthroat Trout were the most abundant fish species found in Bench Creek with estimated densities varying from 17.0 fish/100 m2 to 9.7 fish/100 m2. Brook Trout densities in Bench Creek varied from 7.8 fish/100 m2 to 1.5 fish/100 m2. In contrast, the Hughes Fork was dominated by Brook Trout with densities varying from 4.3 fish/100 m2 to 0.7 fish/100 m2. Westslope Cutthroat Trout in the Hughes Fork varied from 1.5 fish/100 m2 to 0.3 fish/100 m2.

DISCUSSION

We observed substantially lower fish densities in Hughes Fork than those observed in Bench Creek. Based on anecdotal observations, differences in fish density were likely related to the availability of quality habitat. We did not formally describe habitat conditions (e.g., width-to-depth ratio, pool frequency) within survey reaches. However, we did generally observe low complexity, low pool frequency, and high width-to-depth ratios in the Hughes Fork. In contrast, Bench Creek exhibited high complexity within the surveyed sections.

Hughes Fork and Bench Creek fish communities exhibited similar patterns of species

composition to those observed in previous surveys. Dupont et al. (2004) found Westslope Cutthroat Trout and Brook Trout to be the prominent species in both the Hughes Fork and Bench Creek. They also described a considerable deviation in density between streams, with higher densities observed in Bench Creek. In contrast, Dupont et al. (2004) suggested Upper Priest River tributaries demonstrated an ongoing trend of Brook Trout expansion. In that work, Brook Trout were present in Bench Creek, but Westslope Cutthroat Trout dominated. The ratio of Westslope Cutthroat Trout to Brook Trout was approximately 3:1 in both surveys, suggesting Brook Trout expansion may have moderated. We make these comparisons cautiously as neither survey likely sampled sufficiently to accurately describe fish abundance or distribution on a drainage–scale, nor did we specifically replicate sample sites. To better describe large-scale or basin-wide patterns of distribution and abundance, we recommend a more complete inventory of drainages in the basin.

Our data provide a baseline from which changes in the fish community associated with

Hughes Meadow may be compared. We anticipate proposed meadow restoration actions (i.e., creating a narrow, sinuous channel) will increase habitat complexity and result in higher quality fish habitat. However, it is difficult to predict the specific level of influence actions may have. We recommend a post-treatment survey of the impacted reaches of the Hughes Fork to better understand the fisheries benefits this project or similar projects may have.

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RECOMMENDATIONS

1. Complete a post-treatment survey of the impacted reaches of the Hughes Fork to better understand the fisheries benefits to the proposed restoration project or similar projects.

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Table 16. Locations of sites sampled during 2015 surveys of Bench Creek and the Hughes Fork. Waypoints represent the approximate uppermost points of each survey section. Section length and average wetted width at the time of sampling are listed for each survey section.

Stream Site Date Latitude Longitude Section Length(m) Avg Width(m) Bench Creek 1 7/13/2015 48.87372 -117.00865 105 3.06 Bench Creek 2 7/13/2015 48.87527 -117.01092 100 4.06 Hughes Fork Priest River 1 7/16/2015 48.85616 -117.00125 100 8.00 Hughes Fork Priest River 2 7/14/2015 48.86332 -117.00740 110 8.29 Hughes Fork Priest River 3 7/14/2015 48.86981 -117.00125 95 7.19 Table 17. Bench Creek and Hughes Fork 2015 survey results by site and species. Total catch references all fish caught. Only

fish ≥ 75 mm were included in estimates of abundance (Est N). Stream Site Passes Species Min TL Max TL Total Catch Est N 80% CI - 80% CI + Fish/100 m2

Bench 1 2 BKT 90 179 24 25 24 27 7.8 Bench 1 2 WCT 51 240 53 55 53 57 17.0 Bench 2 2 BKT 55 165 6 6 6 6 1.5 Bench 2 2 WCT 47 182 39 40 39 41 9.7 Hughes Fork 1 2 BKT 42 258 31 31 31 31 3.9 Hughes Fork 1 2 WCT 67 96 6 6 6 6 0.8 Hughes Fork 2 2 BKTa 44 126 6 6 --- --- 0.7 Hughes Fork 2 2 WCT 75 86 3 3 3 3 0.3 Hughes Fork 3 3 BKT 47 167 25 29 25 35 4.3 Hughes Fork 3 3 BLTa 167 167 1 1 --- --- 0.1 Hughes Fork 3 3 WCT 64 137 9 10 9 13 1.5 a Minimum estimate due to non-declining catch or single fish samples

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Figure 16. Bench Creek and Hughes Fork survey locations sampled in 2015.

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HAYDEN AND PRIEST LAKES MYSID SURVEYS

ABSTRACT

Historically, mysid shrimp were introduced into the Panhandle Region in Pend Oreille, including Hayden and Priest lakes with the objective of enhancing forage for existing fisheries. Both intended and unintended consequences resulted from these introductions. Recent declines in mysid abundance in Lake Pend Oreille prompted investigation of Hayden and Priest lake mysid abundance. We sampled Priest and Hayden lakes on June 17 and 18, 2015 to estimate lake-wide mysid densities. We found mysid densities were low. Estimated total mysid densities were 180 mysids/m2 and 98 mysids/m2 in Hayden and Priest lakes, respectively. Densities estimates represented an increase from the previous year in Hayden Lake and a decrease from the previous year in Priest Lake. Estimated changes in mysid density were not considered to represent large changes in abundance in either lake. Author: Rob Ryan Regional Fisheries Biologist

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INTRODUCTION

Mysid shrimp Mysis diluviana, have been stocked around the globe in attempts to increase the forage base for sportfish. Mysids were introduced into Priest Lake and Lake Pend Oreille from 1965 to 1968 with the objective of benefiting the kokanee Oncorhynchus nerka population. Mysids were also introduced into Hayden Lake in 1974.

In Hayden Lake, no adverse effects from mysids have been described. Black Crappie Pomoxis nigromaculatus, Westslope Cutthroat Trout Oncorhynchus clarki lewisi, and Rainbow Trout Oncorhynchus mykiss are all believed to consume mysids at some level. Though the impact of mysids on fish growth in this system has not been definitively assessed, mysids are generally considered to be a benefit to the fishery.

In Priest Lake, mysids were credited with increasing kokanee growth (Irizarry 1974).

However, the kokanee fishery subsequently collapsed by 1976 due to predation from an increased abundance of Lake Trout Salvelinus namaycush. Mysids provided an abundant food source for juvenile Lake Trout, which increased their survival and allowed for population expansion (Martinez et al. 2009). The resulting Lake Trout fishery in Priest Lake largely replaced fisheries for kokanee and Westslope Cutthroat Trout (Liter et al. 2009). In recent years, kokanee have demonstrated somewhat of a resurgence in abundance accompanied by increasing interest by anglers (Watkins et al in prep). However, it is unclear whether mysids have played a role in the kokanee increase.

Mysids have not been routinely sampled in northern Idaho lakes. The exception to this

has been Lake Pend Oreille where a long history of monitoring has been completed. Annual sampling of Lake Pend Oreille showed a sharp decline in mysids beginning in 2011 (Wahl et al. 2015). Observed declines in abundance could have major effects on the food web and the resulting sport fisheries. The collapse of mysids in Lake Pend Oreille prompted an investigation of the densities of mysids in other northern Idaho lakes. In 2015, we continued efforts to understand mysid density in Priest and Hayden lakes to better understand regional trends.

METHODS

We sampled mysid shrimp to estimate density in Priest and Hayden lakes on June 17 and 18, 2015, respectively. All sampling occurred at night during the dark phase of the moon. A total of twelve random sites were sampled on each water body. Vertical net tows were made from a depth of 46 m or the lake bottom to the surface with a 1 m hoop net. We used a 1,000 micron mesh net with a 500 micron bucket. Area of the net mouth was 0.8 m2. Each mysid collected was counted, measured, and sexed. Young-of-the-year (YOY) mysids were classified as individuals less than 14 mm. We calculated density as mysids per square meter based on the area of the net mouth. We reported arithmetic mean density and 80% confidence intervals around each estimate.

RESULTS

Mysid density of all combined life stages in Hayden Lake varied from 94 to 269 mysids/m2 with a mean of 180 mysids/m2 (± 20, 80% C.I.; Table 18). Young-of-the-year (YOY) represented approximately 20% of the total sample (Table 18). Average density of immature

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and adult mysids was 144 mysids/m2. Sizes of immature and adult mysids were large and varied from 14 mm to 24 mm (Figure 17).

Average density of mysids from all life stages in Priest Lake was 98 mysids/m2 (± 23, 80% C.I.; Table 19). YOY represented approximately 78% of the total sample with a mean density of 77 mysids/m2. Average density of immature and adult mysids was 22 mysids/m2. Sizes of immature and adult mysids varied from 14 mm to 22 mm (Figure 18).

DISCUSSION

Estimated mysid density from Hayden Lake represented an increase from levels reported in 2014, but remained well below the reported density in 2010 (Figure 19; Ryan et al. 2014, Maiolie et al. 2011). Density estimates from Priest Lake between 2013 and 2015 were similar, with overlapping confidence bounds around mean densities suggesting little change has occurred. (Figure 19; Ryan et al. 2014, Watkins et al. in review).

Our survey continued to represent relatively new efforts to describe regional trends in mysid abundance. Although available historical data on mysids is limited, our recent data suggest densities in both Hayden and Priest lakes were low. Regionally, Lake Pend Oreille offers the only other Idaho water with available data for comparison of mysid densities, and reported densities from that effort have typically been considerably greater than densities in our survey waters (Wahl et al. 2015). However, mysid densities declined dramatically between 2011 and 2013 in Lake Pend Oreille for unknown reasons (Wahl et al. 2015). We recommend continued monitoring of mysid abundance in Hayden and Priest lakes in an effort to describe the significance of the densities we observed. More specifically, investigations should focus on whether observed densities represent a population decline similar to that observed in Lake Pend Oreille. We also recommend periodic monitoring of fish communities in these waters to better understand the impact mysid densities have on regional fisheries.

RECOMMENDATIONS

1. Continue monitoring mysids in regional lakes annually

2. Complete periodic monitoring of fish communities in waters with mysids to better understand the impact of mysid densities on regional fisheries

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Table 18. Densities of mysids (per m2) collected from Hayden Lake on June 18, 2015. Densities were listed by location (UTM, zone 11, WGS84) and life stage (young-of-year [YOY], immature and adults).

Sample Site Z E N Datum YOY/m2 Immature and Adult/m2 All Ages/m2 1 11 522993 5291926 WGS84 6 245 251 2 11 523200 5291590 WGS84 5 193 198 3 11 522585 5290715 WGS84 16 253 269 4 11 521993 5290062 WGS84 35 116 152 5 11 522002 5289626 WGS84 55 179 234 6 11 522545 5289421 WGS84 24 155 180 7 11 521691 5289295 WGS84 49 45 94 8 11 521033 5290028 WGS84 61 131 192 9 11 521031 5290326 WGS84 69 127 196 10 11 520034 5290017 WGS84 35 131 166 11 11 519229 5289187 WGS84 48 60 108 12 11 518786 5289208 WGS84 32 91 122 Table 19. Densities of mysids (per m2) collected from Priest Lake on June 17, 2015. Densities were listed by location (UTM,

zone 11, WGS84) and life stage (young-of-year [YOY], immature and adults). Sample Site Z E N Datum YOY/m2 Immature and Adult/m2 All Ages/m2 1 11 511202 5394109 WGS84 18 6 24 2 11 509162 5392132 WGS84 35 29 65 3 11 510996 5390163 WGS84 31 24 55 4 11 510469 5387060 WGS84 113 18 131 5 11 509056 5384168 WGS84 67 17 84 6 11 510983 5381069 WGS84 103 45 148 7 11 506795 5379120 WGS84 29 27 56 8 11 509038 5377626 WGS84 135 17 152 9 11 511004 5378149 WGS84 126 28 154 10 11 510983 5373105 WGS84 28 13 42 11 11 508934 5372141 WGS84 20 22 42 12 11 511896 5382095 WGS84 218 10 228

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Figure 17. Length distribution by life stage of mysid shrimp sampled from random locations

in Hayden Lake, Idaho on June 18, 2015.

Figure 18. Length distribution of Mysis shrimp collected from random locations in Priest

Lake, Idaho on June 17, 2015.

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Figure 19. Estimated density (per m2) of immature and adult mysid shrimp from Hayden and

Priest lakes in 2010, 2013, 2014, and 2015. Error bars represent 80% confidence intervals. No survey was completed on Priest Lake in 2010.

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SPOKANE BASIN WILD TROUT MONITORING

ABSTRACT

Long-term data obtained from historical snorkeling transects have been critical for informing management of wild salmonids in the upper Spokane River Basin over the past several decades. In the Coeur d’Alene and St. Joe rivers, maintenance of long-term datasets has allowed the Idaho Department of Fish and Game to document responses of Westslope Cutthroat Trout Oncorhynchus clarki lewisi to environmental conditions, habitat rehabilitation, and angling regulations. During July 27–August 6, 2014, we used daytime snorkeling to observe fishes at historical sampling transects in the Coeur d’Alene River (n = 44) and St. Joe River (n = 35) basins. We estimated total Westslope Cutthroat Trout densities of 1.06 fish/100 m2 in the North Fork Coeur d’Alene River (including Teepee Creek), 1.93 fish/100 m2 in the Little North Fork Coeur d’Alene River, and 2.75 fish/100 m2 in the St. Joe River. For Westslope Cutthroat Trout ≥ 300 mm in total length, we estimated densities of 0.30 fish/100 m2 in the North Fork Coeur d’Alene River, 0.15 fish/100 m2 in the Little North Fork Coeur d’Alene River, and 0.88 fish/100 m2 in the St. Joe River. Densities of Rainbow Trout O. mykiss remain at relatively low abundances in both drainages, and our estimates were similar to the past 15–20 years. Size structure tended to be slightly better in the St. Joe River compared to the Coeur d’Alene River system. Overall, trends in abundance and size structure of Westslope Cutthroat Trout in the upper Spokane River Basin have increased substantially over the past decade and continue to improve. Future monitoring should continue in order to better inform management of Westslope Cutthroat Trout and to demonstrate progress toward conservation objectives. Current catch-and-release angling regulations for Westslope Cutthroat Trout and liberal harvest regulations for non-native salmonids (i.e., Rainbow Trout, Brook Trout Salvelinus fontinalis) appear to be effective methods for maintaining good abundance and size structure of Westslope Cutthroat Trout.

The Pacific Northwest experienced record-setting weather conditions during 2015 that

contributed to abnormal summer water temperatures and lower river flows in the Upper Spokane River Basin. Overall, the unseasonable conditions do not appear to have significantly affected mortality of Westslope Cutthroat Trout. We did not observe dead fish during sampling, nor did Idaho Fish and Game personnel receive reports of fish kills during the peak of the summer. Any natural mortality resulting from extreme weather was likely compensatory and not likely to influence long-term abundance of adult Westslope Cutthroat Trout. The effects that lower flows and warmer summer water temperatures may have on recruitment are poorly understood, but will be evaluated during future monitoring. Author:

Carson Watkins Regional Fishery Biologist

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INTRODUCTION

Westslope Cutthroat Trout Oncorhynchus clarki lewisi is one of 14 subspecies of Cutthroat Trout O. clarki native to North America. The native distribution of Westslope Cutthroat Trout is the most widespread of the 14 subspecies spanning both sides of the Continental Divide (Behnke 1992; Behnke 2002). Their native distribution west of the Continental Divide includes the Salmon River and its tributaries, as well as all major drainages throughout the Idaho Panhandle. Despite their widespread distribution, declines in occurrence and abundance of Westslope Cutthroat Trout have been documented throughout their native range (Shepard et al. 2005). In fact, Westslope Cutthroat Trout now occupy 85% of their historical range in Idaho (Wallace and Zaroban 2013). Populations of Westslope Cutthroat Trout have been negatively influenced for a variety of reasons. Extensive land- and water-development activities, which have reduced available instream habitat and altered flows and thermal regimes, have negatively affected Westslope Cutthroat Trout (Peterson et al. 2010). Another important factor related to range and abundance reductions has been interaction with nonnative salmonids (i.e., Rainbow Trout O. mykiss, Brook Trout Salvelinus fontinalis), which often leads to competition and hybridization (Rainbow Trout only; Marnell 1988; Allendorf et al. 2004; Shepard et al. 2005; Muhlfeld et al. 2009).

Concerns about the status of Westslope Cutthroat Trout have resulted in two petitions

for listing under the U.S. Endangered Species Act (ESA 1973, as amended) in 1997 and 2001. Subsequent evaluations of extant populations determined that the relatively broad distribution and persistence of isolated populations in Oregon, Washington, and Canada did not warrant protection under the ESA (U.S. Federal Register 1998, 2003). However, the U.S. Forest Service and Bureau of Land Management regard Westslope Cutthroat Trout as a sensitive species, and the Idaho Department of Fish and Game (IDFG) has designated it as a Species of Greatest Conservation Need (IDFG 2006; IDFG 2013). Due to their importance as a recreational, cultural, and socioeconomic resource, the IDFG has intensely managed Westslope Cutthroat Trout populations for both general conservation and to provide quality angling opportunities.

The Spokane River Basin represents one of the most important areas for Westslope

Cutthroat Trout conservation in Idaho and the Pacific Northwest; specifically, because major tributaries to the Spokane River (i.e., Coeur d’Alene River, St. Joe River) provide strongholds for this sensitive species (DuPont et al. 2009; Stevens and DuPont 2011). In addition, Westslope Cutthroat Trout populations in the upper Spokane River Basin support important recreational fisheries. The close proximity of the Coeur d’Alene River and St. Joe River to large communities (i.e., Coeur d’Alene, Spokane) makes these waters popular destination trout fisheries, and angling pressure has increased in recent times (Fredericks et al. 1997; DuPont et al. 2009).

Over the past century, Westslope Cutthroat Trout angling regulations have become

increasingly conservative with a shift toward catch-and-release fishing rules (Hardy and Fredericks 2009; Kennedy and Meyer 2015). For example, prior to 2008 the lower portions of the Coeur d’Alene River (Lake Coeur d’Alene to confluence of Yellow Dog Creek) and St. Joe River (Lake Coeur d’Alene to confluence of North Fork St. Joe River) were managed under a two fish daily bag and slot limit (none between 203–406 mm; Hardy and Fredericks 2009). However, currently the entire Spokane River Basin within Idaho is managed under a catch-and-release regulation for Westslope Cutthroat Trout, with the exception of the St. Maries River (2 fish daily bag limit). The shift to catch-and-release led to improvements in these populations; however, increased education, enforcement of regulations, and habitat rehabilitation have also contributed. Westslope Cutthroat Trout populations responded positively to regulation changes and angler use followed suit. Improvements in the quality of the fishery, combined with the

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elimination of season restrictions, also increased angler use in the Coeur d’Alene and St. Joe rivers (IDFG 2013). In fact, an economic survey of angler use estimated that the number of angler trips increased from 35,000 2003 to 50,000 in 2011 (IDFG 2013). Long-term monitoring has been tremendously important for formulating effective management plans for conservation of Westslope Cutthroat Trout in Idaho. Standardized monitoring has allowed IDFG to evaluate population-level responses to environmental change and management activities (Copeland and Meyer 2011; Kennedy and Meyer 2015), and thus improve the quality of the fishery in the Spokane River Basin.

OBJECTIVES

1. Monitor trends in abundance, distribution, and size structure of wild salmonids in the upper Spokane River Basin, with focus on Westslope Cutthroat Trout populations.

2. Monitor fish assemblage structure and species distribution to identify shifts in community

assembly and occurrence patterns of native and non-native fishes alike.

3. Maintain long-term trend data to provide information related to management of Westslope Cutthroat Trout.

STUDY AREA

The Coeur d’Alene and St. Joe rivers are the largest tributaries to Lake Coeur d’Alene and combined these drainages comprise ~50% of the greater Spokane River watershed. Both rivers originate in the Bitterroot Mountains along the Idaho-Montana border and are greatly influenced by spring runoff and snowmelt. Approximately 90% of the land area within the drainages is publically-owned by the U.S. Forest Service (Strong and Webb 1970). Dominant land-use practices in both drainages include hard rock and placer mining and extensive timber harvest (Strong and Webb 1970; Quigley 1996; DEQ 2001). While the combination of these activities has negatively influenced instream habitat and water quality, increased oversight and regulation of land-use have improved environmental conditions for native fishes in both the Coeur d’Alene and St Joe. river drainages (DEQ 2001).

Historical sampling reaches were established on the Coeur d’Alene River in 1973 (n =

42; Figure 20; Bowler 1974) and St Joe River in 1969 (n = 35; Figure 21; Rankel 1971; Davis et al. 1996). Sampling has been conducted on an annual basis for each reach since the beginning of the monitoring program with the exception of 7 reaches added to the St. Joe River in 1996 (Davis et al. 1996). Sampling reaches in the St. Joe River drainage occur only along the mainstem St. Joe River (Figure 21), while reaches within the Coeur d’Alene River drainage occur on the North Fork Coeur d’Alene River, Little North Fork Coeur d’Alene River, and Teepee Creek (Figure 20).

METHODS

Standardized index reaches in the North Fork of the Coeur d’Alene (including Teepee Creek), Little North Fork Coeur d’Alene, and St. Joe rivers were sampled during July 27–August 6, 2015 using daytime snorkeling (DuPont et al. 2009; Thurow 1994). One (wetted width ≤ 10 m wide) or two (wetted width > 10 m wide) observers slowly snorkeled downstream identifying

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fishes to species and estimating total length (TL; inches) of all salmonid species. Transects have been permanently marked with a global positioning system (GPS) and digital photographs provided reference to the upper and lower terminus of each reach. Estimates of salmonid abundance was limited to age-1+ fish, as summer counts for young-of-year (YOY) Westslope Cutthroat Trout and Rainbow Trout are typically unreliable. After completion of each sampling reach, each species was enumerated and salmonid species (i.e., Westslope Cutthroat Trout; Rainbow Trout; Mountain Whitefish [Prosopium williamsoni]) were separated into 75 mm length groups. Nongame fish species (e.g., Cottus spp. and Catostomus spp.) were enumerated, but lengths were not estimated.

Reach length and wetted width were measured at each sampling site with a laser

rangefinder. The habitat type (pool, riffle, run, glide, pocket water), maximum depth, dominant cover type and amount of cover (estimated as % of surface area) in the area sampled was measured to assess if changes in habitat were responsible for any changes in fish abundance and assemblage structure. Surface area (m2) was estimated at each site to provide a measure of sampling effort. The number of salmonids observed was divided by the surface area sampled to provide a standardized relative abundance measure. We calculated a mean relative density that could be compared to previous years (DuPont et al. 2009). Non-target species were enumerated and reported as the total number observed.

Size structure of Westslope Cutthroat Trout was also estimated for each river system.

Proportional size distribution (PSD) was used to summarize length-frequency distributions (Neumann et al. 2012) and describe size structure. Proportional size distribution was calculated as

PSD = (a / b) × 100,

where a is the number of fish greater than or equal to the minimum quality length and b is the number of fish greater than or equal to 300 mm length (Neumann and Allen 2007; Neumann et al. 2012).

RESULTS

North Fork Coeur d’Alene River

A total of 1,453 Westslope Cutthroat Trout, 112 Rainbow Trout, and 5,388 Mountain Whitefish was observed among the 44 sampling sites in the North Fork Coeur d’Alene River drainage. In addition, we observed 190 Largescale Sucker Catostomus macrocheilus, 15 Brook Trout, and 2,756 Northern Pikeminnow Ptychocheilus oregonsis. We noted presence of adult and juvenile Redside Shiner Richardsonius balteatus, and Longnose Dace Rhinichthys cataractae as well. Mean total density of Westslope Cutthroat Trout was 1.06 fish/100 m2 in the North Fork Coeur d’Alene River (including Teepee Creek) and 1.93 fish/100m2 in the Little North Fork Coeur d’Alene River (Figure 22). Mean density of Westslope Cutthroat Trout ≥ 300 mm was 0.30 fish/100 m2 in the North Fork Coeur d’Alene River and 0.15 fish/m2 in the Little North Fork Coeur d’Alene River (Figure 23). For Westslope Cutthroat Trout during 2015, the mean estimates of total density and density of fish ≥ 300 mm either met or surpassed the 10-year average (total Westslope Cutthroat Trout = 1.06 fish/100 m2; Westslope Cutthroat Trout ≥ 300 mm = 0.24 fish/100 m2) in the combined reaches. Mean total density of Rainbow Trout in the North Fork Coeur d’Alene River was 0.05 fish/ 100 m2 and 0.43 fish/100m2 in the Little North Fork Coeur d’Alene River (Figure 24). Mean total density of Mountain Whitefish was 3.40

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fish/100 m2 in the North Fork Coeur d’Alene River and 0.56 fish/100 m2 in the Little North Fork Coeur d’Alene River (Figure 25).

St. Joe River

A total of 1,122 Westslope Cutthroat Trout, 14 Rainbow Trout, and 2,049 Mountain Whitefish was observed among the 35 sampling sites in the St. Joe River. In addition, we observed 339 Largescale Sucker, 490 Northern Pikeminnow. No Bull Trout S. confluentus were observed during 2015 sampling. Unlike the Coeur d’Alene River, no Brook Trout or Redside Shiners were observed in the St. Joe River. Mean total density of Westslope Cutthroat Trout was 2.75 fish/100 m2 (Figure 26). Mean density of Westlope Cutthroat Trout ≥ 300 mm was 0.77 fish/100 m2 (Figure 27). The mean total density estimate of Westslope Cutthroat Trout for 2015 was the highest on record and surpassed the 10-year average (1.92 fish/100 m2). The mean density of Westslope Cutthroat Trout ≥ 300 mm in 2015 surpassed the 10-year mean (0.64 fish/100 m2). Mean total density of Rainbow Trout and Mountain Whitefish was 0.01 fish/ 100 m2 and 2.69 fish/100 m2, respectively (Figure 28; Figure 29). In general, size structure of Westslope Cutthroat Trout in the St. Joe River (RSD-300 = 55.72) was better than in the Coeur d’Alene River Basin (RSD-300 = 45.43; Figure 30).

DISCUSSION

The upper Spokane River Basin represents one of Idaho’s most important systems for conservation of Westslope Cutthroat Trout. Previous work on Westslope Cutthroat Trout showed that declines in abundance and size structure in both the Coeur d’Alene River and St. Joe River were directly related to recruitment overfishing and habitat degradation (Rankel 1971; Mink et al. 1971; Lewynsky 1986). However, in the Spokane River Basin and elsewhere in Idaho, Westslope Cutthroat Trout populations have positively responded to changes in angling regulations and habitat quality.

Westslope Cutthroat Trout densities have increased markedly since the beginning of this

monitoring program and continue to show improvement (Maiolie and Fredericks 2014). Although we have documented a considerable amount of variability in annual density estimates, the past decade is characterized by the highest densities in both the North Fork Coeur d’Alene and St. Joe rivers. In particular, increased densities of Westslope Cutthroat Trout ≥ 300 mm have reflected substantial improvements in size structure. We continue to see increases in Mountain Whitefish densities in the lower portions of the Coeur d’Alene River and St. Joe River. Rainbow Trout densities remain at extremely low abundance throughout the St. Joe River and North Fork Coeur d’Alene River. We continued to document relatively high densities of Rainbow Trout in the Little North Fork Coeur d’Alene River; notwithstanding, Westslope Cutthroat Trout densities also remain high in the Little North Fork Coeur d’Alene River. Rainbow Trout are known to compete and hybridize with Westslope Cutthroat Trout and the IDFG manages for low abundance of Rainbow Trout in the Spokane River Basin to reduce the potential for such interactions. The recent increase in density of Rainbow Trout in the Little North Fork Coeur d’Alene does not correspond to an increase in other portions of the basin, and is not currently a major management concern.

During 2015, record warm temperatures affected much of the Pacific Northwest. Unseasonably warm spring temperatures melted snowpack earlier than usual and higher-than-normal temperatures persisted throughout the summer. As early as June, discharge was well

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below average throughout the upper Spokane River Basin and anglers were reporting daytime water temperatures as high as 20° C (E. L. Lider, personal communication). The environmental conditions experienced during 2015 were some of the most severe in recent history, and the long-term ecological effects of those conditions are still not fully understood. However, based on our 2015 sampling we can conclude that total density of wild salmonids was not negatively influenced by resulting conditions in either the Coeur d’Alene or St. Joe river basins. However, density of WCT ≥ 300 mm in the Little North Fork Coeur d’Alene River had declined substantially from 2014, and our 2015 estimate was below the 10-year mean (0.18 fish/100 m2; SD = 0.13). The Little North Fork Coeur d’Alene River watershed is lower in elevation compared to that of its parent drainage and peak runoff tends to occur earlier in the year, as a result. In addition, base summer flows were reached earlier in the Little North Fork Coeur d’Alene River compared to the North and South Fork Coeur d’Alene rivers, both of which drain higher elevation watersheds and have slower spring snowmelt. Even during late-summer, water temperatures are typically higher in the Little North Fork Coeur d’Alene River because groundwater influence is also relatively minimal (Findlay 1995; WSI 2007). In fact, mean daytime water temperatures were around 3° C higher in the Little North Fork Coeur d’Alene compared to the North Fork Coeur d’Alene, which has known areas with cold groundwater input (WSI 2007). As such, the Little North Fork Coeur d’Alene River probably did not have sufficient habitat to support large adult Westslope Cutthroat Trout during late-summer. We hypothesize that adult Westslope Cutthroat Trout emigrated from the Little North Fork Coeur d’Alene River seeking more desirable conditions in the North Fork Coeur d’Alene or mainstem Coeur d’Alene rivers.

It appears that severe weather during 2015 did not cause substantial direct mortality of Westslope Cutthroat Trout. Further, any mortality that may have resulted from conditions experienced during 2015 is likely compensatory and not sufficient to alter population characteristics. We did not observe any dead Westslope Cutthroat Trout at any of our snorkel sites nor did we receive public comments about dead fish being observed during the summer and early fall months. Although anecdotal, such observations might indicate a negative relationship between extreme environmental conditions and Westslope Cutthroat Trout mortality. The long-term effects of severe summer drought conditions on recruitment dynamics and somatic growth are not yet understood, but should be revealed through continued annual monitoring.

Salmonid recruitment is primarily influenced by over-winter survival in most western lotic

systems (Giannico and Hinch 2003), but the effect of prolonged drought and summer conditions has not been fully evaluated. There are several ways that summer conditions potentially act to influence salmonid recruitment dynamics. Juvenile salmonids tend to have higher upper thermal maxima than their adult counterparts and warm water temperatures can positively influence growth, particularly in the case of Westslope Cutthroat Trout (Bear 2005; Bear et al. 2007). Improved body condition and length from higher somatic growth can likely negate the effects of winter conditions on survival, thus improving recruitment. On that contrary, warm summer water conditions and low base flows associated with drought have the potential to reduce growth of adult Westslope Cutthroat Trout (Bear et al. 2007) and indirectly affect recruitment. Maturity and fecundity of fishes are directly proportional to fish size (Neumann et al. 2012), and thus reduced growth due to conditions that somatic development may reduce total reproductive output in subsequent years.

In 2015, many anglers expressed concern regarding potential for increased hooking

mortality during the extreme summer weather. In addition, catch-and-release angling during extreme summer weather also does not appear to influence adult Westslope Cutthroat Trout

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mortality. The Westslope Cutthroat Trout fisheries in the Coeur d’Alene and St. Joe rivers sustained high levels of controlled angler exploitation for several decades that caused compensatory mortality. Considering this knowledge, angling-induced mortality that occurs during extreme summer conditions is certainly compensatory to natural mortality and not likely to adversely affect the population at-large. It is more likely that effects on year-class strength during years of extreme drought will influence Westslope Cutthroat Trout abundance than catch-and-release angling. Ultimately, results from our 2015 sampling showed that Westslope Cutthroat Trout in the upper Spokane River Basin are resilient to extreme environmental conditions, and that substantial direct mortality is probably not a concern. However, the effects of sustained drought conditions on Westslope Cutthroat Trout recruitment dynamics in the Upper Spokane River basin will be better understood by future monitoring.

MANAGEMENT RECOMMENDATIONS

1. Continue to monitor wild trout abundance and population characteristics in the upper Spokane River Basin.

2. Continue to monitor trends in fish assemblage characteristics.

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Figure 20. Location of 44 index reaches sampled using snorkeling in the Coeur d’Alene

River, Idaho during July 26–31, 2015.

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Figure 21. Location of 35 index reaches sampled using snorkeling in the St. Joe River,

Idaho during August 3–6, 2015.

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Figure 22. Mean density of Westslope Cutthroat Trout observed during snorkeling in the

North Fork of the Coeur d’Alene River and Little North Fork of the Coeur d’Alene River (1973–2015).

