CHAPTER 2 MONITORING PROGRAM

CHAPTER 2

MONITORING PROGRAM This chapter of the OLAP report includes routine data collection of physical and chemical limnology, phytoplankton, zooplankton, and fish. This work has been conducted on an annual basis to ensure that a consistent, long term database is established so that trends in water chemistry, plankton, zooplankton, and fish can be tracked. Data collected by this set of activities allows OLAP workers to understand changes in production and the interrelationships between the trophic levels. Standardized sampling protocols also allow for direct comparisons from year to year as well as comparisons with other large lake systems that also have similar monitoring programs. Mysid densities and annual biomass estimates have been invaluable for the developing mysid fishery.

Okanagan Lake Action Plan – Year 10 Chapter 2 – Page 63

PHYSICAL AND CHEMICAL LIMNOLOGY OF OKANAGAN LAKE

Year 10, 2005

Rowena Rae1 and Andrew Wilson2

INTRODUCTION The limnology of Okanagan Lake has been intensively monitored since the inception of the Okanagan Lake Action Plan (OLAP) in 1996. OLAP uses the data to support its objective of recovering wild kokanee in the lake. Limnological data provides information about the lake’s trophic status, biological relationships, and limiting factors. The importance of limnological information for managing Okanagan Lake has long been recognized (Stockner and Northcote 1974; Ashley et al. 1998), and data have been collected on the lake for over 20 years, although measurements were generally limited to the spring and fall. Since 1973, the Ministry of Environment has monitored water quality and other limnological parameters to determine nutrient status and the impact of treated effluent discharge. The trends and ongoing sampling program are presented by Jensen (in Ashley et al. 1999). Data collected monthly by OLAP add to the existing database, allow for annual comparisons, and increase the understanding of in-lake processes. Monthly measurements and samples have now been collected by OLAP for a 10 year period (1996-2005). Physical characteristics are examined by depth profiles of temperature, oxygen, and Secchi depth measured at five stations along the length of Okanagan Lake. Chemical characteristics are analyzed by phosphorus and nitrogen measurements at the same stations. Biological characteristics are determined through the analysis of phytoplankton chlorophyll a, phytoplankton species abundance and composition, and invertebrate species abundance and composition (including cladoceran and copepod zooplankton and the freshwater opossum shrimp, Mysis relicta). Water chemistry and biological samples are taken to obtain a vertical profile at each sampling station; each profile includes one sample from an integrated water column of 0-10 metres and one discrete sample from each of 20 and 45 metres. In 2005, primary productivity measurements were conducted at two stations (north and south) in early September. In the first phase (1996-2001) of OLAP, results indicated that kokanee stock decline is due to both reduced spawning habitat and low in-lake survival (Ashley et al. 1999; Andrusak et al. 2001). Limnological assessments of Okanagan Lake suggested that an imbalance of nitrogen and phosphorus nutrients may be responsible for a trophic bottleneck that contributes to low in-lake survival of kokanee (Andrusak et al. 2002). In

1 Sumac Writing and Editing, Summerland, BC. 2 Fisheries Stock Assessment Biologist, Ministry of Environment, Province of BC, 102 Industrial Place,

Penticton, V2A 7C8.

Okanagan Lake Action Plan – Year 10 Chapter 2 - Page 65

2005, water chemistry samples continued to be collected and analyzed specifically to determine the seasonal dynamics of nitrogen and phosphorus. This report summarizes the physical, chemical, and chlorophyll a data collected in 2005. Measurements from previous years are discussed in relation to this data, and whenever possible, previous years data are included in tables and graphs. However, the number of years shown is restricted for clarity in several of the graphs. Previous years data can be found in earlier OLAP annual reports. Analysis is presented in this OLAP report of the 2005 phytoplankton community by Stockner, primary productivity by Harris, and zooplankton and M. relicta by Rae and Vidmanic. MATERIALS AND METHODS Physical and chemical data are collected at established OLAP sampling sites simultaneously with the collection of phytoplankton, zooplankton, and M. relicta samples (see Maps 1 and 2 in the Introduction of this OLAP report). Sampling has been conducted from April or May to November in 1997-2005, with additional sampling in July to October of 1996, and during the winter (February) of 1997-1999 and 2003-2005. Samples have been collected from up to seven stations, but consistently from five stations (OK 1, OK 3, OK 6, OK 7, OK 8), with samples collected seasonally from OK 4. In 2003, the epilimnion was examined in more detail during July and September by taking discrete depth samples over the 0-15 m depth range. These data are available in Andrusak et al. (2004) but this sampling was not repeated in either 2004 or 2005. Vertical profiles of water temperature and dissolved oxygen concentration were measured at each station with a YSI digital oxygen-temperature meter. Readings were taken at 2 m intervals from 0-20 m and then at 4 m intervals from 20-40 m. A standard 20 cm Secchi disk was used to measure relative water clarity at each station. The depth recorded was the mean of the point where the disk disappears from vision upon lowering and reappears upon raising.


Table 1. Okanagan Lake Action Plan limnological sampling sites, 1996-2005.

Site IDa Site No. Site Name Depth (m)

OK 1 0500454 South of Prairie Creek 90

OK 3 E223295 Opposite Rattlesnake Island 140

OK 4b 0500236 Downstream of Kelowna Sewage Treatment Plant 90

OK 5 0500456 Upstream of Kelowna Sewage Treatment Plant 146

OK 6 0500730 North of Okanagan Centre 225

OK 7 E206611 Vernon Arm 90

OK 8 0500239 Centre of Armstrong Arm 55

a See Map 2 (in Introduction of this OLAP annual report). b Sampled seasonally; April, August, and November.

At each station, water chemistry samples were taken from three depths. A Van Dorn sample bottle was used to obtain discrete water samples at 20 m and 45 m depths and a tygon tube with a 2.5 cm inside diameter was used to obtain an integrated sample from the surface to a depth of 10 m. Water samples were placed in 1 L polyethylene bottles, stored in a cooler with ice, and shipped within 24 hours to Maxxam Analytics Inc. in Burnaby, BC. (Note that from 1996-2001, water chemistry samples were analyzed at the Pacific Environmental Centre, Environment Canada, North Vancouver.) Samples were analyzed for total nitrogen (TN), ammonia-nitrogen (NH3+NH4-N), nitrate-nitrogen (NO2+NO3-N, or NO2+3), total phosphorus (TP), orthophosphorus or soluble reactive phosphorus (SRP), and total dissolved phosphorus (TDP). In 1996, pH and reactive silica concentrations were also measured (McEachern in Ashley et al. 1998), but these analyses have not been repeated in subsequent years. Following collection in the field, samples for SRP were passed through a filter with a pore size of 0.45 µm. Chlorophyll a concentrations were determined by filtering a portion of the 0-10 m integrated sample through a filter with 0.45 µm pore size. At the lab, the filters were placed in centrifuge tubes with 90% buffered acetone and sonicated to rupture the algal cells and homogenize the filters. Chlorophyll a concentrations were then calculated from formulae using the absorbance of the supernatant at specific wavelengths. All data are on file at the BC Ministry of Environment office in Penticton. The limnological sampling methods on Okanagan Lake have remained consistent since 1996. Because of the low nutrient concentrations in Okanagan Lake at certain times of year, water samples frequently have concentrations below the detection limit of the machines used in analysis (Table 2). In these cases, one half of the detection limit is used when graphing the data.


Table 2. Detection limits for water chemistry analyses performed by Maxxam

Analytics Inc.

Analysis Detection Limit

Total nitrogen (TN) Ammonia nitrogen (NH3+4) Nitrate nitrogen (NO2+3) Total phosphorus (TP) Soluble reactive phosphorus (SRP) Total dissolved phosphorus (TDP) Chlorophyll a

0.02 mg·L-1

0.005 mg·L-1

0.002 mg·L-1

0.002 mg·L-1

0.001 mg·L-1

0.002 mg·L-1

0.5 µg·L-1

Quality control samples were submitted to the water chemistry lab along with lake water samples from each sampling session. Three replicate samples of de-ionized water were submitted and analyzed following the same methods as for lake water samples. In 2005, all water chemistry parameters were consistently below detection limits in the control samples. RESULTS AND DISCUSSION Physical Limnology Okanagan Lake is classified as a monomictic lake, mixing from late fall to early spring (Stockner and Northcote 1974; McEachern in Ashley at al. 1998). February sampling showed an isothermal water column close to 4 ºC. When spring sampling began in April 2005, surface warming and thermal stratification of the water column had begun in Armstrong Arm (OK 8) but not in the main basins of the lake (Fig. 1). Surface warming is often detected earlier in Armstrong Arm than in the main lake. In previous years, especially 2001 and 2004, significant surface warming had already occurred by April, but the sampling dates in these years were later in the month. In 2005, northern sites (OK 6 and OK 8) warmed more rapidly and attained slightly higher surface temperatures than the southern sites (OK 3). Surface water temperatures in the main body of Okanagan Lake tend to peak around 20ºC during July, and this was the case in 2005. In some years, such as 2003, the July peak has reached 25ºC at some sites. In 2005, the epilimnion at OK 6 extended to a depth of 10-12 m with the thermocline between approximately 12-18 m depth (determined visually from temperature profiles). The thermocline at OK 3 was poorly defined in 2005. Although OK 3 usually has a more distinct thermocline, the 2005 profiles fit within the range of thermal regimes measured in previous years. Temperatures have been consistently near 5-6ºC at 40 m throughout OLAP’s monitoring. Epilimnetic temperatures in 2005 decreased to 14-16ºC by October as the epilimnion and thermocline increased in depth (Fig. 1). By November, the lake usually has isothermal

Okanagan Lake Action Plan – Year 10 Chapter 2 - 8

conditions, although temperature profile measurements were not made in November 2005. In Armstrong Arm (OK 8), the thermal regime tends to differ from the main lake. The epilimnion is generally 3-5 m shallower throughout the stratification period, and this was observed again in 2005 (Fig. 1). As noted above, thermal stratification usually begins earlier in the spring in Armstrong Arm compared with the rest of the lake and, therefore, the water column mixes for a shorter time during winter and the hypolimnion is isolated for a longer time over summer. Water temperature at 40 m depth can also be a few degrees warmer than in the main lake. Dissolved oxygen profiles recorded in the main body of the lake have generally shown concentrations increasing very slightly with depth during summer, with concentrations >7.5 mg·L-1 (Fig. 2). These are orthograde profiles and typical of lakes with low productivity (Wetzel 2001). In 2005, oxygen profiles were similar to those measured in previous years, except for 2003 when an oxygen maxima of 14-15 mg·L-1 was evident at a depth of 16 m at stations OK 1, OK 3, and OK 6. A clinograde profile, which shows a decrease in oxygen concentration below the epilimnion and are typical of more productive lakes (Wetzel 2001), was evident in Armstrong Arm (OK 8) in 2005 and in previous years. At this station, concentrations in July were <8 mg·L-1 at 40 m depth, compared to values >10 mg·L-1 at the main lake stations. By October in 2005, as in previous years, oxygen concentrations were <2 mg·L-1 at 40 m and <1 mg·L-1 deeper in the water column. These low concentrations persist until turnover later in the fall. The Armstrong Arm is a shallow basin and has experienced high nutrient loading from human activities (Bryan 1990; Jensen in Ashley et al. 1999). It exhibits higher seasonal nutrient concentrations compared to the main lake (see next section), and therefore has greater algal and zooplankton production. When these organisms die and sink to the sediment, they are decomposed by bacteria that consume oxygen (Wetzel 2001). Since oxygen cannot be replenished in the hypolimnion during thermal stratification, it remains depleted in the hypolimnion until turnover in November. McEachern (in Ashley et al. 1999) discussed the implications of low seasonal oxygen concentrations on macrozooplankton populations in Armstrong Arm. The mysid population density declines to near zero at OK 8 each fall (Rae and Vidmanic, in this OLAP report), most likely because mysids are sensitive to low oxygen concentrations in the deeper water yet want to avoid the warmer temperatures and higher light intensity in the upper water column. Therefore, the mysids either migrate out of the area, as has been noted elsewhere (Martinez and Bergersen 1991), or they are preyed upon by fish as they rise in the water column. In 2005, water clarity measured by Secchi disk was comparable to measurements made in previous years (Fig. 3, Table 3). Since 1997, Secchi disk transparencies during summer stratification (late April/early May to October) have been similar from year to year and between the south (OK 1-3) and north basins (OK 6-7) of the lake, with an


average of 6.5 m (Table 3). The summer values were highest in 1998 and lowest in 1999. Recent values are part of a longer term decrease in water clarity since highs around 12 m were recorded in the late 1980s (Jensen in Ashley et al. 1999). The long term data set is based on fall values, which have been similar (within 0.5 m) to the summer averages reported here. The seasonal pattern in 2005 was also similar to previous years. In 2005, water clarity decreased from a high of 11 m in February (not measured in each year shown on Fig. 3) to <5 m in early May when the spring phytoplankton bloom occurred. This was followed by an increase in water clarity to about 7 m through the summer and early fall (Fig. 3). Armstrong Arm (OK 8) has water clarity averaging 3.8 m, which is about half the values measured in the rest of Okanagan Lake (Table 3). Table 3. Average Secchi disk depth in metres from late April/early May to October for

the south (OK 1-3), north (OK 6-7) and Armstrong Arm (OK 8) of Okanagan Lake, 1997-2005.

Year Station Main Lake Armstrong Arm

OK 1-3 OK 6-7 Average OK 8 1997 6.7 6.1 6.4 3.1 1998 8.1 7.1 7.6 3.4 1999 5.8 5.8 5.8 3.1 2000 6.0 6.5 6.2 3.5 2001 6.7 6.6 6.7 4.2 2002 6.2 6.4 6.3 3.7 2003 6.4 6.7 6.6 4.9 2004 7.1 6.8 6.9 4.7 2005 6.5 6.3 6.4 3.8

Average 6.6 6.5 6.5 3.8

Chemical Limnology The pH of water in Okanagan Lake was measured in 1996 at 7.6-8.6, indicating that the lake is slightly alkaline and within the typical range for lakes. Silica concentrations in the summer of 1996 ranged from 6-10 mg·L-1 with very little temporal variation (McEachern in Ashley et al. 1998) and are well above 0.5 mg·L-1, which is the level considered to limit diatom algae (Wetzel 2001). Spring TN and TP Total nitrogen (TN) and total phosphorus (TP) in the main body of Okanagan Lake averaged 0.22 and 0.006 mg·L-1, respectively, during spring (April) in the nine years from 1997-2005 (Table 4). TN values are comparable between the south and north basins of the lake, but phosphorus usually increases from the south (OK 1-3) to the north (OK 6-7). Values of both TN and TP are higher at OK 8 in the Armstrong Arm (Table 4), as has been noted in the past (Jensen in Ashley et al. 1999). In this basin, spring values averaged 0.27 mg·L-1 for TN and 0.018 mg·L-1 for TP, although TP in the past three years has been one third to one half of TP in 1997-1999 (Table 4). The


higher concentrations in Armstrong Arm compared with the main lake have been attributed to past sewage disposal practices and internal recycling of nutrients (Jensen in Ashley et al. 1999). Inter-annual spring TP variation in the main lake ranged from a high of 0.012 mg·L-1 in 1997 to a low of 0.004 mg·L-1 measured in 1998, 2003, and 2004. TN ranged from 0.25 mg·L-1 in 2000 to 0.18 mg·L-1 in 2001 (Table 4). In 2005, spring TN was at its highest concentration since 2000, and TP was the same in the south (OK 1-3) and slightly higher in the north (OK 6-7) than it had been in previous years. Nevertheless, the overall trends of TN and TP in Okanagan Lake remain the same. TP values have been decreasing steadily since 1996 (Fig. 4A), while no significant change has occurred for TN (Fig. 4B). A period of relatively high values recorded in 1995-1997 was associated with a series of wet years and increased runoff (Jensen in Ashley et al. 1999). Since 2003, dry conditions and low snowpacks have reduced the amount of runoff from the watershed, thus decreasing nutrient loading to the lake. Table 4. Concentrations of total nitrogen and total phosphorus in April for the south

(OK 1-3), north (OK 6-7) and Armstrong Arm (OK 8) of Okanagan Lake. Values are the average of the 0-10 m composite, 20 m, and 45 m samples; units in mg·L-1.