Figure 23. Mean density of Westslope Cutthroat Trout larger than 300 mm TL observed

during snorkeling in the North Fork of the Coeur d’Alene River and Little North Fork of the Coeur d’Alene River (1973–2015).

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Figure 24. Mean density of Rainbow Trout observed during snorkeling in the North Fork of

the Coeur d’Alene River and Little North Fork of the Coeur d’Alene River (1973–2015).

Figure 25. Mean density of Mountain Whitefish observed during snorkeling in the North Fork

of the Coeur d’Alene River and Little North Fork of the Coeur d’Alene River (1973–2015).

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Figure 26. Mean density of Westslope Cutthroat Trout observed during snorkeling in the St.

Joe River (1969–2015).

Figure 27. Mean density of Westslope Cutthroat Trout larger than 300 mm TL observed

during snorkeling in the St. Joe River (1969–2015).

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Figure 28. Mean density of Rainbow Trout observed during snorkeling in the St. Joe River

(1969–2015).

Figure 29. Mean density of Mountain Whitefish observed during snorkeling in the St. Joe

River (1969–2015).

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Figure 30. Length-frequency distributions of Westslope Cutthroat Trout observed during

snorkeling in the North Fork Coeur d’Alene River (includes Little North Fork Coeur d’Alene River and Teepee Creek) and St. Joe River (2015).

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LITTLE NORTH FORK CLEARWATER RIVER FISHERY EVALUATION

ABSTRACT

We conducted fish sampling in the Little North Fork Clearwater River during the summer of 2015, primarily to evaluate trends in abundance of wild salmonids and to estimate angler exploitation of Westslope Cutthroat Trout Oncorhynchus clarkia lewisi. To understand harvest, we used angling to sample and tag 134 Westslope Cutthroat Trout ≥ 305 mm total length during 6–8 July, 2015. We used daytime snorkeling to sample 48 index reaches in the Little North Fork Clearwater River from near Foehl Creek upstream to Lund Creek during 10–13 August, 2015. We observed a total of 481 Westslope Cutthroat Trout, 69 Rainbow Trout, 143 Bull Trout, and 300 Mountain Whitefish. Mean total density of Westslope Cutthroat Trout was 2.39 fish/100 m2 and density of Westslope Cutthroat Trout ≥ 305 mm was 0.68 fish/100 m2. Both total density and density of Wesstslope Cutthroat Trout ≥ 305 mm were above the 15 year mean. One tag was reported via the “Tag You’re It!” reporting hotline in August 2015 and a second during July 2016. We estimated an adjusted annual exploitation rate of 1.55%, down from an exploitation rate of 2.89% in 2012. Overall, the trend in abundance and size structure of Westslope Cutthroat Trout has been positive since monitoring began in 1997. Mean estimated angler exploitation over the past 6 years has declined eight fold. It is likely that a combination of habitat improvement from reduced land use and decreased exploitation have contributed to the observed increase in abundance and size structure. The Little North Fork Clearwater River is meeting management objectives and continues to support a quality native wild trout fishery. Author:

Carson Watkins Regional Fishery Biologist

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INTRODUCTION

The Little North Fork Clearwater River is one of northern Idaho’s most remote rivers and supports a variety of native fish species. The river provides important habitat for native Westslope Cutthroat Trout and Bull Trout (Watson and Hillman 1997; DuPont and Horner 2006) in addition to supporting a fishery for both species. Historically, anadromous Chinook Salmon and steelhead were found throughout the Little North Fork Clearwater River which provided an abundance of spawning and rearing habitat. Anadromous fish were extirpated from the North Fork Clearwater River drainage following the completion of Dworshak Dam in 1973 (Pettit and Wallace 1975), and the fishery is now composed of resident fluvial and adfluvial fishes.

The Little North Fork Clearwater River is one of the most remote river systems in Idaho.

The river corridor has very minimal access for full-sized vehicles, and road access is primarily limited to the uppermost portion of the river corridor. An extensive trail system allows access to a majority of the river, and some trails are open to motorcycle use. During 2001–2008 the U.S. Forest Service (USFS) undertook significant efforts to upgrade and improve the trail network to provide better access to the Little North Fork Clearwater River, particularly for motorcycles (Hardy and Fredericks 2010). Because Westslope Cutthroat Trout are highly vulnerable to exploitation (Rankel 1971; Bowler 1974), fishery managers have been concerned about the effect that improved access may have on fishery quality in the Little North Fork Clearwater River. The ability to harvest wild trout is an important and valued opportunity by many Idahoans in places where it can be sustained. As such, a major focus of fishery monitoring in the Little North Fork Clearwater River has related to evaluating angler exploitation and spatiotemporal shifts in harvest. In addition, population- and assemblage-level trend monitoring has been used to compliment other long-term monitoring efforts for Westslope Cutthroat Trout and Bull Trout throughout the state (Kennedy and Meyer 2015; High et al. 2008). Periodic standardized monitoring has been tremendously important for formulating effective management plans for conservation of native resident salmonids in Idaho, and for maintaining quality angling opportunity.

OBJECTIVES

1. Monitor trends in abundance, distribution, and size structure of fish populations in the Little North Fork Clearwater River.

2. Evaluate exploitation and harvest patterns of Westslope Cutthroat Trout in the Little

North Fork Clearwater River.

3. Maintain long-term data to provide information related to fishery management in the North Fork Clearwater River system.

STUDY AREA

The Little North Fork Clearwater River is the largest tributary to the North Fork Clearwater River and located in the southern portion of Idaho Department of Fish and Game’s (IDFG) Panhandle Region (Figure 31). Management of the Little North Fork Clearwater River is unique because its parent system lies entirely in another IDFG management region (i.e., Clearwater Region). It originates in the Clearwater Mountains within the St. Joe National Forest and flows through portions of Shoshone and Clearwater counties. Land ownership within the

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Little North Fork Clearwater River drainage is dominated by the USFS and State of Idaho (i.e., Floodwood State Forest; Idaho Department of Lands).

With the exception of Dworshak Dam and Reservoir, land use and water development

throughout the Little North Fork Clearwater River watershed have been fairly minimal. Historically, timber harvest in the uplands of the watershed has been the dominant form of land-use. Overall, declines in timber harvest on USFS lands have led to improvements in aquatic habitat throughout the watershed. Much of the upper watershed along the Clearwater River-St. Joe River divide has a checkerboard-style land ownership pattern with every other sections being privately- (i.e., Forest Capital Partners) and publically-owned (i.e., USFS or state endowment lands). As such, the potential for changes in water quality and aquatic habitat is high, and may negatively influence sensitive fish species. Long-term monitoring in the Little North Fork Clearwater River has been important for informing habitat-related management decisions, especially those related to sensitive species.

The Little North Fork Clearwater River watershed is ~53,000 ha in area and elevations

range from 2,081 m at Widow Mountain to 1,640 m at the flatwater section of Dworshak Reservoir. The downstream-most reach of the Little North Fork Clearwater River is no longer free-flowing, as it has been flooded by the impoundment created by Dworshak Dam on the Lower North Fork Clearwater River. At full pool, the reservoir inundates the lower 8 km of the Little North Fork Clearwater River upstream to Meadows Creek. A large majority of the drainage is roadless, with much of the road network concentrated near the headwaters from past logging operations. Most recreational access to the mainstem Little North Fork Clearwater River is gained by way of Gateway Point, Surveyor Ridge, Buzzard Roost, and Twin Creek (in ascending upstream order). USFS Trail 50 extends the length of the river from Foehl Creek to Twin Creek and provides good access along the river.

The portion of the Little North Fork Clearwater River that was sampled during this study extends 34 km from approximately 1.15 km below the confluence of Foehl Creek upstream to the confluence of Lund Creek (Figure 31). Forty-eight standard index reaches were established in 1997 to monitor population trends of wild salmonids throughout the Little North Fork Clearwater River (DuPont and Horner 2006; Figure 31). The IDFG has conducted sampling at all index reaches on a triennial basis since 1997.

METHODS

Fish Assemblage Monitoring

Index reaches in the Little North Fork Clearwater River were sampled during August 10–13, 2015 using daytime snorkeling (DuPont et al. 2009; Thurow 1994). One (wetted width ≤ 10 m wide) or two (wetted width > 10 m wide) observers slowly snorkeled downstream identifying fishes to species and estimating total length (TL; mm) of all salmonid species. Transects have been permanently marked with a global positioning system (GPS) and digital photographs provided reference to the upper and lower terminus of each reach. Estimates of salmonid abundance were limited to age-1+ fish, as summer counts for young-of-year (YOY) Cutthroat and Rainbow trout O. mykiss are typically unreliable. After completion of each sampling reach, each species was enumerated and salmonid species (i.e., Westslope Cutthroat Trout; Rainbow Trout; Bull Trout; Mountain Whitefish Prosopium williamsoni) were separated into 75 mm length groups. Nongame fish species (e.g., Cottus spp. and Catostomus spp.) were enumerated, but lengths were not estimated.

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Reach length and wetted width were measured at each sampling site with a laser

rangefinder. The habitat type (pool, riffle, run, glide, pocket water), maximum depth, dominant cover type and amount of cover (visually estimated as % of surface area) in the area sampled was measured to assess if changes in habitat were responsible for any changes in fish abundance and assemblage structure. Surface area (m2) was estimated at each site to provide a measure of sampling effort. The number of salmonids observed was divided by the surface area sampled to provide a standardized relative abundance measure. We calculated a mean relative density that could be compared to previous years (DuPont and Horner 2006). Non-target species were enumerated and reported as the total number observed.

Exploitation and Harvest Patterns of Wild Trout

We sampled Westslope Cutthroat Trout in the Little North Fork Clearwater River using angling during July 6–8, 2015 to estimate annual angler exploitation and patterns of harvest. The Little North Fork Clearwater drainage is mountainous and receives relatively high winter precipitation (140–165 cm; DuPont and Horner 2006), so the angling season is typically short. High runoff often persists well into the middle of summer, thus prolonging poor angling and dangerous wading conditions. In addition, high flows can preclude access at river crossings during the early part of the season. As such, sampling was conducted as early as possible and we assumed that our sampling occurred prior to the angling season. Westslope Cutthroat Trout ≥ 305 mm were tagged with non-reward FD-94 T-bar anchor tags (76 mm; Floy Tag Inc., Seattle, Washington, USA). The Westslope Cutthroat Trout population in the Little North Fork Clearwater River is not managed using a minimum length limit; however, we assumed that stock length (203 mm TL) and larger individuals would be desirable to harvest-oriented anglers. As such, our resulting estimate of angler exploitation is only representative of stock length and larger fish. Each tag was uniquely-numbered and inserted near the posterior end of the dorsal fin of each fish. Tags also possessed the telephone number and website address for the IDFG’s “Tag! You’re It!” reporting outlets. Angler exploitation of Westslope Cutthroat Trout was estimated using the non-reward tag reporting estimator described by Meyer et al. (2012), incorporating estimates of tag loss and tagging mortality. We also corrected exploitation estimates from previous years to make comparative and time series analyses more meaningful. Prior to 2012, tag loss and tagging mortality adjustments were not incorporated into exploitation estimates because the information was not yet available.

RESULTS

Fish Assemblage Monitoring

In total, we observed 481 Westslope Cutthroat Trout, 69 Rainbow Trout, 143 Bull Trout, and 300 Mountain Whitefish using snorkeling. Mean total density of Westslope Cutthroat Trout was 2.39 fish/100 m2 and density of Westslope Cutthroat Trout ≥ 305 mm was 0.68 fish/100 m2, representing a sustained increase in relative abundance from previous sampling years (Figure 32). Westslope Cutthroat Trout were encountered at 47 of 48 sampling sites, and generally the highest densities were downstream of Rutledge Creek in the lower portion the study area. We estimated Rainbow Trout density to be 0.52 fish/100 m2. Rainbow Trout occurred at 21 of 48 sites and were most abundant at sites located between Adair and Montana creeks. Mean total density was 0.87 fish/100 m2 and 1.00 fish/100 m2 for Bull Trout and Mountain Whitefish, respectively. Bull Trout were observed at 16 sites throughout the study area, with the highest abundances observed between Lund and Adair creeks around the upstream-most portion of the

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system. Mountain Whitefish were only observed in sites located downstream of Adair Creek, and the highest abundances were found between Spotted Louis and Foehl creeks. Length distributions for salmonid species sampled in the Little North Fork Clearwater River are provided in Figure 33.

Exploitation and Harvest Patterns of Wild Trout

A total of 134 stock-length and larger Westslope Cutthroat Trout were tagged during July 6–8, 2015. Length of tagged fish varied from 256–446 mm TL (Figure 34). Westslope Cutthroat Trout were tagged throughout the Little North Fork Clearwater River between Adair and Foehl creeks. Sampling was not conducted downstream of Foehl Creek due to limited access. One tagged fish was reported from the 2015 angling season. That individual was harvested by the angler and was caught on 9 August, 2015. We calculated an adjusted annual exploitation rate of 1.55%, a decrease of 15.11% since 1997 (Figure 35).

During 2016, two additional tagged Westslope Cutthroat Trout were caught by anglers and both were released. One was caught on 9 April, 2016 in the Breakfast Creek arm of Dworshak Reservoir and the other on 11 September, 2016 in the Little North Fork Clearwater near the mouth of Culdesac Creek.

DISCUSSION

Westslope Cutthroat Trout are a popular game fish and the species’ high catchability attracts a good deal of interest from anglers. Westslope Cutthroat Trout have been shown to be vulnerable to recruitment overfishing (Rankel 1971; Sissenwine and Shepherd 1987), and even low rates of harvest can drastically alter size structure. This dynamic has been demonstrated in many systems throughout the state and prompted conservative angling regulations (i.e., catch and release; high minimum length limits) in many popular Westslope Cutthroat Trout fisheries (e.g., St. Joe River, North Fork Clearwater River, Middle Fork Salmon River) (Flinders et al. 2013; Hardy and Fredericks 2010). In many cases, conservative regulations are required in highly accessible systems where the potential for additive fishing mortality is high. In addition, non-consumptive trout anglers are becoming more common and often desire large fish; thus, fishery managers must consider the effect of harvest on population size structure, in addition to abundance.

Since fishery monitoring in the Little North Fork Clearwater River began in 1997, the

drainage has seen very limited development and changes to land use. In fact, the only major (and most concerning) sources of development have been in regard to trail access to the river. The issue of access has been central to fishery monitoring in the system because the trail system has undergone a series of improvements over the last 17 years. The majority of the trail network remains open to motorized use (i.e., motorcycles only), but is only reasonably accessed by foot. For instance, the USFS motorized vehicle use plan allows motorcycle use on FS Trail 50, which parallels the course of the Little North Fork Clearwater River from the confluence of Twin Creek to Foehl Creek; however, little maintenance of brush and downed timber prohibits motorized vehicle access for the entirety of the trail below Spotted Louis Creek. Additionally, motorcycle access is allowed on recently (i.e., 2014) improved FS Trail 13 via FS Road 363 near Buzzard Roost, but up- and down-river access from its intersection with FS Trail 50 is severely limited. Ultimately, access to the majority of the lower Little North Fork Clearwater River has been relegated to foot traffic only and is likely to continue to be limited until FS Trail 50 is substantially cleared.

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Although periodic improvements to the trail network have occurred in the Little North Fork Clearwater River and have the potential to increase angling effort, it is unlikely that such activities have negatively influenced the fishery. Access is not the only factor that may influence angling effort, and potentially harvest. Idaho’s population is quickly growing and major cities around the Panhandle Region (i.e., Lewiston, Coeur d’Alene, Spokane) demonstrate that trend. Idaho Department of Fish and Game conservation officers and the public have noted an anecdotal increase in angling activities on the Little North Fork Clearwater River, despite access difficulty (J. Lininger, personal communication). Although most wild trout anglers willing to embark on a trip into the Little North Fork Clearwater River are typically not harvest-oriented, the potential for exploitation to increase with increasing angler use does exist. Nonetheless, tag return data and population monitoring surveys shown that abundance of Westslope Cutthroat Trout has increased and annual angler exploitation has decreased eight-fold over the past 18 years. The trend can likely be attributed to a combination of factors including improved aquatic habitat from evolving forest management practices and reduced harvest from a growing catch-and-release angling culture. Future monitoring should focus on evaluating changes in angler exploitation and trends in population characteristics of wild salmonids in the Little North Fork Clearwater River.

MANAGEMENT RECOMMENDATIONS

1. Continue to periodically monitor fish population trends and angler exploitation of Westslope Cutthroat Trout on a quinquennial schedule in the Little North Fork Clearwater River.

2. Pair assemblage monitoring with Bull Trout redd sampling in Little North Fork and North

Fork Clearwater rivers to maintain consistency of fishery sampling in the system.

3. Move sites 5, 8, 19, 22, 33, 40, and 44 to nearby run or pool macrohabitats. Shifting channel morphology has resulted in these sites being difficult to efficiently sample.

4. Maintain existing 2 fish daily bag limit.

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Figure 31. Location of 48 index reaches sampled using snorkeling in the Little North Fork

Clearwater River, Idaho (2015).

Figure 32. Mean total density of Westslope Cutthroat Trout and mean density of Westslope

Cutthroat Trout ≥ 305 mm TL observed by snorkeling in the Little North Fork Clearwater River, Idaho (1997–2015).

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Figure 33. Length-frequency distribution of salmonid species observed by snorkeling in the

Little North Fork Clearwater River, Idaho (2015).

Figure 34. Length-frequency distribution of Westslope Cutthroat Trout tagged to evaluate

angler exploitation in the Little North Fork Clearwater River, Idaho (2015).

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Figure 35. Estimated annual angler exploitation of Westslope Cutthroat Trout in the Little

North Fork Clearwater River (1997–2015).

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LAKE COEUR D’ALENE CHINOOK SALMON EVALUATIONS

ABSTRACT

We evaluated escapement of fall Chinook Salmon Oncorhynchus tshawytscha to assess trends in adult abundance by enumerating redds at standard index reaches of the Coeur d’Alene and St. Joe rivers. In 2015, we observed the highest adult escapement since redd monitoring began in 1990. A total of 303 redds was observed in the Coeur d’Alene and St. Joe rivers combined. Of those, 288 were observed in the Coeur d’Alene River system and 15 were observed in the St. Joe River. While redd abundance in the St. Joe River has remained relatively stable over the past five years, redd abundance in the Coeur d’Alene River has increased substantially. Chinook Salmon are piscivorous during adulthood and have strong potential to alter pelagic prey (i.e., kokanee O. nerka) communities, necessitating continued monitoring to ensure the quality of both fisheries. Future assessments should include annual monitoring of adult escapement and spawner age structure so that changes in abundance and age-at-maturity can be identified. Information related to population characteristics can be used to assess population-level changes and facilitate better management of the Lake Coeur d’Alene fishery.

In addition to adult abundance monitoring, we continued efforts to improve hatchery fall

Chinook Salmon performance. Similar to 2014, fall outplants during 2015 were experimentally stocked into Wolf Lodge Creek and Wolf Lodge Bay to evaluate relative return-to-creel. We also sought to collect eggs from locally-adapted individuals that home to tributaries in the north end of Lake Coeur d’Alene. Eggs were to be used for the following year’s stocking. We operated a weir on Wolf Lodge Creek near the Interstate-90 bridge to collect upstream migrants during September 14–October 9. A total of 32 Fall Chinook Salmon was collected during weir operation, most of which were adipose-removed individuals of hatchery origin. Too few wild Chinook Salmon were available to satisfy broodstock requirements. We recommend continued monitoring of hatchery fish performance using fishery-dependent data obtained from angler records. Additionally, improving survival of hatchery fall Chinook Salmon and dispersing the fall fishery should remain a priority. Efforts to improve performance should focus on utilizing locally-adapted adlfuvial stocks to avoid post-smolting emigration. We recommend continuing efforts to trap adult Chinook Salmon in Wolf Lodge and other tributaries to Lake Coeur d’Alene to collect locally-adapted broodstock for hatchery supplementation. Author:

Carson Watkins Regional Fishery Biologist

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INTRODUCTION

Chinook Salmon Oncorhynchus tshawytscha is an anadromous Pacific salmon species historically found throughout the Columbia River Basin (Wallace and Zaroban 2013). While anadromy is the natural life history form of Chinook Salmon, they have been successfully stocked into lentic systems outside of their native distribution where they exhibit adlfuvial life histories. For example, both Chinook Salmon and Coho Salmon O. kisutch have been stocked into large lakes and reservoirs in the northern United States where they have naturalized and provide important angling opportunities (Diefenbach and Claramunt 2013; MFWP 2013). With adequate fluvial spawning habitat, many landlocked Pacific salmon populations are able to adopt adfluvial life history strategies and naturalize in lentic systems, persisting well outside of their native distribution.

Fall Chinook Salmon were first stocked into Lake Coeur d’Alene in 1982 as a

biomanipulation tool to reduce kokanee O. nerka abundance. Kokanee exhibit density-dependent growth, and increases in population abundance commonly reduce length-at-age. This relationship has been evident in Lake Coeur d’Alene; fishery managers noted declines in size structure of kokanee during the late-1970s and concluded that fishing mortality could not sufficiently influence abundance. Goodnight and Mauser (1980) recommended an increase in the daily bag limit of kokanee from 25 to 50 fish following the 1979 season. The following year, Mauser and Horner (1982) noted that “the population size still exceeded the capacity of the system to produce fish of a desirable size to anglers” and recommended that predators be used to reduce abundance. Although kokanee harvest had reached an all-time high of ~578,000 fish in 1979, managers were convinced that improvements in size structure were needed to maintain angler interest. The semelparous life history and short life span of Chinook Salmon made it a desirable predator, and it was thought that their abundance could be regulated by stocking alone. An added benefit of Chinook Salmon was the creation of an additional fishery in the system. Previous managers had no expectation of naturalization and wild reproduction from Chinook Salmon introduced into Lake Coeur d’Alene; however, Chinook Salmon were observed spawning in Wolf Lodge Creek as early as 1984 and wild fish had become common in the fishery by 1986. Wild Chinook Salmon redds were observed in the Coeur d’Alene River and St. Joe River around 1988, and by then wild fish dominated the angler catch (Horner et al. 1989; Fredericks and Horner 1999).

The Idaho Department of Fish and Game (IDFG) continues to utilize Chinook Salmon as

one tool for managing the kokanee population in Lake Coeur d’Alene. In addition to natural reproduction, stocking supplements the fishery by providing additional harvest opportunity. The IDFG’s management objective regarding Lake Coeur d’Alene has been to maintain predator stocking at a rate that does not depress the kokanee population, yet helps to achieve kokanee size structure objectives. Combinations of redd excavation and stocking (or lack thereof) have been used to regulate abundance for Chinook Salmon. Estimates of wild production have been obtained by coupling redd survey information with known egg-fry survival rates; subsequently, redds have been destroyed during some years to bring estimated production in line with objectives. Historically, Chinook Salmon redd objectives have been 100 total redds among both the Coeur d’Alene and St. Joe Rivers. During years when the objective was exceeded, redds have been excavated, and supplemental stocking has been used during years when wild redd abundance was below objective. However, the effectiveness of managing adult Chinook Salmon densities using supplemental stocking and redd excavation has been unsubstantiated. In addition, the kokanee population appears to be influenced more by environmental conditions rather than predator abundance. As such, in recent years the IDFG has not excavated Chinook

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Salmon redds, but monitors trends in redd abundance and supplemental stocking has been maintained at ~20,000 individuals annually since 2010 to supplement harvest.

One factor that has influenced the IDFG’s ability to control adult Chinook Salmon

abundance in Lake Coeur d’Alene is related to performance and retention of hatchery fish. Although 20,000 individuals are stocked annually, return-to-creel of hatchery fish is very low. Creel surveys conducted at angling tournaments and anecdotal evidence from avid Chinook Salmon anglers suggest that recruitment of hatchery fish to the fishery is close to zero. Maiolie and Fredericks (2014) evaluated performance of hatchery Chinook Salmon among rearing hatcheries and between spring and fall stocking seasons. The authors reported that hatchery fish performance may be lower among cohorts that were raised at Nampa Fish Hatchery and released in spring stocking groups. These results have influenced current management and the IDFG now rears supplemental Chinook Salmon for Lake Coeur d’Alene at Cabinet Gorge Hatchery in Clark Fork, Idaho. In addition, stocking has been moved to early fall (i.e., late September or early October) when fish are larger and near smoltification. Anglers have reported that hatchery Chinook Salmon (identified by a clipped adipose fin) were more commonly encountered during 2013–2014, suggesting that those individuals are now recruiting to the fishery at higher rates, but perhaps still at lower rates than desired by managers.

Because Chinook Salmon occur naturally with anadromous life histories, it is likely that

many attempt to emigrate shortly after release. Pacific Salmon demonstrate strong homing behavior and life history fidelity. However, bypassing critical early life stages (i.e., smoltification), imprinting of juveniles, or stocking brood derived from locally-adapted individuals may be used to overcome this tendency. By stocking after smolting occurs and simulating migration from a lotic to lentic environment, managers may be able to impose an adfluvial life history on a historically anadromous hatchery stock. Mimicking a migratory life history and imprinting juveniles to a adfluvial, “natal” environment is critical for establishing resident land-locked populations from anadromous fishes. For example, Alaska Department of Fish and Game (ADFG) has documented low retention of anadromous fishes stocked directly into freshwater lakes. In contrast, ADFG has obtained higher retention and higher return-to-creel among groups that are held in lake tributaries, imprinted, and allowed to emigrate to the respective lake where they carry out their adult life history (Havens et al. 1987). An additional hypothesis is that smolt-related emigration can be reduced by using locally-adapted adfluvial broodstock. The utilization of locally-adapted brood has been demonstrated in many systems, especially in anadromous fish populations (Taniguchi 2003), and may likely increase retention of hatchery Chinook Salmon in Lake Coeur d’Alene.

Both kokanee and Chinook Salmon provide popular angling opportunities in Lake Coeur d’Alene. The IDFG’s objective for Lake Coeur d’Alene is to manage for a kokanee yield fishery (15 fish daily bag limit) and limited trophy Chinook Salmon fishery (2 fish daily bag; none under 508 mm). Prior to the introduction of Chinook Salmon, nearly all (~99%) of the angling effort in Lake Coeur d’Alene has been targeted at kokanee (Rieman and LaBolle 1980); however, more recent studies have shown that most effort (~42%) is now targeting Chinook Salmon (Hardy et al. 2010). Chinook Salmon are highly-desired by anglers because they often grow to trophy sizes and have very palatable flesh. As such, monitoring the Chinook Salmon population and understanding factors that regulate it is critical for providing quality angling opportunities.

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OBJECTIVES

1. Monitor trends in adult Chinook Salmon abundance

2. Evaluate stocks and stocking strategies for hatchery Chinook Salmon to improve return-to-creel of supplemental fish.

STUDY AREA

Lake Coeur d’Alene is a natural mesotrophic water body located in the Panhandle of northern Idaho (Figure 36). Lake Coeur d’Alene lies within Kootenai and Benewah Counties and it is the second largest natural lake in Idaho with a surface area of 12,742 ha, mean depth of 24 m, and maximum depth of 61 m (Rich 1992). The Coeur d’Alene and St. Joe rivers are the major tributaries to Lake Coeur d’Alene; however, many smaller 2nd and 3rd order tributaries contribute flow as well. The outlet to Lake Coeur d’Alene is the Spokane River, a major tributary to the Columbia River. Water resource development in the watershed includes Post Falls Dam, which was constructed on the Spokane River in 1906, and raised the lake level approximately 2.5 m.

The fish assemblage in Lake Coeur d’Alene is composed of three native sport fish species, five native nongame species, 16 introduced sport fish species, and one introduced nongame species. The fishery in the lake, however, can be broadly summarized as belonging to one of three components: kokanee, Chinook Salmon, or littoral species; all of which are popular among anglers. Increased fish assemblage complexity has undoubtedly resulted in increased biological interactions, but also diversified angler opportunity. Because of its close proximity to several major cities (i.e., Coeur d’Alene; Spokane), Lake Coeur d’Alene generates high angling effort, contributing considerably to both state and local economies. In fact, according to a 2011 survey of the economic impact of angling in Idaho, the Lake Coeur d’Alene fishery generated approximately $11 million and 84,000 angler trips (IDFG, unpublished data). This estimated economic value was tenth highest in the state along with other important fisheries like the Henry’s Fork, Clearwater River, CJ Strike Reservoir, Henrys lake and Pend Oreille Lake. .

METHODS

Spawner abundance

Chinook Salmon escapement has been monitored using annual redd counts in the Coeur d’Alene and St. Joe rivers since 1990. Standardized index reaches (Table 20) have been sampled annually sometime during late September–early October to estimate relative redd abundance. Early surveys were done via helicopter, but since 2012 surveys have been conducted using canoes (Maiolie and Fredericks 2014). Two canoeists floated the Coeur d’Alene River index reaches during October 2–3, 2014 and the St. Joe index reach during October 6, 2014. During sampling, each redd was enumerated and georeferenced with a global positioning system. Redd abundance was estimated as the total number of redds observed among all index reaches. We compared among previous years’ surveys to provide insight on trends in abundance.

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Performance of supplemental Chinook Salmon

Eggs from Tule Fall Chinook Salmon were purchased from Big Creek Fish Hatchery located near Astoria, Oregon, and were hatched and reared at Cabinet Gorge Hatchery in Clark Fork, Idaho. The adipose fin was completely removed from all individuals (n = 22,530), but they were not tagged as in previous years. Approximately half of the hatchery individuals (i.e., tributary group) were held in two submerged live cages (1.0 × 2.4 m) near the Interstate-90 bridge in Wolf Lodge Creek (Figure 36) for 10 days prior to release on September 11, 2015. We sampled individuals daily to assess scale sloughing and held individuals until sloughing (indicating smoltification) has ceased. The other remaining (i.e., in-lake group) brood were stocked in Wolf Lodge Bay on September 14, 2015 when surface water temperatures were similar to Wolf Lodge Creek. Relative return-to-creel will be evaluated using adults captured in the fishery during future years.

Specific comparisons between stocking groups will require sampling of adults with known origin and treatment histories. As such, future stocking groups will require unique marks for purposes of differentiating among groups and years. To address this, the in-lake and tributary stocking groups will be uniquely thermal marked by Cabinet Gorge Hatchery staff. Analysis of variance (ANOVA) with post-hoc multiple comparisons will likely be used to compare return-to-creel among years and between stocking groups.

RESULTS

We summarized redd abundance to provide insight on adult escapement and to monitor trends in natural production. We observed a total of 288 redds at index reaches in the Coeur d’Alene River basin. Of these, we observed 210 redds in the mainstem Coeur d’Alene River between Cataldo and the confluence of the South Fork Coeur d’Alene River, 68 redds in the North Fork Coeur d’Alene River between the confluence of the South Fork Coeur d’Alene River and the confluence of the Little North Fork Coeur d’Alene River, and 10 redds in the South Fork Coeur d’Alene River between the mouth and Pine Creek (Table 20). A total of 15 redds was observed in the St. Joe River between St. Joe City and the Calder Bridge (Table 20). Chinook Salmon redd abundance has shown an increasing trend over the past two years in the Coeur d’Alene River, and 2015 marks the highest redd abundance observed since monitoring began in 1990 (Figure 37).

Thirty-two adult Chinook Salmon were trapped at the weir on Wolf Lodge Creek during September and October, of which 25 were hatchery origin individuals. Ripe eggs were harvested from the seven wild origin fish collected at the weir; however, we were unable to meet total egg needs. We chose to only harvest eggs from wild origin individuals to ensure that our broodstock had been removed from anadromous ancestors by at least one generation.

DISCUSSION

The Chinook Salmon fishery has improved substantially over the past decade, and during 2015 anglers enjoyed some of the best fishing in recent history. The combination of several factors (i.e., stable environmental conditions, abundant forage [kokanee]) has likely allowed the population to rebound from the low abundances observed in the late 1990s (Watkins et al. in review). The most recent redd survey (Fall 2015) marked the highest redd abundance since monitoring began in 1990. Between 2007 and 2012, redd abundance was

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relatively stable, but there has been a sharp increase over the past few years. Anglers will likely benefit from the increase in Chinook Salmon abundance in the short-term; however, it will be difficult to predict the persistence of current trends without additional population information.

The Chinook Salmon fishery in Lake Coeur d’Alene has historically been supported almost entirely by naturally-produced individuals. Anecdotal evidence from anglers suggests that age-1 and age-2 adipose-clipped individuals have been more common in the fishery during 2014–2015. The IDFG has made the following advances in Chinook Salmon rearing and stocking which may be contributing to improved performance of hatchery individuals: 1) fall Chinook Salmon rearing has been moved from Nampa Hatchery to Cabinet Gorge Hatchery where rearing temperatures are colder and the transport distance to Lake Coeur d’Alene is shorter, and 2) size-at-release has been improved by switching from spring to fall stocking. The combination of changes in rearing and release timing are expected to improve survival of hatchery fish; however, we will be unable to fully-quantify the effect of these management actions until 2014 outplants recruit to the fishery. While the direct results of these actions are difficult to substantiate, we cannot attribute this change in occurrence of hatchery individuals to any other major management changes. This is consistent with previous studies showing that performance of hatchery fish is often directly related to length-at-release where larger individuals typically exhibit higher survival and return-to-creel than their smaller counterparts (Henderson and Cass 2011).