Station Variable Year

OK 1-3 OK 6-7 Main Lake Average

Armstrong Arm OK 8

Total Nitrogen 1997 0.21 0.22 0.22 0.47 1998 0.24 0.20 0.22 0.30 1999 0.24 0.24 0.24 0.25 2000 0.24 0.25 0.25 0.30 2001 0.20 0.17 0.18 0.20 2002 0.21 0.21 0.21 no data 2003 0.21 0.20 0.21 0.20

2004 0.20 0.20 0.20 0.19 2005 0.25 0.25 0.25 0.21 Average 0.22 0.21 0.22 0.27 Total Phosphorus 1997 0.010 0.013 0.012 0.045 1998 0.002 0.006 0.004 0.019 1999 0.007 0.011 0.009 0.022 2000 0.007 0.008 0.007 0.013 2001 0.005 0.007 0.006 0.012 2002 0.004 0.006 0.005 no data 2003 0.004 0.005 0.004 0.011 2004 0.003 0.004 0.004 0.010 2005 0.003 0.006 0.005 0.009 Average 0.005 0.007 0.006 0.018


Nitrogen In 2005, TN concentrations in the epilimnion were, on average, 0.01-0.02 mg·L-1 higher than in 2003 and 2004 (Fig. 5). However, the 2005 values were within the relatively stable range of concentrations measured since 1997 (0.16-0.37 mg·L-1) during summer stratification in the main lake. Average TN concentrations tend to be slightly higher in Armstrong Arm, although in the past three years, these values fell within the same range as main lake values. TN concentrations were similar at 20 m depth in both main lake basins in 2005 and also similar to previous years, with the exception of an increase above 0.3 mg·L-1 at OK 6-7 in November 2005 that hadn’t been observed in past years. However, the sampling may have been conducted later than usual in 2005 and coincided with vigorous fall mixing of the water column. Since 2000, TN at 20 m in Armstrong Arm has been similar to the rest of Okanagan Lake, with the same November 2005 exception noted for OK 6-7. Hypolimnetic (45 m depth) TN concentrations in the main lake were, on average, the same as in the two previous years at 0.22 mg·L-1 (Fig. 5). An increase that had been observed on an annual basis between 1997 and 2002 (Rae and Wilson in Andrusak et al. 2005) has not continued in 2003-2005. In these past three years, hypolimnetic TN has also shown little variation throughout the sampling period. As indicated earlier, Okanagan valley has experienced low runoff years since 2003, and these dry years are clearly affecting the nutrient loading to the lake. Hypolimnetic TN concentrations at OK 8 differ significantly from the main lake, with values often twice as high, particularly in late summer and early fall. They fluctuate more during summer and showed an overall declining trend from 1996-2003 with a slight increase in late summer and fall values in 2004 and 2005 (Fig. 5). Nitrate and ammonia are inorganic forms of nitrogen and are most readily available to primary producers such as phytoplankton. Ammonia is generated as a waste product by aquatic animals and the bacterial decomposition of organic matter. In the absence of anthropogenic sources, ammonia concentrations are usually low as it is quickly converted to nitrite and then to nitrate by nitrifying bacteria (Wetzel 2001). Ammonia concentrations in Okanagan Lake are usually at or below the detection limit (0.005 mg·L-1), and 2005 was no exception (Fig. 6). When detectable, measurements range from 0.005-0.020 mg·L-1 throughout the water column, with higher values measured occasionally in the hypolimnion of Armstrong Arm. Nitrate is usually the most common form of nitrogen available to biota (Wetzel 2001), and in the main part of Okanagan Lake it has been 2-40 % of spring (April) TN from 1996-2005. The remainder of ambient nitrogen is refractory, or not readily available to biota. In spring, nitrate concentrations averaged 0.048 mg·L-1 across all depths sampled in the main lake (Table 5). Since 1997, epilimnetic (0-10 m) nitrate concentrations have been rapidly depleted over the growing season by an order of magnitude to <0.002 mg·L-1 (detection limit), and this occurred again in 2005 at all stations (Fig. 7). The sharp decline occurs in May and early June, and the nitrate level then remains below detection until fall turnover. This pattern also occurs at 20 m in the main basin of


the lake, although the nitrate level does not always drop below detection level and is more variable during the summer. In Armstrong Arm, the sharp decline is sometimes seen in the epilimnion samples (0-10 m) but it is not evident at 20 m, possibly because of greater light limitation at 20 m in this area of the lake and, therefore, limited nitrate uptake by phytoplankton. Nutrient fluxes between the water strata may also differ in Armstrong Arm. Nitrate depletion does not occur in the hypolimnion (45 m) of Okanagan Lake, where concentrations average 0.057-0.081 mg·L-1 in the south and 0.046-0.077 mg·L-1 in the north (Fig. 7). The summer epilimnetic inorganic nitrogen (ammonia+nitrate) concentrations in Okanagan Lake are generally below 0.020 mg·L-1, which is the approximate concentration thought to limit phytoplankton (Wetzel 2001). This low inorganic nitrogen suggests that nitrogen may limit the growth of some phytoplankton species in the lake during summer. Other indications of nitrogen limitation are N:P ratios and phytoplankton species composition (discussed below). Table 5. Concentrations of nitrite+nitrate-nitrogen (NO2+3-N) and total dissolved

phosphorus (TDP) in April for the south (OK 1-3), north (OK 6-7) and Armstrong Arm (OK 8) of Okanagan Lake. Values are the average of the 0-10 m composite, 20 m and 45 m samples; units in mg·L-1.

Station Variable Year


Armstrong Arm OK 8

NO2+3-N 1997 0.044 0.042 0.043 0.146 1998 0.060 0.027 0.043 0.147 1999 0.076 0.043 0.060 0.012 2000 0.062 0.048 0.055 0.015 2001 0.054 0.027 0.040 0.010 2002 0.066 0.031 0.049 no data 2003 0.066 0.056 0.061 0.009

2004 0.039 0.026 0.032 0.007 2005 0.064 0.041 0.052 0.003

Average 0.059 0.038 0.048 0.043 TDP 1997 0.007 0.008 0.008 0.031 1998 0.002 0.004 0.003 0.013 1999 0.004 0.005 0.005 0.007 2000 0.006 0.006 0.006 0.006 2001 0.003 0.001 0.002 0.001 2002 0.003 0.002 0.003 no data 2003 0.005 0.004 0.004 0.005 2004 0.001 0.002 0.002 0.002 2005 0.002 0.001 0.002 0.002 Average 0.004 0.004 0.004 0.008


Phosphorus Total phosphorus (TP) and total dissolved phosphorus (TDP) concentrations have displayed an overall decreasing trend in the main body of Okanagan Lake since OLAP began in 1996 (Figs. 4, 8, 9). This trend continued in 2005, although epilimnetic TP was slightly higher at the north end of the lake compared with 2004 (Fig. 8). TP concentrations from 1996-2005 have not differed between the epilimnion and hypolimnion, with an average of 0.007 mg·L-1 (range 0.001-0.024) in the epilimnion and 0.006 mg·L-1 (range 0.002-0.023) in the hypolimnion (Fig. 8). Since 2003, epilimnetic TP has been lower on average (0.003-0.004 mg·L-1) than in earlier years. This low TP is likely due to the dry conditions in recent years that have reduced runoff, and therefore the input of nutrients, to the lake in spring. Because of this, phosphorus limitation of phytoplankton growth may have been greater in 2003-2005 than in earlier years. In Armstrong Arm, TP concentrations have a greater range than in the main lake, but this has also been decreasing over time, with less variability now observed in epilimnetic and 20 m depth TP concentrations (Fig. 8). However, in the hypolimnion of Armstrong Arm, TP concentrations continue to increase over the period of summer stratification and peak in fall with values of 0.07-0.10 mg·L-1. In 2005, total dissolved phosphorus (TDP) concentrations averaged 0.001-0.002 mg·L-1 in spring (Table 5) and summer (Fig. 9) at all depths sampled in the main lake. These values are the same as 2004 and lower than earlier years. In Armstrong Arm, TDP showed a pattern similar to TP, with occasionally higher concentrations over the summer stratified period than elsewhere in the lake (Fig. 9). Soluble reactive phosphorus (SRP) data were first collected in 2000 and have continued each year since then; however, there are no data for July to November 2005. SRP concentrations in the first four sampling months of 2005 were similar to earlier years with values fluctuating between the detection limit (0.001 mg·L-1) and 0.005 mg·L-1 (Fig. 10). Nitrogen to Phosphorus Ratios The productivity of lakes and the seasonal succession of planktonic species are linked to the ratio of nitrogen to phosphorus in lake water (Downing and McCauley 1992; Wetzel 2001). The N:P ratio is used as a relative measure of nutrient limitation and, to some extent, primary productivity in a lake. Ratios greater than 15 (by weight) indicate phosphorus limitation, ratios less than 10 indicate nitrogen limitation, and ratios between 10 and 15 indicate neither, or both nutrients, are capable of limiting algal growth (Downing and McCauley 1992). Due to the large proportion of refractory, or biologically unavailable, forms of N and P, the most accurate and applicable method for Okanagan Lake is to compare nutrient forms that are available to phytoplankton for growth, such as inorganic nitrogen (nitrite+nitrate) and dissolved phosphorus in the epilimnion (Stockner in Andrusak et al. 2001). A ratio of inorganic nitrogen to total dissolved phosphorus of 7 or greater is suggested by Stockner for a “healthy” population of all


phytoplankton species to co-exist. When inorganic nitrogen is depleted, growth becomes limited for most phytoplankton. The exception is for cyanobacteria (blue-green algae), some of which do not depend on nitrates and can fix inorganic nitrogen from atmospheric sources (Pick and Lean 1987; Stockner and Shortreed 1989). The inorganic nitrogen to total dissolved phosphorus ratio (NO2+3:TDP, by weight) in the epilimnion of Okanagan Lake decreases below 7:1 in May at all sampling stations and is less than 2:1 by June. The ratio then remains low during the remainder of the growing season (Fig. 11). Cyanobacteria tend to increase in the late summer and into the early fall, particularly at stations OK 6, 7, and 8, while the N:P ratio remains low (Fig. 12; Stockner, in this OLAP report). This pattern repeated in 2005, with fall cyanbacteria being more prevalent in 2005 than in 2003 and 2004. The average NO2+3:TDP ratio in the main lake for 1997-2005 was 3.2, and over these years it has consistently been below the threshold of 7:1 identified by Stockner (in Andrusak et al. 2001) (Table 6). In Armstrong Arm, the ratio is even lower at an average of 1.1. These numbers contrast over the last five years to N:P ratios in the range of 10-62 throughout the water column from February to April (Fig. 11). Although highly variable, N:P ratios in the hypolimnion during summer are also most often higher than 10. Cyanobacteria, which have dominated and are still a significant component (30-70%) of phytoplankton in surface waters during late summer and fall, contain few fatty acids and are a poor food source for zooplankton (Brett and Muller-Navarra 1997). This in turn makes the zooplankton a poor quality food item for kokanee in Okanagan Lake. A lake survey was conducted among nearby large southern British Columbia lakes in 2004 to evaluate the composition of the phytoplankton community and their fatty acid content at different N:P ratios and the results were reported by Rae and Ashley (in Andrusak et al. 2005).


Table 6. The N:P ratio (nitrate+nitrite-nitrogen, NO2+3 : total dissolved phosphorus, TDP; by weight) in the epilimnion (0-10 m) averaged over the period late April/early May to October for the south (OK 1-3), north (OK 6-7) and Armstrong Arm (OK 8) of Okanagan Lake.

Station Year


Armstrong Arm OK 8

1997 0.8 0.5 0.7 0.1 1998 8.7 1.0 4.8 no data 1999 2.3 1.5 1.9 0.3 2000 1.6 0.3 0.9 0.3 2001 5.2 9.7 a 7.5 0.2 2002 1.4 0.8 1.1 0.3 2003 3.9 2.7 3.3 3.6 2004 5.7 3.1 4.2 3.5 2005 6.9 1.1 4.0 0.8

Average 4.1 2.3 3.2 1.1 a An estimate since all TDP values were below detection limit.

Chlorophyll a Chlorophyll a concentrations are used as an index of phytoplankton standing crop and, to a lesser extent, productivity (Burgis and Morris 1987). Chlorophyll a generally increases slightly from south to north in Okanagan Lake, with 1997-2005 averages of 2.8 µg·L-1 at OK 1-3 and 3.0 µg·L-1 at OK 6-7 (Table 7). In 2005, the recent trend of particularly low chlorophyll a concentrations continued. Low values of 1.4-1.6 µg·L-1 were first measured by OLAP in 2003 and persisted in 2004 and now in 2005. Consistent with nutrient concentrations, chlorophyll a concentrations were highest in Armstrong Arm, averaging 3.8 µg·L-1; again, 2003-2005 have experienced lower concentrations than in earlier years (Table 7). The lowest growing season (May to October) average for the main lake has been 1.5 µg·L-1 in each of 2003, 2004, and 2005 and the highest 5.7 µg·L-1 in 1999. Seasonally, chlorophyll a is usually 2-4 µg·L-1 in April and exhibits spring and fall peaks indicating phytoplankton blooms at times of water column mixing (Fig. 13). Chlorophyll a in Okanagan Lake in the last three years is at the low end of the range measured in other large lakes in the Okanagan Valley. Average chlorophyll a measured from July to October in 2003 was 0.8 µg·L-1 in Kalamalka Lake, 1.9 µg·L-1 in Wood Lake, 3.6 µg·L-1 in Osoyoos Lake and 4.0 µg·L-1 in Skaha Lake (Ministry of Environment, Penticton, unpublished data). Okanagan Lake also has similar chlorophyll a concentrations compared with large lakes in southeastern British Columbia, where the April to November averages since 1997 have ranged from 1.1-3.7 µg·L-1 in Kootenay Lake and from 1.2-3.3 µg·L-1 in Arrow Lakes Reservoir (E. Schindler, Ministry of Environment, Nelson, personal communication).


Table 7. The chlorophyll a concentration (µg·L-1) in the epilimnion (0-10 m) averaged over the period late April/early May to October for the south (OK 1-3), north (OK 6-7) and Armstrong Arm (OK 8) of Okanagan Lake.

Station Year


Armstrong Arm OK 8

1997 2.3 2.9 2.6 5.7 1998 3.4 4.1 3.5 5.2 1999 5.6 5.7 5.7 5.9 2000 4.0 3.4 3.7 4.6 2001 2.5 3.5 3.0 3.7 2002 2.5 2.7 2.6 3.2 2003 1.6 1.4 1.5 1.4 2004 1.5 1.5 1.5 2.2 2005 1.4 1.5 1.5 2.4

Average 2.8 3.0 2.8 3.8

CONCLUSIONS According to nutrient and chlorophyll a measurements taken in the main lake from 1997-2002, Okanagan Lake classifies as an oligotrophic lake. Environment Canada’s definition of oligotrophic is TP at 0.004-0.010 mg·L-1 (Environment Canada 2004). Since 2003, however, Okanagan Lake would be better classified as approaching ultra-oligotrophic status (TP<0.004 mg·L-1). Oxygen profiles in the north and south basins have an orthograde curve during summer that is also consistent with the oligotrophic condition. In 2005, phosphorus and chlorophyll a in the main lake were among the lowest recorded since the start of OLAP. The oligotrophic conditions observed in water chemistry data from 2003-2005 have been mirrored in phytoplankton population dynamics (see Stockner, in this OLAP report), and are most likely due to the particularly dry conditions that the Okanagan valley has been experiencing recently. The Armstrong Arm basin is more productive than the main lake with chlorophyll a and water clarity values in the oligo-mesotrophic range and a clinograde oxygen profile in late fall. Even in this arm of the lake, however, nutrient and chlorophyll a concentrations have declined since the late 1990s. The differences between Armstrong Arm and the main lake in nutrients, oxygen, and water clarity probably stem from historical nutrient loading and from the relatively shallow depth of the basin. Prior to treatment of sewage from the City of Armstrong, effluent was released into this basin and contributed organic matter and nutrients to the sediments (Jensen in Ashley et al. 1999). Decomposition of organic matter consumes oxygen in the hypolimnion (Wetzel 2001), which can lead to internal nutrient loading if conditions become anoxic (Burgis and Morris 1987). Okanagan Lake appears to be phosphorus limited with additional limitation by nitrogen playing an important role from spring to early fall. In spring, nitrate-nitrogen concentrations in the epilimnion and at 20 m are depleted below detection limits. TDP stays more constant but occasionally shows epilimnetic depletion, with the result that


N:P ratios (as NO2+3:TDP) are generally <2:1 in summer. These nutrient limitations seem to favour the growth of cyanobacteria as a substantial component of the phytoplankton community (Stockner, in this OLAP report). Several species of cyanobacteria grow well when nitrogen limits other phytoplankton species, and cyanobacteria are generally unpalatable to zooplankton, which limits zooplankton populations (Stockner and Shortreed 1989) and the nutritional value of zooplankton for fish (Brett and Muller-Navarra 1997). The exceptionally dry years from 2003-2005 have had considerable impact on Okanagan Lake. Several variables measured throughout the stratified period were at or near record lows (e.g., chlorophyll a, spring TP). The low spring runoff in dry years likely induces phosphorus limitation in the epilimnion of Okanagan Lake, which leads to nitrogen and phosphorus co-limitation. This co-limitation could limit juvenile kokanee growth due to overall reduced nutrient concentrations that lead to low algal productivity. Nevertheless, the kokanee population over the last three years has continued to show a steady increase in number of fish (Sebastian et al., in this OLAP report). Therefore, it is possible that the low phosphorus concentrations in dry years may drive algal production away from cyanobacterial dominance. This situation would be of benefit to kokanee as it could help to alleviate the trophic bottleneck associated with cyanobacterial production (see Stockner, in this OLAP report). However, the overall reduction in Okanagan Lake’s productivity, with or without a shift in phytoplankton species, will nonetheless limit kokanee recovery. If very dry years in the Okanagan Basin become more frequent with climate change, the implications for lake productivity in general and kokanee recovery in particular will be of concern. RECOMMENDATIONS 1. For Year 11 of OLAP and beyond, reduce water chemistry and chlorophyll a

monitoring to four stations sampled four times during the year (spring/April, summer/July, summer/August, and fall/October).

2. In the next wet year, repeat the measurements of vertical distribution of nutrients

and chlorophyll a concentrations in the epilimnion. In a wet year, epilimnetic productivity will be higher and nitrate limitation, in particular, may be more evident. This analysis was done in 2003 but was not repeated in 2004 or 2005.

3. Continue sending de-ionized water samples for analysis as a component of the

quality control process with water chemistry samples. ACKNOWLEDGMENTS Limnology sampling on Okanagan Lake was conducted by David Cassidy and Nick Ipatowicz, both with BC Conservation Foundation.


REFERENCES Andrusak, H., S. Matthews I. McGregor, K. Ashley, G. Wilson, L. Vidmanic, J. Stockner,

K. Hall, D. Sebastian, G. Scholten, G. Andrusak, J. Sawada, D. Cassidy, J. Webster. 2001. Okanagan Lake Action Plan Year 5 (2000) Report. Fisheries Project Report No. RD 89, 2001. Fisheries Management Branch, Ministry of Water, land and Air Protection, Province of British Columbia.