Despite ongoing efforts to identify factors influencing return-to-creel of hatchery

produced Chinook Salmon, the post-release fate of those individuals remains unknown. Previous research has addressed factors that limit survival (Maiolie and Fredericks 2013; Maiolie and Fredericks 2014), but no work has sought to understand retention of hatchery-origin Chinook Salmon and whether post-release emigration may be a limiting factor. Future work will be aimed at evaluating relative return-to-creel by comparing stocking strategies that are hypothesized to improve retention. Anglers often catch adipose-removed Chinook Salmon in Lake Roosevelt which have presumably emigrated from Lake Coeur d’Alene and become entrained in that reservoir (William Baker, Washington Department of Fish and Wildlife, personal communication). These reports are not uncommon and are received from both anglers and Washington Department of Fish and Wildlife personnel. Post-release emigration has been documented in other lentic systems in Idaho where fall Chinook Salmon are stocked. For instance, hatchery Chinook Salmon stocked into Deadwood Reservoir in the Southwest Region have been sampled in Black Canyon Reservoir on the Payette River (Koenig et al. 2015). Additionally, hatchery Chinook Salmon stocked into Anderson Ranch Reservoir have been reported in Arrowrock Reservoir and Lucky Peak Reservoir (Arthur Butts, personal communication). This raises serious concern about post-release retention of hatchery stock and its effect on return-to-creel. It is likely that Chinook Salmon from anadromous stocks have a strong tendency to emigrate after release, particularly when stocked into waters within the Columbia River Basin. The maintenance of this life history may lead to a substantial portion of the hatchery fish attempting to emigrate after release. Improving retention will likely require the use of a method that imposes an adfluvial life history on hatchery individuals, or require the use of a landlocked, adfluvial stock (i.e., Lake Coeur d’Alene) for hatchery production.

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MANAGEMENT RECOMMENDATIONS

1. Continue evaluation of hatchery Chinook Salmon performance; specifically, the influence of alternative stocks and stocking strategies.

2. Continue to monitor spawner abundance and population characteristics at index reaches

in the Coeur d’Alene River and St. Joe River.

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Table 20. Location, description of index reaches, and number of Chinook Salmon redds counted during surveys from the most recent five years. Surveys are conducted in the Coeur d’Alene River and St. Joe River. Reaches include only those with long time series information used to index Chinook Salmon redd abundance.

Year Reach Description 2015 2014 2013 2012 2011 Coeur d’Alene River CDA 1 Cataldo to S.F. Coeur d’Alene River confluence 210 104 108 65 79 CDA 2 S.F. to L.N.F Coeur d’Alene River confluence 68 62 2 7 12 CDA 3 S.F. Coeur d’Alene River 10 4 14 13 17 St. Joe River SJR 1 St. Joe City to Calder bridge 15 9 4 9 --

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Figure 36. Location of Lake Coeur d’Alene, Idaho. The black dot represents the location of

the adult trap and where juvenile hatchery Chinook Salmon were released.

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Figure 37. Number of Chinook Salmon redds counted during sampling of index reaches in

the Coeur d’Alene River and St. Joe River from 1990–2015.

0

50

100

150

200

250

300

350N

umbe

r of r

edds

Year

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LAKE COEUR D’ALENE AND SPIRIT LAKE KOKANEE EVALUATIONS

ABSTRACT

We estimated age-specific abundance, density, and population characteristics of kokanee Oncorhynchus nerka in Lake Coeur d’Alene and Spirit Lake to monitor population trends. A modified midwater trawl was used to sample kokanee during July 14–17, 2015. We estimated a total abundance of 9,457,551 and 2,541,479 kokanee in Lake Coeur d’Alene and Spirit Lake, respectively. The Lake Coeur d’Alene kokanee population had good abundance of adult fish during 2015, but relatively low abundance of age-0 fish suggested poor strength of the 2015 year-class. Overall, estimated abundance increased by around 1.3 million fish from 2014. Mean total length of adult kokanee in Lake Coeur d’Alene was 246 mm, which is below the management objective of 250–280 mm. We documented the highest adult kokanee densities on record for Spirit Lake, likely the result of good recruitment in recent years. Size structure of kokanee in Spirit Lake was poor (mean age-3 TL = 188 mm), body condition was fair (mean Wr = 84), and the population continues to show strong density-dependent growth. Recruitment has been stable, suggesting that the trends in growth, and subsequently size structure, will persist at least through 2016. However, we found that the 2015 year-class was relatively weak, a pattern consistent with Lake Coeur d’Alene. Overall, brood years 2014 and 2015 produced weak year-classes relative to the preceding 10 years. We recommend continued monitoring of the Lake Coeur d’Alene kokanee population to assess trends in age-specific abundance and growth. Follow-up monitoring in Spirit Lake will be needed to document population-level responses to the recently increased daily bag limit. Monitoring should also focus on assessing the fishery-level effects of recruitment in both lakes from the 2015 year-classes. Author:

Carson Watkins Regional Fishery Biologist

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INTRODUCTION

Kokanee Oncorhynchus nerka are a popular sport fish across much of the western U.S. because of their high catchability and table value. Kokanee angling is especially popular among local anglers because it is family-oriented, consistently entertaining, and can be done using simple gear. Kokanee comprise much of the fishing effort in northern Idaho lakes, making them an important focus for management. The Idaho Department of Fish and Game’s (IDFG) current policy is to manage for adult kokanee populations that support high annual harvest and provide forage for trophy species such as Gerrard Rainbow Trout and Chinook Salmon. Current and continued evaluations of kokanee populations in Lake Coeur d’Alene and Spirit Lake will provide information necessary to manage these fisheries.

Kokanee were introduced to Lake Coeur d’Alene in 1937 by the IDFG to establish a harvest-oriented fishery (Goodnight and Mauser 1978; Hassemer and Rieman 1981; Maiolie and Fredericks 2013). Initial introductions were made from a late-spawning shoreline stock from Lake Pend Oreille (originally Lake Whatcom, WA stock). During the early 1970s, attempts were made to introduce kokanee from an early-spawning stock (Meadow Creek, British Columbia) into Lake Coeur d‘Alene; however, early-spawning kokanee failed to establish a wild population and had dwindled by 1981 (Goodnight and Mauser 1980; Mauser and Horner 1982). Despite unsuccessful attempts to establish early-spawners, the kokanee fishery peaked in the mid-1970s and the wild, late-run stock was producing annual yields between 250,000–578,000 fish during that time (Goodnight and Mauser 1976; Goodnight and Mauser 1980; Rieman and LaBolle 1980). By the early 1980s, fishery managers had documented density-dependent effects on adult size structure of kokanee, which prompted an increase in the daily bag limit from 25 to 50 fish per day and the introduction of Chinook Salmon O. tshawytscha as a biomanipulation tool to reduce kokanee abundance (Mauser and Horner 1982). Chinook Salmon naturalized in the system and are now an important component of the Lake Coeur d’Alene fishery. In recent history, the kokanee population has not been highly influenced by abundance of predators, but rather by environmental conditions, particularly spring flooding.

Kokanee populations are greatly influenced by environmental conditions. For example, stochastic natural events can alter dynamic rate functions and have long-lasting effects on a population (Hassemer 1984). Poor recruitment commonly results from adverse environmental conditions and can be problematic from a fisheries management standpoint because kokanee are semelparous, and thus it may take several generations for recruitment to return to form. This dynamic was shown in Lake Coeur d’Alene where weak year-classes have resulted from high spring runoff events (i.e., 1996 flooding). The weak 1996 year-class resulted in low recruitment during subsequent years and translated into low abundance of harvestable age-3 and age-4 kokanee during 1998–2003. Lake Coeur d’Alene supports several predator species which prey upon kokanee at various life stages. As such, poor environmental conditions coupled with high predator abundance can have cumulative negative effects on kokanee dynamic rate functions, and thus abundance. The IDFG maintains long-term data on the kokanee population dynamics and abundance in Lake Coeur d’Alene to continually evaluate population-level changes resulting from environmental factors and fishery management. In addition, annual assessment of the kokanee population provides IDFG with valuable information that can be provided to anglers.

Late-spawning kokanee were also transplanted from Lake Pend Oreille to Spirit Lake in the late 1930s (Maiolie and Fredericks 2013), and this stock has essentially supported the wild component of the fishery. According to Rieman and Meyers (1990), Spirit Lake historically produced some of the highest relative annual yields of kokanee throughout the western U.S.

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and Canada. Attempts have been made to establish early-spawning kokanee to diversify the fishery, the last being in 2008 (Maiolie and Fredericks 2013). However, it has been thought that beaver dams and limited spawning habitat precluded them from naturalizing and significantly contributing to the fishery. Recent population assessments have shown that abundance of wild late-spawning adults has been high, so stocking was discontinued in 2010. In fact, recent kokanee assessments have shown fish are exhibiting slow growth relative to other systems, likely due to density-dependent effects.

OBJECTIVES

1. Maintain long-term monitoring data to provide information related to kokanee management in Lake Coeur d’Alene.

2. Estimate population characteristics of kokanee populations in Lake Coeur d’Alene and

Spirit Lake.

STUDY AREA

Lake Coeur d’Alene

Lake Coeur d’Alene is a mesotrophic natural lake located in the Panhandle of northern Idaho (Figure 38). Lake Coeur d’Alene lies within Kootenai and Benewah Counties and it is the second largest natural lake in Idaho with a surface area of 12,742 ha, mean depth of 24 m, and maximum depth of 61 m (Rich 1992). The Coeur d’Alene and St. Joe rivers are the major tributaries to Lake Coeur d’Alene; however, many smaller tributaries contribute flow as well. The outlet to Lake Coeur d’Alene is the Spokane River, a major tributary to the Columbia River. Water resource development in the lake includes Post Falls Dam which was constructed on the Spokane River in 1906, and raised the water level approximately 2.5 m. In addition to creating more littoral habitat and shallow-water areas, the increased water level created more pelagic habitat for open-water salmonids (e.g., kokanee, Chinook Salmon).

The fishery in Lake Coeur d’Alene can be broadly characterized as belonging to one of three components—kokanee, Chinook Salmon, or warmwater species; all of which are popular among anglers. The fish assemblage has become increasingly complex over time, particularly during the past 30 years. Increased fish assemblage complexity has undoubtedly resulted in increased biological interactions, but also diversified angler opportunity. Because of its close proximity to several major cities (i.e., Coeur d’Alene, Spokane), Lake Coeur d’Alene generates high angling effort, contributing considerably to state and local economies. According to a 2011 survey of the economic impact of angling in Idaho, Lake Coeur d’Alene generated ~ $11.1 million in total expenditures and 84,000 angler trips (IDFG, unpublished data). This impact was 10th in the state.

Spirit Lake

Spirit Lake is located in Kootenai County near the town of Spirit Lake, Idaho (Figure 39). The lake has a surface area of 596 ha, a mean depth of 11.4 m, and a maximum depth of 30.0 m. Brickel Creek is the largest tributary to the lake and drains a forested interstate watershed extending into eastern Washington. Brickel Creek originates on the eastern slope of Mount Spokane at approximately 744 m in elevation and flows in an easterly direction before forming

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Spirit Lake. Spirit Lake discharges into Spirit Creek, an intermittent outlet located at the northeastern end of the lake; Spirit Creek flows into the Rathdrum Prairie where flow typically becomes subterraneous and contributes to the Rathdrum Aquifer. Spirit Lake is considered mesotrophic having the following water quality concentrations: chlorophyll a = 5.3 µg/L (Soltero and Hall 1984), total phosphorus = 18 µg/L, and Secchi depth = 3.9 m (Rieman and Meyers 1992).

The fishery in Spirit Lake has two main components — kokanee and warmwater species. The size structure of kokanee in Spirit Lake has been poor in recent years and anglers have generally lost interest in the fishery. When conditions allow, the lake supports a popular ice fishery targeting kokanee and yellow perch Perca flavescens.

METHODS

Fish sampling and hard structure processing

During 2015, kokanee were sampled from Spirit Lake and Lake Coeur d’Alene on July 14 and July 16–17, respectively. Kokanee were sampled using a modified midwater trawl (hereafter referred to as the trawl) towed by an 9.2 m boat at a speed of 1.55 m/s. The trawl is a gear that has been successfully employed in large lentic systems for sampling kokanee (Rieman 1992). The trawl consisted of a fixed frame (3.2 m × 2.0 m) and a single-chamber mesh net (6.0-mm delta-style No. 7 multifilament nylon twine, knotless mesh). Further, the trawl assembly consists of two winch-bound cable towlines which are each passed through a single pulley block. The pulley blocks are vertically-attached to a 2.4 m-tall frame mounted to the stern of the boat allowing the trawl to be easily deployed and retrieved during sampling. Further information on the trawl can be found in Bowler et al. (1979), Rieman (1992), and Maiolie et al. (2004).

Trawling was conducted at 21 and 5 predetermined transects throughout Lake Coeur d’Alene and Spirit Lake, respectively (Figure 38; Figure 39). Transects were originally assigned using a systematic sampling design within three arbitrary strata (i.e., Sections 1, 2, and 3) and have remained the same to standardize abundance estimates (Maiolie and Fredericks 2014). During fish sampling, the bottom and top of the kokanee layer was identified by the boat operator and the trawl was towed for three minutes in a stepwise pattern with 2.4-m increments to capture the entire layer at each transect (Rieman 1992). Upon retrieval of the trawl, kokanee were measured for total length (TL; mm), weighed (g), and saggital otoliths were collected from 10 individuals per 1-cm length group if available. Otoliths were removed following the procedure outlined by Schneidervin and Hubert (1986) and horizontally mounted in epoxy using PELCO flat embedding molds (Ted Pella, Inc., Redding, California, USA). Otoliths were cross-sectioned transversely with sections bracketing the nucleus to capture early annuli. Resulting cross-sections were polished with 1,000 grit sandpaper and viewed using a dissecting microscope to estimate age.

We sampled adult kokanee from Lake Coeur d’Alene to estimate spawner length and age structure to evaluate growth objectives. Spawning adults were sampled on December 2, 2015 using an experimental gill net (46.0 m × 1.8 m with panels of 25, 32, 38, 44, and 50-mm bar-measure mesh). The net was set for ~20 minutes near Higgens Point in Wolf Lodge Bay. Sampled fishes were sexed and measured for TL (mm). In addition, otoliths were removed from five individuals per 1-cm length group immediately after sampling. Whole otoliths were viewed by a single reader using a dissecting microscope with reflected light to estimate age.

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Data Analysis

Body condition of kokanee was evaluated using relative weight (Wr; Neumann et al. 2012). Relative weight values were calculated as

Wr = (W / Ws) × 100, where W is the weight of an individual and Ws is the standard weight predicted by a species-specific length-weight regression (Neumann et al. 2012). A Wr value of 100 indicates average body condition, Wr values below 100 indicate poor body condition, and Wr values above 100 indicate good body condition.

Age structure of both populations and Lake Coeur d’Alene spawners was estimated using an age-length key (Isermann and Knight 2005; Quist et al. 2012). Age data was then used to generate estimates of age-specific abundance. Total population abundance estimates have traditionally been used to index the kokanee populations in both Spirit and Coeur d’Alene lakes. Therefore, we calculated total age-specific abundance (N) which could be compared to prior surveys.

Length-frequency information from trawling and spawner index netting was summarized to provide insight on size structure and length-at-age. Growth was summarized by fitting a von Bertalanffy growth model (von Bertalanffy 1938)

Lt = L∞ [1 – e –K (t – t0)]

where Lt is the mean length at age of capture, L∞ is the theoretical maximum length, K is the growth coefficient, and t0 is the theoretical age when length equals 0 mm. Models were fit with nonlinear regression techniques using Program R (nlstools package; R Development Core Team 2012; Seber and Wild 2006).

RESULTS

Lake Coeur d’Alene

Population monitoring

We sampled a total of 784 kokanee by trawling in Lake Coeur d’Alene during July 16–17, 2015. We estimated a total abundance of 9,457,551 (90% CI = 5,939,459–10,341,459) kokanee and density of 861 kokanee/ha. Age-specific abundance was estimated in order to make prior year comparisons and to provide insight on recruitment of adults to the fishery. We estimated abundances of approximately 350,000 age-0, 3.6 million age-1, 5.3 million age-2, and 135,000 age-3/4 kokanee based on trawling (Table 21). The highest kokanee fry densities were observed in the northern portion of the lake (Section 1; Figure 38), particularly near Wolf Lodge Bay. We observed much lower abundance of fry in sections 2 and 3. The highest adult abundance was observed in Section 2.

Kokanee sampled by trawling varied in length from 23–221 mm TL (Figure 40) and varied in age from 0–3 years old (Figure 41). Estimates of mean length-at-age were only slightly variable and represented very uniform growth rates among individuals (Figure 42). Kokanee

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were in fair body condition (Wr = 84.20 [SD = 9.3]), and body condition increased slightly as a function of age (Figure 43).

Spawner assessment

Spawning kokanee varied in length from 220–290 mm TL and all were estimated to be 3 years old. Similar to past years, female kokanee represented a smaller proportion of the sample (Figure 44). Mean TL was 247.05 mm (SD = 12.26) and 237.06 mm (SD = 9.24) for male and female kokanee, respectively. Overall mean TL was 245.90 mm (SD = 12.35). Mean TL of kokanee spawners in 2015 was similar to 2014, but below the adult length objective (Figure 45).

Spirit Lake

Population monitoring

We sampled a total of 1,293 kokanee by trawling in Spirit Lake on July 14, 2015. We estimated a total abundance of 2,541,479 (90% CI = 1,657,043 – 3,425,915) kokanee. We estimated abundances of 7,598 age-0, 60,828 age-1, 2,104,886 age-2, and 368,167 age-3/4 kokanee based on trawling (Table 22). We estimated a total density of around 4,344 kokanee/ha and a density of 629 age-3 kokanee/ha (Table 22). Few fry were sampled, and there did not appear to be any pattern in fry abundance around the lake. In addition, adults were well distributed around the lake and high abundances were observed at all transects.

Kokanee sampled during trawling varied in length from 34 – 211 mm TL (Figure 46; mean = 165.93, SD = 13.48) and varied in age from 0 – 3 years old (Figure 47). Estimates of mean length-at-age had little variability and represented uniform growth rates (Figure 42). Kokanee were in fair body condition (Wr = 79, SD = 8.0) and body condition decreased as a function of age (Figure 48).

DISCUSSION

Lake Coeur d’Alene

The kokanee population in Lake Coeur d’Alene has supported a productive harvest fishery over the past several years, and angling was reportedly good again during 2015. In the past, the population has been negatively affected by adverse environmental conditions, namely spring flooding (Maiolie and Fredericks 2013). However, stable conditions in recent history have improved the population. Recruitment has been stable over the past three years, and we expect good adult recruitment to the fishery into 2016. Abundance of young-of-year kokanee, as indexed by trawling, appears to be lower than normal and about five-fold below the ten-year mean. This pattern is consistent with age-0 abundance in Spirit Lake and could be a product of regional environmental conditions. Regardless of the cause, a weak year-class may actually benefit the fishery by improving growth and increasing mean adult size. It is also probable that the below average estimate of age-0 abundance is simply an artifact of sampling and does not accurately reflect true abundance due to sampling bias. Kokanee fully-recruit to the trawl at age-1, thus sampling during 2016 will confirm whether the 2015 year-class was abnormally weak.

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We again documented adult spawner size that was below the desired range and below the most recent 20-year average (Figure 46). Our mean length estimate in 2015 (TL= 245.90 mm) was only slightly below the minimum bound of the desired range, and we believe that the majority of adult kokanee in the population are still reasonably desirable to anglers. While potential management options for influencing the kokanee fishery are limited, continued population monitoring is important for understanding kokanee ecology and for providing public information.

Spirit Lake

Spirit Lake has historically been one of Idaho’s top kokanee fishing waters (Maiolie and Fredericks 2013). The lake supports a summer troll fishery and winter ice fishery making it an important regional resource. The kokanee population has a long history of being highly variable in terms of recruitment and growth, and this has continued over the last 15 years (Maiolie and Fredericks 2013). The fishery has tended to follow suit whereby angling effort tracks adult abundance and size structure; however, the fishery can be variable due to winter ice conditions as well. The variability in the fishery seems to have persisted in recent history. Spirit Lake does not have any pelagic predators, unlike other large northern Idaho lakes (i.e., Lake Pend Orielle, Lake Coeur d’Alene), so its kokanee population serves as a baseline for which other populations can be compared (Maiolie and Fredericks 2013). The absence of predators, however, also allows kokanee to reach high densities in Spirit Lake. As such, the kokanee population often exhibits strong density-dependent growth, thus depressing size structure and leading to decreased interest among anglers.

Based on sampling in 2015, kokanee in Spirit Lake have reached the highest adult (i.e., age-3) densities since sampling began in 1981. Total abundance was nearly 75% higher than the most recent (2014) survey and age-3 abundance in 2015 was around six-fold higher than the long-term mean, following an upsurge beginning in 2011 (Maiolie and Fredericks 2013). High recruitment has apparently persisted and created strong density dependent growth. Few age-3 kokanee from the 2015 sample surpassed 200 mm TL and mean length of age-3 fish was ~188 mm. The relatively small size of adults has reduced angler interest. Consistent with results from Lake Coeur d‘Alene, we found that 2015 produced a weak year-class of kokanee in Spirit Lake. At this stage, a weak year-class may benefit the fishery as long as the 2015 cohort sustains a spawning stock size for sufficient replacement. Follow-up sampling will be necessary in the future to document whether high adult abundance persists and to assess if a recent (2015) increase in the daily bag limit (i.e., 25 fish/day) has had an effect on the quality of the fishery.

MANAGEMENT RECOMMENDATIONS

1. Continue annual kokanee population monitoring on Lake Coeur d’Alene.

2. Perform follow-up sampling on Spirit Lake during 2016 to evaluate population-level changes to daily bag limit increase.

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Table 21. Estimated abundance of kokanee made by midwater trawl in Lake Coeur d’Alene, Idaho, from 1979–2014.

Year Age class

Total Age-0 Age-1 Age-2 Age-3/4 2015 349,683 3,664,419 5,307,640 135,809 9,457,551 2014 2,877,209 2,153,877 2,790,295 319,080 8,140,461 2013 1,349,000 3,663,000 1,319,000 373,000 6,704,000 2012 -- -- -- -- -- 2011 3,049,000 1,186,000 1,503,000 767,000 6,505,000 2010 660,400 2,164,100 1,613,300 506,200 4,943,900 2009 731,600 1,611,800 2,087,400 333,600 4,764,400 2008 3,035,000 3,610,000 1,755,000 28,000 8,428,000 2007 3,603,000 2,367,000 136,000 34,000 6,140,000 2006 7,343,000 1,532,000 91,000 33,900 8,999,000 2005 -- -- -- -- -- 2004 7,379,000 1,064,000 141,500 202,400 8,787,000 2003 3,300,000 971,000 501,400 182,300 4,955,000 2002 3,507,000 934,000 695,200 70,800 5,207,000 2001 7,098,700 929,900 193,100 25,300 8,247,000 2000 4,184,800 783,700 168,700 75,300 5,212,600 1999 4,091,500 973,700 269,800 55,100 5,390,100 1998 3,625,000 355,000 87,000 78,000 4,145,000 1997 3,001,100 342,500 97,000 242,300 3,682,000 1996 4,019,600 30,300 342,400 1,414,100 5,806,400 1995 2,000,000 620,000 2,900,000 2,850,000 8,370,000 1994 5,950,000 5,400,000 4,900,000 500,000 12,600,000 1993 5,570,000 5,230,000 1,420,000 480,000 12,700,000 1992 3,020,000 810,000 510,000 980,000 5,320,000 1991 4,860,000 540,000 1,820,000 1,280,000 8,500,000 1990 3,000,000 590,000 2,480,000 1,320,000 7,390,000 1989 3,040,000 750,000 3,950,000 940,000 8,680,000 1988 3,420,000 3,060,000 2,810,000 610,000 10,900,000 1987 6,880,000 2,380,000 2,920,000 890,000 13,070,000 1986 2,170,000 2,590,000 1,830,000 720,000 7,310,000 1985 4,130,000 860,000 1,860,000 2,530,000 9,370,000 1984 700,000 1,170,000 1,890,000 800,000 4,560,000 1983 1,510,000 1,910,000 2,250,000 810,000 6,480,000 1982 4,530,000 2,360,000 1,380,000 930,000 9,200,000 1981 2,430,000 1,750,000 1,710,000 1,060,000 6,940,000 1980 1,860,000 1,680,000 1,950,000 1,060,000 6,500,000 1979 1,500,000 2,290,000 1,790,000 450,000 6,040,000

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Table 22. Estimated abundance of kokanee made by midwater trawl in Spirit Lake, Idaho, from 1981–2014.

Age class Year Age-0 Age-1 Age-2 Age-3 Total Age-3/ha 2015 7,598 60,828 2,104,886 368,167 2,541,479 629 2014 44,295 720,648 653,945 231,356 1,650,245 396 2013 -- -- -- -- -- -- 2012 -- -- -- -- -- -- 2011 1,092,000 185,700 382,300 65,500 1,725,400 112 2010 138,200 459,900 88,800 61,600 748,500 105

2009 260,700 182,600 75,900 30,000 549,200 51

2008 281,600 274,400 188,800 56,400 801,200 96 2007 439,919 210,122 41,460 20,409 711,910 35 2006 -- -- -- -- -- -- 2005 508,000 202,000 185,000 94,000 989,100 161 2001–04 -- -- -- - -- -- 2000 800,000 73,000 6,800 7,800 901,900 13 1999 286,900 9,700 50,400 34,800 381,800 61 1998 28,100 62,400 86,900 27,800 205,200 49 1997 187,300 132,200 65,600 6,500 391,600 11 1996 -- -- -- -- -- -- 1995 39,800 129,400 30,500 81,400 281,100 142 1994 11,800 76,300 81,700 19,600 189,400 34 1993 52,400 244,100 114,400 11,500 422,400 20 1992 -- -- -- -- -- -- 1991 458,400 215,600 90,000 26,000 790,000 45 1990 110,000 285,800 84,100 62,000 541,800 108 1989 111,900 116,400 196,000 86,000 510,400 150 1988 63,800 207,700 78,500 148,800 498,800 260 1987 42,800 164,800 332,800 71,700 612,100 125 1986 15,400 138,000 116,800 35,400 305,600 62 1985 149,600 184,900 101,000 66,600 502,100 116 1984 3,300 16,400 148,800 96,500 264,900 168 1983 111,200 224,000 111,200 39,200 485,700 68 1982 526,000 209,000 57,700 48,000 840,700 84 1981 281,300 73,400 82,100 92,600 529,400 162

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Section 1

Section 2

Section 3

Figure 38. Approximate location of historical trawling transects used to estimate abundance

of kokanee in Lake Coeur d’Alene.

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Figure 39. Approximate location of historical trawling transects used to estimate abundance

of kokanee in Spirit Lake, Idaho.

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Figure 40. Length-frequency distribution for kokanee sampled using a modified-midwater

trawl from Lake Coeur d’Alene, Idaho (July 16–17, 2015).

0.00

0.05

0.10

0.15

0.20

0.25R

elat

ive

frequ

ency

Length (mm)

n = 783

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Figure 41. Age-frequency distribution for kokanee sampled using a modified-midwater trawl

from Lake Coeur d’Alene, Idaho (July 16–17, 2015).

0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3

Rel

ativ

e fre

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cy

Age

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Age

0 1 2 3 4

Leng

th (m

m)

0

50

100

150

200

250

Lake Coeur d'AleneSpirit Lake

Figure 42. Mean length-at-age of kokanee sampled from Lake Coeur d’Alene and Spirit

Lake, Idaho (July 14, 2015).

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Figure 43. Relationship between total length and body condition of kokanee sampled from

Lake Coeur d’Alene, Idaho (July 16–17, 2015).

R² = 0.0528

0

20

40

60

80

100

120

140

0 50 100 150 200 250

Rel

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eigh

t

Length (mm)

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Figure 44. Length-frequency distribution for male and female kokanee sampled from Lake

Coeur d’Alene, Idaho (December 2, 2015).

0

10

20

30

40

50

60N

umbe

r

Length (mm)

MaleFemale

n (male) = 131 n (female) = 17

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Figure 45. Mean total length of mature male and female kokanee sampled near Higgens

Point in Lake Coeur d’Alene Idaho (1954–2015). Horizontal lines indicate the upper and lower limit of the adult length management objective (250–280 mm).

200

250

300

350

400

450Le

ngth

(mm

)

Year

males females

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Figure 46. Length-frequency distribution for kokanee sampled using a modified-midwater

trawl from Spirit Lake, Idaho (July 14, 2015).

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40R

elat

ive

frequ

ency

Length (mm)

n = 1,293

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Figure 47. Age-frequency distribution for kokanee sampled using a modified-midwater trawl

from Spirit Lake, Idaho (July 14, 2015).

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

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Figure 48. Relationship between total length and body condition of kokanee sampled from

Spirit Lake, Idaho (July 14, 2015).

R² = 0.2174

0

20

40

60

80

100

120

140

160

0 50 100 150 200 250

Rel

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WINDY BAY NORTHERN PIKE MANAGEMENT

ABSTRACT

Adfluvial populations of Westslope Cutthroat Trout in the Lake Coeur d’Alene basin have declined in recent history. Predation by nonnative Northern Pike has been demonstrated to be a significant factor limiting the recovery of certain adfluvial Westslope Cutthroat Trout subpopulations in the basin. Following two years of research evaluating food habitats and predation patterns of Northern Pike in Lake Coeur d’Alene, the Coeur d’Alene Tribe identified predation-related mortality as a critical factor hampering population growth of Westslope Cutthroat Trout in Lake Creek. Lake Creek enters Lake Coeur d’Alene in Windy Bay, an area that provides ample spawning habitat for Northern Pike during the spring. Seasonal occupancy of Northern Pike around the mouth of Lake Creek coincides with emigration of sub-adult Westslope Cutthroat Trout and immigration of adult Westslope Cutthroat Trout. Ecological overlap lends itself to high consumption rates of adfluvial Westslope Cutthroat Trout and creates a mortality “bottleneck.” In cooperation with the Coeur d’Alene Tribe, we implemented a Northern Pike management strategy that would alleviate the predation risk to migrating Westslope Cutthroat Trout, but not adversely affect the popular Northern Pike fishery. During 12 March–30 April, 2015 we captured 311 Northern Pike from Windy Bay around the inlet of Lake Creek using experimental mesh gill nets. Northern Pike were translocated to the northern portion of Lake Coeur d’Alene (~22.9 km from Windy Bay) where the risk to native fishes is lower and where they are readily available to more anglers. Mean total length of Northern Pike was 563.80 mm and varied from 288–1,020 mm. Mean Catch-per-unit-effort (CPUE) across all sampling events was 0.15 fish/net hr and CPUE decreased markedly through the duration of the removal period. We used a simple depletion model to estimate a total subpopulation abundance of 327.72 Northern Pike which is similar to previous subpopulation abundance estimates in Windy Bay. In total, 234 Northern Pike were translocated to Cougar Bay and 40 of those were reportedly caught by anglers. Anglers harvested 35 of the 40 reported Northern Pike, and we estimated an annual exploitation rate of 34.3%. Size structure of angler-caught Northern Pike closely matched that of the translocated population. Short-term site fidelity of Northern Pike appears to be very low and only one translocated individual migrated back to Windy Bay after removal. We will continue this Northern Pike management strategy in Windy Bay through 2017 on a trial basis. During that time we will continue to evaluate site fidelity of translocated Northern Pike, angler exploitation, and recolonization rates in Windy Bay. Author: Carson Watkins Regional Fishery Biologist

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INTRODUCTION

Worldwide, fish species have been introduced to waters outside of their native distribution for centuries (Gozlan et al. 2010). As a result, various ecosystems have experienced increased species richness (Horak 1995) and fish assemblages are becoming increasingly homogenized (Rahel 2000). In western North America, fish introductions by both legal (e.g., biomanipulation; fishery supplementation) and illegal (e.g., release of live baits; release of aquarium pets; anglers introduce desired fish species) means have occurred since the late 19th century. However, the rate of nonnative species spread has increased substantially since the early 1900s, mostly due to deliberate movement of desirable sportfishes (Cambray 2003). Regardless of the cause by which nonnative species are introduced, their establishment and proliferation can result in the decline of native species with significant social, economic, and ecological importance. The change to native fish assemblages from species introductions increases biotic interactions and creates the potential to precipitate negative ecological effects. Native species are often influenced by nonnative fishes through either direct (e.g., predation; Ruzycki et al. 2003) or indirect (e.g., competition for food and space; Thompson and Rahel 1996; Gido and Brown 1999) mechanisms. Effects resulting from the former are manifested in the interactions between nonnative top-level predators and native prey species. Additive mortality from predation can hamper recruitment and lead to declines in abundance of native fishes over time. Nonnative predators are regarded as posing the most imminent threat to fish community structure and species persistence in North America.

Examples of the negative effects of top-down predation on native fishes have been widely demonstrated in the literature. For instance, Ruzycki et al. (2003) reported declines in Yellowstone Cutthroat Trout Oncorhynchus clarki bouvieri abundance in Yellowstone Lake following the introduction of nonnative Lake Trout Salvelinus namaycush. Similarly, introductions of Northern Pike in western North America have been highly prolific and altered the dynamics of native prey species. Muhlfeld et al. (2008) documented the predation effects of Northern Pike on native salmonids (i.e., Westslope Cutthroat Trout Oncorhynchus clarki lewisi and Bull Trout Salvelinus confluentus) in the Flathead River system, Montana. Similarly, Johnson et al. (2008) reported that Northern Pike predation ranked as a top threat to native cyrprinus and catostomus spp recovery in the Yampa River basin, Colorado.

The Northern Pike is a top-level predator that prefers warm, slow-moving water around vegetated rivers or lake bays (Scott and Crossman 1973). Northern Pike have a circumpolar distribution, but their native distribution with in the lower 48 states is limited to the upper Mississippi River basin (Pflieger 1975). Northern Pike were illegally introduced to the state of Idaho around the early 1970s in the “Chain Lakes” along the lower Coeur d’Alene River. Since that time, Northern Pike have spread throughout the Lake Coeur d’Alene basin and have been introduced to many neighboring water bodies in the Idaho Panhandle, to which their current distribution in Idaho is limited (Watkins et al. in review). Northern Pike are classified as a game fish species in Idaho; however, Idaho Department of Fish and Game’s (IDFG) management policy prohibits fish introductions (IDFG 2013). The policy attempts to discourage illegal fish introductions by forbidding the use of special rules (including bag limitations) and mandating catch-and-kill angling tournaments focused on illegally introduced species. The Lake Coeur d’Alene system has the longest history of Northern Pike occupancy among all North Idaho waters (Rich 1992). The lake also serves as important habitat for adult adfluvial Westslope Cutthroat Trout, which have been in decline in some tributaries (Vitale et al. 2004). Adfluvial Westslope Cutthroat Trout in the system have been negatively affected by a variety of anthropogenic factors including land use, water development, and overexploitation (Rankel

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1971; DuPont and Horner 2009). Until recently, however, the extent to which predation from nonnative fishes may be limiting Westslope Cutthroat Trout stocks was poorly understood. Over the past 20 years, the Coeur d’Alene Tribe has been engaged in active restoration of adlfuvial Westslope Cutthroat Trout populations within tribal jurisdiction. The Coeur d’Alene Tribe’s work has documented low (~1.7%) juvenile-to-adult return rates of adfluvial Westslope Cutthroat Trout in Lake Creek over a 6 year period (Firehammer et al. 2012). Low adult returns were hypothesized to result from predation-induced mortality during migration. Walrath (2013) complimented this baseline work, demonstrating that total consumption of Westslope Cutthroat Trout by Northern Pike was high (N = 5,564; 95% CI = 3,311–10,979) throughout Lake Coeur d’Alene, but that impacts were site-dependent. Predation was highest during spring when adult Westlsope Cutthroat Trout are returning to spawning tributaries and juveniles are immigrating to Lake Coeur d’Alene (Walrath 2013; Walrath et al. 2015). Springtime immigration-emmigration for Westslope Cutthroat Trout coincides with high Northern Pike activity (i.e., spawning). The spring freshet in tributaries to Lake Coeur d’Alene triggers migration of Westslope Cutthroat Trout and inundates areas around tributary inlets which provide ideal spawning habitat for adult Northern Pike (Firehammer et al. 2012; Scott and Crossman 1973). Thus, the ecology of both species leads to substantial spatiotemporal overlap in occurrence near tributary inlets, creating a critical bottleneck for vulnerable Westslope Cutthroat Trout. Moreover, given the reported consumption demand of Northern Pike, it is sufficient to substantially influence recruitment potential of individual Westslope Cutthroat Trout populations.

Predator-induced declines of native fishes necessitate interferential management to reduce interactions between native and nonnative fishes, and management usually involves predator removal of some sort (Koel et al. 2005). In Idaho, managing Northern PIke predation is challenging because they are often highly valued by anglers. Angling clienteles develop around introduced sportfishes and those groups lobby to conserve the species. Ruzycki et al. (2003) cautioned that fishery managers must demonstrate the effects of predation on native fishes before controversial management actions are taken. The authors also caution that fishery managers can avoid the development of an angling clientele by demonstrating those effects before serious declines occur in native populations, and before the introduced predator population can provide a fishery. However, this is nearly impossible in most cases, and a clientele will almost certainly develop before effects can be adequately evaluated. As such, fishery managers require management alternatives that address the values of several competing public interests. Here, we present a removal-translocation program designed to mitigate for nonnative Northern Pike predation on Westslope Cutthroat Trout. Overall, our management objective was to develop a strategy that could minimize the impact to the popular Lake Coeur d’Alene Northern Pike fishery and also alleviate predation risk to native fishes. We worked cooperatively with public interest groups and the Coeur d’Alene Tribe to remove Northern Pike from a localized area of Lake Coeur d’Alene where predation was significantly limiting Westslope Cutthroat Trout. Our strategy involves translocation of a problem subpopulation to a portion of the lake where they are readily available to more anglers.

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OBJECTIVES

1. In cooperation with Coeur d’Alene Tribe fisheries staff, mitigate predation risk to adfluvial Westslope Cutthroat Trout through seasonal removal of Northern Pike in Windy Bay.

2. Estimate removal efficiency of Northern Pike in Windy Bay.

3. Evaluate angler exploitation of translocated Northern Pike.

4. Evaluate site fidelity of translocated Northern Pike.

STUDY AREA

Lake Coeur d’Alene is a mesotrophic natural lake located in the Panhandle of northern Idaho (Figure 49). Lake Coeur d’Alene lies within Kootenai and Benewah Counties and it is the second largest natural lake in Idaho with a surface area of 12,742 ha, mean depth of 24 m, and maximum depth of 61 m (Rich 1992). The Coeur d’Alene and St. Joe rivers are the major tributaries to Lake Coeur d’Alene; however, many smaller tributaries contribute flow as well. The outlet to Lake Coeur d’Alene is the Spokane River, a major tributary to the Columbia River. Water resource development in the lake includes Post Falls Dam which was constructed on the Spokane River in 1906, and raised the water level approximately 2.5 m, creating more littoral habitat and shallow-water areas around the lake’s periphery.

Lake Creek is a third order perennial tributary to Lake Coeur d’Alene that flows into the

lake at Windy Bay (Figure 49). The headwaters of Lake Creek originate near Mica Peak and it flows in a southeasterly direction until it joins the lake. Lake Creek has an interstate watershed encompassing portions of eastern Washington and Idaho. The majority of the Lake Creek watershed lies within the Coeur d’Alene Tribe Indian Reservation and has been the focus of long-term habitat enhancement aimed at restoring adfluvial Westslope Cutthroat Trout.

METHODS

Northern Pike were sampled daily (Monday–Friday only) during March 12–April 30, 2015 using 45 × 1.8 m experimental gill nets (5 panels with 25, 32, 38, 44, and 50-mm bar-measure mesh). Sampling consisted of a single gill net deployed at each of 6–8 randomly selected sites during each day following the design described by Walrath (2013). Our goal was to minimize capture mortality of Northern Pike, so gill nets were soaked for 3–4 hours before retrieval. Several overnight gill net sets were conducted on a trial basis to evaluate Northern Pike survival from longer soak times. Mortality from overnight gill net sets was relatively high, so short daytime sets were used in all subsequent sampling. Catch-per-unit-effort (CPUE) was estimated as the number of Northern Pike captured per net/h. We used the DeLury depletion method to estimate the population size of Northern Pike in Windy Bay. We modelled the relationship between mean weekly CPUE and cumulative catch, and estimated the extrapolation point where CPUE is zero (i.e., initial population size; Ricker 1975).

Total length (TL; mm) and weight (g) were measured from all fish. Proportional size distribution (PSD) was estimated to summarize length-frequency information for Northern Pike (Neumann et al. 2012). The post-capture condition of each Northern Pike was assessed after gill net retrieval; individuals determined to be in good (i.e., actively swimming in an upright

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fashion) condition were tagged with non-reward FD-94 T-bar anchor tags (76 mm; Floy Tag Inc., Seattle Washington, USA). Each tag was uniquely numbered and inserted near the posterior end of the dorsal fin of each Northern Pike. All tags also possessed the telephone number and website for IDFG’s “Tag! You’re It!” reporting hotline. Tags were used as a mark to evaluate site fidelity and angler exploitation of Northern Pike. Angler exploitation was estimated using the non-reward tag reporting estimator described by Meyer et al. (2012), namely,

µ' = µ / [λ (1–Tagl)(1–Tagm)] where µ' is the adjusted angler exploitation rate, µ is the unadjusted exploitation rate (i.e., number of fish reported divided by the number of fish tagged), λ is the species-specific angler reporting rate (53.0%), Tagl is the tag loss rate (10.2%), and Tagm is the tagging mortality rate (3.0%).

Northern Pike were then transported to Cougar Bay near the north end of Lake Coeur d’Alene, approximately 22.9 air km from the capture site. Condition of translocated Northern Pike was again assessed after they had been transported to the release location; individuals in poor condition (i.e., likely to expire) were destroyed.

RESULTS

A total of 311 Northern Pike was captured during the seven-week-long event. Of these, 234 were translocated to Cougar Bay. Gill net bycatch was minimal, overall; the most common species comprising the bycatch were Largescale Sucker Catostomous macrocheilus, Brown Bullhead Ameiurus nebulosus, and Northen Pikeminnow Ptychocheilus oregonesis. Observed survival of Northern Pike captured was 62.69% (SE = 5.11) and 75.38% (SE = 9.71) for overnight and daytime gill net sets, respectively. Although higher mortality resulted from longer soak time, the degree of gill net entanglement and handling time was thought to be the most influential factor on mortality. Overall, 75.2% of Northern Pike survived and were successfully translocated to Cougar Bay.

Catch rates of Northern Pike declined substantially over the course of the removal effort from 0.44 fish/net/h during the first week of removal to 0.04 fish/net/h during the last, and averaged 0.15 fish/net/h (Table 23). Total subpopulation abundance in Windy bay was estimated at 327.72 fish (Figure 50). Mean total length was 563.80 mm (288–1,020mm) for all Northern Pike captured in Windy Bay, 568.74 (296–1,000 mm) for Northern Pike translocated to Cougar Bay, and 609.88 mm (452–955 mm) for translocated Northern Pike caught by anglers (Figure 51). Angler exploitation of translocated Northern Pike was 34.3% after 1 year at-large. All of the harvested fish were reportedly caught in the north portion of Lake Coeur d’Alene. Size structure of Northern Pike translocated to Cougar Bay was similar to that of all Northern Pike captured in the study. Of the Northern Pike translocated, those caught by anglers tended to be the largest individuals (Figure 51). The majority of translocated Northern Pike were caught by anglers within three months of the end of the removal effort. In fact, with the exception of 2 fish caught during October, all translocated Northern Pike were caught during spring and early summer (Figure 52).

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DISCUSSION

The management strategy that we implemented was developed following a comprehensive evaluation of the effects of Northern Pike predation on adfluvial Westslope Cutthroat Trout and extensive public input. Our strategy focuses on small scale removal that will not adversely affect the fishery at large. Over the course of this effort, we removed 311 Northern Pike from Windy Bay in the vicinity of the Lake Creek inlet. We estimated a total population size of 327.72 Northern Pike which is similar to previous population estimates in Windy Bay; Walrath (2013) estimated a total population size of 290.65 (95% CI = 236.15–375.72) using multiple mark-recapture techniques. Given the congruency in population size estimates, we are confident that we removed the majority of Northern Pike residing in Windy Bay. The shape of our depletion curve is somewhat nontraditional and peculiar. We observed a small spike in CPUE during the second to last week of removal and suspect that this may have been due to adult spawners leaving Lake Creek. Multiple years of sampling will likely confirm whether adult movement from Lake Creek is responsible for this pattern.

Site fidelity of Northern Pike in the Lake Coeur d’Alene system is poorly understood, but there is some evidence suggesting that site fidelity may be quite high. Walrath (2013) sampled various bays around Lake Coeur d’Alene and did not document movement of Northern Pike between sampling sites. Additionally, tagged Northern Pike caught by anglers in the author’s study were usually caught in the general vicinity of the initial capture location. We assume that movement of Northern Pike is minimal and that they have a high affinity for particular locations that provide good habitat. However, we are unsure whether fish that are translocated many km will display high movement or strong fidelity to their capture location. Thus far we documented only a single translocated Northern Pike that moved back to Windy Bay from its translocation site. The large majority of translocated Northern Pike reported by anglers were also caught in the general vicinity of Cougar Bay and around the Spokane River. No Northern Pike were reportedly caught south of the north pool of Lake Coeur d’Alene (i.e., south of the area near Arrow and Threemile Point).

Angler exploitation of translocated Northern Pike was consistent with estimates reported by Walrath (2013) for Lake Coeur d’Alene (µ = 31.0%), but higher than estimates for other Northern Pike populations around the region (i.e., Hayden Lake [µ = 15.0%]; Killarney Lake [µ = 22.2%]). Cougar Bay typically receives high angler use due to its close proximity to Coeur d’Alene and its good shoreline access. Much of the northwest shore of Cougar Bay is owned by the Bureau of Land Management and has ample roadside parking along Highway 95. As such, many anglers make the short drive from town to target Northern Pike in Cougar Bay, likely resulting in higher annual exploitation relative to other popular angling locations (i.e., Wolf Lodge Bay, Harrison area) around the lake (J.P. Fredericks, personal communication). We are confident that translocation of Northern Pike to Cougar Bay maximizes their susceptibility to angler harvest.

Size structure of Northern Pike from our removal effort (PSD = 58) was considerably lower than estimates reported by Walrath et. al (2015; PSD = 86). We did not observe a difference in size structure between our full sample and fish translocated to Cougar Bay suggesting that mortality from gill netting and handling was not size related. Size structure of Northern Pike harvested in the fishery was higher than that of the translocated population indicating that either catch, harvest, or angler reporting was probably biased. The smallest translocated Northern Pike harvested from Cougar Bay was a 451 mm individual. Based on anecdotal information, we know that the smallest individuals we translocated would have been fully-recruited to common angling gear and were probably caught by anglers. Empirically,

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Northern Pike anglers appear to selectively harvest the largest individuals. However, another possibility is that angler reporting is biased toward larger fish, a phenomenon known as prestige bias. Prestige bias in angler reporting may influence our understanding of angler selectivity, but also our estimate of total annual exploitation.

Biological invasions are the leading cause of native species declines, second only to habitat degradation (Simberloff 2001), and the effects of introduced predators are well-understood by ecologists (Rahel 2000). On a global scale, resource managers have undertaken aggressive conservation measures to maintain native fish assemblages and ensure the persistence of the benefits they provide. Of such measures, controlling introduced species is one of the most common, yet publically contentious, strategies. As such, developing socially-desirable management plans to accomplish conservation goals is something that has long vexed resource managers. Strong socioeconomic and cultural values lie at the interface of native-nonnative fishery management issues, and passionate beneficiaries of the resource are on both sides. To facilitate public support of contentious fishery management actions, it is important to justify control actions by effectively communicating the actual or potential negative impacts of the introduced species. In addition, managers must acknowledge the benefits and values associated with fisheries formed by nonnative fishes, and develop management strategies within that constraint. Minimizing the net loss in terms of both native species conservation and angling opportunity is critical when developing control action plans. Here, we demonstrate the use of a relatively benign control method for a nonnative species to benefit a native species. Our approach has been met with broad public support and has not adversely affected angling opportunity for Northern Pike in Lake Coeur d’Alene. Overall, we are confident that we were able to maintain an area free of adult Northern Pike during the spring of 2015 and that these efforts compliment the objectives of the Coeur d’Alene Tribe’s Westslope Cutthroat Trout restoration efforts in Lake Creek.

MANAGEMENT RECOMMENDATIONS

1. Complete pilot project in 2017 under the same primary objectives.

2. Cooperate with Coeur d’Alene Tribe to understand the population response of adult Westslope Cutthroat Trout returning to Lake Creek.

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Table 23. Weekly catch information for Northern Pike management in Windy Bay including sampling time period, gill net set type, and catch statistics. Recapture information includes the year of during which recaptured Northern Pike were initially translocated in parentheses.

Total length (mm)

Week Period Set n

(captured) n

(translocated) CPUE

(fish/net hr) Mean Min–Max

1 3.12–3.20 Day 113 93 0.44 564

288–1,000

2 3.23–3.27 Day 47 43 0.24 588 420–850

3 3.30–4.3 Overnight 59 40 0.10 571

329–1,020

4 4.6–4.10 Overnight 33 19 0.04 460 254–795

5 4.13–4.16 Day 11 10 0.07 592 480–947

6 4.20–4.24 Day 30 22 0.11 582 410–825

7 4.27–4.30 Day 18 7 0.04 615 494–870

Total 311 234

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Figure 49. Map of the Lake Coeur d’Alene system in North Idaho. Capture and translocation

areas are indicated by bold text.

Lake Creek

Windy Bay

Cougar Bay Spokane River

St. Joe River

Coeur d’Alene River

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Figure 50. Relationship between catch-per-unit-effort and cumulative catch of Northern Pike

sampled in Windy Bay, Lake Coeur d’Alene (2015). Estimated abundance of Northern Pike in Windy Bay was 327.72.

0

0.1

0.2

0.3

0.4

0.5

0 50 100 150 200 250 300 350

CPU

E (fi

sh/n

et h

r)

Cummulative catch

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Figure 51. Length frequency distribution of all Northern Pike captured in Windy Bay (top panel), Northern Pike that were

translocated to Cougar Bay (middle panel), and translocated Northern Pike caught by anglers (bottom panel; 2015).

0

0.05

0.1

0.15n = 310 PSD = 58

0

0.05

0.1

0.15n = 234 PSD = 56

0

0.05

0.1

0.15

Length (mm)

n = 40 PSD = 66

Rel

ativ

e fre

quen

cy

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Figure 52. Tag returns of translocated Northern Pike caught by anglers during 2015 (based

on capture date).

0

2

4

6

8

10

12N

umbe

r cau

ght

Month

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NORTHERN PIKE ANGLER EXPLOITATION

ABSTRACT

Northern Pike Esox lucius were illegally introduced into Idaho’s Coeur d’Alene Lake system in the early 1970’s. Since their introduction, Northern Pike have been illegally transferred to numerous other northern Idaho waters. Currently, the known distribution of Northern Pike in Idaho is restricted to the five northern counties. For better or worse, Northern Pike have created some of the region’s more popular fisheries. General observations of Northern Pike fisheries suggest that angler exploitation and environmental conditions may combine to limit Northern Pike abundance and minimize their potential impact on native and other game fishes. In 2014 and 2015, we estimated exploitation of Northern Pike in Hayden and Killarney lakes in an effort to better understand how angling mortality influences these populations. In addition, we described Northern Pike growth rates. Exploitation was estimated from angler tag reports of harvested Northern Pike. Growth was described by estimating mean length-at-age. Angler exploitation of Northern Pike was 40% to 50% in Hayden Lake and 23% in Killarney Lake. Northern Pike in Hayden Lake grew faster than in Killarney Lake. Average length of eight-year-old fish in Hayden Lake was 718 mm. In contrast, fish from Killarney Lake averaged 571 mm at the same age. Our results suggested that Northern Pike exploitation rates are generally high, but vary among regional waters. We found evidence that angler exploitation on Northern Pike may influence growth. Based on our observations, we recommend continuation of unlimited harvest rules as a tool for limiting Northern Pike abundance, while simultaneously providing faster growth rates that support trophy fishing opportunities. Author: Rob Ryan Regional Fishery Biologist

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INTRODUCTION

Northern Pike Esox lucius were illegally introduced into Idaho’s Coeur d’Alene Lake system in the early 1970’s. Since their introduction, Northern Pike have been illegally transferred to numerous other northern Idaho waters. Currently, their known distribution in Idaho has been restricted to the five northern counties. For better or worse, Northern Pike have created some of the region’s more popular fisheries. Although classified as a game fish in Idaho, management policy prohibits the intentional introduction of Northern Pike into new waters and discourages illegal introductions into other waters by mandating unlimited harvest rules and prohibiting catch-and-release tournament events.

General observations of Northern Pike populations have suggested angler exploitation and environmental conditions may combine to limit Northern Pike abundance and minimize their potential impact on native and other game fishes. Previous estimates of angler exploitation have been high and relative fish densities generally have been low (Walrath 2013). However, contemporary estimates of angler exploitation and descriptions of population characteristics are lacking in most waters. As such, information gaps have limited our ability to understand Northern Pike population dynamics in Idaho.

In 2014 and 2015, we estimated exploitation of Northern Pike in Hayden and Killarney lakes in an effort to better understand how angling mortality influences these populations. In addition, we described Northern Pike growth in these waters.

OBJECTIVE

1. Describe Northern Pike exploitation in Hayden and Killarney lakes to provide insight on the influence of angling mortality on Northern Pike populations.

2. Describe Northern Pike growth rates in Hayden and Killarney lakes.

METHODS

We sampled and tagged Northern Pike from Hayden Lake between May 19 and July 1, 2014 and March 17 and April 14, 2015. We also sampled Northern Pike from Killarney Lake between March 30 and April 10, 2015. We used primarily sinking multiple mesh gill nets with mesh sizes from 3.8 cm to 20.3 cm stretch mesh. Gill nets were 46 m and 91 m in length. Short (1-2 hour) net sets were used to reduce mortality. We also tagged several Northern Pike caught in 46 m floating gill nets (3.8 cm – 12.7 cm; stretch mesh) used in other sampling efforts on Hayden Lake. Nets were set in non-random locations to specifically target Northern Pike habitat. Net set depths varied from one to nine meters. Northern Pike captured in nets were measured and tagged at the anterior base of the dorsal fin with a non-reward T-bar tag (Floy Tag Inc.). T-bar tags were labeled with a unique identification number and telephone reporting number for anglers to call and report information about the fish captured. IDFG operates a toll-free automated hotline and website through which anglers can report tags. Additionally, IDFG distributes posters and stickers to license vendors, regional offices and sporting goods outlets to publicize the Tag-Your-It program.

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We estimated exploitation of Northern Pike using angler tag returns. Adjusted exploitation rate (u’) incorporated angler tag reporting rate, tag loss, and tag mortality, using the following formula as described by Meyer et al. (2012):

𝑢′ =u

λ(1 − 𝑇𝑇𝑇𝑙 )(1 − 𝑇𝑇𝑇𝑚)

Defined terms included: µ the unadjusted exploitation rate (the number of non-reward

tags recovered from fish that were harvested divided by the number of fish released with non-reward tags), λ the angler tag reporting rate (55%; Meyer et al. 2012), 𝑇𝑇𝑇𝑙 tag loss (10.2%; Meyer et al. 2012), and 𝑇𝑇𝑇𝑚 the tagging mortality rate (9.1%; McDonald 1969). Exploitation rate estimates used tag returns from a period of 12 months post-tagging. Estimates did not include tag returns from released fish or fish anglers indicated were harvested only because the fish was tagged. We did report all catch types (harvest, released, harvest because tagged) in reference to overall angler use of Northern Pike in our study waters.

Pelvic fin rays were collected from each Northern Pike caught during our surveys to estimate fish age and growth rate. Leading pelvic fin rays were removed at the proximal end using wire dykes. Fin rays were air-dried, mounted in epoxy, cross sectioned at the base on a Buehler Isomet saw (Illinois Tool Works Inc., Lake Bluff, Illinois), sanded for viewing clarity, and viewed on a compound microscope under 10 x magnification. We described growth by reporting mean length-at-age.

RESULTS

In Hayden Lake, we tagged 56 Northern Pike in 2014 and another 102 fish in 2015. Tagged fish varied from 304 mm to 995 mm in length (Figures 53 and 54). Anglers reported catching 23% of tagged fish from each tagging group (Table 24). In 2014, 18% of tagged Northern Pike were reported as harvested. Two additional fish were released. One fish was harvested only because it was tagged. In 2015, all fish caught and reported by anglers were harvested. Adjusted exploitation was estimated at 40% in 2014 and 50% in 2015.

A total of 76 Northern Pike were tagged in 2015 from Killarney Lake. Tagged fish varied from 283 mm to 1100 mm in length (Figure 55). Anglers reported catching 17% of tagged fish in Killarney Lake. Tagged fish that were harvested represented 11% of all tagged fish. Five individual fish were caught and released (Table 24). Adjusted exploitation was estimated at 23%.

Age of Northern Pike was estimated from the majority of fish sampled in Hayden Lake (n = 91) and Killarney Lake (n = 74). Northern Pike in Hayden Lake grew faster than those from Killarney Lake. Maximum age observed in both waters was eight years. Average total length at age-8 in Hayden Lake was 718 mm (Figure 56). In contrast, age-8 fish in Killarney Lake averaged 571 mm (Figure 57). Based on our age estimates, individual growth rates appeared to be quite variable. The coefficient of variation for mean ages varied from 6% to 23% for Hayden Lake fish and from 5% to 44% for Killarney Lake fish. A more divergent growth pattern was observed in Killarney Lake Northern Pike that was not observed in Hayden Lake fish. Specifically, a small segment of our sample (n = 3) from Killarney Lake exhibited much faster growth after age-3 than observed in other fish from the same population (Figure 58).

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DISCUSSION

Our results added to an understanding of angler exploitation on Northern Pike in northern Idaho lakes and suggested that angler exploitation rates are generally high, but vary among waters in the region. This is consistent with prior exploitation estimates for Northern Pike in northern Idaho. Walrath (2013) reported 31% exploitation for Coeur d’Alene Lake, and Rich (1992) estimated 59% exploitation in Killarney Lake between 1989 and 1990. Variability in angler exploitation on Northern Pike is common with exploitation rates varying from 4-46% within their native distribution (Pierce and Tomcko 1995). The cause of variability was not investigated in this study, but likely is related to angler effort. Anglers fished an estimated total of 58,839 hours in 2009 among the lateral lakes of the Coeur d’ Alene River, which includes Killarney Lake (Hardy et al. 2010). The estimated harvest of Northern Pike in that period was 368 fish. In contrast, more than 74,000 angler hours were spent on Hayden Lake in 2010, with Northern Pike harvest estimated at 476 fish (Maiolie et al. 2011).

We found evidence that angler exploitation on Northern Pike likely influenced growth in our study waters. Northern Pike in Hayden Lake experienced both high exploitation and fast growth relative to average rates observed in Killarney Lake. Rich (1992) reported that growth rates were faster in Killarney Lake historically. Mean length of age-3 Northern Pike was 591 mm during their study, as compared to 496 mm during our study. However, at that time, exploitation in Killarney Lake was much higher (59%; Rich 1992) than during our study (23%). Margenau et al. (1998) suggested Northern Pike growth is density-dependent, with lower density populations exhibiting faster growth. Although we did not directly evaluate density in this study, we assumed fishing mortality had the potential to influence density, especially under high exploitation rates. Although our observations generally conformed to the expected pattern of faster growth in more exploited populations, there are likely other explanatory variables to consider. As an example, Northern Pike in Coeur d’Alene Lake grew faster than we observed in Hayden Lake, yet angler exploitation (31%) was lower (Walrath 2013). This type of deviation suggests other factors also influence Northern Pike growth rates. Environmental factors such as food availability have been suggested to influence Northern Pike growth (Margenau et al. 1998) and may be acting on Northern Pike populations in our waters as well.

As a non-native illegally introduced fish, Northern Pike in northern Idaho waters are believed to have negatively impacted native species and other sport fisheries (IDFG 2013). To reduce the impact of Northern Pike on other existing fisheries, anglers are generally encouraged to harvest Northern Pike and all populations are managed under an unlimited harvest rule scenario. In this study, anglers harvested Northern Pike at levels high enough to likely reduce abundance and increase growth rates. Based on our observations, unlimited harvest rules appear to be a useful management tool for limiting Northern Pike abundance while simultaneously providing faster growth rates that support trophy fishing opportunities. We recommend to continue this management strategy to mitigate threats posed by Northern Pike.

We observed a small portion of the Northern Pike in Killarney Lake that grew faster than the majority of the sampled population. This divergent growth pattern was unique and was not observed in Hayden Lake. We were unable to determine the cause of the unique growth pattern. We hypothesized one possible explanation for the observed differences in growth could be fish movement within the basin. For example, faster growing fish from Coeur d’Alene Lake may move into the lower Coeur d’Alene River basin. Our hypothesis was similar to observations by Vehanen et al. (2006) who noted Northern Pike maintained relatively small home ranges, but a smaller portion of their studied population in Finland were also observed migrating long distances. However, previous observations from the Coeur d’Alene system did not support our

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hypothesis. Rich (1992) found Northern Pike in the Coeur d’Alene river system moved very little, maintaining small home ranges. In addition, tag returns by anglers indicated fish caught and reported came from the water in which the individual was tagged providing evidence large movements by tagged fish did not occur.

MANAGEMENT RECOMMENDATIONS

1. Continue to implement unlimited harvest rules as a tool for limiting the abundance of Northern Pike.

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Table 24. Parameters used to estimate angler exploitation (µ) of Northern Pike on Hayden and Killarney lakes in northern Idaho.

Value Hayden 2014 Hayden 2015 Killarney 2015 Tagged 56 102 76 Caught 13 23 13 Harvested 10 23 8 Released 2 0 5 Harvest Because Tagged 1 0 0 Unadjusted µ 18% 23% 11% *Tag Loss 10% 10% 10% *Reporting Rate 55% 55% 55% *Tagging Mortality 9% 9% 9% Adjusted µ 40% 50% 23%

*Estimated values from Meyer et al. 2012 and McDonald 1969

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Figure 53. Length distribution of Northern Pike tagged in Hayden Lake in 2014.

Figure 54. Length distribution of Northern Pike tagged in Hayden Lake in 2015.

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Figure 55. Length distribution of Northern Pike tagged in Killarney Lake in 2015.

Figure 56. Mean length-at-age (± one standard deviation) for Northern Pike sampled from

Hayden Lake in 2015.

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Figure 57. Mean length-at-age (± one standard deviation) for Northern Pike sampled from

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Figure 58. Length-at-age for Northern Pike sampled from Killarney Lake in 2015. The

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HATCHERY TROUT STOCKING EVALUATIONS

ABSTRACT

In 2015, we continued evaluations of hatchery trout stocked in regional waters. Evaluations included estimation of the relative return of fingerling Rainbow Trout Oncorhynchus mykiss and Westslope Cutthroat Trout Oncorhynchus clarkii lewisi stocked in Hayden and Cocolalla lakes. We also estimated angler exploitation on catchable size Rainbow Trout in Hayden, Avondale, Freeman, and Crystal (LP Slough) lakes. We described the relative contribution of stocked fingerling trout based on catch rates (CPUE) in standard experimental floating gill nets. Angler exploitation was estimated from angler caught tag returns. No Rainbow Trout were caught in Hayden Lake, suggesting stocked fingerlings did not contribute to the fishery at a substantial rate. Rainbow Trout were also poorly represented (0.4 fish/net) in Cocolalla Lake. In contrast, Westslope Cutthroat Trout were relatively abundant in Cocolalla Lake (1.0 fish/net). Estimated angler exploitation in our study lakes ranged from 1% to 5.4%. Author:

Rob Ryan Regional Fishery Biologist

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INTRODUCTION

Hayden Lake, located northeast of Hayden, Idaho in the Panhandle Region, provides a multiple species fishing opportunity and is a popular destination for anglers. A mix of warmwater species are the primary focus of anglers (Maiolie et al. 2011). Kokanee Oncorhynchus nerka were recently introduced in Hayden Lake and have noticeably increased angling effort in the pelagic areas of the lake. Historically, Hayden Lake also provided a popular pelagic troll fishery for Rainbow Trout Oncorhynchus mykiss and Westslope Cutthroat Trout Oncorhynchus clarkii lewisi. Trout represented an insignificant proportion of the fishery over the last several decades, but trout fishing is still important to some anglers (Mauser 1978, Nelson et al. 1997, Maiolie et al. 2011). General observations do indicate Rainbow Trout have the potential to grow large in Hayden Lake, with trophy size fish caught occasionally. However, estimated Rainbow Trout catch rates typically less than 0.10 per hour since the late 1970’s suggests return of stocked fish has been poor (Mauser 1978, Ellis 1983, Nelson et al. 1997, Maiolie et al. 2011). Rainbow Trout were primarily stocked in Hayden Lake at catchable sizes (>152 mm) prior the late 1970’s (Figure 59). Fingerling Rainbow Trout have been the primary hatchery product used since that time. Westslope Cutthroat Trout also have a long stocking history in Hayden Lake, but stocking was discontinued in 2014 as a result of poor return on stocked fish (Jim Fredericks, IDFG, personal communication).