Andrusak, H., S. Matthews I. McGregor, K. Ashley, G. Wilson, L. Vidmanic, J. Stockner,

D. Sebastian, G. Scholten, P. Woodruff, D. Cassidy J. Webster, , K. Rood, A. Kay. 2002. Okanagan Lake Action Plan Year 6 (2001) Report. Fisheries Project Report No. RD 96, 2002. Fisheries Management Branch, Ministry of Water, land and Air Protection, Province of British Columbia.

Andrusak, H., S. Matthews I. McGregor, K. Ashley, R. Rae, A. Wilson, D. Sebastian,

G. Scholten, P. Woodruff, D. L. Vidmanic, J. Stockner, G. Wilson, , B. Jantz, J. Webster, H. Wright, C. Walters and J. Korman. 2004. Okanagan Lake Action Plan Year 8 (2003) Report, Fisheries Project Report No. RD 108, 2004, Fisheries Management Branch, Ministry of Water, Land and Air Protection, Province of British Columbia.

Andrusak, H., S. Matthews, I. McGregor, K. Ashley, R. Rae, A. Wilson, J. Webster,

G. Andrusak, L. Vidmanic, J. Stockner, D. Sebastian, G. Scholten, P. Woodruff, B. Jantz, D. Bennett, H. Wright, R. Withler, S. Harris. 2005. Okanagan Lake Action Plan, Year 9 (2004) Report, Fisheries Project Report No. RD 111, 2005. Biodiversity Branch, Ministry of Environment, Province of British Columbia.

Andrusak, H., S. Matthews, A Wilson, G. Andrusak, J. Webster, D. Sebastian,

G. Scholten, P. Woodruff, R. Rae, L. Vidmanic, J. Stockner, northwest hydraulic consultants. 2006. Okanagan Lake Action Plan Year 10 (2005) Report. Fisheries Project Report No. RD 115. Ecosystems Branch, Ministry of Environment, Province of British Columbia.

Ashley, K., Bruce Shepherd, Dale Sebastian, Lisa Thompson, Lidija Vidmanic, Dr. Peter

Ward, Hansen A. Yassien, Laurie McEachern, Rick Nordin, Dr. Dave Lasenby, Janice Quirt, J.D. Whall, Dr. Peter Dill, Dr. Eric Taylor, Susan Pollard, Cecilia Wong, Jan den Dulk, George Scholten. 1998. Okanagan Lake Action Plan Year 1 (1996-97) and Year 2 (1997-98) Report. Fisheries Project Report No. RD 73, Province of British Columbia, Ministry of Fisheries, Fisheries Management Branch.

Ashley, K., I. McGregor, B. Shepherd, D. Sebastian, S. Matthews, L. Vidmanic,

P. Ward, H. Yassien, L. McEachern, H. Andrusak, D. Lasenby, J. Quirt, J. Whall, E. Taylor, A. Kuiper, P.M. Troffe, C. Wong, and G. Scholten, M. Zimmerman, P. Epp, V. Jensen and R. Finnegan. 1999. Okanagan Lake Action Plan Year 3 (1998) Report. Fisheries Project Report No. RD 78, 1999. Fisheries Management Branch, Ministry of Fisheries, Province of British Columbia.


Brett, M.T. and D.C. Muller-Navarra. 1997. The Role of Highly Unsaturated Fatty Acids

in Aquatic Food Web Processes. Freshwater Biol. 38: 483-499. Bryan, J.E. 1990. Water quality of Okanagan, Kalamalka and Wood Lakes. BC

Ministry of Environment, Penticton. Burgis, M.J. and Morris, P. 1987. The Natural History of Lakes. Cambridge University

Press. Cambridge. 33, 39 pp. Downing, J.A., and E. McCauley. 1992. The Nitrogen:Phosphorus Relationship in

Lakes. 37(5): 936-945. Environment Canada. 2004. Canadian Guidance Framework for the Management of

Phosphorus in Freshwater Systems. Ecosystem Health: Science-based Solutions Report No. 1-8. National Guidelines and Standards Office, Water Policy and Coordination Directorate, Environment Canada. 114 p.

Martinez, P. and E. Bergenson. 1991. Interactions of Zooplankton, Mysis relicta and

Kokanee in Lake Granby, Colorado. Am. Fish. Soc. Symp. 9: 49-64. Pick, F.R. and D.R.S. Lean. 1987. The Role of Macronutrients (C, N, P) in Controlling

Cyanobacteria Dominance in Temperate Lakes. New Zealand Journal of Marine and Freshwater Research, Vol. 21:425-434.

Stockner, J.G and T.G. Northcote. 1974. Recent Limnological Studies of Okanagan

Lakes and their Contribution to Comprehensive Water Resource Planning. J. Fish. Res. Board Can. 31:955-976.

Stockner, J.G., and K.S. Shortreed. 1989. Algal Picoplankton Production and

Contribution to Food Webs in Oligotrophic British Columbia Lakes. Hydrobiologia, 173, 151-166.

Wetzel, R.G. 2001. Limnology. 3rd Ed, Academic Press, San Diego, CA.


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Figure 4. Trends in (A) total phosphorus and (B) total nitrogen for the south (OK 1-3)

and north (OK 6-7) arms of Okanagan Lake, 1996-2005. There were no significant trends observed in the TN data, so regression lines were not included.


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Figure 5. Total nitrogen concentrations averaged from stations in the south (OK 1-3),

north (OK 6-7), and Armstrong Arm (OK 8) of Okanagan Lake, 2001-2005. Graphs show 0-10 m composite sample (top), 20 m (middle), and 45 m (bottom) discrete samples. Note: The Y-axis scale differs for the 45 m data.


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Figure 6. Ammonia-nitrogen concentrations averaged from stations in the south

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south (OK 1-3), north (OK 6-7), and Armstrong Arm (OK 8) of Okanagan Lake, 2001-2005. Graphs show 0-10 m composite sample (top), 20 m (middle), and 45 m (bottom) discrete samples. Note: The Y-axis scale differs for each graph.


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Figure 8. Total phosphorus (TP) concentrations averaged from stations in the south

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Figure 9. Total dissolved phosphorus (TDP) concentrations averaged from stations in

the south (OK 1-3), north (OK 6-7), and Armstrong Arm (OK 8) of Okanagan Lake, 2001-2005. Graphs show 0-10 m composite sample (top), 20 m (middle), and 45 m (bottom) discrete samples. Note: The Y-axis scale differs for the 45 m data.


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Figure 10. Soluble reactive phosphorus (SRP) concentrations from stations in the

south (OK 1-3), north (OK 6-7), and Armstrong Arm of Okanagan Lake, 2001-2005. Graphs show 0-10 m composite sample (top), 20 m (middle), and 45 m (bottom) discrete samples. There are no data for July-November 2005. Note: The Y-axis scale differs for the 45 m data.


Figure 11. Ratio of nitrate+nitrite-nitrogen to total dissolved phosphorus (NO2+3:TDP)

averaged from stations in the south (OK 1-3), north (OK 6-7), and Armstrong Arm (OK 8) of Okanagan Lake, 2001-2005. Graphs show 0-10 m composite sample (top), 20 m (middle), and 45 m (bottom) discrete samples. Note: Y-axis scale differs for the 45 m data.

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Lake, 2001-2005. Nutrients are nitrite+nitrate-nitrogen (NO2+3) and total dissolved phosphorus (TDP). Phytoplankton biovolume is shown for cyanobacteria, dinoflagellates, and other phytoplankton (chrysophytes, cryptophytes, chlorophytes, diatoms). OK 1 and OK 3 are in the south of the lake, OK 6 and OK 7 in the north, and OK 8 is the Armstrong Arm. Note: Both left and right Y-axis scales differ among graphs.


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PHYTOPLANKTON POPULATIONS IN OKANAGAN LAKE, BRITISH COLUMBIA

2005

by

John G. Stockner1

INTRODUCTION Okanagan Lake is a deep, interior, fjord-type oligotrophic lake with a low ambient nutrient concentration, plankton biomass, and fish production (Stockner and Northcote 1974; Ashley et al. 1999; Andrusak et al. 2003, 2004). Despite it’s oligotrophic status, concerns have arisen about the lake’s recurring late summer blue-green algal ‘blooms’, notably in northern sectors of the lake, e.g., Armstrong Arm (Ashley et al. 1999; Andrusak et al. 2004). Recently, a more subtle signal of an impending nutrient problem has emerged that is related to very low dissolved inorganic nitrogen (DIN) concentrations and an imbalanced DIN:TDP (total dissolved phosphorus) ratio. These have the potential to create a carbon (C) ‘sink’ and cause inefficient C transfer within the pelagic food web of the lake (Stockner et al. 1999; Stockner in Ashley et al. 1999; Stockner in Andrusak et al. 2004). Finally, long-term fisheries data indicates a substantial reduction in kokanee numbers (Andrusak in Andrusak et al. 2004) and anecdotal reports suggest that rainbow trout populations are also declining. Causal factors remain elusive, but ‘best’ evidence points either to competition between kokanee fry and freshwater shrimp (Mysis relicta) for scarce zooplankton ‘forage,’ and or to excessive biomass of inedible blue-green algae and chain-forming diatoms. It is well known that inedible filamentous blue-greens and colonial diatoms often create ‘C sinks’ that constrain carbon flows and severely impact annual zooplankton forage production and pelagic fisheries in large interior lakes (Stockner 1987, Ashley et al. 1999; Rae and Ashley in Andrusak et al. 2004, Pieters et al. 2003). Study Objectives Commencing in 1999, as part of the Okanagan Lake Action Plan (OLAP), an initiative was undertaken to more intensively examine the plankton populations (Stockner in Andrusak et al. 2004). This work has focused on food web interaction and species composition, succession, abundance, and biomass of microbial (e.g., picoplankton, flagellates, ciliates), phytoplankton and zooplankton populations. This report presents, discusses and summarizes phytoplankton and microbial population trends for the growing season, February to October 2005.

1 Eco-Logic Ltd., 2614 Mathers Avenue, West Vancouver BC V7V 2J4


Study Limitations As a caveat, it should be noted that the number of stations sampled (6), the sampling frequency (monthly), and effort (1 sample/station, depth-integrated 0-10 m) only provide a monthly ‘snapshot’ of phytoplankton population abundance, biomass, diversity and spatiotemporal variability in a very large Okanagan Lake basin. Further, in 2005 sampling was terminated the 1st week of October so comment on autumnal increases/declines coincident with overturn (mixing) cannot be made. In year 2003, some limited effort was made to examine vertical population structure by discrete-depth sampling, so in the 2003 report some interpretations of vertical population trends were reported (Stockner in Andrusak et al. 2004). Most interpretations reported here are largely based on seasonal fluctuations of two variables: abundance (cells/mL) of genera, some species and their respective taxonomic Classes, and biovolume (mm3/L) or biomass of genera and Classes. This report should not be considered as a comprehensive ‘synthesis’ of the Okanagan Lake phytoplankton community dynamic, but rather as an ‘overview’ of current phytoplankton population ‘trends’ after 7 years of single sample/station monitoring. Finally, an attempt has been made to provide the ‘best’ interpretation of the most notable seasonal population trends, but these have been made without the support of additional data, e.g., chlorophyll, nutrients, primary production, zooplankton, and therefore, reported results and accompanying discussions must, by necessity, remain preliminary and speculative. METHODS Sampling Protocol and Station Locations (see Map 2) A single, depth integrated (0-10 m) sample from each of 5 stations - OK 1, 3, 6, 7, and 8 along a north/south axis of Okanagan Lake (Map 2) were obtained monthly from February to the middle of October, 2005. Stations 1 and 3 were representative of pelagic conditions in the south basin of the lake off of S. Prairie Creek (station depth – 90 m) and Rattlesnake Island (140 m), respectively. Station 6 (225 m) was the deepest station and was located mid-lake off N. Okanagan Centre. Stations 7 and 8 were located in the two most northerly lake sub-basins, Vernon Arm (90 m) and Armstrong Arm (55 m). In recent years, the Armstrong Arm (OK8) has consistently shown the greatest algal biomass typifying the more ‘enriched’ conditions of the shallower Armstrong Arm of the lake’s north basin. Station 4, mid-lake south basin, in past years was sampled at irregular intervals, but in 2005 was sampled monthly for the first time, hence results are discussed briefly in this report. Enumeration Protocol Phytoplankton samples from monthly surveys were preserved in acid Lugol’s iodine preservative. The samples were gently shaken for 60 seconds and poured into 25 mL settling chambers and allowed to settle for a minimum of 8 hr prior to quantitative enumeration (Utermohl 1958). Counts were done using a Carl Zeiss© inverted phase-contrast plankton microscope. Counting followed a 2-step process. Initially,


several (5-10) random fields were examined at low power (250X magnification) for large micro-phytoplankton (20-200μ), e.g., colonial diatoms, dinoflagellates, filamentous blue-greens. A second step involved counting all cells within a random transect ranging from 10 to 15 mm at high power (1562X magnification) that permitted a semi-quantitative enumeration of minute (< 2μ) autotrophic picoplankton cells (1.0-2.0μ) [Class Cyanophyceae], and of small, delicate auto-, mixo-, and heterotrophic nano-flagellates (2.0-20.0μ) [Classes Chrysophyceae and Cryptophyceae]. Observations on the relative abundance of ciliates in each sample were also noted on the count sheets. In total, between 250-300 cells were enumerated in each sample to assure counting consistency and statistical accuracy (Lund et al. 1958). A species list of phytoplankton identified from Okanagan Lake in 2005 together with their respective cell bio-volumes is presented in Appendix 1. RESULTS Recent Phytoplankton Trends 2003-2005 This discourse begins with year 2003, a year when major deviations from the typical, seasonal successional patterns were observed in Okanagan Lake phytoplankton populations for the first time since 1999 (Stockner in Andrusak et al. 2003, 2004). Notable components of change were: • The occurrence of an immense blue-green ‘bloom’ in Armstrong Arm (OK 8) in

March consisting of colonial nitrogen-fixing species, i.e., Aphanizomenon, Oscillatoria, and Anabaena that was not seen at other stations in the lake.

• A large dinoflagellate ‘bloom’ (Gymnodinium spp.) in June at Station OK 1 near

Summerland that extended up-lake as far as OK 3 off Rattlesnake Island, but not beyond.

• The absence of a typical spring diatom increase at OK 1, 2 and 8 that normally

occurs at all lake stations in May. • A phytoplankton population depression that lasted from mid-July through to early

October with extraordinarily low densities of all major species and groups at all stations in the lake.

In year 2004, phytoplankton abundance at all stations on average (Fig. 1) declined to even lower values than noted in 2003, especially during the months of August and September when densities fell to levels more typically seen in ultra-oligotrophic coastal BC lakes (Stockner 1981, 1987). In previous ‘normal’ years, the late summer and early autumn periods were characterized by moderately high densities of blue-greens and mixed flagellate populations. These high densities were sequentially followed by a moderate diatom ‘bloom’ associated with lake overturn (deep mixing) in late October. However, this succession was not seen in 2004, instead populations remained low well into November. To summarize, both 2003 and 2004 were uncharacteristic years for


Okanagan Lake phytoplankton populations with unprecedented low density populations, attaining levels heretofore unseen in this lake over the last 4-5 decades of study. In 2005, the more typical spring succession occurred with a pronounced May diatom bloom followed by moderate densities of mixed flagellates, and then by a modest mid-summer depression in July and August. This depression was then followed by a moderate increase of Cyanophytes in September and October, notably at stations OK 6, 7 and 8 (Figs. 1, 2). Whole-lake average phytoplankton densities in 2005 (3,249 cells/mL) were higher than in 2004 (2,651 cells/mL) but were still lower than previous years (Fig. 3a, Table 1). Average biovolume or biomass estimates in 2005 were considerably higher (0.74 mm3/L) than in 2004 (0.54 mm3/L), most notably at OK 7 where the highest value (0.79 mm3/L) hitherto observed were recorded (Fig. 3b, Table 1). The Seven-Year OLAP Time Series – Phytoplankton from 1999-20052

The lowest average phytoplankton abundance was noted in 2004 (2,651 cells/mL) and the next lowest occurred in 2005 (3,249 cells/mL). The lowest average phytoplankton biovolume was in 2004 and the highest was in 2003 (0.85 mm3/L), owing to the ubiquity of large-celled, colonial blue-greens at the north basin stations (OK 7, 8) and the occurrence of large dinoflagellate blooms at southern stations - OK 1 and 3. In the first three years of the OLAP phytoplankton monitoring there was a well defined biomass gradient decreasing from highs at northern stations (OK 7, 8) to lows at the southern stations (OK 1, 3). However, the gradient was not apparent from 2002-2004, owing to the increasing abundance and biomass of phytoplankton at southern stations (OK 1 and 3) and the declining values at Stations 6 and 7 in the northern basin (Table 1, Fig. 3b). In 2005, the biomass gradient was restored and there was a clear, albeit gradual, gradient from north to south, but there was no discernable gradient in abundance. In the first five years of OLAP there was a clear progression of steadily increasing phytoplankton biomass in the Armstrong Arm at station OK 8, rising from 0.88 in 1999 to a peak of 1.39 mm3/L in 2003, and then collapsing in 2004 to 0.68 mm3/L and partially restored in 2005 with a value of 1.17 mm3/L, the fourth highest in the seven year OLAP time series. Since Year 2000, Station 1 has shown the greatest rate of change of any lake station, particularly marked in values of average biomass in 2003 (dinoflagellate blooms). Similar to OK 8, station 1 biomass plummeted to the second lowest recorded level in 2004, and increased slightly to 0.59 mm3/L in 2005, comparable to previous ‘normal’ years. Finally, it is noteworthy to see that the trend at stations OK 6 and 7, where there was a gradual decline in abundance and biomass of phytoplankton that has remained intact over the past six years, but rose sharply in 2005 making these north basin stations the second and third ranked stations after OK 8.