The cause and remedy for poor Rainbow Trout performance in Hayden Lake has been an ongoing focus of fisheries managers (Ellis 1983, Nelson et al. 1997, Maiolie et al. 2011). Multiple management actions have been attempted to increase trout survival and abundance and improve the recreational fishery. Management actions have included introduction of freshwater shrimp Mysis diluviana as an alternative food source, stocking rate manipulations, and experimentation with stocked strains, sizes, timing, and stocking locations. Recent shifts in Rainbow Trout rearing location from southern Idaho to Cabinet Gorge Hatchery in northern Idaho have also been speculated to provide potential improvements in post-stocking survival by providing consistency in water chemistry between rearing and stocking locations. Despite these efforts, apparent survival of stocked Rainbow Trout and subsequent angler catch rates on these fish continued to be low (Nelson et al. 1997, Maiolie et al. 2011, Ryan et al. 2014, Watkins et al. in review). Recent efforts to improve the performance of stocked Rainbow Trout fingerlings have focused on stocking large (≥ 152 mm) Rainbow Trout fingerlings from Cabinet Gorge Hatchery in the fall.

Fingerling Rainbow Trout have also been used in Cocolalla Lake. Prior to the late 1990’s, catchable size (> 152 mm) Rainbow Trout were primarily stocked in Cocolalla Lake (Figure 60). No specific information was found describing the rationale for transitioning from catchable size Rainbow Trout to fingerlings. Contemporary angler catch rate information was not available to evaluate the success of fingerling Rainbow Trout in returning to the Cocolalla Lake fishery. However, Rainbow Trout were not abundant in the catch during a 2008 lakewide survey (Fredericks et al. 2009). Westslope Cutthroat Trout fingerlings were also stocked in Cocolalla Lake in recent years (Figure 61). Although Westslope Cutthroat Trout were stocked at similar rates to Rainbow Trout, they were previously found to be more abundant in the lake (Fredericks et al. 2009).

In effort to describe the performance of stocked fingerling Rainbow Trout regionally, we evaluated survival of hatchery products in both Hayden and Cocolalla lakes. We used relative abundance to generally describe how well fingerling trout survived post-stocking. We included Westslope Cutthroat Trout in our evaluation to determine if species type influenced performance

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of fingerling hatchery products. To further investigate potential influences on hatchery trout, zooplankton quality and quantity were measured in both waters.

Throughout the Panhandle Region, catchable size Rainbow Trout are used to provide put-and-take type fishing opportunities. Exploitation on stocked catchable size trout varies among waters and seasons. The cause of variability in fishery performance is not always clear. However, maximizing use of hatchery products is important as they represent a large component of regional fisheries and a substantial expenditure of license dollars. As such, periodic evaluation of angler use of hatchery products is completed to ensure these resources are used effectively.

In 2015, we estimated exploitation of catchable size hatchery Rainbow Trout from Hayden, Avondale, Freeman, and Crystal (LP Slough) lakes. Catchable size Rainbow Trout have not routinely been stocked in Hayden Lake in recent years. However, a small stocking group of catchable size Rainbow Trout was shown to return to Hayden Lake anglers at reasonable rates (30% exploitation; Ryan Hardy, IDFG, personal communication) in 2011. In 2015, we stocked Hayden Lake with catchable size (254 mm average length) Rainbow Trout and evaluated their performance in the fishery by estimating exploitation of those fish. Avondale Lake had not previously been stocked with Rainbow Trout. In 2015, Rainbow Trout were stocked in Avondale Lake with the intent of enhancing a winter fishery close to the urban center of Coeur d’Alene. We used estimated exploitation to determine the performance of this new fishery. Freeman and Crystal lakes have long histories of catchable size Rainbow Trout stocking to provide fishing opportunities. However, exploitation of stocked catchable size trout in these waters was previously estimated to be low (Fredericks et al. 2013, Koenig 2012). We estimated exploitation rates on catchable size Rainbow Trout in Freeman and Crystal lakes in 2015 to evaluate variability in exploitation rates and make recommendations regarding future use of hatchery products in these waters.

OBJECTIVES

1. Estimate relative abundance of Rainbow Trout in Hayden and Cocolalla lakes as an evaluation of current stocking strategies.

2. Estimate relative abundance of Westslope Cutthroat Trout in Cocolalla Lake as an

evaluation of current stocking strategies.

3. Measure zooplankton quality and quantity in Hayden and Cocolalla lakes to assess food availability for stocked fingerling trout.

4. Estimate exploitation of stocked catchable size Rainbow Trout in targeted regional

waters.

METHODS

Fingerling Trout Evaluations

We sampled Hayden and Cocolalla lakes using IDFG standardized floating experimental gill nets to describe relative abundance of hatchery trout. Twelve nets were fished in each lake between April 14 and 17, 2015. Net set locations were randomly selected throughout the lake (Table 25). All nets were fished overnight. We reported mean catch per unit effort (CPUE) as a

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measure of relative abundance. Captured fish were recorded by net location. We identified all fish, measured total length (mm), and checked for marks.

We intended to use proportional differences in relative abundance to assess the success of different Rainbow Trout stocking groups in Hayden Lake. We anticipated encountering multiple stocking groups, including triploid Troutlodge Kamloops Rainbow Trout fingerlings stocked in September 2011 (≥ 152 mm, adipose clipped), Hayspur triploid Rainbow Trout fingerlings stocked in June 2012 (76 mm to 152 mm, no mark), Hayspur triploid Rainbow Trout catchables stocked in June 2012 (> 152 mm, no mark), Hayspur triploid Rainbow Trout fingerlings stocked in October 2013 ( ≥ 152mm, no mark) and Hayspur triploid Rainbow Trout fingerlings stocked in September 2014 ( ≥ 152mm, adipose clipped mark) (Table 26). Although marks were not available to distinguish every stocking group, length differences were anticipated to allow coarse separation.

In Cocolalla Lake, we assumed fish length differences could be used to distinguish stocking cohorts. Troutlodge triploid Kamloops Rainbow Trout fingerlings (< 76 mm) were stocked in April of 2011, 2012, and 2013 (Table 27). Hayspur triploid Rainbow Trout fingerlings were stocked in April 2014 (Table 27). No marked Rainbow Trout had been stocked in the lake prior to our survey. We also looked for the presence of Westslope Cutthroat Trout in our sample. Cocolalla Lake was stocked annually between 2011 and 2014 with Westslope Cutthroat Trout fingerlings from Cabinet Gorge Hatchery (Table 27).

We monitored zooplankton quality and quantity to describe food availability for stocked hatchery products. Dillon and Alexander (1996) indicated survival of stocked fingerling Rainbow Trout can be influenced by zooplankton quality and quantity. Zooplankton were sampled on August 17 and 18, 2015 from Cocolalla and Hayden Lakes. We sampled zooplankton using a sweet of three 0.5 m hoop-style plankton nets in 153 µm, 500 µm, and 750 µm mesh sizes. A single tow with each net was taken at three randomly selected locations on Cocolalla Lake and six randomly selected locations on Hayden Lake. Tow depths ranged from seven to eight meters on Cocolalla Lake and generally began at the lake bottom. All six tows on Hayden Lake were nine meters, where total water depth was deeper than the tow. The samples were preserved in denatured ethyl alcohol at a concentration of 1:1 (sample volume: alcohol). After approximately ten days in alcohol, phytoplankton were removed from the samples and each sample was re-sieved through 153 µm mesh. Each sample was blotted dry and weighed to the nearest gram (wet weight).

We summarized zooplankton quality and quantity using the zooplankton productivity ratio (ZPR) and the zooplankton quality index (ZQI) as defined by Teuscher (1999). ZPR was calculated as the ratio of sample weights from the 750 µm and 500 µm mesh samples (750:500 µm), representing preferred to usable size zooplankton. ZQI also incorporated sample weights from 750 µm and 500 µm mesh samples and included estimated ZPR. ZQI was calculated as:

ZQI = ((500 µm +750µm) ZPR) Total density of zooplankton was described as the weight of collected zooplankton in the 153 µm net corrected for sample tow depth (g/m). Values were reported as means representing all sampled sites.

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Catchable Rainbow Trout Evaluations

The exploitation of hatchery Rainbow Trout by anglers was evaluated in Hayden Lake, Crystal Lake (LP Slough), Freeman Lake, and Avondale Lake. We tagged and stocked catchable size Rainbow Trout with individually numbered T-bar style tags (Floy, Inc.). Tags were inserted at an angle into the dorsal musculature just below the dorsal fin of each fish. A total of 200 tagged fish were released in Hayden Lake (April stocking), 149 in Avondale Lake (September stocking), 138 in Freeman Lake (September stocking), and 50 in Crystal Lake (May stocking). Each tag was printed with the Idaho Department of Fish and Game “Tag You’re It” phone number for reporting. No reward was offered for tag returns. Angler tag returns were collected by phone, online (IDFG website), and in person at the IDFG Panhandle Regional Office through February 2016.

Exploitation rates on catchable Rainbow Trout were estimated using the methods described by Meyer et al. (2012). We corrected tag returns for tag loss (8.2%), tagging mortality (1.0%), and reporting rate (54.5%) based on reported averaged values for hatchery Rainbow Trout in Meyer and Schill (2014). Reported exploitation estimates represented angler harvest over one year post-release.

RESULTS

Hayden Lake

No Rainbow Trout were caught during our survey of Hayden Lake. Gill nets did capture Brown Bullhead Ictalurus nebulosus, Black Crappie Pomoxis nigromaculatus, Bluegill Lepomis macrochirus, Kokanee, Northern Pike Esox lucius, Pumpkinseed Lepomis gibbosus, Tench Tinca tinca and Yellow Perch Perca flavescens (Table 28). Catch rates were highest for Black Crappie and kokanee. Kokanee (CPUE = 1.6 ± 0.8, 80%CI) were captured most consistently among all net sets. Kokanee CPUE was lower than observed in similar surveys in 2013 and 2014 (2.5 ± 1.9, 1.9 ± 0.5; 80% CI), but overlapping confidence bounds suggested differences in catch may not be significant (Ryan et al. 2014, Watkins et al. in review). We measured surface water temperature during the survey at 10 °C.

Average zooplankton density for Hayden Lake was 0.07 g/m (± 0.01, 80% CI; Table 30). We estimated average ZPR and ZQI at 0.43 (± 0.2, 80% CI) and 0.03 (± >0.01, 80% CI), respectively. We found warm water temperatures and moderate dissolved oxygen concentrations down to nine meters in Hayden Lake at the time of zooplankton survey (Figure 62). It appeared a thermocline was present between nine and 10 meters of water where dissolved oxygen levels increased and water temperature cooled.

Anglers reported catching five of the 200 hatchery Rainbow Trout stocked in Hayden Lake in April 2015. Four of the reported fish were harvested. We estimated anglers harvested four percent of the total catchable Rainbow Trout (2500) stocked in April. Total use of stocked rainbow trout was five percent.

Cocolalla Lake

We caught few Rainbow Trout among all net locations on Cocolalla Lake, with a total sample of five fish (CPUE = 0.4; Table 29). Sampled Rainbow Trout ranged from 356 mm to

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505 mm, representing three approximate size groups. Based on the observed fish sizes, we speculated our catch represented stocked fingerlings from 2014, 2013, and 2012. Westslope Cutthroat Trout had a higher catch rate (CPUE = 1.0; Table 29) than Rainbow Trout. Total length of Westslope Cutthroat Trout ranged from 170 mm to 455 mm.

Gill nets also captured Black Crappie, Brook Trout Salvelinus fontinalis, Brown Bullhead, Brown Trout Salmo Trutta, Channel Catfish Ictalurus punctatus, Largemouth Bass Micropterus salmoides, Largescale Sucker Catostomus macrocheilus, Longnose Sucker Catostomus catostomus, Peamouth Mylocheilus caurinus, Rainbow x Westslope Cutthroat Trout Hybrids, and Yellow Perch (Table 29). Peamouth and Channel Catfish were the most abundant fishes in our survey. Brown Trout and Westslope Cutthroat Hybrids were the most abundant salmonids in our survey. We identified seven fish as Rainbow Trout x Westslope Cutthroat Trout hybrids. The appearance of hybrid fish was variable, but several appeared to be Westslope Cutthroat Trout with faint throat slashes. Phenotypic Rainbow Trout, with strongly present throat slashes were also present in the sample and identified as hybrid trout. We measured surface water temperatures during the gill net survey at approximately 12 °C.

Average zooplankton density from Cocolalla Lake was 0.40 g/m (± 0.02, 80% CI; Table 30). We estimated average ZPR and ZQI at 0.95 (± 0.09, 80% CI) and 0.42 (± 0.08, 80% CI), respectively. We found warm water temperatures and moderate dissolved oxygen concentrations down to seven meters in Cocolalla Lake at the time of the zooplankton survey (Figure 62). Dissolved oxygen levels were insufficient for trout below seven meters.

Avondale Lake

Anglers reported catching seven of the 149 hatchery marked Rainbow Trout stocked in Avondale Lake during September 2015. Four of the reported fish were harvested. We estimated anglers harvested 5.4% of the 2000 total hatchery Rainbow Trout stocked in September. Total use of stocked Rainbow Trout was 9.5%.

Freeman Lake

One tag was returned from hatchery Rainbow Trout stocked during September 2015 in Freeman Lake. We estimated anglers harvested 1% of the 900 hatchery Rainbow Trout stocked.

Crystal Lake

Anglers reported catching and harvesting one of the 50 tagged hatchery Rainbow Trout stocked in Crystal Lake during May 2015. We estimated angler harvest and use of the 500 total hatchery Rainbow Trout stocked in May was 4.0%.

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DISCUSSION

Hayden Lake

We were unable to determine differences in the relative contribution of fingerling stocking events in Hayden Lake, as we did not catch any Rainbow Trout in our surveys. We concluded that survival was likely poor for all recent stocking events. Our observations were consistent with investigations in the previous two years (Ryan et al. 2014; Watkins et al. in review). Anecdotally, angling effort in the form of an open water troll fishery has increased dramatically since 2011 due to the success of a recently established kokanee fishery. We expected incidental catch of Rainbow Trout in the kokanee fishery would be high if a viable fishery were present. Miscellaneous angler reports have suggested Rainbow Trout catch continues to be poor, supporting our observations.

Zooplankton biomass and ZQI values from Hayden Lake indicated zooplankton abundance was low (ZQI <0.1, density 0.01 g/m). We observed a reduction of the proportion of large or preferred zooplankton between 2014 (ZPR, 0.81; Watkins et al. in review) and 2015 (ZPR, 0.43). However, we noted considerable variability in individual samples that limited our confidence in describing shifts in zooplankton size structure. Our estimates did provide indication that food availability for Rainbow Trout remained poor. Teuscher (1999) suggested fingerling stocking rates of 75 fish per hectare or catchables be used when ZQI values are measured at <1.0. Rainbow Trout fingerlings have been stocked in Hayden Lake at levels (approximately 13 fish/hectare; IDFG, unpublished data) well below the suggested level for current zooplankton densities, but may still be impacted by food availability.

Exploitation of catchable Rainbow Trout was estimated to be low in Hayden Lake in 2015. Our estimate of five percent total use on stocked catchable size Rainbow Trout was well below the exploitation estimate in 2011 for catchable Rainbow Trout in Hayden Lake (Ryan Hardy, IDFG, personal communication). We are uncertain as to the cause of the disparity between these exploitation estimates. However, the 2011 estimate accounted for tag returns over more than one year post-stocking. We recommend continued monitoring of released tags to allow for early spring fishing effort and at least one year of tags being at-large. We also suggest replication of the tagging effort to further evaluate annual variation in estimates.

Rainbow Trout fingerlings were again stocked in Hayden Lake in the fall of 2015. Approximately half of the stocked group was marked with an adipose clip. In addition, catchable size Rainbow Trout were stocked during the spring in 2015. Continued evaluation of the contribution of hatchery products seems prudent given the recent stocking events and is recommended for 2016. To improve our ability to identify stocking groups in future evaluations, we recommend a batch mark (e.g., thermal mark) be applied to fingerling hatchery trout prior to stocking.

Cocolalla Lake

Rainbow Trout catch rates from our 2015 gill net survey of Cocolalla Lake suggested stocked fingerlings did not survive and contribute to the fishery at high rates. Our observations were consistent with lake-wide survey results from Cocolalla Lake in 2008 (Fredericks et al. 2009). The results of our Cocolalla Lake survey were similar to evaluations of Hayden Lake

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fingerling Rainbow Trout stocking and collectively provide some evidence that fingerling Rainbow Trout may not be suitable for northern Idaho waters.

The survival of stocked fingerling Rainbow Trout may have been negatively impacted by food availability in Cocolalla Lake. We found zooplankton quality, or the proportion of large zooplankton, to be high (ZPR = 0.9), but quantity was low (ZQI, = 0.43; density = 0.40 g/m). As in Hayden Lake, ZQI values fell within the low range corresponding to recommendations from Teuscher (1999) for low density fingerling stocking or the use of catchable size Rainbow Trout. We also observed poor water quality conditions, with low D.O. and warm water temperatures, potentially limiting the available habitat for trout in late-summer.

Our metric used to evaluate the relative contribution of Rainbow Trout in Cocolalla Lake was coarse. As such, we could not describe how Rainbow Trout recruited to the fishery (i.e., catch rates), nor could we identify potential wild recruits in our sample. Davis et al. (1996) suggested a portion of the Rainbow Trout caught in their survey of Cocolalla Lake were wild in origin. To improve evaluations of Rainbow Trout hatchery products, we recommend a batch mark on fingerling trout also be used on Cocolalla Lake. Our evaluation would also benefit from an angler survey evaluating angler use and species-specific catch rates.

Westslope Cutthroat Trout were more abundant in our survey of Cocolalla Lake, suggesting these stocked fingerlings may survive at higher rates than Rainbow Trout. The mechanism for this difference is unclear. We also identified Rainbow Trout x Westslope Cutthroat Trout hybrids in our sample. The presence of hybrid trout suggests wild recruitment is occurring. As such, our catch of Westslope Cutthroat Trout may be influenced by wild recruitment. Application of the previously suggested batch mark would also improve our ability to identify hatchery Westslope Cutthroat Trout in future evaluations.

Avondale Lake

We estimated low exploitation of stocked Rainbow Trout in Avondale Lake. Although exploitation was low, we recommend continued evaluation of Rainbow Trout use into the future. Rainbow Trout stocked in Avondale Lake represented the first use of hatchery trout in the lake and were introduced with the intent of enhancing the winter fishery. Continued evaluation is recommended because current estimates of exploitation only encompassed a short window of fishing opportunity (October – February). In addition, poor ice conditions during the winter fishery limited angler effort in 2015.

Freeman Lake

Estimated use of catchable Rainbow Trout in Freeman Lake was very low. Previous evaluation of exploitation on Rainbow Trout in Freeman Lake suggested anglers caught 17% of fish stocked in the spring (Fredericks et al. 2013). Although both evaluations reflect low use by anglers, our observations of fall use were considered to be significantly lower. Based on these evaluations, we recommend fall outplants be discontinued. In addition, we recommend further evaluation of the suitability of Freeman Lake for hatchery Rainbow Trout use. The current fish community may be limiting the survival of hatchery products. Both Tiger Muskie Esox masquinongy × E. lucius (hatchery origin) and Northern Pike Esox lucius (illegally introduced) are present in the lake in unknown abundance and may prey on stocked trout. As such, we

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recommend a lowland lake survey be completed to describe the current composition of fish species present and their relative abundance.

Crystal Lake

We found exploitation rates on catchable Rainbow Trout from Crystal Lake continued to be low. Our results were consistent with previously estimated exploitation rates in Crystal Lake of 2.2% to 8.7% for May-stocked catchable Rainbow Trout (Koenig 2012; John Cassinelli, IDFG, personal communication). Based on these evaluations, we recommend consideration be given to discontinuing catchable Rainbow Trout stocking in Crystal Lake.

RECOMMENDATIONS

1. Continue to evaluate survival and fishery contribution of large (≥ 152 mm) fall fingerling and catchable (> 250 mm) Rainbow Trout stocked in Hayden Lake.

2. Continue to evaluate survival and fishery contribution of fingerling Rainbow Trout and

Westslope Cutthroat Trout in Cocolalla Lake.

3. Use batch marked fish to identify specific stocking groups in Hayden and Cocolalla lakes.

4. Continue monitoring zooplankton quality and quantity in association with stocking

evaluations.

5. Continue monitoring the return of catchable Rainbow Trout stocked in Avondale Lake.

6. Complete a lowland lake survey of Freeman Lake to evaluate the suitability of the

lake for a put-and-take Rainbow Trout fishery.

7. Discontinue fall stocking of catchable Rainbow Trout in Freeman Lake.

8. Discontinue stocking of catchable Rainbow Trout in Crystal Lake.

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Table 25. Date, time (hours), and sampling locations (UTM) for Hayden Lake and Cocolalla Lake gill net surveys completed during 2015.

Water Date set Net Time Datum Z E N Hayden Lake 4/13/15 1 16:57 WGS84 11 522589 5294215 Hayden Lake 4/13/15 2 16:19 WGS84 11 523221 5294332 Hayden Lake 4/13/15 3 15:59 WGS84 11 522471 5293013 Hayden Lake 4/13/15 4 15:24 WGS84 11 524274 5291664 Hayden Lake 4/13/15 5 15:02 WGS84 11 523857 5291187 Hayden Lake 4/13/15 6 14:43 WGS84 11 523874 5290736 Hayden Lake 4/14/15 7 16:59 WGS84 11 523416 5289096 Hayden Lake 4/14/15 8 16:54 WGS84 11 522029 5288921 Hayden Lake 4/14/15 9 16:56 WGS84 11 522053 5288608 Hayden Lake 4/14/15 10 16:53 WGS84 11 520923 5288947 Hayden Lake 4/14/15 11 17:03 WGS84 11 520037 5289280 Hayden Lake 4/14/15 12 17:07 WGS84 11 518338 5288678 Cocolalla Lake 4/15/15 1 18:55 WGS84 11 529590 5331757 Cocolalla Lake 4/15/15 2 19:44 WGS84 11 528682 5331967 Cocolalla Lake 4/15/15 3 20:34 WGS84 11 528494 5331254 Cocolalla Lake 4/15/15 4 21:00 WGS84 11 528331 5331058 Cocolalla Lake 4/15/15 5 21:03 WGS84 11 528315 5330523 Cocolalla Lake 4/15/15 6 21:20 WGS84 11 527710 5330199 Cocolalla Lake 4/16/15 7 19:33 WGS84 11 528135 5329826 Cocolalla Lake 4/16/15 8 19:45 WGS84 11 527934 5329561 Cocolalla Lake 4/16/15 9 20:02 WGS84 11 527871 5329212 Cocolalla Lake 4/16/15 10 20:05 WGS84 11 528290 5328690 Cocolalla Lake 4/16/15 11 20:38 WGS84 11 528645 5329362 Cocolalla Lake 4/16/15 12 21:00 WGS84 11 528738 5329794 Table 26. History of Rainbow Trout stocking in Hayden Lake, Idaho from 2011 to 2014. Date Stocked Species Type Size Number 9/21/2014 Hayspur Rainbow Triploid Fingerling (3-6 Inches) 38,400 10/1/2013 Hayspur Rainbow Triploid Fingerling (3-6 Inches) 39,312 6/18/2012 Hayspur Rainbow Triploid Fingerling (3-6 Inches) 18,000 6/18/2012 Triploid Troutlodge Kamloop Catchable (6+ Inches) 4,832 9/29/2011 Triploid Troutlodge Kamloop Fingerling (3-6 Inches) 39,600 6/16/2011 Triploid Troutlodge Kamloop Catchable (6+ Inches) 472 4/26/2011 Triploid Troutlodge Kamloop Fingerling (3-6 Inches) 268,800

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Table 27. Table 3. History of Westslope Cutthroat Trout and Rainbow Trout stocking in Cocolalla Lake, Idaho from 2011 to 2014.

Date Stocked Species type Size Number 4/30/2014 Westslope Cutthroat Fingerling (3-6 Inches) 5,490 4/29/2014 Westslope Cutthroat Fingerling (3-6 Inches) 14,640 4/30/2013 Westslope Cutthroat Fingerling (3-6 Inches) 19,984 5/10/2012 Westslope Cutthroat Fingerling (3-6 Inches) 20,750 9/30/2011 Westslope Cutthroat Catchable (6+ Inches) 1,140 9/29/2011 Westslope Cutthroat Catchable (6+ Inches) 600 5/23/2011 Westslope Cutthroat Fingerling (3-6 Inches) 22,548 4/29/2014 Hayspur Rainbow Triploid Fingerling (3-6 Inches) 27,150 4/25/2013 Triploid Troutlodge Kamloop Fingerling (3-6 Inches) 26,000 4/23/2012 Triploid Troutlodge Kamloop Fry (0-3 Inches) 30,405 4/26/2011 Triploid Troutlodge Kamloop Fingerling (3-6 Inches) 25,200 Table 28. Species, minimum and maximum total length (TL), catch (n), and catch rate

(CPUE) from a Hayden Lake gill net survey completed during April, 2015. Species n CPUE (± 80%CI) Min TL Max TL Black Crappie 15 1.3 (± 1.1) 147 280 Bluegill 1 0.1 (± 0.1) 191 191 Kokanee 19 1.6 (± 0.8) 307 351 Northern Pikeminnow 3 0.3 (± 0.2) 786 1120 Rainbow Trout 0 --

Tench 4 0.3 (± 0.3) 255 429 Yellow Perch 1 0.1 (± 0.1) 148 148

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Table 29. Species, minimum and maximum total length (TL), catch (n), and catch rate (CPUE) from a Cocolalla Lake gill net survey completed during April, 2015.

Species Count CPUE ± 80% C.I. Min TL Max TL Black Crappie 4 0.3 (± 0.2) 230 242 Brook Trout 9 0.8 (± 0.5) 174 333 Brown Bullhead 1 0.1 (± 0.1) 232 232 Brown Trout 20 1.7 (± 0.9) 320 505 Channel Catfish 65 5.4 (± 4.1) 284 592 Largemouth Bass 2 0.2 (± 0.1) 341 355 Largescale Sucker 19 1.6 (± 1.4) 313 550 Longnose Sucker 3 0.3 (± 0.2) 379 410 Peamouth 152 12.7 (± 3.6) 232 356 Rainbow Cutthroat Hybrid 7 0.6 (± 0.2) 359 447 Rainbow Trout 5 0.4 (± 0.2) 356 505 Westslope Cutthroat Trout 12 1.0 (± 0.4) 170 455 Yellow Perch 10 0.8 (± 0.5) 150 217 Table 30. Annual ZPR and ZQI indices and density estimates estimated from zooplankton

sampling in Hayden and Cocolalla lakes. Water Year ZPR ZQI Density Hayden Lk 2010 0.93 0.28 0.66

2011 0.74 0.22 0.3

2014 0.81 0.09 0.01

2015 0.43 0.03 0.07

Cocolalla Lk 2011 0.24 0.48 4.33 2015 0.95 0.42 0.4

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Figure 59. Number of Rainbow Trout stocked from 1942 to 2015 in Hayden Lake, Idaho.

Figure 60. Number of Rainbow Trout stocked from 1951 to 2015in Cocolalla Lake, Idaho.

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Figure 61. Number of Westslope Cutthroat Trout stocked from 1957 to 2015 in Cocolalla

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Figure 62. Temperature (C) and DO (mg/L) profiles of Hayden and Cocolalla lakes

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REGIONAL LOWLAND LAKE INVESTIGATIONS

ABSTRACT

Lowland lake surveys were conducted on Brush and MacArthur Lakes in June 2015. We also completed an electrofishing survey of Avondale Lake in June 2015. Lowland lake surveys were conducted using Idaho Department of Fish and Game lowland lake standard survey methods.

Brush Lake

We observed a simple fish assemblage in Brush Lake, including Bluegill Lepomis macrochirus, Largemouth Bass Micropterus salmoides, and hatchery Rainbow Trout Oncorhynchus mykiss. Bluegill were the most abundant species sampled, comprising 63% of the catch by number and 54% of the biomass. We found Bluegill in Brush Lake grew well and achieved sizes that offer a quality fishery. Rainbow Trout caught in our sample were representative of recently stocked catchable size fish. Brush Lake Largemouth Bass were primarily stock length (200 mm – 300 mm). We found the fish assemblage of Brush Lake was similar to observed conditions in previous years. Bluegill and Largemouth Bass were dominant species in both 1997 and 2005 surveys, at similar relative proportions. Largemouth Bass growth rates observed in our survey of Brush Lake were slow and suggested the presence of an abundant Bluegill population did not notably benefit growth rates. As such, we do not recommend increasing prey availability in Boundary County lakes for the purpose of enhancing Largemouth Bass angling opportunities. The absence of carryover hatchery Rainbow Trout in Brush Lake may be influenced by late-summer habitat availability. No kokanee or Westslope Cutthroat Trout were sampled, despite annual stocking events prior to 2015. We recommended current Rainbow Trout stocking rates and frequencies were desirable for maintenance of the coldwater fishery and that consideration should be given to how hatchery fingerling products are used in Brush Lake.

McArthur Lake

McArthur Lake supported a diverse fish assemblage. We sampled nine species, including Black Crappie Pomoxis nigromaculatus, Brook Trout Salvelinus fontinalis, Brown Bullhead Ameiurus nebulosus, Largemouth Bass, Largescale Sucker Catostomus macrocheilus, Pumpkinseed Lepomis gibbosus, Rainbow Trout, Tench Tinca tinca, and Yellow Perch Perca flavescens. Yellow Perch were the most abundant species sampled, comprising 45% of the total catch by number. The majority (95%) of Largemouth Bass in our McArthur Lake sample were from year classes produced from 2012 to 2014. Yellow Perch in our sample had a skewed age distribution, with 85% of the fish sampled from the 2013 year class. Trout species by number in our sample were poorly represented, but by size they represented a potential quality component of the fishery. The fish assemblage in our survey differed somewhat from observations in 2011 and 1992 surveys. Most notably, we observed a sharp decline in the proportion of Largemouth Bass. The McArthur Lake fish assemblage was likely negatively impacted by lake level drawdown in 2011, but our results suggest that sufficient spawning stock remained in the lake to re-establish depleted fish populations.

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Avondale Lake

We observed a moderately diverse fish assemblage in Avondale Lake. We sampled six species, including Black Crappie, Bluegill, Largemouth Bass, Pumpkinseed, Tench, and Yellow Perch. Yellow Perch were the most abundant species sampled, comprising 45% of the total catch by number. Yellow Perch lengths in our sample varied from 52 mm to 294 mm, with 36% of the sample greater than 200 mm in length. Bluegill lengths in our samples varied from 63 mm to 197 mm. Stock and sub-stock length Largemouth Bass were dominate in our samples from Avondale Lake. Our survey of Avondale Lake suggested the fishery is generally comprised of moderate densities of small warmwater fish. Yellow Perch in our sample represented an exception to the general observations of mediocrity of the Avondale Lake fishery. We recommend consideration be given to enhancing the Avondale Lake fishery to provide improved angling opportunities. Author(s): Rob Ryan Regional Fishery Biologist Dan Kaus Fishery Technician

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INTRODUCTION

Lowland lakes provide a diversity of angling opportunities in the northern Idaho Panhandle Region. Lowland lake surveys are conducted periodically to monitor the composition and quality of these fisheries. Multiple lowland lakes within the Panhandle Region are routinely stocked to enhance fishing opportunities. Thus, lowland lake surveys also provide a means of evaluating the current stocking practices. In 2015, we completed standardized lowland lake surveys on Brush and McArthur Lakes. We also conducted a standard electrofishing survey on Avondale Lake.

Brush Lake

Brush Lake is located in Boundary County, Idaho, approximately 22.5 km north of Bonners Ferry, Idaho (Figure 1). The lake is surrounded by Federal lands managed by the U.S. Forest Service. A public access area is available on the west side of the lake, which consists of a primitive boat ramp and outhouses. Watercraft use on the lake for fishing is restricted to electric motors only.

Brush Lake is managed as a mixed species fishery under general regional bag and possession limits. Catchable size Rainbow Trout Oncorhynchus mykiss, fingerling Westslope Cutthroat Trout Oncorhynchus clarkia, and fingerling kokanee Oncorhynchus nerka are stocked annually in the lake. Warmwater species, including Largemouth Bass Micropterus salmoides and Bluegill Lepomis macrochirus, are also present.