2 Because of identical station, sampling and enumeration protocols used in the phytoplankton program

since 1999, for ease of between year comparison and interpretation year 2005 phytoplankton results are graphically presented and discussed with those from 1999-2005 (Figs.4 & 5).


Table 1. Average phytoplankton abundance and biomass in Okanagan Lake, 1999-2005.

Station Year OK 1 OK 3 OK 6 OK 7 OK 8 Lake

Average Abundance (cells/mL)

1999 2000 2001 2002 2003 2004 2005

4,780 3,960 3,465 5,271 4,753 2,541 3,221

5,060 4,571 3,497 4,323 4,496 2,406 2,966

5,263 4,873 4,082 4,745 3,810 2,404 2,966

5,949 5,649 3,671 4,762 4,582 2,646 3,441

5,721 5,994 5,175 7,622 5,651 3,275 3,667

5,354 5,010 3,978 5,345 4,658 2,651 3,249

Biovolume (mm3/L)

1999 2000 2001 2002 2003 2004 2005

0.56 0.41 0.50 0.54 0.87 0.47 0.59

0.73 0.55 0.56 0.57 0.74 0.56 0.60

0.84 0.60 0.59 0.77 0.62 0.51 0.67

0.84 0.75 0.57 0.77 0.65 0.47 0.79

0.88 1.12 1.18 1.35 1.39 0.68 1.17

0.77 0.69 0.68 0.80 0.85 0.54 0.74

Phytoplankton Blooms In 2005, the largest population increases or ‘mini-blooms’ occurred at OK 6, 7 and 8 in mid-April and were largely comprised of a diverse assemblage of diatoms together with some pico- and filamentous cyanobacteria. As previously discussed the 1999-2005 abundance and biovolume datasets (Figs. 4 and 5) display some striking changes most notably commencing in 2003. In that year, populations basically collapsed in the summer without the usual late-summer and autumn phytoplankton increases leading to ‘bloom’ conditions (>10 to15 fold increase in population abundance). In 2003, dinoflagellate blooms were large and conspicuous at OK 1 and 3 in June and at OK 8 from late February to April peak [colonial blue-green and diatom blooms] (Figs. 4 and 5). The 2003 blooms resulted in major biovolume peaks because the species responsible were large-celled or colonial (Fig. 4). It is important to note however, that not all numerical abundance peaks necessarily resulted in biomass peaks, as some peaks occurred among populations with minute cells with little biomass, e.g., pico-cyanobacteria (Synechococcus spp.), small diatoms (Cyclotella spp.), and nano-flagellates (Chromulina, Kephrion, Chroomonas spp. etc.). It is also of significance to note that in November 2002 an atypical ‘mini-bloom’ occurred in the Armstrong Arm (OK 8) that was comprised primarily of colonial blue-greens and diatoms, but three months later in February, 2003 populations of the same species had markedly increased in size, ultimately leading in March/April 2003 to the largest blue-green and to a lesser extent diatom bloom recorded in the lake since commencement of the OLAP time series in 1999. Early spring phytoplankton blooms are most unusual since the winter period is normally a quiescent time of low growth, characterized by low light conditions and cold temperatures with isothermal winter mixing and/or in some winters with ice-cover. During this time species usually sink to the sediment surface to over-winter and grow


again when spring mixing (overturn) brings cells to the surface where there is a prevalence of dissolved nutrients and high irradiance to initiate significant phytoplankton population growth. Some key questions remain unanswered - were climatic conditions, e.g., mild, warm winter, responsible for the early bloom in Armstrong Arm? Why was the bloom not sustained into mid-summer, instead of collapsing by early June and gradually increasing again in November 2004? Was it co-limitation (both N & P)? It is quite likely that co-limitation triggered the onset of a lake-wide population depression in 2003 and 2004, coupled with small nutrient inputs from low tributary flows. In 2005, there was not a massive blue-green and diatom bloom in early spring that was observed in 2004, only a moderate increase, normal for this time period. Perhaps 2005 was a ‘normal’ hydrologic/climatic year in the Okanagan Basin. Population Depressions The usual seasonal phytoplankton successional pattern for Okanagan Lake is best represented by the 1999 dataset (Figs. 4, 5). It begins with the onset of a spring diatom and flagellate increase followed by a short August population depression, termed by plankton ecologists the ‘clear-water period’, caused by heavy zooplankton grazing and nutrient limitation. In Okanagan Lake the clear-water period is followed by a gradual increase in colonial blue-green algal populations from late August to October that is often accompanied by a late autumn diatom increase in late October and early November. As mentioned there were several major departures from this typical seasonal pattern during 2003 and 2004, and these ‘depressions’ can readily be seen in the time-series graphs (Figs. 4, 5). Apart from the ‘bloom’ occurrences in 2003, the most puzzling feature of 2003 but especially the 2004 season was the phytoplankton population depressions that occurred from August to October in 2003 and from early June to November in 2004. Okanagan Lake phytoplankton monitoring spans close to 55 years, and the phytoplankton densities of 2004 are close to, if not the lowest yet, to be recorded. A key question is what are some of causal factors responsible for these heretofore unseen successional patterns in 2003 and 2004? Trends in Major Phytoplankton Groups At all stations and all years in Okanagan Lake in terms of both biomass and abundance, blue-green algae (Cyanophytes) were the major algal group followed next by diatoms (Bacillariophytes) and a diverse assemblage of nano-flagellates (Chrysophytes and Cryptophytes). Green algae (Chlorophytes) and dinoflagellates (Dinophytes) were the least abundant groups in terms of their contributions to density or biomass, the exception being 2003 at southern stations where Gymnodinium populations exploded. From March to early June at all stations in 2004 and 2005 there were moderately high populations of the pico-cyanobacteria Synechococcus spp. at Stations OK 3, 6, and 7, but these picoplankters were not as abundant at OK 1 and 8 as in previous years. Prior to 2004, pico-cyanobacteria populations in Okanagan Lake were prominent in spring, peaking in May/June. Pico-cyanobacteria are a minute (1.5-2.0 μm) and ubiquitous group of autotrophic blue-green algae that occur in greatest abundance in oligotrophic lakes and oceans [see Photo 1] (Stockner 1991). They are thought to be unable to fix


nitrogen, but owing to their small cell size they contribute greatly to pelagic carbon production because of their rapid growth rates and ability to sequester nutrients at low concentrations (Stockner and Antia 1986). The decline of Synechococcus in late June, early July in Okanagan Lake is concurrent with the increase of moderate populations of filamentous/colonial blue-greens, e.g., Lyngbya, Oscillatoria spp., Aphanizomenon, Aphanothecae, Anabaena, Gomphosphaeria, and Coelosphaeria and a few dinoflagellates. In past years, these blue-greens were the predominant contributors to total phytoplankton biomass and abundance at all stations in Okanagan Lake from July to November. But in 2003, they were predominant only from May to July, remaining scarce to the end of the sampling season in November. In 2004, unprecedented low numbers were recorded at all stations from June to November, returning in 2005 to ‘normal’ average densities, notably in the northern sector of the lake, i.e., OK 6, 7, 8. Small nano-flagellate (2-20 μ) species (e.g., Cryptomonas, Chrysochromulina, Chroomonas, Rhodomonas, Kephrion, Pseudokephrion, Dinobryon) in past years usually comprised about 15% of the phytoplankton biomass at all stations throughout much of the growing season. They were most common in late spring and early summer following decline of the spring diatoms. In 2003, flagellate populations were comprised of larger species, and their populations peaked in May and June concurrent with the pico-cyanobacteria increase. In 2004, flagellates followed the same seasonal trends but were less abundant throughout the lake, notably at OK 1. In 2005, nano-flagellates were more abundant and their population density near ‘normal’ at ~1-3,000 cells/mL. In nearly all years, and at all lake stations diatom populations were most common in the spring, reaching peak abundance in May/June especially so at station OK 7 and 8, in Armstrong and Vernon Arms. But the spring pulse occurred a month earlier in 2004 and did not achieve the densities of previous spring increases. In 2005, there was a moderate abundance and wide diversity of diatoms. At all stations the most abundant diatom genera were Cyclotella spp., Fragilaria crotonensis, Fragilaria acus, Asterionella formosa, Aulacoseira and Rhizosolenia erinensis. A distinct autumnal diatom peak occurred in November 2003 only at OK 8 but no pulses occurred in 2004. Major pulses in 2005 were in April and May with rising populations again observed at the last sampling in early October. The least abundant phytoplankters in Okanagan Lake from 1999 to 2003 were dinoflagellates (Dinophytes) and green algae (Chlorophytes). Though genera from each class were present at all stations through much of the growing season (e.g., Peridinium, Gymnodinium, Cosmarium, Planctonema, Oocystis, Chlorella, Ankistrodesmus, Elakatothrix) they were never common except in 2003. In that year a striking bloom of Gymnodinium occurred in June at OK 1 and 3 and a small Chlorella-like coccoid green reached bloom concentrations at the end of August at Stations OK 3 and 7 - > 2,500 cells/mL. This chlorophyte mini-bloom in 2003 remains enigmatic. It only occurred at these two stations located at opposite ends of the lake! In 2004 and again in 2005, there were no major dinoflagellate blooms and their populations were low throughout the lake as was the case for green algae. The only


noteworthy exception was in 2004 at stations OK 3 and 6 where they contributed significantly to total biomass in October. Phytoplankton Vertical Distribution in 2003 There was no discrete depth vertical phytoplankton sampling in Okanagan Lake in 2005, but some of the major findings from the July and September 2003 vertical series taken from all stations (except OK 4) are informative: 1. The highest overall abundance of phytoplankton (at all depths) occurred at OK 1

with a peak densities at 7.5 m. OK 3 had the next highest overall abundance but peak concentrations were deeper - 10 m. Stations 6, 7 and 8 had similar overall abundances, and peak densities at 15 m.

2. The Class compostion of each of the vertical samples was similar throughout all depths and among all stations with higher densities of diatoms at deeper depths. At OK 6 and 7 blue-greens were more abundant than diatoms, with nearly a 2-fold higher abundance at the 4 m depth.

3. Phytoplankton biomass in July profiles showed greatest abundance at stations OK 1 and 3 at 7.5 m and 15 m depths, and blue-greens comprised the highest percentage of total biomass.

4. In the September profiles blue-greens contributed the most to biomass at all depths

and stations, with the highest abundances at 15 m at OK 8 and 4 m at OK 1 and OK 7.

5. Overall there was less depth variance (vertical difference) in biomass than in cell

abundance on both sampling dates. DISCUSSION Estimates of Okanagan Lake seasonal average values of phytoplankton abundance and biomass from 1999 to 2003 and in 2005 have been within ranges commonly observed in large, BC interior oligotrophic lakes (Stockner and Shortreed 1975, 1994; Pieters et al. 2003). In 2004, lake averages were exceptionally low and similar to values common to coastal, fast-flushing lakes (Stockner 1981, 1987). A small to moderate vernal diatom increase followed by an increase of nano-flagellates and dinoflagellates is the most common spring phytoplankton successional pattern in ‘interior’ oligotrophic lakes (Stockner and Shortreed 1975). The spring flagellate sequence is tightly coupled to the cellular release of dissolved organic carbon (DOC) by senescent diatoms that trigger the exponential growth of bacteria and autotrophic picoplankton (Photo 1), the primary food of heterotrophic flagellates and ciliates. This pattern was not exhibited in either 2003 or 2004 when most spring populations were small, but returned in 2005. The early February to April blue-green blooms at OK 8 in 2003 occurred at a most unusual time. It is speculated that they were responding to increasing irradiation and high over-winter


nutrient concentrations (high P, low N), but this conjecture needs verification. Another unusual occurrence in June 2003 was dinoflagellates bloomed at OK 1 and 3 (Fig. 4). This event was likely related to large bacteria and pico-cyanobacteria population increases, since dinoflagellates are known to be bacterivores as well as phototrophs and are capable of consuming large numbers of minute picoplankters (Stockner and Porter 1988). The long summer/fall period of population depressions in both 2003 and 2004 were probably related to hydrologic/climatic conditions, i.e., low water inputs and very strong and stable epilimnetic stratification resulting in severe N & P nutrient co-limitation (Rae and Ashley in Andrusak et al. 2004). In normal or ‘average’ climatic years Okanagan Lake diverges from the more typical phytoplankton successional pattern of small populations of flagellates and greens in late June, to one of colonial blue-green algal dominance. This pattern is not common in other large, interior oligotrophic BC lakes, e.g., Shuswap, Chilco, Quesnel (Stockner 1987). Summer occurrence of blue-greens in meso/oligotrophic lakes is normally caused by the rapid disappearance of dissolved inorganic nitrogen (DIN) from the epilimnion in late May or early June that often creates a very low DIN:TDP ratio (< 2.0). This is the normal pattern for Okanagan Lake where the epilimnion is usually nitrogen depleted by June/July. Moderate TDP concentrations and depleted DIN create ‘optimal’ conditions for growth for both colonial N2-fixing and non N2-fixing blue-green algae. Under these conditions, the diatoms have sunk out or, if edible, have been grazed out of the epilimnion. This protracted state of epilimnetic N-depletion in ‘normal’ years occurs throughout the lake until fall overturn (deep mixing) entrains meta/hypolimnetic DIN and TDP to surface waters again that can produce a small fall diatom pulse. But in summer 2003 and once again in 2004, this successional phase of blue-green increase was abbreviated, lasting only to the end of July in 2003 and June in 2004, when all phytoplankton populations collapsed (population depression). This collapse was probably due to nutrient co-limitation. In 2005, conditions were not as severe as in the previous two years and a more normal successional sequence was partially restored. It is theorized that loss of both N and P in Okanagan Lake are correlated with the population depressions of 2003 and 2004, i.e., nutrient co-limitation in the epilimnion. Also, hydrologic/climatic factors during the second and third consecutive warm, low water years in the Okanagan Valley resulted in low nutrient input that most likely were catalysts for the collapse! By virtue of its predominantly xeric bio-geoclimatic zone, the period of Okanagan Lake epilimnetic DIN depletion tends to be more protracted, lasting well into early November and fall overturn (deep mixing), but in 2003 and especially in 2004 low or trace levels of TDP must also have been depleted (or at detection limits), leading to the collapse of all populations. Even in the nutrient enriched Armstrong Arm, where large populations of blue-greens are common, summer populations were abnormally low. Are these trends heralding the onset of the ‘oligotrophication’ of Okanagan Lake? Quite possibly so, as it is clear that phytoplankton populations for the past three years are responding, changing, and adapting to a low and scarce nutrient regime that seems to have been partially restored in 2005! Why phytoplankton populations were at such unprecedented low levels from July to October in 2004 remains conjectural. However, causality must come either from top-down biological


control, (e.g., grazing) or bottom-up physico-chemical, (e.g., protracted nutrient limitation), or a combination of both. It is believed the former control mechanism is the more likely one, i.e., bottom-up control. Regardless, further research with a greater sampling effort will be required to resolve the issue. Comparisons with Other Large Reservoirs A comparison of average seasonal abundance and biovolume estimates from Okanagan Lake in 2005 with several other large BC reservoirs underscores the paucity of its population especially compared to more productive Kootenay Lake and treated Arrow Reservoir. Okanagan phytoplankton abundance in 2005 was similar to Revelstoke in 2003 but higher than Kinbasket Reservoir, the least productive (ultra-oligotrophic) of pelagic habitats compared (Table 2). It is particularly instructive to compare the 1999-2005 seven year phytoplankton time-series from Arrow Reservoir with Okanagan Lake (Table 3). It is clear that on average, the occurrence of the summer/fall colonial blue-green populations in Okanagan Lake create a greater biomass (biovolume) and slightly higher average population density than in Arrow Reservoir, even under treated conditions (Table 3). But the comparison for Year 2005 shows Okanagan’s phytoplankton densities much lower than in Arrow Reservoir, but owing to the greater numbers of colonial blue-greens in Okanagan, the biomass values were similar between systems. Since 1999, Upper Arrow Reservoir has been subjected to experimental fertilization (Pieters et al. 2003) and the ambient early spring DIN is nearly 3-fold higher than in Okanagan Lake and ambient concentrations remain higher through much of the growing season. As a result large filamentous N2 - fixing blue-greens have been either rare or completely absent, but in 2004 and 2005 with the occurrence of Anabaena spp. for the first time, they may be increasing with successive years of treatment. With high DIN and TDP supplementation from a point source of application (Upper Arrow Lakes Reservoir ferry crossing) diatoms are now prevalent throughout much of the growing season and in recent years inedible species have become dominant creating a notable carbon ‘sink’. In 2003 and especially in 2004, Okanagan Lake (all station average) had lower phytoplankton abundance but a larger biomass than fertilized Arrow Reservoir in its sixth year of treatment. It is interesting to note that though average phytoplankton abundance in most of the early years in both systems is similar, owing to the prevalence of colonial blue-greens, Okanagan Lake has always had a much higher average phytoplankton biomass than Arrow (Table 3).


Table 2. Comparison of phytoplankton abundance, and biomass in Okanagan Lake with Williston, Arrow, Revelstoke, Kootenay, Kinbasket Reservoirs, 2005.

Year Okanagan Williston Arrow Revelstoke Kootenay Kinbasket

Abundance (Cells/mL) 2005 3,249 4,5711 4,806 3,2852 5,645 1,582

Biovolume (mm3/L) 2005 0.74 0.241 0.72 0.202 1.01 0.23

1 Data from 2000 2 Data from 2003 Table 3. Comparison of phytoplankton abundance and biovolume 7-yr time series in

Okanagan Lake with Arrow Reservoir, 1999-2005.

Year Okanagan Arrow Abundance (Cells/mL)

1999 2000 2001 2002 2003 2004 2005

5,354 5,100 3,978 5,345 4,658 2,651 3,249

5,274 5,086 6,173 4,713 6,239 4,183 4,806

Average (n=7) 5,211 4,334

Biovolume (mm3/L)

1999 2000 2001 2002 2003 2004 2005

0.77 0.69 0.75 0.80 0.85 0.50 0.74

0.29 0.46 0.67 0.51 0.67 0.63 0.72

Average (n=7)

0.73 0.56

One of many unanswered questions about Okanagan Lake is whether the productive capacity of the lake or its ability to support productive fisheries, has changed since the early 1970s when one of the first multidisciplinary studies of the basin was completed (Stockner and Northcote 1974). A collation of water quality data gathered over the past 3 decades provides some evidence of change (Jensen in Ashley et al. 1999). Some of the more salient points are: • TP and TDP values increased through the late 1970s and early 1980s, declined

briefly through the late 1980s and early 1990s, and then rose again in the mid-1990s to a peak in 1997 then declined in 1998 and 1999 to values similar to those reported in 1973. Is this downward trend continuing? Recent evidence supports the continuing downward trend (see Rae et al. in Andrusak et al. 2004).


• TN and spring NO3 values may have gradually risen over the past 3 decades but rates of epilimnetic NO3 depletion appear to have increased and now occur earlier and extend later into the growing season, e.g., Armstrong Arm bloom commencement in February, peak in April 2002, 2003 and a much smaller May peak in 2004, with the latter two peaks not sustainable into the summer period. Co-limitation by TDP as well as DIN is suspected (see Rae and Wilson in Andrusak et al. 2004).

• After May/June, dissolved nitrogen is the limiting nutrient for phytoplankton growth,

though co-limitation (both N & P) is likely to occur in late summer and fall. Co-limitation was speculated to be chronic in 2004, the third consecutive dry, low-water year (2003 and 2004) and also prevalent in 2005 despite slightly higher plankton densities.

• Phytoplankton densities were relatively stable for two decades but have increased in

the 1990s, with a notable increase in blue-green algal populations. The TDP levels have not yet increased to concentrations sufficient to create ‘mini-bloom’ conditions, but may be near ‘critical’ levels to trigger a bloom at the northern end of the lake (e.g., OK 8 in 2004, OK 7 and 8 in 2005). It was speculated that mini blooms may possibly occur at station OK1 near Summerland by 2005, but this was detected in 2005; in fact densities at this stations were among the lowest in 2005. The long-term stable phytoplankton successional trends appear to have been reversed starting in 2003 and strikingly so in 2004. In 2005 however, some sense of restoration of a normal pattern was observed.

• The fall increase of diatoms that is coincident with deep mixing events in October

and November, common in the 1970s, has been eliminated from most stations of Okanagan Lake by extended strong autumnal temperature gradients, i.e., stable stratification, and protracted periods of DIN depletion and suspected TDP co-limitation in 2003, 2004, and 2005 (see Rae and Wilson in Andrusak et al. 2004).

In 2001, the first of a series of ‘low water’ years average phytoplankton abundance and biomass were the lowest recorded in five years of more intensive monitoring. In 2002, the phytoplankton populations were moderate but showed changes in seasonal patterns from the more typical 1999 pattern. In 2003 and 2004, major deviations were observed from the more typical phytoplankton seasonal succession. This was likely related to hydrologic/climatic factors and was exacerbated by hot and dry summers, strong stratification and likely nutrient co-limitation. The nutrient retention by Okanagan Lake’s aerobic deep-water sediments coupled with the long hydraulic water-residence time, which in dry years can be > 90 years, helps to maintain the lake’s oligotrophic condition. Based on several physico-chemical criteria, Okanagan Lake can still be considered as oligotrophic, but based simply on abundance and biomass of phytoplankton the trophic state of the lake in the last two years has declined to near ultra-oligotrophic levels (Stockner 1987). Despite the rapid scale of development within the drainage basin, at least until 2003 and 2004, there have been


only small changes in the dynamic of phytoplankton populations (e.g., increases in abundance of blue-greens and gradual elimination of the autumnal diatom increase) but overall population successional patterns have remained quite predicable. However, in 2003 and 2004, major changes in the dynamic were observed and several of these portend the ‘oligotrophication’ of the lake with its attendant affects on the lakes fisheries, such as low production status (see Stockner et al. 2000). It is likely that unless steps are taken to rectify the lake’s epilimnetic DIN:TDP imbalance that now quite possibly includes a scarcity of TDP as well as DIN, that large macro-zooplankton forage production will continue to decline either from blue-green population increases (inedible C sinks) or more likely from oligotrophication (inefficient microbial food webs). Whether the composition and/or scarcity of large macro-zooplankters has been significant enough to affect juvenile kokanee growth/survival in the pelagic over the past few decades still remains uncertain and will require further study.


RECOMMENDATIONS 1. Further studies should be done to assess the vertical distribution of phytoplankton.

Limited sampling in 2003 suggested greater biomass and densities at deeper depths, but the database is limited to 2 dates and shows too high a variance to properly assess depth distribution patterns. Attempts should be made to assure that discrete-depth samples from each station are taken on the same day (if possible) or at minimum over 2 consecutive days. Further, they should be taken monthly through the growth season (April to October) and an additional sample from 20 m should be included at all stations.

2. Limited (3 runs) size-fractionated primary production studies (14C assimilation)

should be done in 2006 (one in April/May, another in July/August, and a final run September/early October) to determine efficiency of phytoplankton growth, and provide estimates of annual system C production (now lacking). 14C production by size-fractions (pico- vs. nano- vs. micro) is recommended to determine carbon flows through the ‘edible’ and ‘inedible’ fractions of phytoplankton communities present at these 3 critical time periods.

3. A more detailed examination of the phytoplankton community of the lake is now warranted in light of the changes now occurring in Armstrong Arm, Vernon Arm and OK 1 off Summerland. Winter sampling should commence in February 2006 to document ambient DIN and TDP levels and phytoplankton abundance, and late-autumn samples must be taken until lake over-turn is completed i.e. November.

4. Epiflouorescence counts of free-living bacteria and pico-cyanobacteria should be incorporated into the monthly monitoring program to determine their seasonal abundance and role in supporting microbial food webs, nutrient fluxes and carbon flows in Okanagan Lake. If these comprehensive OLAP monitor studies are ever to be published in peer-reviewed journals, then these data on picocyanobacteria and bacteria will be essential for the interpretation of carbon flux/flow in Okanagan Lake as it impacts forage base and the fisheries. This is important information that would be of great interpretive value as the lake changes from the oligotrophic to the ultra-oligotrophic condition.


REFERENCES Andrusak, H., S. Matthews I. McGregor, K. Ashley, G. Wilson, L. Vidmanic, J. Stockner,

D. Sebastian, G. Scholten, P. Woodruff, D. Cassidy, J. Webster, A. Wilson, M. Gaboury, P. Slaney, G. Lawrence, W.K. Oldham, B. Jantz and J. Mitchell. 2003. Okanagan Lake Action Plan Year 7 (2002) Report. Fisheries Project Report No. RD 106, 2003. Fisheries Management Branch, Ministry of Water, Land and Air Protection, Province of British Columbia.


G. Scholten, P. Woodruff, D. L. Vidmanic, J. Stockner, G. Wilson, , B. Jantz, J. Webster, H. Wright, C. Walters and J. Korman. 2004. Okanagan Lake Action Plan Year 8 (2003) Report. Fisheries Project Report No. RD 108. 2004. Fisheries Management Branch, Ministry of Water, Land and Air Protection, Province of British Columbia.

Ashley, K., I. McGregor, D. Sebastian, B. Shepherd, Lidija Vidmanic, P. Ward,

H. Yassien, L. McEachern, H. Andrusak, D. Lasenby, J. Quirt, J. Whall, E. Taylor, A. Kuiper, P. Troffe, C. Wong, S. Matthews, G. Scholten, M. Zimmerman, P. Epp, V. Jensen, and R. Finnegan. 1999. Okanagan Lake Action Plan, Year 3 (1998) Report. Fisheries Project Report No. RD 78. Fisheries Management Branch, Ministry of Fisheries, Province of British Columbia.

Lund J.G., C. Kipling, and E.D. LeCren. 1958. The Inverted Microscope Method of

Estimating Algal Numbers and the Statistical Basis of Estimations by Counting. Hydrobiologia. 11: 143-170.

Pieters, R., L. Vidmanic, S. Harris, J. Stockner, H. Andrusak, M. Young, K. Ashley, B.

Lindsay, G. Lawrence, K. Hall, A. Eskooch, D. Sebastian, G. Scholten and P.E. Woodruff. 2003. Arrow Reservoir Fertilization Experiment - Year 3 (2001/2002) Report. Fisheries Project Report No. RD 103. Ministry of Water, Land and Air Protection, Province of British Columbia.

Stockner, J.G. 1981. Whole-Lake Fertilization for the Enhancement of Sockeye

Salmon (Oncorhynchus nerka) in British Columbia, Canada. Verh. Internat. Verein. Limnol. 21: 293-299.

Stockner, J.G. 1987. Lake Fertilization: The Enrichment Cycle and Lake Sockeye

Salmon (Oncorhynchus nerka) Production, pp. 198-215. In: H.D. Smith, L. Margolis and C.C. Wood (eds.). Sockeye Salmon (Oncorhynchus nerka) Population Biology and Future Management. Can. Spec. Publ. Fish. Aquat. Sci. 96, 486 P.

Stockner, J.G. 1991. Autotrophic Picoplankton in Freshwater Ecosystems: The View

From the Summit. Int. Rev. gesamten Hydrobiol. 76: 483-492.


Stockner, JG and TG Northcote. 1974. Recent Limnological Studies of Okanagan Basin Lakes and their Contribution to Comprehensive Water Resource Planning. J. Fish. Res. Board Can. 31: 955-976.

Stockner, JG and KS Shortreed. 1975. Phytoplankton Succession and Primary

Production in Babine Lake, British Columbia. J. Fish. Res. Bd. Can. 32: 2413-2427.

Stockner, J.G. and N.J. Antia. 1986. Algal Picoplankton from Marine and Freshwater

Ecosystems: A Multidisciplinary Perspective. Can. J. Fish. Aquat. Sci. 43: 2472-2503.

Stockner, J.G. and K.G. Porter. 1988. Microbial Food Webs in Fresh Water Planktonic

Ecosystems, Carpenter SR (ed), Complex Interactions in Lake Communities, pp71-84, Springer Verlag, New York, NY.

Stockner, J.G. and K.S. Shortreed. 1994. Autotrophic Picoplankton Community

Dynamics in a Pre-Alpine Lake in British Columbia, Canada. Hydrobiologia 274: 133 142.

Stockner, J.G., C. Callieri, and G. Cronberg. 1999. Picoplankton and Other Non-Bloom

Forming Cyanobacteria in Lakes, pp 195-230, In: B.A. Whitton and M. Potts. (eds.), The ecology of Cyanobacteria. Kluwer Press, Amsterdam, Holland.

Stockner, J.G., E. Rydin, P. Hyenstrand. 2000. Cultural Oligotrophication. Fisheries 25:

7-14. Utermohl, H. 1958. Zur Vervollkommnung der Quantitativen Phytoplankton Methodik.

Int. Verein. theor. angew. Limnologie, Mitteilung 9.


Appendix 1. Okanagan Lake phytoplankton species, codes and biovolumes 2005. Code Class Bvol. Genus & Species

Bacillariophyte - diatoms AM Bacillariophyte 80 Achnanthes sp AY Bacillariophyte 100 Asterionella formosa var1 AZ Bacillariophyte 120 Asterionella formosa var2 CP Bacillariophyte 200 Cocconeis sp. CU Bacillariophyte 500 Cyclotella bodanica CZ Bacillariophyte 350 Cyclotella comta CJ Bacillariophyte 350 Ceratoneis sp. CS Bacillariophyte 150 Cyclotella stelligera CW Bacillariophyte 50 Cyclotella glomerata CT Bacillariophyte 150 Cyclotella sp CM Bacillariophyte 500 Cymbella sp. (large) CO Bacillariophyte 250 Cymbella sp. DF Bacillariophyte 150 Diatoma sp. EV Bacillariophyte 250 Eunotia sp. FF Bacillariophyte 80 Fragilaria construens FC Bacillariophyte 120 Fragilaria crotonensis FG Bacillariophyte 100 Fragilaria capucina GG Bacillariophyte 750 Gomphonema sp. MD Bacillariophyte 350 Aulacoseira distans MI Bacillariophyte 200 Aulacoseira italica MJ Bacillariophyte 250 Aulacoseira granulata MZ Bacillariophyte 350 Aulacoseira sp. NV Bacillariophyte 500 Navicula sp. NZ Bacillariophyte 200 Nitzschia sp. RC Bacillariophyte 50 Rhizosolenia sp. SH Bacillariophyte 500 Stephanodiscus hantschii. SE Bacillariophyte 1500 Stephanodiscus sp. SN Bacillariophyte 100 Fragilaria acus SO Bacillariophyte 150 Fragilaria angustissima SU Bacillariophyte 1000 Fragilaria ulna SS Bacillariophyte 500 Suriella SR Bacillariophyte 250 Fragilaria sp. PI Bacillariophyte 2000 Pinnularia sp. TF Bacillariophyte 500 Tabellaria fenestrata TB Bacillariophyte 500 Tabellaria flocculosa DL Bacillariophyte 250 Diploneis sp. Chryso-Cryptophyte flagellates BS Chryso-cryptophyte 200 Bitrichia sp. CH Chryso-cryptophyte 250 Chilomonas sp. XX Chryso-cryptophyte 20 Chromulina sp1 CA Chryso-cryptophyte 150 Chroomonas acuta YO Chryso-cryptophyte 500 Chryptomonas sp. CC Chryso-cryptophyte 75 Chrysochromulina sp. DN Chryso-cryptophyte 150 Dinobryon sp1


DO Chryso-cryptophyte 200 Dinobryon sp2 KA Chryso-cryptophyte 50 Kephyrion sp. IS Chryso-cryptophyte 200 Isthmochloron MH Chryso-cryptophyte 500 Mallomonas sp1 MG Chryso-cryptophyte 700 Mallomonas sp2 SX Chryso-cryptophyte 75 Stenokalyx YZ Chryso-cryptophyte 15 Small microflagellates OC Chryso-cryptophyte 250 Ochromonas sp. PT Chryso-cryptophyte 100 Pseudokephrion sp. PP Chryso-cryptophyte 150 Pseudopedinella sp. CI Chryso-cryptophyte 75 Chrysoikos sp. SY Chryso-cryptophyte 700 Synura RO Chryso-cryptophyte 100 Rhodomonas sp. CF Chryso-cryptophyte 250 Chrysidiastrum Dinophyte GY Dinophyte 500 Gymnodinium sp1 GZ Dinophyte 1500 Gymnodinium sp2 CE Dinophyte 5000 Ceratium PJ Dinophyte 350 Peridinium sp1 PK Dinophyte 700 Peridinium sp2 Chlorophyte XC Chlorophyte 80 Ankistrodesmus sp. CX Chlorophyte 150 Coccomyxa sp. CL Chlorophyte 500 Coelastrum sp. CN Chlorophyte 500 Cosmarium sp. CK Chlorophyte 200 Crucigenia sp. XU Chlorophyte 700 Crucigeniella apiculata DI Chlorophyte 900 Dichtyosphaerium LA Chlorophyte 30 Langerheimia EL Chlorophyte 250 Elakatothrix sp3 EU Chlorophyte 2500 Euglena GO Chlorophyte 500 Gonium OO Chlorophyte 500 Oocystis sp. SI Chlorophyte 60 Scenedesmus sp. SD Chlorophyte 1500 Staurodesmus sp. QD Chlorophyte 250 Quadrigula UL Chlorophyte 700 Ulothrix CD Chlorophyte 150 Closteriopsis MO Chlorophyte 200 Monoraphidium NE Chlorophyte 350 Nephrocytium ST Chlorophyte 1000 Staurastrum sp. PL Chlorophyte 350 Planctonema sp. PA Chlorophyte 1000 Planctosphaeria PS Chlorophyte 100 Paulschultzia sp. CB Chlorophyte 20 Chlorella KI Chlorophyte 50 Kirchneriella sp. PE Chlorophyte 1000 Pediastrum sp. PA Chlorophyte 1500 Pandorina sp.


TE Chlorophyte 50 Tetraedron VO Chlorophyte 4000 Volvox XI Chlorophyte 700 Xanthidium Cyanophyte AB Cyanophyte 300 Anabaena sp AC Cyanophyte 900 Anabaena circinalis AH Cyanophyte 100 Aphanothecae sp. AP Cyanophyte 1500 Aphanizomenon sp. MS Cyanophyte 20 Merismopedia sp. ZN Cyanophyte 20 Oscillatoria sp2 ZO Cyanophyte 350 Oscillatoria limnetica SC Cyanophyte 5 Synechococcus sp. (<2 um) CY Cyanophyte 10 Synechocystis MX Cyanophyte 500 Microcystis sp. LB Cyanophyte 500 Lyngbya sp. OA Cyanophyte 750 Oscillatoria agardhii


Photo 1.

Photo 1. Electron micrograph of Synechococcus (top) (size of cell is 1μ), free-living

bacteria (center) (size of cells is 0.5 μ), seasonal morphs of pico-cyanobacteria (bottom). Photo M. Klut & J. Stockner, UBC, Vancouver, BC.