We surveyed Brush Lake in 2015 to describe Largemouth Bass growth potential in a northern Idaho lake with a simple fish assemblage including Bluegill. Previous lowland lake surveys on Bonner and Smith Lakes, also located in Boundary County, suggested Largemouth Bass growth was slow relative to other regional waters (Watkins et al. in review). However, fish communities in Bonner and Smith lakes included few or no prey species for Largemouth Bass. Introduction of Bluegill as a prey fish was considered in Bonner and Smith lakes as a means of improving Largemouth bass growth. Brush Lake supports both Largemouth Bass and Bluegill and is located at similar latitude to Brush and Smith lakes. Thus, it provided a suitable location to compare Largemouth Bass growth in a lake with Bluegill.

McArthur Lake

McArthur Lake is a small reservoir located south of Naples, Idaho in the Deep Creek drainage, a tributary of the Kootenai River. The 243 ha reservoir was constructed primarily for waterfowl production. McArthur Lake and much of the surrounding uplands are managed by the Idaho Department of Fish and Game (IDFG) as the McArthur Lake Wildlife Management Area. A boat launch and fishing dock are available on the northeast side of the reservoir.

McArthur Lake is managed as a mixed species fishery under general regional bag and possession limits. Primary species of angling interest include Largemouth Bass, Pumpkinseed Sunfish Lepomis gibbosus, and Yellow Perch Perca flavescens. Wild Rainbow Trout and Brook Trout Salvelinus fontinalis are also present. A fish passage structure at the dam provides two-way volitional fish passage between the reservoir and Deep Creek.

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We surveyed McArthur Lake in 2015 to evaluate the quality and composition of the fish assemblage following a dewatered period. In May 2012, McArthur Lake was drained in an effort to enhance reservoir productivity for the benefit of waterfowl production. Our intent was to determine the current status of fish populations and evaluate the need for fishery enhancement following lake drawdown.

Avondale Lake

Avondale Lake is a small (8 ha) natural lake located west of Hayden Lake. The lake is surrounded by private ownership, but public access is allowed at an undeveloped site on the southwest end of the lake. Watercraft use on the lake is restricted to small boats (no developed boat ramp) and electric motors.

Avondale Lake is managed as a mixed species fishery under general regional bag and possession limits. Primary species of angling interest include Largemouth Bass, Pumpkinseed Sunfish, Bluegill, Black Crappie Pomoxis nigromaculatus, and Yellow Perch.

We conducted a standard electrofishing survey on Avondale Lake in 2015 to assess the quality and composition of the fishery. A standard lowland lake survey was initiated in 2011, but electrofishing effort was minimal due to equipment failure. We combined and reported gill net data from that survey with our current electrofishing results.

METHODS

During 2015, we surveyed Brush Lake from June 15 to 19, McArthur Lake on June 4 and 5, and Avondale Lake on June 25 and 26. Lowland lake surveys were conducted using IDFG lowland lakes standard survey methods (IDFG 2012). In Brush and McArthur lakes, we completed five trap net nights, four gill net nights (two floating and two sinking standard experimental gill nets), and electrofished the entire shoreline at night (Table 31). We only sampled fish using electrofishing gear on Avondale Lake.

Fish sampled during surveys were identified, measured (total length, mm) and weighed (g). Due to equipment failure, no fish were weighed from McArthur Lake. We estimated relative abundance as catch per unit effort (CPUE) for electrofishing (fish/10 minute effort) and netting (fish/net) samples. We described the general structure of the fish assemblage in each lake as the relative abundance of each species sampled and the relative biomass of each species sampled when adequate weight information was collected. We estimated weights for fish sampled from Avondale Lake using linear regression of log10 transformed length and weight from a subsample of fish weighed. Size structure of sampled species was described using length-frequency histograms and stock density indices (Anderson and Neumann 1996) for primary species targeted by anglers. We used Fisheries Analysis and Modeling Simulator (FAMS, Slipke and Maceina 2014) software to calculate stock density indices. Average relative weight (Wr, Wege and Anderson 1978) was used to describe the condition of Largemouth Bass and Bluegill where weight data were available.

Age structures were collected from a subsample of targeted species sampled during our surveys and used to describe patterns of growth, mortality, and recruitment. We collected dorsal spines from a representative subsample of Largemouth Bass in all waters and otoliths from a subsample of Yellow Perch in McArthur Lake and Bluegill in Brush Lake. Dorsal spines were

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mounted in epoxy, cross sectioned on a Buehler Isomet saw (Illinois Tool Works Inc., Lake Bluff, Illinois), sanded for viewing clarity, and viewed on a compound microscope under 10x magnification. Otoliths were broken centrally on the transverse plane, browned, sanded on the broken surface, and viewed under a dissecting microscope using a fiber optic light to illuminate the broken surface. One trained reader conducted all ageing estimates. Length-at-age was reported as an index of growth where applicable. Age-length keys were used to predict ages for the entire sample using subsampled age estimates. We used a frequency of catch by age for sampled fish when describing general patterns of recruitment and for estimating total annual mortality. Annual mortality of Largemouth Bass and Bluegill from Brush Lake was estimated using weighted catch curve analyses in Fisheries Analysis and Modeling Simulator (FAMS, Slipke and Maceina 2014). Limited samples from McArthur and Avondale lakes prevented estimates of annual mortality rates from those waters.

Zooplankton were sampled in Brush Lake to evaluate the quality and quantity of available food for planktivorous fishes. Zooplankton samples were collected on August 4 from three randomly selected locations distributed throughout the lake. Zooplankton were collected using three 0.5 m nets fitted with small (153µm), medium (500µm) and large (750µm) mesh. Nets were lowered to the bottom and retrieved to the surface for each tow. Samples were preserved in denatured ethyl alcohol and were processed using methods described by Teuscher (1999). We used the zooplankton ratio method (ZPR) and the zooplankton quality index (ZQI) to assess zooplankton quality and quantity (Teuscher 1999). Zooplankton collections in Brush Lake were paired with measured temperature and dissolved oxygen profiles. Temperature and dissolved oxygen profiles were also measured in Avondale Lake. Profiles were used to describe the general habitat conditions in the lake during a period potentially limiting for coldwater fishes, such as Rainbow Trout.

RESULTS

Brush Lake

We observed a simple fish assemblage in Brush Lake, with only three species sampled, including Bluegill, Largemouth Bass, and hatchery Rainbow Trout (Table 32). Bluegill were the most abundant species sampled, comprising 63% of the catch by number and 54% of the biomass. Rainbow Trout and Largemouth Bass were less abundant, respectively comprising 25% and 12% by number. We did not detect kokanee or Westslope Cutthroat Trout despite stocking of both species in the lake on an annual basis prior to 2015. Electrofishing was the most efficient method of capture for both Bluegill and Largemouth Bass (electrofishing CPUE = Bluegill 48, Largemouth Bass 8; Table 32). In contrast, gill nets were most efficient for sampling Rainbow Trout (gill net CPUE = 22; Table 32).

Bluegill in Brush Lake grew well and achieved sizes that offer a quality fishery (Figure 63). Total length of Bluegill varied from 82 mm to 211 mm, with a size distribution represented by a PSD of 82. We estimated it took Bluegill three to four years to grow to quality length (150 mm; Figure 64). Bluegill in our sample were robust. Relative weight of Bluegill varied from 107 (RSD 150 ± 2, 80% C.I.) for stock length fish to 95 (RSD 200 ± 1, 80% C.I.) for preferred length fish (Figure 65). Annual mortality estimated from our sample of fish from ages three to 11 at the time of capture was 18.2%. The frequency of catch by age was variable, suggesting annual recruitment was inconsistent (Figure 66).

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Rainbow Trout caught in our sample were representative of recently stocked catchable size fish. Mean length of Rainbow Trout was 253 mm, with measured lengths varying from 168 to 306 mm. We did not observe Rainbow Trout that were believed to be holdover fish from stocking events in prior years.

Largemouth Bass in Brush Lake grew slowly with stock length (200 mm – 300 mm) fish being most common in our sample. Total length of sampled fish varied from 65 mm to 416 mm with a size distribution represented by a PSD of 4 (Figure 63). We estimated the majority of fish did not reach 300 mm despite reaching ages of up to 11 years at the time of capture (Figure 64). Largemouth Bass in our sample generally exhibited below average condition. Average relative weight of stock length fish was 82 (± 1.7, 80% C.I.; Figure 65). Annual mortality for fish from two to 11 years of age was low (15.1%). Similar to Bluegill, the frequency of catch by age for Largemouth Bass was highly variable (Figure 66).

Zooplankton biomass averaged 0.14 g/m among all sites. ZPR and ZQI were estimated at 0.58 and 0.32, respectively. However, we were only able to estimate ZPR and ZQI values from one sample. Sample volumes of two out of three samples were too small to weigh accurately.

Late-summer water temperature and dissolved oxygen profiles in Brush Lake indicated suitable habitat for coldwater fishes was limited (Figure 67). Anoxic hypolimnetic conditions and warm epilimnetic water temperatures were present at the time of measurements. thus limiting coldwater habitat availability.

McArthur Lake

The McArthur Lake fish assemblage was diverse. We sampled nine species, including Black Crappie, Brook Trout, Brown Bullhead, Largemouth Bass, Largescale Sucker, Pumpkinseed, Rainbow Trout, Tench, and Yellow Perch (Table 33). Yellow Perch were the most abundant species sampled, comprising 45% of the total catch by number (electrofishing CPUE = 106.7; Table 31). Largemouth Bass and Tench were also well represented (electrofishing CPUE = Largemouth Bass 9.8, Tench 6.4; Table 33). Other species were less common.

The majority (95%) of Largemouth Bass were from year classes produced from 2012 to 2014 (Figure 69). Lengths of Largemouth Bass varied from 86 mm to 310 mm (Table 33; Figure 68). The distribution of lengths was represented by a PSD of 6.4. Growth rate was estimated to be moderate, with individuals reaching 300 mm by 6 years of age (Figure 70).

Yellow Perch also exhibited a skewed age distribution, with 85% of the fish coming from the 2013 year class (Figure 69). Few fish were sampled from age classes prior to 2013. Length of Yellow Perch varied from 68 mm to 260 mm (Figure 68). The distribution of lengths was represented by a PSD of 6.5. On average, age-three Yellow Perch exceeded 200 mm in length (Figure 70).

Trout species by number in our sample were poorly represented, but by size represented a potential quality component of the fishery. Rainbow Trout lengths varied from 171 mm to 432 mm (Table 33; Figure 68). Brook Trout lengths varied from 259 mm to 324 mm (Table 33).

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Avondale Lake

We observed a moderately diverse fish assemblage in Avondale Lake. We sampled six species, including Black Crappie, Bluegill, Largemouth Bass, Pumpkinseed, Tench, and Yellow Perch (Table 34). Yellow Perch were the most abundant species sampled, comprising 45% of the total catch by number (gill net CPUE = 17.8; Table 34). Bluegill and Largemouth Bass were also well–represented, comprising 28% and 20% of the population, respectively (electrofishing CPUE = Bluegill 16.7, Largemouth Bass 10.7; Table 34). Other species were less commonly sampled.

Yellow Perch lengths varied from 52 mm to 294 mm, with 36% of the fish greater than 200 mm in length (Table 34; Figure 71). The distribution of lengths was represented by a PSD of 41.7. Yellow Perch were in below average condition, with a relative weight for stock length fish of 81 (± 2.0, 80% C.I.; Figure 72). Bluegill lengths varied from 63 mm to 197 mm (Table 34; Figure 71). Population size structure was poor, with a PSD of 10.7. The distribution of lengths was represented by a PSD of 10.7. Age estimation was not conducted; however, distribution of fish lengths in the electrofishing sample were indicative of inconsistent annual recruitment (Figure 73). Bluegill were in excellent condition with an average relative weight for stock length fish of 110 (± 2.5, 80% C.I.; Figure 72). Stock and sub-stock length Largemouth Bass were dominant in our samples from Avondale Lake. Total lengths varied from 86 mm to 388 mm (Table 34; Figure 71). However, only one fish longer than 300 mm was sampled. As a result, population size structure was poor (PSD = 12.5). Largemouth Bass appeared to grow at an average rate for the region, reaching approximately 300 mm at five years of age (Figure 74). However, our ability to accurately assess age-related indices of growth and mortality was limited by a small sample size with a limited distribution of age classes. We sampled Largemouth Bass representing four age classes, including ages one, two, three, and five (Figure 74). In general, Largemouth Bass were in good condition, with an average relative weight for stock length fish of 91 (± 2, 80% C.I.) and 102 (± 6, 80% C.I.) for sub-stock length fish (Figure 72).

Late-summer water temperature and dissolved oxygen profiles in Avondale Lake indicated suitable habitat for coldwater fishes (e.g. Rainbow Trout) was present at depths between the surface and four meters (Figure 75). Water temperature was 18˚C or less throughout the water column. However, dissolved oxygen was low (i.e. > 4 mg/l) below four meters.

DISCUSSION

Brush Lake

We found the fish assemblage of Brush Lake was similar to previous years (Table 35). Bluegill and Largemouth Bass were dominant species in both 1997 and 2005 surveys at similar relative proportions (Fredericks et al. 2000; Liter et al. 2008). Size structure and condition were also similar. Although similar in most respects, we found Largemouth grew more slowly than described in 1997. Fredericks et al. (2000) estimated fish grew to 300 mm in approximately seven years. We also found PSD of Bluegill improved since 1997, with quality and preferred

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size Bluegill making up a larger proportion of the population in our sample (Fredericks et al. 2000; Liter et al. 2008).

Slow Largemouth Bass growth rates observed in our survey suggest the presence of an abundant Bluegill population was not sufficient to improve growth rates relative to nearby waters. In 2014, Watkins et al. (in review) recommended a survey be completed on Brush Lake to evaluate the effect of Bluegill presence on Largemouth Bass growth. They reported slow Largemouth Bass growth rates in nearby lakes with simple fish communities and speculated prey fish introductions may improve growth rates. However, Largemouth Bass in Brush Lake grew slowly, despite the presence of abundant prey fish. Largemouth Bass in Idaho typically grow to 300 mm in 2.8 to 7.3 years, with northern Idaho waters representing the slower end of the growth distribution (Dillon 1990). Fish in our sample took 11 years to reach a similar size. Growth rates were also not likely impacted by intraspecific competition. Our Largemouth Bass relative abundance estimates represented low to moderate density relative to other area lakes. Watkins et al. (in review) reported mean Largemouth Bass CPUE estimates of 53 and 34 fish/unit from Bonner and Smith lakes, respectively. In general, our findings were comparable to Dillon (1990) and Fredericks et al. (2000) who suggested the presence of Bluegill did not improve Largemouth Bass growth in Idaho waters. As such, we do not recommend increasing prey availability in Boundary County lakes for the purpose of enhancing Largemouth Bass angling opportunities.

We estimated annual Largemouth Bass annual mortality was low (15 %) in Brush Lake. Annual mortality was on the lower end of rates observed in Largemouth Bass populations throughout the region, but comparable to waters near Brush Lake in Boundary County (see Population Characteristics And Exploitation Of Largemouth Bass In North Idaho Lakes in this report). Our result was consistent with a population of slow growing long lived individual as was observed in Brush Lake. We did not estimate angler exploitation of Largemouth Bass in Brush Lake, but our results suggest fishing mortality on the population is minimal.

The absence of carryover stocked Rainbow Trout in Brush Lake may be influenced by late-summer habitat availability. Temperature and dissolved oxygen profiles from August suggested suitable dissolved oxygen levels for Rainbow Trout were limited or absent. Rainbow Trout were released in Brush Lake on June 11, just prior to our survey. As such, Rainbow Trout were abundant in our survey and represented a significant portion of the biomass observed in the lake at that time. Qualitatively, their abundance suggested stocking efforts provided a quality fishing opportunity during cool water periods. Because survival during late-summer is likely low, we expect annual stocking in spring and early summer is necessary to maintain that portion of the fishery. We recommend continued stocking of catchable size Rainbow Trout at rates that maximize return to the creel. Current rates appear to be working, although exploitation was not estimated.

Kokanee and Westslope Cutthroat were not sampled in our survey of Brush Lake despite annual stocking events prior to 2015. The cause of poor return on fingerling outplants is uncertain, but may also relate to poor water quality in late-summer. Zooplankton quality and quantity identified in ZPR and ZQI indices may also play a role in fingerling survival. Teuscher (1999) suggested return on hatchery fingerlings may decline when zooplankton quality and quantity is low (ZQI <1.0), as in Brush Lake. Similar zooplankton quality and quantity levels were observed in Bonner and Smith lakes, located near Brush Lake. Low density stocking rates of kokanee and Westslope Cutthroat Trout fingerlings also occurred in those lakes with no returns detected (Watkins et al. in review).

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McArthur Lake

The fish assemblage observed in our survey differed somewhat from surveys in 2011 and 1992 (Table 36; IDFG unpublished data; Davis et al. 1996). Most notably, we observed a sharp decline in the proportion of the assemblage comprised of Largemouth Bass. We also detected a higher proportion of Tench in our survey than previously reported. Although shifts in species composition were observed, Yellow Perch remained the most abundant species in the lake. Other less abundant species were present in all surveys in comparable proportions.

The McArthur Lake fish assemblage was likely negatively impacted by lake level drawdown in 2011. We observed evidence of drawdown impacts in the form of failed age classes. Specifically, few Largemouth Bass or Yellow Perch sampled in McArthur Lake were produced in 2011 or earlier. Dominant year classes from 2013 and 2014 made up the majority of fish sampled. Although the fishery was negatively impacted by drawdown, the presence of well-represented year classes post-drawdown suggested enough spawning stock remained in the lake to re-establish depleted fish populations.

Avondale Lake

Our survey of Avondale Lake suggested the fishery is generally comprised of moderate densities of small warmwater fish. We found Largemouth Bass and Bluegill were in good condition, but were represented by poor size structure. The cause of the current condition is uncertain. However, length distribution and age distribution (Largemouth Bass only) of both species exhibited gaps that suggested recruitment was sporadic and/or exploitation was high. No specific evaluation was completed to identify causal factors. We recommend further evaluation of angler effort and exploitation on Avondale Lake be considered if an enhanced warmwater fishery is desired. Other fishery enhancement opportunities may also be suitable for Avondale Lake. Supplementation is one additional option for improving the existing fishery. Hatchery Rainbow Trout could benefit the fishery by providing a quality size fish for anglers. Water quality measures suggested adequate habitat existed for Rainbow Trout.

Yellow Perch in our sample represented an exception to the general observations of mediocrity of the Avondale Lake fishery. Yellow Perch were moderately abundant in Avondale Lake and exhibited a size distribution of a balanced population (PSD 41.7). Anderson and Weithman (1978) reported PSD values of 30-60 were acceptable for balanced populations of Yellow Perch. Although no age related information was collected on Yellow Perch, individuals in our sample reached total lengths of 200 mm and greater, suggesting growth is adequate to provide quality and preferred length fish.

RECOMMENDATIONS

1. Continue current Rainbow Trout stocking rates and frequencies in Brush Lake.

2. Consider how fingerling hatchery products are used in Brush Lake and other nearby regional lakes.

3. Do not consider introduction of prey species in northern Idaho lowland lakes as a viable

strategy for enhancing Largemouth Bass growth.

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4. Estimate angler effort and exploitation on Avondale Lake if an enhanced warmwater fishery is desired.

5. Look for other opportunities to enhance the quality of the Avondale lake fishery through

supplementation using hatchery trout.

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Table 31. Sample locations by date and method for lowland lakes surveyed in 2015. Water Date Method Unit Latitude Longitude Brush Lake 6/15/2015 Electrofishing 1 48.891939 -116.330273 Brush Lake 6/15/2015 Electrofishing 2 48.493032 -116.325878 Brush Lake 6/16/2015 Electrofishing 3 48.890504 -116.327615 Brush Lake 6/16/2015 Electrofishing 4 48.888998 -116.328195 Brush Lake 6/19/2015 Trap Net 5 48.892300 -116.329600 Brush Lake 6/19/2015 Trap Net 6 48.893000 -116.328800 Brush Lake 6/19/2015 Trap Net 7 48.893000 -116.326100 Brush Lake 6/19/2015 Trap Net 8 48.890200 -116.327800 Brush Lake 6/19/2015 Trap Net 9 48.889500 -116.328000 Brush Lake 6/19/2015 Sinking Gill Net 10 48.892000 -116.327400 Brush Lake 6/19/2015 Floating Gill Net 11 48.889500 -116.327500 McArthrur Lake 6/4/2015 Trap Net 1 48° 31.152' 116° 26.730' McArthrur Lake 6/4/2015 Trap Net 2 48° 31.065' 116° 26.741' McArthrur Lake 6/4/2015 Trap Net 3 48° 31.144' 116° 27.100' McArthrur Lake 6/4/2015 Trap Net 4 48° 30.596' 116° 27.238' McArthrur Lake 6/4/2015 Trap Net 5 48° 30.747' 116° 26.891' McArthrur Lake 6/4/2015 Sinking Gill Net 6 48° 30.699' 116° 26.955' McArthrur Lake 6/4/2015 Floating Gill Net 7 48° 30.857' 116° 27.115' McArthrur Lake 6/4/2015 Floating Gill Net 8 48° 30.429' 116° 27.268' McArthrur Lake 6/4/2015 Sinking Gill Net 9 48° 30.857' 116° 27.115' McArthrur Lake 6/4/2015 Boat Electrofishing 10 48° 31.205' 116° 26.552' McArthrur Lake 6/4/2015 Boat Electrofishing 11 48° 30.819' 116° 26.857' McArthrur Lake 6/4/2015 Boat Electrofishing 12 48° 30.560' 116° 27.013' McArthrur Lake 6/5/2015 Boat Electrofishing 13 48° 30.482' 116° 27.294' McArthrur Lake 6/5/2015 Boat Electrofishing 14 48° 30.692' 116° 27.397' Avondale Lake 6/25/2015 Boat Electrofishing 1 47.771883 -116.758726 Avondale Lake 6/25/2015 Boat Electrofishing 2 47.775906 -116.756056 Avondale Lake 6/25/2015 Boat Electrofishing 3 47.775033 -116.753931 Avondale Lake 6/25/2015 Boat Electrofishing 4 47.771291 -116.754688 Avondale Lake 6/11/2011 Gill Net Floating 6 -- -- Avondale Lake 6/11/2011 Gill Net Floating 7 -- -- Avondale Lake 6/11/2011 Gill Net Sinking 5 -- -- Avondale Lake 6/11/2011 Gill Net Sinking 8 -- --

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Table 32. Descriptive statistics for fish sampled from Brush Lake in June 2015. Statistics summarized include catch, proportion of catch by number and biomass, minimum and maximum total length (TL), and catch rates (CPUE; 80% confidence intervals) by gear type.

CPUE

Species Catch % of Catch % of Biomass Min TL Max TL Electrofishing Gill Net Trap Net Bluegill 193 63% 54% 40 212 48(19.9) 0(0) 0.2 (.3) Rainbow Trout 77 25% 35% 168 306 7.3(6.1) 22(23.1) 0.8(.7) Largemouth Bass 37 12% 11% 65 416 8(4.9) 2.5(1.9) 0(0) Table 33. Descriptive statistics for fish sampled from McArthur Lake in June 2015. Statistics summarized include catch,

proportion of catch by number and biomass, minimum and maximum total length (TL), and catch rates (CPUE; 80% confidence intervals) by gear type.

CPUE

Species Catch % of Catch % of Biomass Min TL Max TL Electrofishing Gill Net Trap Net Black Crappie 6 1% -- 66 225 0.2 (0.3) 0.5 (0.5) 0.2 (0.3) Brook Trout 2 0% -- 259 324 0 (0) 0.3 (0.2) 0 (0) Brown Bullhead 14 2% -- 0 275 2 (1.7) 0.4 (0.3) 0.2 (1.7) Largemouth Bass 141 16% -- 0 310 9.8 (7.6) 8.1 (5.3) 0 (0) Largescale Sucker 2 0% -- 266 286 0 (0) 0.3 (0.2) 0 (0) Pumpkinseed 61 7% -- 0 154 3.7 (1.9) 2.5 (2.1) 0.6 (1.9) Rainbow Trout 28 3% -- 171 432 0 (0) 3.5 (4.1) 0 (0) Tench 233 26% -- 52 474 6.4 (1.2) 0.5 (0.2) 1 (1.2) Yellow Perch 406 45% -- 0 260 106.7 (10.1) 10.1 (5.4) 0.6 (7.4)

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Table 34. Descriptive statistics for fish sampled from Avondale Lake in June 2015. Statistics summarized include catch, proportion of catch by number and biomass, minimum and maximum total length (TL), and catch rates (CPUE; 80% confidence intervals) by gear type.

CPUE

Species Catch % of Catch % of Biomass Min TL Max TL Electrofishing Gill Net Trap Net Bluegill 59 28% 11% 63 197 16.7 (1.0) 0.8 (1.0) -- Largemouth Bass 43 20% 32% 86 388 10.7 (4.5) 2.3 (2.1) -- Pumpkinseed 11 5% 3% 112 142 0.3 (.4) 2.5 (2.4) -- Tench 1 0% 9% 502 502 0.3 (.4) 0 -- Yellow Perch 96 45% 44% 52 294 8 (6.5) 17.8(20.3) -- Black Crappie 1 0% 1% 208 208 0 0.3 (0.3) -- Table 35. Summary of lowland lake survey metrics from past and present surveys of Brush Lake, Idaho. Metrics include percent

of catch by number (% #), percent of catch by weight (% Wt), proportional stock density (PSD), relative stock density of preferred size fish (RSD-P), relative weight range (Wr Range), relative weight at 200 mm (Wr 200), and total length-at-age (TL @ 3, TL @ 6).

Year Species % # % Wt PSD RSD-P Wr Range Wr-200 TL @ 3 TL @ 6 1997 BG 65% 39% 19 2 103-112 112 139 --- 2005 BG 52% 41% 54 22 106-125 --- --- --- 2015 BG 63% 54% 82 12 85-107 95 135 ---

1997 LMB 20% 29% 9 --- 87-106 --- --- 320

2005 LMB 43% 45% 1 --- --- --- --- --- 2015 LMB 12% 11% 4 4 70-121 --- --- 221

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Table 36. Summary of species proportions in samples from past and present surveys of McArthur Lake, Idaho.

Species 1992 2011 2015 Black Crappie 0% 4% 1% Brook Trout 1% 1% < 1.0% Brown Bullhead 3% 2% 2% Largemouth Bass 13% 45% 16% Largescale Sucker 0% 0% < 1.0% Pumpkinseed 21% 7% 7% Rainbow Trout 1% 0% 3% Tench 0% 7% 26% Yellow Perch 61% 34% 45%

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Figure 63. Size structure of Bluegill, Largemouth Bass, and Rainbow Trout sampled via boat

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Figure 64. Mean (± one standard deviation) length-at-age for Bluegill and Largemouth Bass

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Figure 65. Bluegill (> 80 mm) and Largemouth Bass (>150 mm) condition as indexed by

relative weight (Wr) for fish sampled from Brush Lake in June 2015.

Figure 66. Age-frequency for Largemouth Bass and Bluegill sampled from Brush Lake in June

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Figure 67. Temperature and dissolved oxygen profiles of Brush Lake on August 4, 2015.

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Figure 68. Size Structure of Rainbow Trout, Largemouth Bass, and Yellow Perch sampled via

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Figure 69. Age-frequency of Yellow Perch and Largemouth Bass sampled from McArthur

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Figure 70. Mean (± SD) length-at-age for Largemouth Bass and Yellow Perch sampled from

McArthur Lake in June 2015.

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Figure 71. Size structure of Yellow Perch, Bluegill, and Largemouth Bass sampled using

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Figure 72. Bluegill (≥ 80 mm), Largemouth Bass (≥150 mm), and Yellow Perch (≥ 130 mm)

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Figure 73. Age-frequency of Largemouth Bass sampled from Avondale Lake in June 2015.

Figure 74. Mean (± one standard deviation) length-at-age for Largemouth Bass sampled from

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Figure 75. Temperature and dissolved oxygen profiles of Avondale Lake on September 11,

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ALPINE LAKE FISHERY EVALUATIONS

ABSTRACT

Wild populations of Brook Trout are common in alpine lakes throughout western North America, including Idaho. Brook Trout tend to be highly prolific and are successful at establishing self-sustaining populations in alpine lakes because they are early-maturing, have few predators, and are able to reproduce with limited spawning habitat. Brook Trout have the potential to reach high abundances in alpine lakes, whereby growth rates can be substantially reduced from intraspecific competition. Oftentimes, this will result in “stunted” populations with poor size structure and few individuals that are desirable to anglers. To evaluate the occurrence of this phenomenon in Panhandle Region alpine lakes, we estimated characteristics of known Brook Trout populations in the Kootenai, Pend Oreille, and Spokane river drainages. This study was a continuation of efforts initiated in 2014 to evaluate all known populations of Brook Trout in alpine lakes in the Panhandle Region. We estimated catch rates, size structure, body condition, and site characteristics to identify alpine lakes that may benefit from treatments aimed at reducing Brook Trout abundance. For alpine lakes sampled during 2015, we estimated growth, total annual mortality, and recruitment stability to provide further insight on Brook Trout population ecology in alpine lakes. Catch rates were highly variable among lakes (4.8–70.0 fish/net night), but only slightly variable within lakes (mean SD = 4.4 fish/net night). The majority of alpine lakes in this study supported Brook Trout ≤ 254 mm in total length, with the exception of Gem Lake, Gold Creek Lake, Upper Glidden Lake, Roman Nose Lake 2, and Lower Stevens Lake which had slightly better size structure. Total annual mortality of populations sampled during 2015 was relatively high (mean = 46.3%) and similar among most alpine lakes. Brook Trout recruitment in these lakes has been stable in recent history and individuals appear to fully-recruit to floating gill nets at age-2. Somatic growth was poor, and individuals tended to be in fair body condition (mean Wr = 94) among all of the study sites Future work may seek to identify alpine lakes that stand to benefit from population suppression (i.e., abundance reduction) or eradication, and also may include estimates of angler use and angler opinion surveys to better inform these decisions. Author:

Carson Watkins Regional Fisheries Biologist

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INTRODUCTION

High alpine lakes are among the most unique and intact lentic systems worldwide. Alpine lakes are also an important resource that attract recreationists for both consumptive (e.g., angling) and non-consumptive (e.g., wildlife viewing, hiking) uses. Mountainous regions throughout the world contain alpine lakes that were formed from the recession of glacial ice during the late Pleistocene Epoch (Knapp et al. 2001b). The glacier-carved landscape left steep topography where alpine lakes have formed, often precluding the colonization of fish into high elevation tributaries and lake outlets. In western North America, nearly all (~ 95%) of alpine lakes were historically fishless; however, many lakes have been stocked over the course of the past century with nonnative fishes (mostly salmonids) to create recreational fisheries (Bahls 1992; Matthews and Knapp 1999; Pister 2001). Overall, around 60% (SD = 12%) of alpine lakes throughout the western United States have been stocked with sport fish species to provide recreational angling opportunities (Bahls 1992).

The first documented stockings of alpine lakes are thought to have occurred during the latter part of the 19th century and were initiated by the Sierra Club. Various salmonid species were loaded into milk cans, packed to stock animals, and released into alpine lakes throughout the Sierra Nevada Mountains (Knapp and Matthews 1998). Following these efforts, state and federal management agencies, along with private citizens, have stocked alpine lakes across the western United States in an effort to establish recreational fisheries (Landres and Matthews 2001). More recently, improvements in technology (i.e., fixed- and rotary-wing aircraft) have allowed management agencies to stock fish into more lakes, thereby expanding the distribution of fish in alpine lakes and increasing stocking frequency. While the increase in alpine lake stocking has provided recreational anglers with more consistent opportunities, it has been shown that faunal communities can be adversely influenced by introduced fishes (Parker et al. 2000). Predation by fishes has been implicated in the decline in abundance and diversity of zooplankton, macroinvertebrate (Knapp et al. 2001a; Parker et al. 2000), and amphibian (Pilliod and Peterson 2000) assemblages in alpine lakes because these species’ metapopulations did not co-evolve in the presence of fish. Particular concern surrounding endemic amphibian species in alpine lakes has resulted in many state agencies implementing efforts to monitor and evaluate stocking (Knapp et al. 2001a; Pilliod and Peterson 2001).