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Figure 1. Seasonal (April to November) epilimnetic abundance and biovolume of the

major phytoplankton classes in Okanagan Lake, 2004-2005.


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abundance (a) and biovolume (b) at different stations in Okanagan Lake, and the whole lake averages 1999-2005.


cell number (x10e4, cells/L) biovolume (x10, mm3/m3)

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major phytoplankton classes in Okanagan Lake, 1999-2005.


ZOOPLANKTON AND MYSID POPULATION ABUNDANCE AND COMPOSITION TRENDS IN OKANAGAN LAKE

2005

Rowena Rae1 and Lidija Vidmanic2

INTRODUCTION During its first 10 years, the Okanagan Lake Action Plan (OLAP) has conducted a monitoring program to collect baseline information about cladoceran and copepod zooplankton populations and mysid shrimp (Mysis relicta) populations in Okanagan Lake. These data help to determine the current status of zooplankton and mysids, including their abundance, biomass, and productivity. The data are used in support of OLAP’s objective to recover wild kokanee in the lake. The freshwater opossum shrimp, Mysis relicta, was introduced to Okanagan Lake in 1966 as an additional food source for fish (Shepherd 1990). Later, biologists realized that these shrimp compete with kokanee for their preferred prey of cladoceran zooplankton, and they have probably contributed to the decline of the kokanee population. Mysid–kokanee competition for zooplankton has been documented in Okanagan Lake (Whall and Lasenby in Andrusak et al. 2000) and other large BC lakes (Ashley et al. 1997). While there are no known means of eliminating these introduced shrimp from a lake (Northcote 1991), one component of OLAP has been to encourage the development of a commercial harvest of mysids (Andrusak and Matthews in Andrusak et al. 2002a; also see Andrusak et al., in this OLAP report). The study of zooplankton and mysid shrimp distribution and abundance in Okanagan Lake are an integral part of OLAP. This report summarizes the zooplankton and mysid shrimp data collected in 2005, with comparisons to previous years. METHODS Zooplankton OLAP began collecting and analyzing Okanagan Lake pelagic zooplankton in August 1996. Samples have been collected from up to eight stations (Table 1), with additional samples collected in the first two years from Kalamalka Lake (Ashley et al. 1998, 1999a). Samples were taken monthly in 1996 (August to October), 1997-1998 (February to December), 1999-2002 and 2004 (April to November), and 2003 and 2005 (April to October) with a vertically hauled Wisconsin net (0.5 m diameter mouth, 153 µm mesh). The net was lowered and then retrieved from a depth of 45 m, and samples 1 Sumac Writing and Editing, Summerland, BC. 2 Limnologist, BC Conservation Foundation, Vancouver, BC.


were preserved in 70% ethanol for later analysis. Two replicate hauls were taken from the deepest part of a transect across the lake at each site from August 1996 to May 1997. This procedure was changed in June 1997 to account for possible patchy distribution of zooplankton due to Langmuir spirals (see McEachern in Ashley et al. 1999a), and three vertical hauls were taken at each site: one sample at mid-lake, and single samples 500 m to the east and west of the mid-lake sample. In 2003-2005, the number of replicates was reduced to two: one sample at mid-lake and one from 500 m to either the west or east of mid-lake. Table 1. Okanagan Lake Action Plan zooplankton sample sites, 1996-2005. Sitea Site Site Name Year Designation Number 1996b 1997c 1998-2005KA1 0500246 Kalamalka Lake, south end x x KA2 0500847 Kalamalka Lake, deep basin x x OK 1 0500454 Okanagan Lake, South Prairie Creek x x x OK 2 0500729 Okanagan Lake, South Squally Point x x OK 3 E223295 Okanagan Lake, opposite Rattlesnake

Island x x x

OK 4 0500236 Okanagan Lake, downstream of Kelowna Sewage Treatment Plant

x x xd

OK 5 0500456 Okanagan Lake, upstream of Kelowna Sewage Treatment Plant

x x

OK 6 0500730 Okanagan Lake, north of Ok. Centre x x x OK 7 E206611 Okanagan Lake, at Vernon outfall x x x OK 8 0500239 Okanagan Lake, centre of Armstrong Arm x x x a See Map 2. b OK 7, OK 6, and OK 5 were the only sites sampled in Nov 1996. c Several stations not sampled in Feb and Mar due to ice cover. d Sampled select months: Feb, Mar, Aug, and Dec 1998; May, Aug, and Nov 1999-2000; Aug 2001; May, Aug, and Nov 2002-2004; Apr, May, and Aug 2005. Samples collected from 1996-1998 were analyzed at the Penticton office of the Ministry of Environment, Lands and Parks (MELP) lab by L. McEachern (see Ashley et al. 1999b). Samples were split using a two-chambered Folsom plankton wheel and counted in a square gridded dish under a microscope at 10X magnification. Cladocerans were identified to genus and copepods to suborder (Calanoida or Cyclopoida). Beginning in June 1997, copepods were also identified to genus. Effective April 1999, the samples have been analyzed at the UBC Fisheries Centre by Dr. L. Vidmanic. Samples were re-suspended in tap water, filtered through a 74-µm mesh, and sub-sampled using a four-chambered Folsom-type plankton splitter. Splits were placed in gridded plastic petri dishes and stained with Rose Bengal to facilitate viewing with a Wild M3B dissecting microscope. For each replicate, organisms were identified to species level and counted until up to 200 organisms of the predominant species were recorded. If 150 organisms were counted by the end of a split, a new split was not started. The length of 30 of the most common cladocerans and copepods were measured for biomass calculations using a mouse cursor on a live video image.


Lengths were converted to biomass (µg dry weight) using empirical length-weight regressions from McCauley (1984). The reproductive stage of females and the number of eggs carried by gravid females (egg-bearing) were recorded for use in fecundity estimates. Density estimates from the MELP lab in Penticton and the UBC Zoology lab were compared and found to be similar (Thompson and Kuzyk in Ashley et al. 1998). Mysid Shrimp Sampling for Mysis relicta in Okanagan Lake was conducted monthly in 1996 (August to November), 1997 (February to December), 1998 (January to October), 1999 (April to December), 2000 (April to November), 2001-2002 and 2004 (February, April to December), 2003 (February, April to November), and 2005 (February, April to October). Sampling occurred around the period of the new moon (moonless nights) from several stations along the length of the lake (Map 2 in the Introduction of this OLAP annual report; Table 2 below). From August to October 1996, two replicate pelagic hauls were taken from the deepest part of a transect across the lake at each station, and two replicate (40 m) hauls were taken from a near-shore area either east or west of the pelagic haul. From November 1996 to December 2002, the procedure was changed to take two replicate hauls from the deepest part of a transect across the lake at each site, and single (40 m) hauls from near-shore areas to the east and west of the pelagic hauls. In 2003-2005, two replicate pelagic hauls were taken and one near-shore haul was taken from either east or west of the pelagic haul. The depth of pelagic hauls varied by site (Table 2), but all near-shore hauls were to a depth of 38-42 m. The mysids were captured using a vertically-hauled net with a 1-m2 mouth, 1,000-µm mesh size net, 210-µm mesh in the terminal cone, and 100-µm mesh in the collecting bucket. Nets were raised with a hydraulic winch at approximately 0.33 m·sec-1, and samples were preserved with 100% denatured alcohol (85% ethanol, 15% methanol) for later analysis. Samples collected in 1996-1998 were analyzed by Dr. D. Lasenby at Trent University in Peterborough, Ontario, where mysids were counted using a low power dissecting scope. Life history analysis was performed on select samples from stations OK 1, OK 3, and OK 6 and station KA 2 in Kalamalka Lake, with methods and results reported by Whall and Lasenby (in Ashley et al. 1999a).


Table 2. Okanagan Lake Action Plan Mysis relicta sample sites, 1996-2005.

Year Site Designationa

Site Number

Site Name Pelagic Haul Sample Depth (m)

1996 1997 1998 1999-2005

KA1 0500246 Kalamalka Lake South End x x xd KA2 0500847 Kalamalka Lake Deep Basin x x xd KA3 Kalamalka xb xe OK 1 0500454 Okanagan Lake South Prairie

Creek 80 x x x x

OK 2 0500729 Okanagan Lake South Squally Point

110 x x xf

OK 3 E223295 Okanagan Lake Op. Rattlesnake Island

140 x x x x

OK 4 0500236 Okanagan Lake DNS Kelowna STP

80 x x xg x

OK 5 0500456 Okanagan Lake UPS Kelowna STP

140 x x x x

OK 6 0500730 Okanagan Lake N. Ok. Centre 220 x x x xi

OK 7 E206611 Okanagan Lake at Vernon Outfall

80 x x x xi

OK 8 0500239 Okanagan Lake Central Armstrong Arm

50 x xc xh xc

a See Map 2 d not sampled Jan, July-Sept f only sampled Jan-Apr b sampled only July-Dec. e only sampled Feb-May g only sampled Apr-Oct. c not sampled due to ice; Feb, Mar, Apr 1997; Feb 1998 & 2000-02 & 2004-05 h only sampled March-Oct. 2000-01 (Feb) i not sampled due to ice; Feb 2005 Since April 1999, samples have been analyzed at the UBC Fisheries Centre by Dr. L. Vidmanic. The entire sample was examined for mysids using a low power dissecting scope. The reproductive stage of males and females was recorded for use in fecundity estimates. Sex was determined by the presence of the antennal peduncle in males or its absence in females, or by the formation of oostegites in females and genitalia in males. Juveniles did not exhibit any of the above sexual characteristics. Maturity in females was confirmed by the complete overlapping of the brood pouch and presence of chromatophores on the pouch. Brooding females were identified by the presence of developing eggs or embryos in the brood pouch. Spent females were those that had recently released their brood as indicated by an open brood pouch. Mature males were distinguished by the extension of the fourth pleopod beyond the base of the telson. Lengths were measured using a mouse cursor on a live video image on 30 organisms of each sex at each stage for use in biomass calculations. Total body length was determined from the tip of the rostrum to the edge of the last segment prior to the base telson. Lengths were converted to biomass (mg dry weight) using length-weight regressions developed from Okanagan Lake mysid samples taken in 1996 (Whall and Lasenby in Ashley et al. 1998). The equipment and techniques used are the same as those employed on Kootenay Lake (Ashley et al. 1997) and Arrow Lakes Reservoir (Pieters et al. 1998, 2000), allowing direct comparison of results between these large lake systems. Estimates of total mysid shrimp biomass in the lake were computed as follows: the lake was divided into zones (based on hydroacoustic work by Sebastian et al., this OLAP report) and the area for each zone at depths of 60 m and 10 m was derived from


Canadian Hydrographic chart 3052 using a polar planimeter. The lake area at each of the seven mysid sampling stations, both for depths > 60 m and 10-60 m, was then determined by matching hydroacoustic zones with mysid sampling stations. Table 3 shows how the zones were proportioned among the seven sampling stations. The areal biomass values for each near-shore (40 m depth) sample was multiplied by the corresponding area of lake between 10 m and 60 m depth, and the pelagic sample areal biomass by the area > 60 m in depth. Depths < 10 m, approximately 15% of total lake surface area of 34,950 ha, were assumed not to contain mysids. Mysid samples collected from 1989 through 1995 were also obtained with a vertically hauled net, but with a circular 0.96-m diameter mouth opening and equipped with a net of variable mesh sizes ranging from 1,000 µm to < 500 µm. These samples were collected only once per year, in late-September or early-October around the period of the new moon. Five of the sites sampled correspond spatially to OLAP stations (OK 1, OK 3, OK 4, OK 6, OK 7), and are therefore, used for historical comparison. A side-by-side comparison of the two nets was conducted in 1997 by McEachern (in Ashley et al. 1999a) to determine the comparability of data collected by the nets. It was determined that the ‘new’ net captured 1.43 times as many mysids per m2 as the ‘old’ net, and this number was used to convert density values from 1989-1995 (original data on file, BC Fisheries, Penticton, #40.3902) to values comparable with data taken from 1996 onward. Table 3. The area of Okanagan Lake at two different depth intervals, corresponding

to the Mysis relicta sampling stations and hydroacoustic zones.

Site Hydroacoustic Zones Lake Area (ha) Total (ha)

Numbera Geographic Reference Marksa 10-60 m >60 m

OK 1 South end to OK 2 2,727 3,521 6,248 OK 3 OK 2 to Powers Ck. 1,346 3,486 4,833 OK 4 Powers Ck. to Kelowna Bridge 1,985 2,347 4,332 OK 5 Kelowna Bridge to Ok. Ctr. Resort 1,044 3,012 4,056 OK 6 Ok. Ctr. Resort to Shorts Ck. 1,234 4,203 5,437 OK 7 Shorts Ck. to north end 2,589 1,208 3,797 OK 8 Armstrong Arm 828 0 828

Total (ha) 11,753 17,777 29,530 a See Map 2.


RESULTS Zooplankton The following analysis is focused on data collected from five stations in Okanagan Lake (OK 1, OK 3, OK 6, OK 7, OK 8) monitored consistently as part of OLAP since 1996. General Trends The abundance of pelagic zooplankton in Okanagan Lake from May to October has averaged 18.5·L-1 since 1999 (Table 4). The range between years has varied considerably, with a high of 25·L-1 in 1999 and a low of 8·L-1 recorded in 1998 (Table 5). In 2005, abundance was 10.5·L-1, which marks a decrease after four years of fairly consistent abundance around 16·L-1 (Table 5). Despite the fluctuations, population composition appears to have remained relatively constant in both the main lake (stations OK 1-7) and the limnologically different Armstrong Arm (OK 8). The population in 2005 was numerically dominated by copepods (calanoid and cyclopoid), which accounted for >99% of the April and May populations and over 90% of June and August to November populations (Fig. 1). This is consistent with the population composition recorded in previous years (Rae and Vidmanic in Andrusak et al. 2004, 2005). The cladoceran population in Okanagan Lake tends to peak at 7-13% of total zooplankton density in mid-late summer (July-September). In 2005, the population exceeded this range and peaked in July at 17.6% (Fig. 1). A peak of 17% was also measured in July 2004 (Rae and Vidmanic in Andrusak et al. 2005). Because of their large size relative to copepods, cladocerans accounted for 40% of total zooplankton biomass in July 2005 when they were at 17.6% of density. Copepod populations have been dominated by the lone cyclopoid captured, Diacyclops, followed by the calanoid Leptodiaptomus and very low numbers of the calanoid Epischura (Table 5). The population composition within the cladocerans has averaged 41% Daphnia, 32% Bosmina, and 27% Diaphanasoma since 1997. However, the population composition varies from month to month (Fig. 1) and from year to year (Table 5). Zooplankton population density generally increases from southern stations (OK 1, OK 3) to northern stations (OK 6, OK 7), with the highest densities found in Armstrong Arm (OK 8; Table 4). In 2005, for example, zooplankton density averaged 8·L-1 at OK 1, 12·L-1 at OK 6, and 14·L-1 in Armstrong Arm (Fig. 2), while biomass averaged 17, 25, and 37 µg·L-1, respectively (Fig. 3).


Table 4. Average abundance and biomass of cladoceran and copepod zooplankton during May-October at five sampling stations in Okanagan Lake, 1999-2005.

OK 1 OK 3 OK 6 OK 7 OK 8 Whole Lake Abundance (# . L-1) Cladocera 0.8 0.7 1.0 1.0 2.1 1.1 Copepoda 12.9 14.8 17.0 15.7 26.6 17.4 TOTAL 13.7 15.5 18.0 16.8 28.7 18.5 Biomass (µg.L-1) Cladocera 7.6 8.3 11.9 12.6 37.0 15.5 Copepoda 24.7 27.4 31.2 30.8 59.5 34.7 TOTAL 32.3 35.7 43.1 43.5 96.4 50.2

Population Composition Copepods have always been the most abundant zooplankton at each station with mean seasonal densities since 1997 generally ranging from 15 to 22·L-1 (Table 5). A much lower density of 7·L-1 was recorded in 1998. The 2005 density was 9.7·L-1, a considerable decline from the constant values of approximately 15-16·L-1 in the previous four years. Copepods dominated during all months sampled with populations at main lake stations in 2001-2004 peaking in June-August at about 15-20·L-1 and in Armstrong Arm (OK 8) at >40·L-1 (Fig. 4). In 2005, the peak timing and size was similar in main lake stations to previous years, but in Armstrong Arm, the peak was 29·L-1, about 25% lower than in past years (Fig. 4). Copepod biomass followed the same spatial and temporal trends as density. Summer copepod biomass in 2005 was close to the 2001-04 range of 25-35 µg·L-1 in the main lake, but at OK 8, summer biomass was about 20 µg·L-1 lower than the previous range of 70-80 µg·L-1 (Fig. 5). Despite their numerical dominance throughout the summer (≈ 90% of density), copepods accounted for only about 60% of total zooplankton biomass when cladoceran populations were at their peak densities, which reflects their small body size relative to cladocerans.


Table 5. Average zooplankton abundance (# animals.L-1) from May-October for Okanagan Lake (all stations averaged), 1997-2005.