Many of the naturalized fish populations in alpine lakes consist of Brook Trout Salvelinus fontinalis. Brook Trout have been extensively stocked into alpine lakes throughout western North America (Hall 1991), including Idaho. Brook Trout stocking mainly took place during the early 20th century, but efforts ceased around the mid-1950s when other species (e.g., Westslope Cutthroat Trout Oncorhynchus clarki lewisi, Golden Trout [O. aguabonita]) could be successfully cultured and stocked into alpine lakes. Brook Trout have been particularly successful at establishing naturalized, self-sustaining populations in alpine lake ecosystems (Hall 1991; Parker et al. 2000; Koenig 2012). Brook Trout are capable of spawning in lake inlets, outlets, and margins even when little habitat is available (Fraser 1989), thus contributing to their continued persistence in alpine lakes. Brook Trout have few predators in high elevation environments, and this, coupled with their early age at maturity, has allowed many populations to reach very high abundances (Donald and Alger 1989). Alpine lakes are often oligotrophic (Parker et al. 2000) and unable to support high densities of fish. Due to the lack of limited primary production in alpine lakes, Brook Trout are prone to exceptionally slow growth once densities reach critical thresholds, thus resulting in poor size structure and limited interest from anglers. Additionally, alpine lakes may act as source populations for downstream colonization of Brook Trout which may pose threats to native fish assemblages in downstream habitats. Brook Trout are known to compete with Cutthroat Trout spp. (Marnell 1988) and hybridize with Bull

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Trout S. confluentus. Dispersal of Brook Trout in response to overcrowding and intraspecific competition in source environments may lead to the invasion of stronghold habitats for native fishes and subsequent displacement of or competition with native fishes (Shepard et al. 2005).

Given the threat to native faunal assemblages and lack of quality fishing opportunity provided by Brook Trout, some agencies have initiated efforts to eradicate Brook Trout from alpine lakes or reduce densities through various biological (e.g., introduction of predators), mechanical (e.g., gill netting), and chemical (e.g., rotenone) techniques. Complete removal of Brook Trout in many alpine lakes presents a significant challenge from a variety of logistical and financial constraints. Therefore, management is often focused on practical means of reducing Brook Trout densities and improving size structure in hopes of providing a quality fishery for anglers and reducing threats to downstream fish assemblages.

There are approximately 140 alpine lakes (defined as lentic system ≥ 1,000 m elevation) within the Panhandle Region that have been previously identified and characterized by Hardy et al. (2009). Fifty-one are managed as put-grow-and-take fisheries and stocked with Westslope Cutthroat Trout, Rainbow Trout O. mykiss, Golden Trout O. aguabonita, or Arctic Grayling Thymallus arcticus. These 51 alpine lakes are stocked on a two-year schedule at densities of ~750 fry/ha based on elevation (Fredericks et al. 2002). Of the remaining 89 alpine lakes that are not stocked, around 15–20 have known populations of wild Brook Trout (Hardy et al. 2009).

Brook Trout are fairly common in alpine lakes throughout much of Idaho, and they often exhibit strong density-dependent growth. For example, Brimmer et al. (2002) reported drastic declines in size structure of a former trophy Brook Trout fishery in Carlson Lake in the Salmon Region following an increase in abundance. Similarly, Schriever and Murphy (2010) reported that Brook Trout size structure increased after a large-scale removal in Ice and Rainbow lakes in the Clearwater Region. Previous investigations of Brook Trout in alpine lakes around Idaho have shown a similar relationship between density and growth (Koenig 2012), and various methods have been used to eradicate Brook Trout and experimentally reduce densities. Depending on the management objective and practicality, it may be advantageous to completely remove Brook Trout and stock a species that is unlikely to successfully reproduce or is less prone to slow growth. For instance, the Idaho Department of Fish and Game used rotenone treatment to eradicate Brook Trout from Porcupine Lake, which was then restocked with Westslope Cutthroat Trout (unpublished data). Alternatively, the objective may be to manage for a quality Brook Trout fishery and encourage harvest-oriented angling. Idaho Department of Fish and Game has also introduced predators (i.e., Bull Trout and Brown Trout Salmo Trutta) to improve size structure of Brook Trout in alpine lakes which are managed as Brook Trout fisheries (Hardy et al. 2009).

OBJECTIVES

1. Estimate and compare population characteristics of Brook Trout populations among alpine lakes.

2. Identify management strategies that may be used to improve angling quality in alpine

lakes with overabundant Brook Trout populations.

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STUDY AREA

The study area consisted of alpine lakes in the Kootenai, Pend Oreille, and Spokane river basins in northern Idaho. All of the alpine lakes in the study area share common characteristics with typical high alpine lakes throughout western North America. This includes high elevations (≥ 1,000 m), small size (< 30 ha), short growing seasons (3–5 months ice-free), cold water temperatures, low productivity, and relatively simple fish assemblages. All of the surveyed alpine lakes (complete list in Table 37) have known Brook Trout populations and are located in IDFG’s Panhandle Region. The fish communities in the study lakes are composed exclusively of Brook Trout, with the exception of Lower Glidden and Elsie lakes which are annually stocked with hatchery Rainbow Trout. Historically, dominant land use activities in this region have included logging, mining, and livestock grazing (DEQ 2001). More recently, declines in timber harvest and mining activity have positively influenced water quality and fish habitat throughout the watersheds included in this study. Despite extensive land use, aquatic habitat in alpine lakes within the study area has remained relatively unaltered due to difficult access and remoteness.

Alpine lakes are commonly characterized by having limited access, low angling effort, and high catch rates. This makes them appealing to anglers seeking a remote angling experience. Elsie Lake and Lower Glidden Lake have direct road access, and as such, are popular destinations for local anglers. Given the high angler use and poor size structure of wild Brook Trout in Elsie and Lower Glidden lakes, the IDFG stocks catchable Rainbow Trout to provide better fishing. With the exception of Elsie and Lower Glidden Lakes, the remaining alpine lakes in this study have fish assemblages composed only of wild Brook Trout.

METHODS

Brook Trout were sampled from 14 alpine lakes in northern Idaho during July–September of 2014 and 2015. The alpine lakes had different characteristics, varying in elevation from 1,548–1,814 m, in surface area from 2–11 ha, and in maximum depth from 2–29 m (Table 37). We sampled fishes using floating experimental gill nets (36.0 m × 1.8 m with panels of 12.70, 19.05, and 25.40-mm stretch-measure mesh). Initially, we made attempts to pair sinking monofilament gill nets with floating gill nets; however, sinking gill nets continually snagged on benthic structure making net retrieval difficult and dangerous. Two gill nets were set in lakes less than 5 ha in surface area and three nets were set in lakes greater than 5 ha in surface area to adequately characterize the population in each lake. Gill nets were deployed approximately one hour before dusk and retrieved shortly after dawn the following day. Upon retrieval, we enumerated the total catch for each net and recorded the mesh size corresponding to each captured fish. We recorded total length (TL; mm) and weight (g) from all sampled fishes. Saggital otoliths were removed from 10 fish per 1 cm length group and used for age estimation (Quist et al. 2012). Maximum lake depth, conductivity, the number of campfire rings, and the number of camp sites were recorded during each sampling event. In addition, we also used a categorical score (Low–High) as a subjective measure of the level of human use at each lake (Knight 2009). Site scoring included an assessment of trail conditions, and number and apparent use of campsites and fire rings.

Catch-per-unit-effort (CPUE) was estimated as the number of fish sampled per gill net per night. Length-frequency distributions were summarized to describe and compare size structure among populations. Body condition of Brook Trout was evaluated using relative weight (Wr; Neumann et al. 2012). Relative weight values were calculated as

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Wr = (W / Ws) × 100, where W is the weight of an individual and Ws is the standard weight predicted by a species-specific length-weight regression (Neumann et al. 2012). A Wr value of 100 indicates average body condition, Wr values below 100 indicate poor body condition, and Wr values above 100 indicate good body condition.

Age was estimated for all Brook Trout sampled from alpine lakes during 2015. Total annual mortality (A) was estimated using a weighted catch-curve whereby only those age classes fully recruited to the sampling gear were retained for analysis (Miranda and Bettoli 2007). In addition, age structure information was used to explain recruitment stability by using the recruitment coefficient of determination (RCD; Isermann et al. 2002). The RCD is simply the coefficient of determination (R2) value that results from a catch-curve regression. Values approaching an RCD of 1.00 indicate higher consistency in recruitment. While indices of recruitment not provide a quantitative measure of total recruits, they are useful for comparing recruitment patterns among water bodies.

Growth was summarized by fitting a von Bertalanffy growth model (von Bertalanffy 1938) to length at age information:

Lt = L∞ [1 – e –K (t – t0)] where Lt is the mean length at age at time of capture, L∞ is the average maximum length of fish in the population, K is the growth coefficient, and t0 is the theoretical age when length equals 0 mm. Models were fit with nonlinear regression techniques using Program R (nlstools package; Seber and Wild 2006; R Development Core Team 2012).

RESULTS

A total of 1,176 Brook Trout was sampled from the 14 lakes. Catch rates were highly variable among lakes, but only slightly variable within lakes (Table 38). Mean total length of Brook Trout was relatively consistent (141–193 mm) among lakes with the exception of Brook Trout in Roman Nose Lake 2 which had a mean TL of 226.6 mm (Table 38). The majority of each population was composed of Brook Trout that were less than quality length (203 mm TL; Figures 76, 77 and 78). Mean weight of Brook Trout varied from 34.9–67.5 g and body condition was slightly below average for most populations (Table 38; Figure 79).

Estimated age of Brook Trout varied from 1 to 9 years old, and longevity averaged ~6 years. Brook Trout tended to recruit to floating gill nets at two years of age, and in one case as late as four (Figure 80). Total annual mortality was similarly high among populations (mean A = 46.30 5) with the exception of Gold Creek Lake (A = 24.9%; 95% CI = 9.01–38.09). Overall, A varied from 24.95% (Gold Creek Lake) to 59.78% (Bottleneck Lake; Figure 80). Recruitment was very stable among all populations and RCD values varied from 0.75 (Gold Creek Lake) to 0.99 (Lake Darling). Brook Trout in alpine lakes grew slowly and few populations showed notable changes in growth trajectory over time (Figure 81). In fact, some populations sustained nearly constant rates of growth across age classes.

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DISCUSSION

Size structure among the Brook Trout populations in our study sites was relatively poor with the majority of individuals being ≤ 200 mm. The vast majority of Brook Trout were small and likely undesirable to most anglers. We did not sample any quality-length or larger Brook Trout in the majority of our study sites, and where we did, sample sizes were not sufficient for calculating size structure metrics. Lower Stevens Lake, Roman Nose Lake 2, and Upper Glidden Lake had more Brook Trout ≥ 230 mm TL than the other study lakes. It is not surprising that Upper Glidden Lake and Roman Nose Lake 2 displayed better size structure because these lakes have been previously stocked with Bull Trout. These introductions were part of a larger project that occurred in 1993 to investigate the use of Bull Trout and Brown Trout in high lakes to reduce Brook Trout abundance (Nelson et al. 1997). Both Upper Glidden Lake and Roman Nose Lake 1 showed significant (P < 0.05) increases in mean length-at-age of Brook Trout; however, Bull Trout persisted longer in these lakes than other lakes included in the study (i.e., Revett Lake, Roman Nose Lake 2). Upper Stevens Lake was used as a control as part of this study and no significant change in mean length-at-age of Brook Trout was detected over the 15 year course of the study (Hardy et al. 2008).

The Brook Trout populations we evaluated showed slow somatic growth and individuals tended to be short-lived, consistent with previous work conducted on other alpine lake fish populations in northern Idaho (Fredericks and Horner 2002). No obvious relationships between size structure and abundance emerged during our study. In fact, the lakes with the highest CPUE estimates also contained the largest Brook Trout we sampled. Ease of access appeared to have a slight effect on size structure, but that pattern was not consistent. For instance, Gold Creek Lake has difficult access (Table 37) and had the best size structure relative to all other lakes surveyed during 2015. Whereas, Lower Glidden, Elsie, and Revett lakes had poor size structure compared to the other study lakes and direct (or closeby) road access for full-size vehicles. However, this pattern did not hold true for Gem, Roman Nose 1, or Roman Nose 2 lakes which had fair to excellent size structure relative to the other study sites and good access. Assuming angler use is proportional to road proximity, this does not seem to have much of an effect on size structure (i.e., harvest does not influence size structure). However, accessibility and angler use appear to have a more noticeable effect on longevity, which may in turn, promote better size structure. For instance, Gold Creek Lake contained some of the oldest Brook Trout in our study and had little evidence of human use. On average, Brook Trout in Gold Creek Lake did not reach stock length until approximately age-3.5 and quality length until age-5.5. In addition, Brook Trout in Gold Creek Lake survived at a 50% higher rate than all other populations surveyed during 2015. Overall, it appears that angler use may have the potential to alter size structure, but that fish in our study populations grow too slowly and are too depauperate to provide an abundance of quality-length Brook Trout. In contrast to many other alpine lake Brook Trout populations described by Hall 1991 and Koenig 2012, the Brook Trout in northern Idaho lakes are short-lived and do not seem to exhibit strong density-dependent growth. Additionally, Brook Trout in northern Idaho alpine lakes have high mortality and rarely survive long enough to reach stock length.

A considerable amount of research and management effort has focused on treatments that may be used to reduce Brook Trout abundances in both lentic and lotic systems. Due to the remoteness of many alpine lakes, biological treatments have been an effective and resourceful way to remove Brook Trout. Koenig (2012) built upon previous management-related work in Idaho by evaluating the use of Tiger Muskellunge Esox masquinongy × E. Lucius to eradicate Brook Trout. The authors reported that some post-treatment lakes showed substantial declines in CPUE and increases in mean length (4–133 mm) of Brook Trout, whereas nearby control

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lakes continued to support slow growing Brook Trout. However, Hardy et al. (2009) showed that predator-induced effects can be subtle and take considerable time to manifest in northern Idaho Brook Trout populations. In addition, both Koenig (2012) and Hardy et al. (2009) reported that Brook Trout populations often reached very low abundances before somatic growth was substantially improved. Our study sites that have not previously received suppression treatments may benefit from predator introductions. Based on information collected during 2014–2015, potential candidate lakes for biological (e.g., predator or YY Brookt Trout introduction) or mechanical (e.g., gillnetting) treatment include Lake Darling, Revett Lake, Roman Nose Lake 1, and Upper Stevens Lake. However, the improved size structure relative to reduced angler catch rates is unlikely to result in a gain. As such, there may be more benefit to eradicating populations that are unlikely to yield quality angling opportunities. We suggest an evaluation of angler use to better understand the potential loss of angling opportunity at candidate treatment lakes. Further, we recommend that management decisions be informed with an understanding of angler preferences for alpine lake Brook Trout fisheries.

MANAGEMENT RECOMMENDATIONS

1. Consider the use of biological treatments and chemical treatments to renovate Brook Trout populations.

2. Estimate angler use at candidate treatment lakes to assess the impacts that may result

from potential management actions.

3. Understand angler sentiment about alpine lake Brook Trout fisheries via future angler opinion surveys.

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Table 37. Sample year and physical characteristics of alpine lakes sampled in the Panhandle Region, Idaho (2014–2015). Alpine lakes are organized by parent drainage.

Lake Yeara Elevation (m)

Surface area (ha)

Maximum depth (m)

Conductivity (µS/cm) pH Relative useb

Kootenai River Drainage Bottleneck 2015 1,716.9 4.4 8.7 Moderate Roman Nose 1 2014 1,800.5 6.8 18.2 9.7 7.7 High Roman Nose 2 2014 1,813.9 3.5 7.0 7.5 7.7 High Pend Oreille River Drainage Darling 2015 1,610.0 4.6 6.6 Moderate Estelle 2015 1,760.8 2.7 7.5 Moderate Gem 2015 1,763.6 2.7 8.8 Moderate Moose 2015 1,660.9 6.3 3.0 Moderate Spokane River Drainage Elsie 2014 1,548.4 6.2 14.6 34.8 8.7 High Gold Creek 2015 1,696.2 2.2 2.3 Low Lower Glidden 2014 1,712.7 5.6 4.5 9.1 7.6 High Lower Stevens 2014 1,692.3 11.2 28.7 52.3 8.0 Moderate Revett 2014 1,730.4 8.2 12.2 6.0 7.7 Moderate Upper Glidden 2014 1,800.5 7.6 28.9 7.8 7.3 Moderate Upper Stevens 2014 1,752.9 4.9 26.0 45.7 8.09 Moderate aMay be expressed as multiple years bSubjective measure of human impact incorporating accessibility, number of campsites, and number of fire rings

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Table 38. Sample size (n), mean catch-per-unit-effort (CPUE = fish/gill net night), total length (mm; Minimum–Maximum [Min–Max]) statistics, weight (g; Minimum–Maximum [Min–Max]) statistics, and relative weight (Wr) for Brook Trout populations sampled from alpine lakes in the Panhandle Region, Idaho (2014–2015). Numbers in parentheses represent one standard error about the mean.

Total length Weight Lake n CPUE Mean Min–Max Mean Min–Max Wr Bottleneck 41 20.5 (0.5) 150.3 (7.4) 83–232 37.2 (4.6) 2–102 83 (2.4) Darling 65 32.5 (6.5) 177.3 (2.9) 123–238 53.5 (2.3) 17–100 90 (1.1) Elsie 29 4.8 (1.6) 141.1 (7.9) 89–216 34.9 (5.9) 6–110 94 (2.9) Estelle 25 12.5 (9.5) 190.0 (7.8) 106–248 66.5 (6.7) 7–131 84 (1.8) Gem 28 14.0 (4.0) 168.6 (8.6) 105–266 53.0 (9.4) 5–167 82 (5.5) Gold Creek 27 13.5 (6.5) 226.6 (7.2) 159–290 111.4 (9.4) 42–191 87 (2.1) Lower Glidden 172 34.0 (7.5) 155.9 (2.4) 83–239 35.5 (1.6) 5–115 86 (0.9) Lower Stevens 84 16.6 (4.3) 191.3 (4.2) 93–247 67.5 (3.7) 10–135 88 (1.4) Moose 66 33.0 (4.0) 193.9 (3.2) 117–248 65.7 (2.8) 14–127 84 (1.3) Revett 130 26.0 (2.5) 162.5 (3.3) 81–254 40.1 (2.2) 5–140 84 (1.2) Roman Nose 1 140 70.0 (2.5) 158.2 (2.8) 77–334 45.3 (3.8) 5–533 97 (0.9) Roman Nose 2 64 32.0 (6.5) 142.1 (7.8) 77–417 50.2 (14.1) 5–827 94 (1.6) Upper Glidden 60 15.0 (2.4) 179.3 (5.9) 93–296 60.7 (5.1) 7–217 88 (1.6) Upper Stevens 245 49.0 (3.9) 183.4 (0.9) 111–230 54.1 (0.9) 12–93 85 (1.1)

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Table 39. Mean length-at-age (mm; [SD]) and von Bertalanffy growth model equation (VBGM) for Brook Trout sampled from alpine lakes in the Panhandle Region, Idaho (2015).

Age (years) Lake 1 2 3 4 5 6 7 8 VBGM

Bottleneck 88.9 (4.6)

130.6 (27.8)

186.4 (8.4)

215.6 (12.0)

225.0 (0.0) Lage = 225(1 – e(-0.63(age – 0.27)))

Darling 139.0 (0.0)

163.0 (15.1)

179.7 (10.5)

202.8 (9.7)

217.8 (9.8)

238.0 (0.0) Lage = 240(1 – e(–0.37(age + 1.22)))

Estelle 152.6 (34.0)

188.3 (3.5)

192.0 (5.9)

212.2 (22.9)

218.0 (17.0)

234.0 (19.8) Lage = 245(1 – e(–0.34(age + 0.96)))

Gem 116.3 (10.8)

150.9 (19.4)

188.0 (17.8)

250.3 (17.8)

244.5 (13.4) Lage = 247(1 – e(–0.58(age – 0.007)))

Gold Creek 174.7 (16.0)

196.7 (25.0)

221.6 (7.6)

242.4 (18.4)

266.0 (11.9)

271.0 (5.7)

290.0 (0.0) Lage = 289(1 – e(–0.37(age + 0.34)))

Moose 168.9 (18.9)

192.9 (10.5)

211.6 (14.3)

236.7 (3.1)

225.5 (31.8) Lage = 228(1 – e(–0.77(age –0.30)))

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Relat

ive fr

eque

ncy

0.00

0.25

0.20

0.15

0.10

0.05

0.00

0.00

0.25

0.20

0.15

0.10

0.05

Roman Nose Lake 1

Roman Nose Lake 2

Length (mm)

20-29

30-39

40-49

50-59

60-69

70-79

80-89

90-99

100-1

0911

0-119

120-1

2913

0-139

140-1

4915

0-159

160-1

6917

0-179

180-1

8919

0-199

200-2

0921

0-219

220-2

2923

0-239

240-2

4925

0-259

260-2

6927

0-279

280-2

8929

0-299

300-3

0931

0-319

320-3

2933

0-339

340-3

4935

0-359

360-3

6937

0-379

380-3

8939

0-399

400-4

0941

0-419

Bottleneck Lake

0.25

0.20

0.15

0.10

0.05

0.00

Figure 76. Length-frequency distributions for Brook Trout sampled from alpine lakes in the

Kootenai River Drainage (2014–2015).

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Gem Lake

Lake Darling

Lake Estelle

Length (mm)

20-2930-39

40-4950-59

60-6970-79

80-8990-99

100-109

110-119

120-129

130-139

140-149

150-159

160-169

170-179

180-189

190-199

200-209

210-219

220-229

230-239

240-249

250-259

260-269

270-279

280-289

290-299

300-309

310-319

320-329

330-339

340-349

350-359

360-369

370-379

380-389

390-399

400-409

410-419

Moose Lake

0.00

0.00

0.25

0.20

0.15

0.10

0.05

0.00

0.25

0.20

0.15

0.10

0.05

0.00

0.25

0.20

0.15

0.10

0.05

0.00

0.25

0.20

0.15

0.10

0.05

Relat

ive fr

eque

ncy

Figure 77. Length-frequency distributions for Brook Trout sampled from alpine lakes in the

Pend Oreille River Drainage (2014–2015).

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Rela

tive

freq

uenc

y

0.0

0.3

0.2

0.1

0.0

0.0

0.3

0.2

0.1

0.0

0.3

0.2

0.1

0.0

0.3

0.2

0.1

0.0

0.3

0.2

0.1

0.4

0.3

0.2

0.1

Elsie Lake

Lower Glidden Lake

Lower Stevens Lake

Revett Lake

Upper Glidden Lake

Upper Stevens Lake

Length (mm)

20-2

930

-39

40-4

950

-59

60-6

970

-79

80-8

990

-99

100-

109

110-

119

120-

129

130-

139

140-

149

150-

159

160-

169

170-

179

180-

189

190-

199

200-

209

210-

219

220-

229

230-

239

240-

249

250-

259

260-

269

270-

279

280-

289

290-

299

300-

309

310-

319

320-

329

330-

339

340-

349

350-

359

360-

369

370-

379

380-

389

390-

399

400-

409

410-

419

0.3

0.2

0.1

0.0

Gold Creek Lake

Figure 78. Length-frequency distributions for Brook Trout sampled from alpine lakes in the

Spokane River Drainage (2014–2015).

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Figure 79. Length-weight relationship for Brook Trout sampled from alpine lakes in the

Panhandle Region (2014–2015).

0

50

100

150

200

250

0 50 100 150 200 250 300 350

Wei

ght (

g)

Length (mm)

R2 = 0.94

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ln(n

umbe

r)

0

1

2

3

4

ln(n

umbe

r)

0

1

2

3

4

Age

0 2 4 6 8 10

ln(n

umbe

r)

0

1

2

3

4

Age

0 2 4 6 8 10

Bottleneck LakeA = 59.78Z = 0.91RCD = 0.95

Lake DarlingA = 56.98Z = 0.84RCD = 0.99

Gem LakeA = 46.91Z = 0.63RCD = 0.88

Lake EstelleA = 44.49Z = 0.59RCD = 0.98

Gold Creek LakeA = 24.95Z = 0.29RCD = 0.75

Moose LakeA = 44.68Z = 0.59RCD = 0.81

Figure 80. Weighted catch-curve regressions used to estimate total annual mortality (A),

instantaneous mortality (Z), and recruitment variability (RCD) for Brook Trout populations sampled from alpine lakes in the Panhandle Region (2015).

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Age

0 2 4 6 8 10

Tota

l leng

th (m

m)

50

100

150

200

250

300

350

Bottleneck LakeGem LakeGold Creek LakeLake DarlingLake EstelleMoose Lake

Figure 81. Mean lengths-at-age of Brook Trout sampled from alpine lakes in the Panhandle

Region (2015).

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LITERATURE CITED

Allen, M. S., and J. E. Hightower. 2010. Fish population dynamics: mortality, growth, and recruitment. Pages 43–79 in W. A. Hubert and M. C. Quist, editors. Inland Fisheries Management in North America, 3rd Edition. American Fisheries Society, Bethesda.

Allen, M. S., and W. E. Pine III. 2011. Detecting fish population responses to a minimum length

limit: effects of variable recruitment and duration of evaluation. North American Journal of Fisheries Management 20:672–682.

Allen, M. S., R. M. Meyers, and C. J. Walters. 2008. Temporal trends in largemouth bass

mortality, with fisheries implications. North American Journal of Fisheries Management 26:108–118.

Allen, S. Sammons, and M. J. Maceina, editors. 2009. Balancing Fisheries Management and

Water Uses for Impounded River Systems. American Fisheries Society Symposium 62, Bethesda.

Allendorf, F. W., R. F. Leary, N. P. Hitt, K. L. Knudsen, L. L. Lundquist, and P. Spruell. 2004.

Intercrosses and the U.S. Endangered Species Act: should hybridized populations be included as Westslope Cutthroat Trout?. Conservation Biology 18:311–318.

Anderson, R.O. 1980. Proportional stock density (PSD) and relative weight (Wr); interpretive

indices for fish populations and communities. Pages 27-33 in S. Gloss and B. Shupp, editors. Practical fisheries management: more with less in the 1980’s. American Fisheries Society, New York Chapter.

Anderson, R.O. and A.S. Weithman. 1978. The concept of balance for coolwater fish

populations. American Fisheries Society Special Publication 11:371-381. Anderson, R.O. and R.M. Neumann 1996. Length, weight, and associated structural indices.

Pages 447-482. In B.R. Murphy and D.W. Willis (eds). Fisheries Techniques. American Fisheries Society, Bethesda, MD.

Bahls, P. 1992. The status of fish populations and management of high mountain lakes in the

western United States. Northwest Science 66:183–193. Baker, William. Washington Department of Fish and Wildlife. Personal Communication. 6

January, 2015. Bartholomew, A. and J. A. Bohnsack. 2005. A review of catch and release angling mortality with

implications for no-take reserves. Reviews in Fisheries Science. 15:75-167. Beamesderfer, R. C. P., and J. A. North. 1995. Growth, natural mortality, and predicted

response to fishing for largemouth bass and smallmouth bass populations in North America. North American Journal of Fisheries Management 15:688–704.

Bear, E. A. Effects of temperature on survival and growth of Westslope Cutthroat Trout and

Rainbow Trout: implications for conservation and restoration. Master’s Thesis. Montana State University, Bozeman.

Page 207: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

194

Bear, E. A., T. E. McMahon, and A. V. Zale. 2007. Comparative thermal requirements of Westslope Cutthroat Trout and Rainbow Trout: implications for species interactions and development of thermal protection standards. Transactions of the American Fisheries Society 136:1113–1121.

Behnke, R. J. 1992. Native trout of western North America. American Fisheries Society,

Monograph 6, Bethesda. Behnke, R. J. 2002. Trout and salmon of North America. Free Press, New York. Bellatty, J. M., 1990. Hayden Lake, Kootenai County, Idaho 1987. Idaho Department of Health

and Welfare, Division of Environmental Quality, Water Quality Bureau, Water Quality Status Report 92, 71 pp.

Bjornn, T.C. 1957. A survey of the fishery resources of Priest and Upper Priest lakes and their

tributaries, 1955-57 completion report, F-24-R 30. Idaho Department of Fish and Game, Boise.

Bonds, C. C., J. B. Taylor, and J. Leitz. 2008. Practices and perceptions of Texas anglers

regarding voluntary release of Largemouth Bass and slot length limits. Pages 219–230 in M. S.

Bowler, B. 1974. Coeur d’Alene River study, 1974 Job Performance Report, F-35-R-9. Idaho

Department of Fish and Game, Boise. Bowler, B., B. E. Rieman, and V. L. Ellis. 1979. Pend Oreille Lake fisheries investigations. job

performance report, F-73-R-1. Idaho Department of Fish and Game, Boise. Brimmer, B., K. Andrews, T. Curet, and A. Brimmer. 2002. Fisheries management

investigations, F-73-R-26. Idaho Department of Fish and Game, Boise. Burnham, K. P., and D. R. Anderson. 2002. Model selection and multi model inference: a

practical information-theoretic approach, 2nd edition. Springer-Verlag, Fort Collins, CO. Butts, Arthur. Idaho Department of Fish and Game. Personal Communication. 3 February, 2015. Cambray, J. A. 2003. Impact on indigenous species biodiversity caused by the globalization of

alien recreational freshwater fisheries. Hydrobiologia 500:217–230. Cline, T. J., B. C. Weidel, J. F. Kitchell, and J. R. Hodgson. 2012. Growth response of

largemouth bass (Micropterus salmoides) to catch-and-release angling: a 27-year mark-recapture study. Canadian Journal of Fisheries and Aquatic Sciences 69:224–230.

Copeland, T., and K. A. Meyer. 2011. Interspecies synchrony in salmonid densities associated

with large-scale bioclimatic conditions in central Idaho. Transactions of the American Fisheries Society 140:928–942.

Davis, J., L. Nelson, and N. Horner. 1995. Fisheries management investigations,1994

panhandle region report, IDFG 00-22. Idaho Department of Fish and Game, Boise.

Page 208: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

195

Davis, J., L. Nelson, and N. Horner. 1996. Fisheries management investigations, 1993 panhandle region report, F-71-R-18. Idaho Department of Fish and Game, Boise.

Davis, J., L. Nelson, N. Horner. 1996. Fishery management investigations, 1992 panhandle

region report, IDFG 96 - 10. Idaho Department of Fish and Game, Boise. Dean Jr., W. J., D. R. Terre, W. B. Dolman, T. W. Schlagenhaft. 1991. Largemouth Bass

population structure changes and harvest under a slot length limit. Proceedings of the Annual Conference of the Southeast Association of Fish and Wildlife Agencies 45:261–269.

DEQ (Department of Environmental Quality). 2001. Subbasin assessment and total maximum

daily loads of the North Fork Coeur d’Alene River, Idaho. Department of Environmental Quality. Coeur d’Alene.

Diefenbach, M. L., and R. M. Claramunt. 2013. Lake Michigan chinook salmon diets: annual

evaluation, 2013. Michigan Department of Natural Resources, Federal Aid in Sport Fish Restoration. Charlevoix, Michigan.

Dillon, J. 1990. Lake and reservoir investigations. Forage development and evaluation:

Largemouth Bass forage investigations, 1990 job performance report. Idaho Department of Fish and Game, Boise.

Dillon, J. C. 1990. Lake and reservoir investigations, F-73-R-12. Idaho Department of Fish and

Game, Boise. Dillon, J.C. and C.B. Alexander. 1996. Hatchery trout evaluations, IDFG 96-28. Idaho

Department of Fish and Game, Boise. Donald, D. B., and D. J. Alger. 1989. Evaluation of exploitation as a mean of improving growth

in a stunted population of brook trout. North American Journal of Fisheries Management 9:177–183.

DuPont J., M. Liter, and N. Horner. 2009. Fisheries management investigations, 2006 job

performance report, IDFG 09-109. Idaho Department of Fish and Game, Boise. DuPont, J., and N. Horner. 2006. Little North Fork Clearwater River fishery assessment, IDFG

06-10. Idaho Department of Fish and Game, Boise. Dupont, J., M. Liter, N. Horner. 2004. Panhandle region Little North Fork Clearwater River and

Priest River tributary investigations, IDFG 07-62. Idaho Department of Fish and Game, Boise.

DuPont, J., M. Liter, and N. Horner. 2007. Fisheries management investigations, Upper Priest

River Bull Trout Redd Surveys, 2005 Job Performance Report, Idaho Department of Fish and Game, Boise.

Ebbers, M. A. 1987. Vital statistics of a Largemouth Bass population in Minnesota from

electrofishing and angler-supplied data. North American Journal of Fisheries Management 7:252–259.

Page 209: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

196

Eder, S. 1984. Effectiveness of an imposed slot length limit of 12.0–14.9 inches on Largemouth Bass. North American Journal of Fisheries Management 4:469–478.

Ellis, V. 1983. Lake and reservoir Investigations. F-73-R-5. Idaho Department of Fish and

Game, Boise. ESA (U.S. Endangered Species Act of 1973), as amended, Pub. L. No. 93-205, 87 Stat. 884

(Dec. 28, 1973). Findlay, S. 1995. Importance of surface-subsurface exchange in stream ecosystems: the

hyporheic zone. Limnology and Oceanography 40:159–164. Firehammer, J. A., A. J. Vitale, S. H. Hallock, and T. Biladeau. 2012. Implementation of fisheries

enhancement opportunities on the Coeur d’Alene Reservation. Annual Report to the Bonneville Power Administration, Project 1990-044-00, Portland.

Fraser, J. M. 1989. Establishment of reproducing populations of brook trout after stocking of

interstrain hybrids in Precambrian Shield lakes. North American Journal of Fisheries Management 9:352–363.