1997 1998 1999 2000 2001 2002 2003 2004 2005 Cladocera Daphnia spp. 0.25 0.11 0.78 0.65 0.29 0.23 0.57 0.45 0.30 Diaphanosoma brachyurum 0.19 0.14 0.65 0.24 0.44 0.22 0.05 0.22 0.16 Bosmina longirostris 0.27 0.06 0.65 0.10 0.42 0.21 0.28 0.64 0.34 Leptodora kindti nda nd <0.01 0.02 <0.01 <0.01 <0.01 <0.01 <0.01Chydorus sphaeriaus nd nd <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Total Cladocera 0.71 0.31 2.07 1.01 1.15 0.66 0.90 1.30 0.80 Copepoda (Calanoida) 7.4c Leptodiaptomus ashlandi nd 3.2 9.9 7.5 5.8 5.8 5.3 3.3 3.1 Epischura nevadensis nd 0.1 0.2 0.2 0.4 0.2 0.2 0.2 0.2 Copepoda (Cyclopoida)

Diacyclops bicuspidatus 13.6d 4.1 12.3 14.4 9.5 10.0 9.1 11.4 6.4 Total Copepoda 21.1 7.4 22.4 22.2 15.7 16.0 14.6 14.9 9.7 Total Density 21.8 7.7 24.5 23.2 16.8 16.6 15.5 16.3 10.5

a Includes Daphnia thorata, D. galeata mendotae, and D. rosea. b No data. c No distinction of genera. d Reported as Cyclopoida. The copepods in Okanagan Lake are generally composed of slightly more cyclopoids then calanoids, with calanoids often dominating in the spring and cyclopoids more numerous in mid-to-late summer. Calanoid copepod densities increase in early spring to peak in April or May, concurrent with the spring phytoplankton bloom (see Stockner, this OLAP report), and they then decrease during summer and into the fall (Fig. 6). The size of the spring peak in the main lake has been declining over time. It was in the range 15-35 µg·L-1 from 1999-2001 (Rae and Vidmanic in Andrusak et al. 2005), but it has been lower more recently with densities at or below 10 µg·L-1 in 2004 and 2005 (Fig. 6). Analysis of copepods to the species level began in mid-1997. Only two calanoid copepods are found in Okanagan Lake: Leptodiaptomus ashlandi, which is dominant at densities of 5-35·L-1, and Epischura nevadensis at <1·L-1 (Table 5, Fig. 7). When more than one calanoid copepod occurs, it is common for one to dominate (Pennak 1957). Enumeration of copepod nauplii began in 1999; peak populations occur in April and May (when sampling begins) at densities of 2-7·L-1 (Fig. 7). Nauplii were present in slightly higher numbers in 2005 than in earlier years, and they also persisted at higher densities into the summer months (Fig. 7).


Only one cyclopoid copepod has been found in Okanagan Lake, Diacyclops bicuspidatus, a common species in pelagic communities (Pennak 1957). They generally reach peak densities of 10-15·L-1 in June or July, except at OK 8 where densities have peaked as high as 30-40·L-1. However, at OK 8 in 2005, Diacyclops density peaked at fewer than 25·L-1 (Fig. 7). Average density from May to October is typically around 11·L-1, but this declined in 2005 to 6.4·L-1 (Table 5). Cladoceran density over the May to October period in Okanagan Lake has averaged 0.7-1.3·L-1, with the exceptions of a low 1998 density of 0.3·L-1 and a high 1999 density of 2.1·L-1 (Table 5). The 2005 density of 0.8·L-1 was a decrease from 2004 but similar to the densities recorded in 2002 and 2003. All three of the dominant cladoceran species, Bosmina, Diaphanosoma, and Daphnia decreased in 2005 compared with 2004. Cladoceran density is comparable at all stations in the main lake, although usually somewhat lower at the south end (OK 1) of the lake. The highest densities are found, on average, in Armstrong Arm (OK 8) (Table 4), but in 2005, cladoceran densities were similar at OK 6, OK 7, and OK 8 (Fig. 2). The greatest abundance of cladocerans is generally found between July and September, with maximum densities in July or August of 2-4·L-1, with some exceptions (Fig. 8). Cladocerans account for 3-8% of the annual zooplankton population density. When considering biomass, however, cladocerans can account for up to 45% of total May to October biomass in the main lake, and > 50% during the mid-summer peak in Armstrong Arm (Fig. 5). Cladoceran biomass is also variable among years; biomass in 2005 was lower at most stations than in 2003 and 2004, but the 2005 measurements were similar or slightly higher than in 2001 and 2002 (Fig. 5). Seven species of cladocerans have been identified in Okanagan Lake, with the cosmopolitan species Daphnia thorata, D. galeata mendotae, D. rosea, Diaphanosoma brachyurum, and Bosmina longirostris together accounting for > 98% of cladoceran abundance (Table 5). Daphnia usually appear in June or July and are often present through October, with abundance peaking in July or August (Fig. 8). Their overall abundance is low, however, generally averaging <0.5·L-1. Spatially, their populations are lowest in the south end of the lake (OK 1-3), increasing slightly towards the north end where density usually peaks at 1-3·L-1, and highest in the Armstrong Arm (OK 8) where Daphnia densities can be up to 6·L-1 (Fig. 8). Diaphanosoma appear concurrently with Daphnia, but their populations usually remain at < 1·L-1. Bosmina tend to be the first cladoceran to appear in spring, with populations peaking at around 2·L-1 in June to July. However, in both 2004 and 2005, their densities were 3-6·L-1 at southern stations (Fig. 8). Bosmina are usually present through November in low numbers (Fig. 8). Leptodora kindti and Chydorus sphaericus are captured infrequently and at densities too low for accurate enumeration. Leptodora have been noted in mid-summer and appeared to be most numerous in the Armstrong Arm (OK 8), while Chydorus have been recorded in the spring and only in the Armstrong Arm.


Zooplankton Fecundity Fecundity data were collected from the two most common copepods (Diacyclops and Leptodiaptomus) and cladocerans (Daphnia and Bosmina) in 1999-2005. Gravid (egg-bearing) copepods usually make up a substantial proportion of the female population in April when sampling begins, and they sometimes show a second smaller peak in the fall. The proportion of gravid Diacyclops females usually peaks in spring at 20-40% of the female population, with gravid females fluctuating in number throughout summer (Fig. 9). The gravid Diacyclops females carry up to 25 eggs each. The proportion of gravid females in late summer is less, and often zero, with those present carrying only 10-15 eggs. Gravid Leptodiaptomus females are also found in spring and summer, and they often have a later summer peak, which was observed at southern stations in 2005 with nearly 100% gravid females (Fig. 10). Leptodiaptomus usually carried 5-15 eggs per gravid female, though the number tends to decline over the summer (Fig. 10). Gravid Daphnia vary considerably among years and stations in Okanagan Lake. Gravid females are usually more numerous at northern stations, where they account for 10-60% of the female population in either a spring or fall peak (Fig. 11). In 2005, however, there was no spring peak at any station, and the fall increase was low at all stations. Generally, gravid Daphnia carry no more than two eggs each. The proportion of gravid Bosmina usually peaks at 20-50% in late fall, with a smaller peak earlier in the summer. At times, however, Bosmina represent 100% of the gravid female population, even in the spring (Fig. 12). In 2005, the spring peaks were equal or greater than the fall peaks at all stations except OK 8. The number of eggs carried by each gravid Bosmina usually varies between 1 and 4 and has been higher at most stations in 2004 and 2005 than in the two previous years (Fig. 12). Historical Zooplankton Populations Okanagan Lake has been sampled periodically for zooplankton over the past three decades. Procedures have been consistent since late-1996 as part of OLAP, with occasional additional sampling by BC Fisheries (McEachern in Ashley et al. 1999a). Earlier work was done in 1971 by Patalas and Salki (1973) and in 1978 by Truscott and Kelso (1979). Comparisons of May-October averages cannot be made between OLAP data and past values as sampling was often conducted at different times of the year (early spring or late fall) and different collection methods and analysis used. However, general abundance trends can be examined by comparing populations in August of each year, the month most commonly sampled when both cladocerans and copepods are present (McEachern in Ashley et al. 1999a). Cladoceran and copepod densities have decreased from the late 1970s to recent years (Fig. 13). In the main lake (OK 1-7), total density averaged 35·L-1 in 1978-80, 21·L-1 in 1991-1993, and 15·L-1 during 1996-2005. Cladoceran populations have declined from values averaging 4·L-1 in 1978-80 to <1·L-1 in 1991-93, and 1·L-1 in 1996-2005. The percent of cladocerans in the total population has ranged from 2-16% in the main body of the lake. In the Armstrong Arm (OK 8), cladoceran densities have fluctuated by a factor of 3, much


more than in the main lake. For example, a spike in cladoceran density in Armstrong Arm in 2004 did not reappear in 2005 (Fig. 13). This arm of the lake has unique limnological features that strongly influence macrozooplankton, particularly the mysid population (discussed below). Mysid Shrimp Sampling of Mysis relicta in Okanagan Lake has been conducted monthly by OLAP since August 1996 from up to eight stations, with additional samples collected in 1997 and 1998 from Kalamalka and Wood lakes (Ashley et al. 1998; 1999a). The following analysis concentrates on data collected from the seven stations monitored annually in Okanagan Lake (OK 1, OK 3-OK 8). Mysis Abundance and Biomass The seasonal abundance of mysids in Okanagan Lake since 1997 has averaged 331·m-2 in the pelagic (deep water) samples and 207·m-2 in the near-shore (40-m depth) samples (Table 6). Abundance in 2005 was nearly double what it had been at both pelagic and near-shore sites in the three previous years. Since 2002, mysid density has been similar in the near-shore and pelagic samples, whereas from 1997-2000 pelagic samples always contained 2-3 times as many mysids as near-shore samples (Table 6). Areal biomass values (dry weights) correlate with abundance, averaging 1.7 g·m-2 in near-shore and 2.7 g·m-2 in pelagic zones (Table 6). When averaged over the 1999-2005 period, the highest May to October abundance and biomass continue to be found in the pelagic samples from station OK 7 near the north end of the lake with average abundance of 721·m-2 at a biomass of 6.7 g.m-2 (Table 7). Pelagic samples from OK 8 have the next highest abundance, which is about half of the OK 7 numbers, at 378·m-2 and biomass of 5.5 g·m-2. In the rest of the main lake, at stations OK 1-6, mysid abundance and biomass are about one third or less than at OK 7 (Table 7). Near-shore samples also have highest abundance and biomass at OK 7 and lowest at OK 1. When averaged over the 7-year period, fewer mysids are found per volume in near-shore than pelagic samples, but as mentioned above, this gap has narrowed in recent years.


Table 6. Average abundance and biomass (dry weight) of Mysis relicta from May to October in the near-shore and pelagic sample hauls of Okanagan Lake (OK 1-7), 1997-2005. (Data also shown in Figs. 14 and 15.)

Year Abundance (#.m-2) Biomass (g dry wt.m-2) Near-shore Pelagic Near-shore Pelagic

1997 130 314 -- -- 1998 128 427 -- -- 1999 68 225 0.48 2.72 2000 128 429 0.56 3.16 2001 312 436 2.55 4.33 2002 232 233 1.65 1.69 2003 251 260 2.17 2.24 2004 214 240 1.74 1.87 2005 400 411 3.03 3.16

Average 207 331 1.74 2.74

Table 7. Average abundance and biomass (dry weight) of Mysis relicta for May to

October in pelagic and near-shore sample hauls from seven sites in Okanagan Lake, 1999-2005.

OK 1 OK 3 OK 4 OK 5 OK 6 OK 7 OK 8 Abundance pelagic 179 281 227 210 269 721 378 (#.m-2) near-shore 124 211 178 196 214 431 277 Biomass pelagic 1.5 2.8 1.6 1.5 1.9 6.7 5.5 (g dry wt.m-2) near-shore 1.0 1.9 1.2 1.1 1.4 3.7 3.7

Peak abundance is usually found in July to August at most stations and can exceed 1,000·m-2, but it is more often < 750·m-2 for pelagic and near-shore samples combined (Fig. 14). In 2005, however, peaks were measured in late spring or summer at OK 1-6 of over 1000·m-2. Station OK 7 consistently has more mysids than other stations in the main lake, with abundance generally reaching 1,000-2,000·m-2, but in 2005 it was nearly 5000·m-2 (Fig. 14). By contrast, mysid abundance at OK 8 was significantly lower in 2005 than in 2004, but the 2005 values were similar to earlier years. Pelagic biomass follows abundance trends, with values in the range of 1.0-6.0 g·m-2 at main lake stations and increasing slightly from south to north. At OK 7, biomass peaked at about 10 g·m-2

in 2002-04, but in 2005, biomass reached 50 g·m-2 (Fig. 15). Average mysid numbers and biomass from pelagic and near-shore hauls have fluctuated at all stations, with no distinct trends. Values were lowest in 1999, while 2000 and 2001 were peak years and similar to 1997 and 1998 (Wilson and Vidmanic in Andrusak et al. 2003). From 2002 to 2004, abundance and biomass were lower than previous years at most stations. In 2005, a resurgence of the population occurred in the


main lake, particularly at OK 7 (Fig. 16). In contrast, the mysid population declined at OK 8 in 2005. The highest mysid densities were regularly captured in the pelagic samples at each station between 1999-2001, with densities 2 to 5-fold higher than at near-shore locations (Rae and Vidmanic in Andrusak et al. 2005). Pelagic abundance at OK 7 averaged 6-fold higher than the near-shore samples. In 2002-2005, however, pelagic and near-shore densities have been similar, and at some stations higher in the near-shore than in the pelagic zone (Fig. 16). In most years, pelagic and near-shore sample densities at OK 8 have been similar, with 2001 and 2004 being exceptions. OK 8 is the shallowest station where pelagic hauls are only 15 m deeper than near-shore hauls. The total mysid biomass (dry weight) estimated in Okanagan Lake has fluctuated from a low of 436 tons in 1999 to a high of 911 tons in 2001; the 2005 biomass of 894 tons is the second highest during the past seven years (Table 8). Compared with the previous three years, the biomass increase in 2005 was particularly pronounced at OK 7 where biomass more than doubled (Fig. 17). The exceptionally high biomass at OK 8 in 2004 was not repeated in 2005, although the 2005 biomass of 87 g·m-2 was still significantly higher than it had been from 1999-2003. Note that the conversion from dry to wet weight is 6.23 for mysids, and therefore, the 7-year average wet weight biomass of mysids in Okanagan Lake is 3,975 metric tons. Table 8. Total biomass (metric tons, dry weight) of Mysis relicta at each station in

Okanagan Lake averaged over May to October, 1999-2005. Data combine the deep and shallow layers of the lake. This data is shown graphically in Figure 18.

Year OK 1 OK 3 OK 4 OK 5 OK 6 OK 7 OK 8 Whole

Lake

1999 68 103 34 43 61 120 6 4362000 87 138 60 52 97 106 11 5522001 106 192 80 66 123 314 30 9112002 46 113 45 38 90 129 17 4782003 75 105 86 61 100 136 45 5612004 63 74 42 54 87 137 177 6362005 113 116 76 82 110 310 87 894

Average 80 120 60 57 95 179 54 638

In most years, mysid abundance in Armstrong Arm (OK 8) declines to fewer than 25 mysids·m-2 in October of each year and remains low through November and December (Fig. 14). Mysids may migrate out of this shallow arm of the lake due to a combination of hypolimnetic oxygen depletion and warm epilimnetic water (McEachern, in Ashley et al. 1999a). Mysids are intolerant of low dissolved oxygen concentrations (Sherman et al. 1987) and water temperatures > 10ºC (Smith 1970). In 2005, mysid numbers


declined in October but not in the precipitous way of other years; they remained at about 160·m-2. Samples were not collected in November or December 2005. Mysis Life History and Fecundity The life cycle of Mysis relicta varies from 1-4 years, depending on limnological characteristics, such as trophic status and water temperature (Lasenby et al. 1986). In Okanagan Lake their life cycle follows a two-year pattern (Whall and Lasenby in Ashley et al. 1999), which has also been reported for populations elsewhere in the region (Ashley et al. 1999b; Andrusak et al. 2002b). The release of juveniles by brooding females has already begun when sampling begins in April of each year, and by August the juveniles have grown into the immature size range (Fig. 18). Immature males and females dominate the population through summer when total abundance is at its peak, with mature and breeding males first appearing in July and increasing to maximum densities in September to October. Mature females are found throughout the year, but increase in density during the summer (Fig. 18). Gravid females are usually at their highest abundance in the spring and fall, but in fall 2005, they occurred at very low density throughout the lake (Fig. 18). Gravid females generally begin to release juveniles in November and continue until July/August, with the majority of releases occurring in March to May (Whall and Lasenby in Ashley et al. 1999a). Mysid females are gravid through winter when sampling has not been conducted. The proportion of gravid females recorded matches this pattern in most years and at most stations as they are generally > 75% of the female population when sample collection starts in spring, and drop to < 20% during summer with an increase in fall to 50-70% (Fig. 19). Again, in 2005, the fall increase was minimal at all stations. Mysid fecundity, measured as the number of eggs per gravid female, was recorded only in 2002. At each station, females were carrying about 15 eggs when sampling started in April. By mid-late summer, the number dropped to zero following the release of juveniles. Eggs per gravid female increased again to 10-20 in the fall as females matured. The seasonal average ranged from 11 eggs per gravid female at stations OK 1 and OK 5 to lows of 8 at OK 4 and OK 7 in the main lake (Fig. 19). Historical Mysis Abundance Trends Long-term spring to fall comparisons of mysids cannot be made, as sampling from 1989-1995 occurred only once per year in late-September or early-October. However, general abundance trends can be examined by comparing populations in the fall of each year at corresponding stations (OK 1, OK 3, OK 4, OK 6, OK 7). This analysis is possible since over the shorter term (1997-2005) the abundance trends from fall samples follow the trends of seasonal (May to October) averaged data. Average mysid abundance in September and October decreased from 450.m-2 in 1989 to 150.m-2 in 1996 (Fig. 20). Mysids then showed an increase to 350 in 2000 and returned close to 1996 levels in 2002-2004. In 2005, they increased again to a level