Fredericks, J, M. Liter, M. Maiolie, R. Hardy, R. Ryan, D. Ayers, and C. Gidley. 2009. Fishery

management investigations, 2008 panhandle region report, IDFG 09-125. Idaho Department of Fish and Game, Boise.

Fredericks, J. 1999. Exotic fish species removal: Upper Priest Lake and Lightning Creek

drainages. Annual progress report, Grant No. E-20. Idaho Department of Fish and Game, Boise.

Fredericks, J. and J. Venard. 2001. Bull Trout exotic fish removal, project completion report.

Idaho Department of Fish and Game, Boise. Fredericks, J. P. Idaho Department of Fish and Game. Personal communication. 13 March,

2014. Fredericks, J., and N. Horner. 2002. Mountain lakes investigations, job performance report.

Idaho Department of Fish and Game, Boise. Fredericks, J., J. Davis, and N. Horner. 1997. Fisheries management investigations.1996

panhandle region report, IDFG 99-22. Idaho Department of Fish and Game, Boise. Fredericks, J., J. Davis, and N. Horner. 1999. Fisheries management investigations. 1998

panhandle region,IDFG 01-07. Idaho Department of Fish and Game, Boise. Fredericks, J., J. Davis, N. Horner, and C. Corsi. 2000. Fisheries management investigations,

1997 Progress Report. Idaho Department of Fish and Game, Boise. Fredericks, J., M. Maiolie, R. Hardy, R. Ryan, and M. Liter. 2013. Fishery management annual

report, 2011panhandle region, IDFG 11-110. Idaho Department of Fish and Game, Boise.

Page 210: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

197

Fredericks, J., M. Maiolie, R. Hardy, R. Ryan, M. Liter. 2013. Fishery management annual report, 2011 panhandle region, IDFG 12-110. Idaho Department of Fish and Game, Boise.

Gablehouse, D. W. 1984. A length-categorization system to assess fish stocks. North American

Journal of Fisheries Management 4:273–285. Garvey, J. E., R. A. Stein, R. A. Russell, and M. T. Bremigan. 2003. Exploring mechanisms

underlying Largemouth bass recruitment along environmental gradients. Pages 7–23 in Philipp, D. P., and M. S. Ridgway, editors. Black Bass: Ecology, Conservation, and Management. American Fisheries Society Symposium 31, Bethesda.

Giannico, G. R., and S. G. Hinch. 2003. The effect of wood and temperature on juvenile Coho

Salmon winter movement, growth, density, and survival in side-channels. River Research and Applications 19:219–231.

Gido, K. B., and J. H. Brown. 1999. Invasion of North American drainages by alien fish species.

Freshwater Biology 42:387–399. Goodnight, W. H., and G. R. Mauser. 1976. Fisheries management investigations. Job

Performance Report, F-71-R-4. Idaho Department of Fish and Game, Boise. Goodnight, W. H., and G. R. Mauser. 1978. Fisheries management investigations. Job

Performance Report, F-71-R-4. Idaho Department of Fish and Game, Boise. Goodnight, W. H., and G. R. Mauser. 1980. Fisheries management investigations. Job

Performance Report, F-71-R-4. Idaho Department of Fish and Game, Boise. . Gozlan, R. E., J. R. Britton, I. Cowx, and G. H. Copp. 2010. Current knowledge on nonnative

freshwater fish introductions. Journal of Fish Biology 76:751–786. Grunder, S. A., T. J. McArthur, S. Clark, and V. K. Moore. 2003. Idaho Department of Fish and

Game 2003 Economic Survey Report. Idaho Department of Fish and Game. Boise. Gulland, J. A. 1982. Why do fish numbers vary? Journal of Theoretical Biology 97:69–75. Guy, C. S., and D. W. Willis. 1995. Population characteristics of black crappies in South Dakota

waters: a case for ecosystem-specific management. North American Journal of Fisheries Management 15:754–765.

Hall, D. L. 1991. Growth, fecundity, and recruitment responses of stunted brook trout population

to density reduction. PhD dissertation. University of British Columbia, Vancouver, British Columbia.

Hall, T. J. 1986. Electrofishing catch per hour as an indicator of Largemouth Bass density in

Ohio impoundments. North American Journal of Fisheries Management 6:397–400. Hardy, R. S., and J. Fredericks. 2009. Fisheries management investigations, St. Joe River and

North Fork Coeur d’Alene River Snorkel Surveys, 2008 panhandle region report, IDFG 09-125. Idaho Department of Fish and Game, Boise.

Page 211: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

198

Hardy, R. S., and J. P. Fredericks. 2010. Fishery management investigations. Little North Fork Clearwater River fishery assessment, IDFG 10-12. Idaho Department of Fish and Game, Boise.

Hardy, R. S., D. Ayers, and J. Fredericks. 2009. Fishery management investigations, 2008

panhandle region high mountain lake investigations. Idaho Department of Fish and Game, Boise.

Hardy, R. S., R. G. Ryan, M. Liter, M. Maiolie, and J. P. Fredericks. 2010. Fishery Management

Investigations, 2009 panhandle region, IDFG 10-112. Idaho Department of Fish and Game, Boise.

Hardy, R., K. Carter-Lynn, and J. Fredericks. 2013. Fishery management investigations. 2011

panhandle report, IDFG 12-110. Idaho Department of Fish and Game, Boise. Hardy, R., R. Ryan, M. Liter, M. Maiolie, and J. Fredericks. 2010. Fishery management

investigations, 2009 panhandle report, IDFG 10-112. Idaho Department of Fish and Game, Boise.

Hassemer, P. F. 1984. Spawning ecology and early life history of kokanee (Oncorhynchus

nerka) in Couer d’Alene and Pend Oreille lakes, Idaho. Master’s thesis. University of Idaho, Moscow.

Hassemer, P. F., and B. E. Rieman. 1981. Observations of deepspawning kokanee on artificially

created spawning habitat. North American Journal of Fisheries Management 1:173–176. Havens, A. C., J. B. Murray, K J. Delaney, and K. J. Roth. 1987. Fishery Data Series No. 33.

Evaluation of enhancement efforts for rainbow trout, coho salmon, and chinook salmon in southcentral Alaska, 1986, F-10-2. Alaska Department of Fish and Game. Juneau.

Hayes, D. B., J. R. Bence, T. J. Kwak, and B. E. Thompson. 2007. Abundance, biomass, and

production in Analysis and interpretation of freshwater fisheries data, C. S. Guy and M. L. Brown, editors. American Fisheries Society, Bethesda, Maryland.

Henderson, M. A., and A. J. Cass. 2011. Effect of smolt size on smolt-to-adult survival for Chilko

Lake sockeye salmon (Oncorhynchus nerka). Canadian Journal of Fisheries and Aquatic Sciences 46:988–994.

High, B., K. A. Meyer, D. J. Schill, and E. R. J. Mamer. 2008. Distribution, abundance, and

population trends of Bull Trout in Idaho. North American Journal of Fisheries Management 28:1687–1701.

Hill, T. D., and D. W. Willis. 1994. Influence of water conductivity on pulsed AC and pulsed DC

electrofishing catch rates for Largemouth Bass. North American Journal of Fisheries Management 14:202–207.

Horak, D. 1995. Native and nonnative fish species used in state fisheries management

programs in the United States. Pages 61–67 in H. L. Schramm and R. G. Piper, editors. Use and Effects of Cultured Fishes in Aquatic Ecosystems, American Fisheries Society, Bethesda.

Page 212: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

199

Horner, N. J., M. A. Maiolie, and C. A. Robertson. 1989. Fisheries management investigations, Idaho Lowland Lake Investigations. Idaho Department of Fish and Game, Boise.

Hunt, L., W. Haider, and K. Armstrong. 2002. Understanding the fish harvesting decisions by

anglers. Human Dimensions of Wildlife 7: 75-89. IDFG (Idaho Department of Fish and Game). 2006. Idaho Comprehensive Wildlife Conservation

Strategy. As approved by the USDI Fish and Wildlife Service, National Advisory Acceptance Team. February 2006. Boise.

IDFG (Idaho Department of Fish and Game). 2012. Standard fish sampling protocol for lowland

lakes and reservoirs in Idaho. Idaho Department of Fish and Game, Boise. IDFG (Idaho Department of Fish and Game). 2013. Management plan for the conservation of

Westslope Cutthroat Trout in Idaho. Idaho Department of Fish and Game, Boise. IDFG (Idaho Department of Fish and Game). 2013. Fisheries management plan 2013-2018.

Idaho Department of Fish and Game, Boise. Irizarry, R. A. 1974. Survival, distribution, and use of Mysis relicta by game fish species in north

Idaho lakes, job performance report, VI-a. Idaho Department of Fish and Game, Boise. Isermann, D. A., and C. T. Knight. 2005. A computer program for age-length keys incorporating

age assignment to individual fish. North American Journal of Fisheries Management 25:1153–1160.

Isermann, D. A., M. H. Wolter, and J. J. Breeggemann. 2010. Estimating Black Crappie age: an

assessment of dorsal spines and scales as nonlethal alternatives to otoliths. North American Journal of Fisheries Management 30:1591–1598.

Isermann, D. A., W. L. McKibbin, and D. W. Willis. 2002. An analysis of methods for quantifying

crappie recruitment variability. North American Journal of Fisheries Management 22:1124–1135.

Johnson, B. M., P. J. Martinez, J. A. Hawkins, and K. R. Bestgen. 2008. Ranking predatory

threats by nonnative fishes in the Yampa River, Colorado, via bioenergetics modeling. North American Journal of Fisheries Management 28:1941–1953.

Kamil Bartoń. 2016. MuMIn: Multi-Model Inference. R package version 1.15.6. https://CRAN.R-

project.org/package=MuMIn. Kennedy, P., and K. A. Meyer. 2015. Westslope Cutthroat Trout Trends in abundance in Idaho.

Journal of Fish and Wildlife Management 6:305–317. Knapp, R. A., and K. R. Matthews. 1998. Eradication of nonnative fish by gill netting from a

small mountain lake in California. Restoration Ecology 6:207–213. Knapp, R. A., K. R. Matthews, and O. Sarnelle. 2001b. Resistance and resilience of alpine lake

fauna to fish introductions. Ecological Monographs 71:401–421.

Page 213: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

200

Knapp, R. A., P. S. Corn, D. E. Schindler. 2001a. The introduction of nonnative fish into wilderness lakes: good, intentions, conflicting mandates, and unintended consequences. Ecosystems 4:275–278.

Knight, A. 2009. Mountain lake investigations, job performance report. Idaho Department of Fish

and Game, Boise. Koch, J. D., and M. C. Quist. 2007. A technique for preparing fin rays and spines for age and

growth analysis. North American Journal of Fisheries Management 27:781–784. Koel, T. M., P. E. Bigelow, P. D. Doepke, B. D. Ertel, and D. L. Mahony. 2005. Nonnative Lake

Trout result in Yellowstone Cutthroat Trout decline and impacts to bears and anglers. Fisheries 30:10–19.

Koenig, M. 2012. Use of tiger muskellunge to remove brook trout from high mountain lakes. .

annual performance report, F-73-R-34. Idaho Department of Fish and Game, Boise. Koenig, M. 2012 Hatchery trout evaluations, IDFG 12-11. Idaho Department of Fish and Game,

Boise. Koenig, M, A. E. Butts, J. R. Kozfkay, J. Yates, and D. Downing. 2015. Fisheries management

investigations. Fisheries Management Annual Report, 15-102, Boise. Landres, P., S. Meyer, and S. Matthews. 2001. The Wilderness Act and fish stocking: an

overview of legislation, judicial interpretation, and agency implementation. Ecosystems 4:287–295.

Lewynsky, V. A. 1986. Evaluation of special angling regulations in the Coeur d’Alene River trout

fishery. M.S. Thesis. University of Idaho, Moscow. Lider, E. L. 2015. Personal communication. 25 August, 2015. Lininger, J. Idaho Department of Fish and Game. Personal communication. 6 July, 2015. Liter, M., J. Dupont, and N. Horner. 2008. Fisheries management investigations, 2005

panhandle region report. Idaho Department of Fish and Game, Boise. Liter, M., J. DuPont, and N. Horner. 2009. Fisheries Management Investigations, 2003

panhandle region report, IDFG 06-21. Idaho Department of Fish and Game, Boise. Loftus, A.J., W.W. Taylor, and M. Keller. 1988. An evaluation of Lake Trout (Salvelinus

namaycush) hooking mortality in the upper great lakes. Canadian Journal of Fisheries and Aquatic Science. 45: 1473-1479.

Love, R.H. 1971. Dorsal-aspect target strength of an individual fish. Journal of the Acoustic

Society of America 49:816-823. Maceina, M. J. 1997. Simple application of using residuals from catch-curve regressions to

assess year-class strength in fish. Fisheries Research 32:115–121. MacLennan, D.N. and E.J. Simmonds. 1992. Fishery Acoustics. Chapman and Hall, New York.

Page 214: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

201

Maiolie, M, and J. Fredericks. 2013. Regional fisheries management investigations, Coeur

d’Alene Lake fishery investigations, 2012 job performance report, IDFG 13-116. Idaho Department of Fish and Game, Boise.

Maiolie, M, and J. Fredericks. 2014. Regional fisheries management investigations, trout

surveys in the Coeur d’Alene and St. Joe Rivers, 2013 job performance report, IDFG 14-102. Idaho Department of Fish and Game, Boise.

Maiolie, M. A., W. Harryman, and W. J. Ament. 2004. Lake Pend Oreille fishery recovery

project, annual performance report 04-40. Idaho Department of Fish and Game, Boise. Maiolie, M., K. Carter-Lynn, J. Fredericks, R. Ryan, and M. Liter. 2013. Fishery management

investigations, 2012 panhandle region report, IDFG 13-116. Idaho Department of Fish and Game, Boise.

Maiolie, M., R. Hardy, M. Liter, R. Ryan, K. Cater-Lynn, J. Fredericks. 2011. Fishery

management investigation, 2010 panhandle region report, IDFG 11-117. Idaho Department of Fish and Game, Boise.

Margenau, T.L., P.W. Rasmussen, and J. M. Kampa. 1998. Factors affecting growth of northern

pike in small northern Wisconsin lakes. North American Journal of Fisheries Management 18:625-639.

Marnell, L. F. 1988. Status of the Westslope Cutthroat Trout in Glacier National Park, Montana.

Pages 61–70 in R. E. Gresswell, editor. Status and management of interior stocks of Cutthroat Trout. American Fisheries Society. Symposium 4, Bethesda.

Martinez, P.J.,P.E. Bigelow, M.A. Deleray, W.A. Fredenberg, B.S. Hansen, N.J. Horner, S.K.

Lehr, R.W. Schneidervin, S.A. Tolentino, and A.E. Viola. 2009. Western lake trout woes. Fisheries, 34:9.

Matthews, K. R., and R. A. Knapp. 1998. Eradication of nonnative fish by gill netting from a

small mountain lake in California. Restoration Ecology 6:207–213. Matthews, K. R., and R. A. Knapp. 1999. A study of high mountain lake fish stocking effects in

the U.S. Sierra Nevada Wilderness. Intermountain Journal of Wilderness 5:24–26. Mauser, G. 1978. Hayden Lake management plan. Idaho Fish and Game, Boise. Mauser, G. R, and N. Horner. 1982. Fishery management investigations, job performance

report, F-71-R-6. Idaho Department of Fish and Game, Boise. Mauser, G.R, R.W. Vogelsang, and C.L. Smith. 1988. Lake and Reservoir Investigations:

Enhancement of trout in large north Idaho lakes; Job Performance Report, Project F-73-R-9. Idaho Department of Fish and Game, Boise.

Mauser, G.R. 1986. Enhancement of trout in large north Idaho lakes, job performance report, F-

73-R-8. Idaho Department of Fish and Game, Boise.

Page 215: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

202

Mauser, G.R., R.W. Vogelsang, and C.L. Smith. 1988. Enhancement of trout in large north Idaho lakes, job performance report, F-73-R-10. Idaho Department of Fish and Game, Boise.

McDonald, D.G. 1969. Post-tagging mortality of pike, perch, walleye and rainbow trout following

dart tag application. Alberta Department of Lands and Forests, Fish and Wildlife Division Management Report 7, Edmonton.

Meyer, K. A., F. S. Elle, J. A. Lamansky Jr., E. R. J. M. Mamer, and A. E. Butts. 2012. A reward-

recovery study to estimate tagged-fish reporting rates by Idaho anglers. North American Journal of Fisheries Management 32:696–703.

Meyer, K.A. and D.J. Schill. 2014. Use of a statewide angler tag reporting system to estimate

rates of exploitation and total mortality for Idaho sport fish. North American Journal of Fisheries Management 34:1145-1158.

Meyer, K.A., S.F. Elle, J.A. Lamansky Jr., E.R. J.M. Mamer, and A.E. Butts. 2012. A reward-

recovery study to estimate tagged-fish reporting rates by Idaho anglers. North American Journal of Fisheries Management 32:696-703.

MFWP (Montana Fish, Wildlife, and Parks). 2012. Fort Peck Reservoir Fisheries Management

Plan 2012–2022. Montana Fish, Wildlife, and Parks, Fisheries Management. Glasgow. Mink, L. L., R. E. Williams, and A. T. Wallace. 1971. Effects of industrial and domestic effluents

on the Coeur d’Alene River basin. Idaho Bureau of Miners and Geology. Pamphlet 140. Moscow.

Miranda, L. E. 2009. Standardized electrofishing power for boat electrofishing. Pages 223–230

in S. A. Bonar, W. A. Hubert, and D. W. Willis, editors. Standard methods for sampling North American freshwater fishes. American Fisheries Society, Bethesda.

Miranda, L. E. and P. W. Bettoli. 2007. Mortality. Pages 229–277 in C. S. Guy and M. L. Brown,

editors. Analysis and interpretation of freshwater fisheries data. American Fisheries Society, Bethesda.

Muhlfeld, C. C., D. H. Bennett, R. K. Steinhorst, B. Marotz, and M. Boyer. 2008. Using

bioenergetics modeling to estimate consumption of native juvenile salmonids by nonnative Northern Pike in the upper Flathead River system, Montana. North American Journal of Fisheries Management 28:636–648.

Muhlfeld, C. C., D. H. Bennett, R. K. Steinhorst, B. Marotz, and M. Boyer. 2008. Using

bioenergetics modeling to estimate consumption of native juvenile salmonids by nonnative Northern Pike in the upper Flathead River system, Montana. North American Journal of Fisheries Management 28:636–648.

Nelson, L., J.A. Davis, and N. Horner. 1997. Fishery management investigations, 1995

panhandle region report, IDFG 99-22. Idaho Department of Fish and Game, Boise. Neumann, R. M. and M. S. Allen. 2007. Size Structure. Pages 37–421 in C. S. Guy and M. L.

Brown, editors. Analysis and interpretation of freshwater fisheries data. American Fisheries Society, Bethesda.

Page 216: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

203

Neumann, R. M., C. S. Guy, and D. W. Willis. 2012. Length, weight, and associated structural

indices. Pages 637–670 in A. V. Zale, D. L. Parrish, and T. M. Sutton, editors. Fisheries Techniques, 3rd Edition. American Fisheries Society, Bethesda, Maryland.

Neumann, R.M. and D.W. Willis. 1995. Seasonal variation in gill-net sample indexes for

Northern Pike collected from a glacial prairie lake. North American Journal of Fisheries Management 15:838-844.

Ng, E. L. 2015. Population dynamics and trophic ecology of nonnative Lake Trout in Priest Lake,

Idaho. Masters Thesis. University of Idaho, Moscow. Ng, E. L., J. P. Fredericks, and M. C. Quist. 2015. Effects of gill-net trauma, barotrauma, and

deep release on post-release mortality of Lake Trout. Journal of Fish and Wildlife Management 6:265–277.

Olson, M. H. 1996. Ontogenetic niche shifts in largemouth bass: variability and consequences

for first-year growth. Ecology 77:179–190. Parker, B. R., D. W. Schindler, D. B. Donald, and R. S. Anderson. 2000. The effects of stocking

and removal of a nonnative salmonid on the plankton of an alpine lake. Ecosystems 4:334–345.

Peterson, D. P., B. E. Reiman, M. K. Young, and J. A. Bramer. 2010. Modeling predicts that

redd trampling by cattle may contribute to population declines of native trout. Ecological Applications 20:954–966.

Pettit, S. W., and R. L. Wallace. 1975. Age, growth, and movement of Mountain Whitefish

Prosopium Williamsoni (Girard), in the North Fork Clearwater River, Idaho. Transactions of the American Fisheries Society 1:68–76.

Pflieger, W. L. 1975. The fishes of Missouri. Cornell Univeristy, Ithaca. Pierce, R.B. and C.M. Tomcko. 1995. Exploitation of Northern Pike in seven small north-central

Minnesota lakes. North American Journal of Fisheries Management 15:601-609. Pilliod, D. S., and C. R. Peterson. 2000. Evaluating effects of fish stocking on amphibian

populations in wilderness lakes. USDA Forest Service Proceedings 5:328–335. Pister. E. P. 2001. Wilderness fish stocking: history and perspective. Ecosystems 4:279–286. Pratt, K.L. 1984. Pend Oreille trout and char life history study. Idaho Department of Fish and

Game, Boise. Quigley, T. M., R. W. Haynes, and R. T. Graham. 1996. Integrated scientific assessment for

ecosystem management in the interior Columbia basin and portions of the Klamath and Great Basins. General Technical Report PNW-GTR-382. United States Forest Service, Pacific Northwest Research Station. Portland.

Quist, M. C. 2007. An evaluation of techniques used to index recruitment variations and year-

class strength. North American Journal of Fisheries Management 27:30–42.

Page 217: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

204

Quist, M. C., and J. R. Speigel. 2010. Population demographics of catostomids in large river

ecosystems: effects of discharge and temperature on recruitment dynamics and growth. River Research and Applications 28:1567–1586.

Quist, M. C., M. A. Pegg, and D. R. Devries. 2012. Age and Growth. Pages 677–731 in A. V.

Zale, D. L. Parrish, and T. M. Sutton, editors. Fisheries techniques, 3rd edition. American Fisheries Society, Bethesda.

Quist, M. C., M. A. Pegg, and D. R. Devries. 2012. Age and Growth. Pages 677–731 in A. V.

Zale, D. L. Parrish, and T. M. Sutton, editors. Fisheries techniques, 3rd edition. American Fisheries Society, Bethesda.

R Core Team. 2015. R: A language and environment for statistical computing. R Foundation for

Statistical Computing, Vienna, Austria. URL https://www.R-project.org/. R Development Core Team. 2012. R: a language and environment for statistical computing. R

Foundation for Statistical Computing, Vienna, Austria. Available: www.R-project.org. (February 2012).

Rahel, F. J. 2000. Homogenization of fish faunas across the United States. Science 288:854–

856. Rankel, G. L. 1971. An appraisal of the cutthroat trout fishery of the St. Joe River. Master’s

Thesis, University of Idaho, Moscow. Rich, B. A. 1992. Population dynamics, food habits, movement, and habitat use of northern pike

in the Coeur d’Alene River system. M.S. Thesis. University of Idaho, Moscow. Rich, B.A. 1992. Population dynamics, food habits, movement, and habitat use of northern pike

in the Coeur d’ Alene Lake system, Idaho. Completion Report F-73-R-14. Idaho Department of Fish and Game, Boise.

Richards, S. A. 2005. Testing ecological theory using the information-theoretic approach:

examples and cautionary results. Ecology 86:2805–2814. Ricker, W. E. 1975. Computation and interpretation of biological statistics of fish populations.

Fisheries Research Board of Canada Bulletin 191. Rieman, B. E. 1987. Fishing and population dynamics of largemouth bass (Micropterus

salmoides) in select northern Idaho lakes. Ph.D. dissertation. University of Idaho, Moscow.

Rieman, B. E. 1992. Status and analysis of salmonids fisheries: kokanee salmon population

dynamics and kokanee salmon monitoring guidelines, job performance report, F-73-R-14. Idaho Department of Fish and Game, Boise.

Rieman, B. E., and D. Meyers. 1991. Kokanee population dynamics, job completion report, F-

73-R-14. Idaho Department of Fish and Game, Boise.

Page 218: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

205

Rieman, B. E., and L. LaBolle. 1980. Lake and reservoir investigations. 1996 job performance report, IDFG F-73-R-2. Idaho Department of Fish and Game, Boise.

Rummer, J. L. and W. A. Bennett. 2005. Physiological effects of swim bladder overexpansion

and catastrophic decompression on Red Snapper. Transactions of the American Fisheries Society. 134: 1457-1470.

Ruzycki, J. R., D. A. Beauchamp, and D. L. Yule. 2003. Effects of introduced Lake Trout on

native cutthroat trout in Yellowstone Lake. Ecological Applications 13:23–37. Ryan, R., M. Maiolie, K. Yallaly, C. Lawson, and J. Fredericks. 2014 Fisheries management

investigations, 2013 panhandle region report, IDFG 14-102. Idaho Department of Fish and Game, Boise.

Schneidervin, R. W., and W. A. Hubert. 1986. A rapid technique for otolith removal from

salmonids and catostomids. North American Journal of Fisheries Management 6:287. Schnell, K. 2014. Predicted effects of angler harvest on largemouth bass populations in northern

Wisconsin lakes. MS Thesis. University of Wisconsin-Steven’s Point, Steven’s Point. Schriever, E. B., and P. D. Murphy. 2012. Utilization of tiger muskellunge for controlling self-

sustaining populations of introduced brook trout in mountain lakes. Regional Fisheries Management Investigations. Idaho Department of Fish and Game. Boise.

Scott, W. B., and E. J. Crossman. 1973. Freshwater fishes of Canada. Fisheries Research

Board of Canada, Ottawa. Seber, G. A., and C. J. Wild. 2006. Nonlinear regression. John Wiley and Sons, Inc., New York.

800 pp. Shepard, B. B., B. E. May, and W. Urie. 2005. Status and conservation of westslope cutthroat

trout within the western United States. North American Journal of Fisheries Management 25:1426–1440.

Simberloff, D. 2001. Biological invasions—how are they affecting us, and what can we do about

them?. Western North American Naturalist 61:308–315. Simmonds, J., and D. MacLennan. 2005. Fisheries acoustics theory and practice. Blackwell

Science, Oxford, United Kingdom. Sissenwine, M. P., and J. G. Shepherd. 1987. An alternative perspective on recruitment

overfishing and biological reference points. Canadian Journal of Fisheries and Aquatic Sciences 44:87–110.

Slipke, J. W., and Maceina, M. J. 2014. Fishery analyses and modeling tools (FAST).

Department of Fisheries and Allied Aquacultures, Auburn University, AL. Soltero, R. A., and J. A. Hall. 1984. Water Quality assessment of Spirit Lake, Idaho. MS Thesis.

Eastern Washington University, Cheney.

Page 219: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

206

Stevens, B. S., and J. M. DuPont. 2011. Summer use of side-channel thermal refugia by salmonids in the North Fork Coeur d’Alene River, Idaho. North American Journal of Fisheries Management 31:683–692.

Strong, C. C., and C. S. Webb. 1970. White pine: king of many waters. Mountain Press

Publishing Co., Missoula. Swain, D. P., A. F. Sinclair, and J. M. Hanson. 2007. Evolutionary response to size-selective

mortality in an exploited fish population. Proceedings of the Royal Society B 274:1015–1022.

Taniguchi, N. 2003. Genetic factors in broodstock management for seed production. Reviews in

Fish Biology and Fisheries 13:177–185. Teuscher, D. 1999. Zooplankton Quality Index. Hatchery Trout Evaluations. Job Performance

Report F-73-R-21. Idaho Department of Fish and Game. Boise, Idaho. Thompson, P. D., and F. J. Rahel. 1996. Evaluation of depletion-removal electrofishing of Brook

Trout in small Rocky Mountain streams. North American Journal of Fisheries Management 16:332–339.

Thurow, R. F. 1994. Underwater methods for study of salmonids in the Intermountain West.

General Technical Reports INT-GTR-307. Ogden, Utah: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 28p.

Thurow, R. F. 1994. Underwater methods for study of salmonids in the Intermountain West.

General Technical Reports INT-GTR-307. Ogden, Utah: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 28p.

U.S. Office of the Federal Register. 1998. Endangered and threatened wildlife and plants; 90-

day finding and commencement of status review for a petition to list the Westslope Cutthroat Trout as threatened. Federal Register 63:111 (10 June 1998):31691–31693.

U.S. Office of the Federal Register. 2003. Endangered and threatened wildlife and plants:

reconsidered finding for an amended petition to list the Westslope Cutthroat Trout as threatened throughout its range. Federal Register 68:152 (7 August 2003):46989–47009.

Vehanen, T., P. Hyvarinen, K. Johansson, and T. Laaksonen. 2006. Patterns of movement of

adult Northern Pike (Esox Lucius L.) in a regulated river. Ecology of Freshwater Fishes 15: 154-160.

Vitale, A. J., D. W. Chess, D. S. Lamb, and M. H. Stranger. 2004. Implementation of fisheries

enhancement opportunities on the Coeur d’Alene reservation. Coeur d’Alene Tribe Department of Natural Resources Fisheries Program, Plummer.

von Bertalanffy, L. 1938. A quantitative theory of organic growth (Inquiries on growth laws. II).

Human Biology 10:181–213.

Page 220: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

207

Wahl, N.C., A. M. Dux, M. R. Campbell, W. J. Ament, and W. Harryman. 2015. Lake Pend Oreille research, 2012 annual progress report, IDFG 15-04. Idaho Department of Fish and Game, Boise.

Wallace, R. L., and D. W. Zaroban. 2013. Native fishes of Idaho. American Fisheries Society,

Bethesda. Walrath, J. 2013. Population dynamics and trophic ecology of Northern Pike and Smallmouth

Bass in Coeur d’Alene Lake: Implications for the conservation of Westslope Cutthroat Trout. Thesis: College of Graduate Studies, University of Idaho.

Walrath, J. D. 2013. Population dynamics and trophic ecology of Northern Pike and Smallmouth

Bass in Coeur d’Alene Lake: implications for the conservation and management of Westslope Cutthroat Trout. Master’s thesis. University of Idaho, Moscow.

Walrath, J. D., M. C. Quist, and J. A. Firehammer. 2015. Population structure and dynamics of

Northern Pike and Smallmouth Bass in Coeur d’Alene Lake, Idaho. Northwest Science 89:280–296.

Walrath, J. D., M. C. Quist, and J. A. Firehammer. 2015. Trophic ecology of nonnative Northern

Pike and their effect on conservation of Westslope Cutthroat Trout. North American Journal of Fisheries Management 35:158–177.

Watkins C. J., Ryan, R. G., J. P. Fredericks, K. Yallaly, and K. Bouwens. In review. Fishery

management investigations, 2014 panhandle region report. Idaho Department of Fish and Game, Boise.

Watson, G., and T. W. Hillman. 1997. Factors affecting the distribution and abundance of Bull

Trout: an investigation at hierarchical scales. North American Journal of Fisheries Management 17:237–252.

Wege, G.J. and R. O. Anderson, 1978. Relative weight (Wr) a new index of condition for

largemouth bass. Pgs 79-91 in G. Novinger and J. Dillard editors. New approaches to the management of small impoundments. American Fisheries Society, Bethesda, MD.

Wersal, R. M., J. D. Madsen, T. E. Woolf, and N. Eckberg. 2010. Assessment of herbicide

efficacy on Eurasian Watermilfoil and impacts to the native submersed plant community in Hayden Lake, Idaho, USA. Journal of Aquatic Plant Management 48:5–11.

Wilde, G. R., 2009. Does venting promote survival of released fish. Fisheries 34:1; 20-28. Winter, J. D. 1977. Summer home range movements and habitat use by four largemouth bass

in Mary Lake, Minnesota. Transactions of the American Fisheries Society 106:323–330. (WSI) Watershed Sciences, Inc. 2007. Airborne thermal infrared remote sensing Coeur d’Alene

River, Idaho. Coeur d’Alene, Idaho: U.S. Department of Agriculture, Forest Service. 22p. Zippin, C. 1958. The removal method of population estimation. Journal of Wildlife Management.

22(1):82-90.

Page 221: IDAHO DEPARTMENT OF FISH AND GAME FISHERY … · 2020. 3. 12. · IDAHO DEPARTMENT OF FISH AND GAME . FISHERY MANAGEMENT ANNUAL REPORT . Virgil Moore, Director . October 2018 . IDFG

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Prepared By:

Approved By:

IDAHO DEPARTMENT OF FISH AND GAME

Rob Ryan

Jeff Dillon Regional Fishery Biologist State Fishery Manager

Carson Watkins

James P. Fredericks Regional Fishery Biologist Chief of Fisheries

Andy Dux Regional Fishery Manager

Kenneth Bouwens Regional Fishery Biologist

Dan Kaus Fishery Technician

Elizabeth Ng University of Idaho