similar to that measured in 1993-95 and 1997-99. Fluctuations in average values over the 1989-2005 period are attributable to large regional changes in density. For example, in the early 1990s, large populations at stations OK 3 and 7 increased the whole lake average. The recent population spike (2000-2001) was centred around OK 7. DISCUSSION Zooplankton Okanagan Lake has a trophic gradient from the somewhat nutrient-rich Armstrong Arm (OK 8) at the north end to nutrient-poor conditions in the south. The gradient is most pronounced in water chemistry and phytoplankton populations (Rae and Wilson, in this OLAP report; Stockner, in this OLAP report), and less so in the zooplankton and mysid populations. The zooplankton data set shows inter-annual variability in the past three decades. However, with the exception of the late 1970s, densities have remained relatively stable. In 1978 and 1979, zooplankton density in the main lake was twice as large as the densities measured during the 1990s. The cladoceran zooplankton, in particular, have had lower density in the past decade than in the late 1970s. Their current density is low at < 8% of total zooplankton density in most months of the year. This low abundance has implications for kokanee, an obligate planktivore, since they and the introduced mysid shrimp both prefer cladoceran zooplankton as a food source. As grazers in the middle of the food web, zooplankton populations are regulated both by predation and by nutrient dynamics. The overall low abundance of zooplankton in recent years may be partly explained by an increase in the kokanee population (Sebastian et al., this OLAP report). Predation pressure by both kokanee and mysids could be maintaining zooplankton, and particularly cladocerans, at low densities. Therefore, predation on zooplankton may be masking their productivity. Secondary production measurements would help to determine the dynamics of the zooplankton community and whether it is sufficiently productive to support increases to the kokanee population. Low nutrient concentrations in the lake likely further limit the zooplankton community through reduced food quality and quantity. For example, poor food quality may have been a factor in the low proportion of gravid Daphnia measured in 2005. The nutrient–productivity relationship in Okanagan Lake is complicated, but a better understanding is being gained through OLAP’s regular monitoring program. The water chemistry data collected since 1996 suggest that nitrogen limitation occurs in the epilimnion during summer and causes the ratio of inorganic nitrogen to dissolved phosphorus (NO2+3:TDP, by weight) to drop below 5 (Rae and Wilson, this OLAP report). This may lead to an increase of nitrogen-fixing cyanobacteria (blue-green algae), which are poor quality food for herbivorous zooplankton such as Daphnia. In addition to the summer nitrogen limitation, pronounced phosphorus limitation also seems to occur in very dry years, such as the past three (2003-05). In these years, the food web is limited by both nitrogen and phosphorus with the result that the quantity of phytoplankton is low and


restricts growth of the zooplankton populations. There is some indication that annual variability in cladoceran zooplankton populations may be related to spring phosphorus concentrations (or nutrient loading), which are particularly low in dry years. Spring total phosphorus (TP) values correlate with summer cladoceran density and the relationship is strengthened when data from the richer Armstrong Arm are included (Fig. 21). Mysid Shrimp Experimental trawl fishing for mysid shrimps began in 1998, and two companies received test fishery permits to fish mysids starting in 2000. The goal of the test fishery is to develop effective techniques for capturing significant numbers of mysids, thereby reducing competition with kokanee (Andrusak and Matthews in Andrusak et al. 2002a). Based on the mysid population data set (Table 8), mysid fishing effort has been focused on high-density areas at station OK 7 (Whiskey Island to Cameron Point), with a combination of nets and techniques used throughout the water column. Total mysid catch was highest in 2001 and lower in 2002-05 (Table 9). However, the catch rate in 2005, at 0.43 tons/day, was equivalent to the catch rate in 2001. In past OLAP annual reports and in this report, mysid biomass data have been reported in dry weight units (g·m-2), but commercial fishing weights are generally reported as wet weights. Smokorowski weighed a sample (N=84) of mysids at various life stages and then dried them to establish a dry weight equivalent (Smokorowski 1998). The conversion factor from dry weight to wet weight was determined to be 6.23. Using this conversion, the proportion of total in-lake mysid biomass removed from Okanagan Lake during the past four years of the test fishery has ranged from 0.8-1.7% with 2005 being 0.8%. Because of the increase in the mysid population in 2005, the percentage removed from the lake was the lowest since 2000, despite a high catch rate and total catch similar to other years. As a proportion of in-lake mysid biomass at station OK 7 alone, the test fishery removed only 2.4% in 2005, down from 6.2% in 2002 (Table 9). In 2005, the mysid population at OK 7 increased significantly over previous years, and interestingly, it decreased at OK 8. Dissolved oxygen concentrations decline at depths greater than 36 m in August at OK 8, and this probably drives mysids out of Armstrong Arm in the late summer and fall. However, the overall decrease in mysids throughout the sampling season in 2005 may also be linked to food availability, since the zooplankton population also declined in Armstrong Arm in 2005. Given the large increase of mysids at OK 7, it is possible that mysids migrated from Armstrong Arm to the main lake in search of food. The test fishery for mysids may be having some impact on the mysid population, but this is difficult to verify given the small catch from the fishery and the population fluctuations exhibited by the mysids.


Table 9. Total catch and catch rates from the experimental Mysid commercial fishery on Okanagan Lake, with the total Mysid biomass (May to October) and percentage of the biomass caught, 1999-2005. Note that Mysid biomass in the lake is given here as a wet weight, which is 6.23 times higher than the dry weight shown in Figure 18. Catch data are from Andrusak et al., this OLAP report.

Year Mysid Catch Mysid Biomass (metric tons wet weight)

% of Mysid Biomass Caught

Total (metric tons wet weight)

Catch Rate (metric

tons/day)

In Whole Lake At OK 7 In Whole

Lake At OK 7 (a)

1999 1.2 2716 750 0.05% 0.2% 2000 15.1 0.12 3440 663 0.4% 2.3% 2001 77.9 0.42 5672 1954 1.4% 4.0% 2002 49.8 0.29 2978 804 1.7% 6.2% 2003 45.7 0.31 3492 846 1.3% 5.4% 2004 37.3 0.36 3964 856 0.9% 4.4% 2005 45.8 0.43 5570 1931 0.8% 2.4%

a the 3,797 ha area around the OK 7 sampling site (Table 3). Comparison with Other Lakes In comparison to several other oligotrophic BC lakes and reservoirs, Okanagan Lake has a moderate zooplankton density. The May to October zooplankton density in Okanagan Lake averaged 17·L-1 (range 8-25) in 1997-2005, the same as Arrow Lakes Reservoir during nutrient additions but lower than Kootenay Lake (average density of 25·L-1) during nutrient additions (Table 10). Predation by mysids on cladoceran zooplankton is well documented (Lasenby et al. 1986, Martinez and Bergenson 1991, Smokorowski et al. 1998, Spencer et al. 1991; Whall 2000). Cladoceran zooplankton account for < 10% of total density in Okanagan Lake, similar to the percentage in Slocan (in 2000) and Kalamalka lakes, which also have mysids, but lower than the percentage in both Kootenay and Arrow during nutrient additions (Table 10). The cladoceran Daphnia is also found in fairly low numbers in these lakes, usually accounting for no more than 3% of the May to October zooplankton population. Lakes with low mysid densities have a greater proportion of cladocerans overall, and Daphnia specifically. For example, Slocan Lake (in 2001) had 19 mysids.m-2, 29% cladocerans, and 8% Daphnia, while Arrow Lakes Reservoir (in 1997-98) had 66 mysids.m-2, 23% cladocerans, and 13% Daphnia (Pieters et al. 1998) (Table 10). Alouette and Williston reservoirs are both large lakes, but neither has mysid shrimp. In both of these, total zooplankton density is low, but Daphnia are 10% of the total population in Williston (Stockner et al. 2001) and, after nutrient additions, 46% in Alouette (Table 10).


Table 10. Seasonal (approx. May to October) density of total zooplankton, cladoceran zooplankton, Daphnia, and Mysis in Okanagan Lake and several other BC lakes and reservoirs. Percentages are of the total zooplankton density. Pre-nutr=before additions of inorganic nutrients began; Nutr=during nutrient additions. Data from: Ashley et al. 1999a, 1999b; Thompson and Vidmanic 1999, 2000; Thompson 1999; Wilson et al. 2002; Pieters et al. 2000; Stockner et al. 2001; E. Schindler, MOE Nelson; S. Harris, MOE Vancouver.

Lake/Reservoir (Year)

Zooplankton density

# of species

Cladocerans only

Daphnia Mysis Density

(#·L-1) % Density % Density (#·m-2) Okanagan Lake (1997-2005) 17 8 6 1.0 2.4 0.4 207d,

331e

Kalamalka Lake (1997-98)a 10 6 4 0.5 1.3 0.1 519f

Slocan Lake (2000) 24 8 6 1.5 0.5 0.12 110 Slocan Lake (2001) 24 8 29 7.0 8.3 2.0 19 Williston Res. (1999-00) 6 15 10 0.7 9 0.6 0 Arrow Res. (Pre-nutr,1997-98) 7 16 23 1.7 13 0.9 66 Arrow Res. (Nutr, 1999-2005) 17 13b 17 2.8 7 1.2 183 Kootenay L. (Pre-nutr, <1992) 14 11 3c 0.4 < 1 0.01 200-500g

Kootenay L. (Nutr, 1997-2005) 25 16b 11 2.9 3 0.8 90-280 Alouette Res. (Pre-nutr, 1998) 1.3 9 20 0.3 < 1 < 0.01 0 Alouette Res. (Nutr, 2000-03) 3.7 8 46 1.7 16 0.6 0 a KA1 station only. b 2004 only. c North basin only. d Near-shore areas. e Pelagic areas. f KA1 and KA2 stations in 1998. g 1980-1990. Data from the basin of Alouette Reservoir (in the coast mountains) that received nutrient additions and Slocan Lake (no nutrient additions) show how cladoceran populations may react under different conditions. In Alouette Reservoir, predation on cladocerans by kokanee is low (~12 kokanee per ha), there are no mysids, and nutrients and phytoplankton are abundant due to nutrient additions. Cladocerans in Alouette Reservoir increased to more than half the zooplankton population and included large numbers of Daphnia (Wilson et al. 2002). Limnological investigations in Slocan Lake illustrate changes in cladoceran zooplankton density in response to large changes in mysid abundance. In 2000, mysid abundance was 110·m-2 but, for reasons not entirely clear, in 2001 it had dropped 5-fold to 19·m-2. Cladoceran density increased 5-fold from an average of 1.5·L-1 in 2000 to 7·L-1 in 2001, while Daphnia density increased by an order of magnitude (Table 10; Andrusak et al. 2002b). This clearly demonstrates the predation pressure that mysids place on cladoceran zooplankton populations.


While these examples demonstrate the links between different components of zooplankton and mysid populations, other factors are also involved in the dynamics of these populations in Okanagan Lake (such as hydrology, nutrient loadings, and fish populations). Productivity data for different trophic levels, in addition to the standing crop (biomass and density) data collected here, are important to the fundamental understanding of trophic dynamics. Information on secondary (zooplankton) and mysid productivity would help achieve the OLAP goal of understanding the limnology of Okanagan Lake for the recovery of indigenous fish populations. CONCLUSIONS In 2005, zooplankton density as a whole declined compared to previous years and, in the main lake, was the lowest measured since 1998. This decline was primarily observed in the copepod population, with the effect that the proportion of cladocerans increased in the total zooplankton community, although it remained below 10%. The cladoceran zooplankton population, and specifically Daphnia that kokanee prefer, are at sufficiently low levels in the lake that they may not provide adequate food resources to support a large recovery of the kokanee population. Conversely, the low Daphnia densities in the lake may be a reflection of heavy grazing pressure by both the kokanee and mysid populations. Mysid shrimp also selectively feed on cladocerans and are good competitors for them. The mysid population increased throughout the main lake in 2005, especially at OK 7. The 2005 population size was comparable to the population in the mid-1990s and was below the recorded highs in 1989 and 1991. Nonetheless, an increase in the mysid population in Okanagan Lake may be of concern if it reduces available food for kokanee. The nutrient imbalance that occurs during summer and fall in Okanagan Lake (Rae and Wilson, in this OLAP report) will have an effect on both the quantity and quality of cladoceran zooplankton. The low ratio of available nitrogen to phosphorus has implications for the type of phytoplankton that grow in the lake, specifically encouraging the growth of cyanobacteria (Stockner, in this OLAP report). Cladocerans (and other zooplankton) have difficulty eating algal colonies or filaments, which are the growth forms of many cyanobacteria. In addition, even if zooplankton are able to ingest cyanobacteria, these phytoplankton have poor nutritional quality in terms of the fatty acids they contain (Brett and Muller-Navarra 1997). Kokanee build up their fatty acid supplies through the food they eat, and they require fatty acids for over-winter survival. The availability of cladocerans with high nutritional quality is key for in-lake growth and survival of kokanee, and is therefore, a fundamental component of kokanee recovery in Okanagan Lake. Two avenues should be examined further: (1) The mysid shrimp harvesting, which has shown promise as a technique for decreasing the shrimp population in the lake, must be increased in scale if it is to have a large impact on the mysids. Details on the fishery and efforts to increase the fishing effort are in Andrusak et al, this OLAP report, and, (2) the quality of cladocerans as a food source must be increased. The proposed method for accomplishing this is to alter the composition of


the phytoplankton population towards more nutritious species by increasing the concentration of available nitrogen during the summer. Details on background work that has been done on nitrogen levels and the nutritional quality of phytoplankton are in Rae and Ashley (in Andrusak et al. 2004 and in this OLAP report). However, it has also become evident that in dry years Okanagan Lake has particularly low phosphorus concentrations in addition to the low summer nitrogen, and this nutrient co-limitation affects the transfer of energy to higher levels of the food web. Therefore, an additional study has been conducted to better understand the dynamics of phosphorus and nitrogen co-limitation and is reported by Harris (in this OLAP report). Without an in-lake environment that supports kokanee growth and survival, all other efforts to restore and protect stream and shoreline habitat may have only limited effects on the long-term kokanee population. ACKNOWLEDGMENTS Zooplankton and mysid shrimp samples were collected from Okanagan Lake by David Cassidy and Nick Ipatowicz, both with BC Conservation Foundation.


REFERENCES Andrusak, H. et al. 2000. Okanagan Lake Action Plan Year 4 (1999) Report. Fisheries

Project Report No. RD 83. Province of British Columbia, Ministry of Agriculture, Food and Fisheries.

Andrusak, H. et al. 2002a. Okanagan Lake Action Plan Year 6 (2001) Report with

reference to the results from 1996-2001. Fisheries Project Report No. RD 96 2002. Fisheries Management Branch, Ministry of Water, Land and Air Protection, Province of British Columbia.

Andrusak, H. et al. 2002b. Slocan Lake Limnology and Trophic Status (2000/2001)

Year 1 Draft Report Fisheries Project Report No. RD 93 BC Fisheries, University of British Columbia.

Andrusak, H. et al. 2003. Okanagan Lake Action Plan Year 7 (2002) Report. Fisheries

Project Report No. RD 106 2003. Fisheries Management Branch, Ministry of Water, land and Air Protection, Province of British Columbia.

Andrusak H. et al. 2004. Okanagan Lake Action Plan Year 8 (2003) Report. Fisheries

Project Report No. RD 108. Province of British Columbia, Ministry of Water, Land and Air Protection.

Andrusak H. et al. 2005. Okanagan Lake Action Plan Year 9 (2004) Report. Fisheries

Project Report No. RD 111. Province of British Columbia, Ministry of Environment.


G. Scholten, P. Woodruff, R. Rae, L. Vidmanic, J. Stockner, northwest hydraulic consultants. 2006. Okanagan Lake Action Plan Year 10 (2005) Report. Fisheries Project Report No. Rd 115. Ecosystems Branch, Ministry Of Environment, Province Of British Columbia.

Ashley, K. et al. 1998. Okanagan Lake Action Plan Year 1 (1996-97) and Year 2

(1997-98) Report. Fisheries Project Report No. RD 73. Province of British Columbia, Ministry of Fisheries, Fisheries Management Branch.

Ashley, K. et al. 1999a. Okanagan Lake Action Plan Year 3 (1998) Report. Fisheries

Project Report No. RD 78. Province of British Columbia, Ministry of Fisheries, Fisheries Management Branch.

Ashley, K.I. et al. 1999b. Kootenay Lake Fertilization Experiment – Year 4 (1995/96)

Report. British Columbia Ministry of Environment, Lands and Parks, Fisheries Project Report No. RD 58.


Ashley, K., L. Thompson, D. Lasenby, L. McEachern, K. Smokorowski, and D. Sebastian. 1997. Restoration of an Interior Lake Ecosystem: the Kootenay Lake Fertilization Experiment. Water Qual. Res. J. Canada. 32:295-323.

Brett, M.T. and D.C. Muller-Navarra. 1997. The Role of Highly Unsaturated Fatty Acids

in Aquatic Food Web Processes. Freshwater Biol. 38: 483-499. Lasenby, D.C., Northcote, T.G. and M. Furst. 1986. Theory, Practice, and Effects of

Mysis relicta Introductions to North America and Scandinavian Lakes. Can. J. Fish. Aquatic. Sci. 43: 1277-1284.

Martinez, P. and E. Bergenson. 1991. Interactions of Zooplankton, Mysis relicta and

Kokanee in Lake Granby, Colorado. Am. Fish. Soc. Symp. 9: 49-64. McCauley, E. 1984. The Estimation of the Abundance and Biomass of Zooplankton in

Samples. In: Downing, J.D. and F. H. Rigler (eds). 1984. A Manual on Methods for the Assessment of Secondary Productivity in Fresh Waters – 2nd ed. Blackwell Scientific Publications.

Northcote, T.G. 1991. Success, Problems and Control of Introduced Mysid Populations

in Lake and Reservoirs. American Fisheries Society Symposium 9:5-16, 1991. Patalas, K. and A. Salki. 1973. Crustacean Plankton and the Eutrophication of Lakes

in the Okanagan Valley, British Columbia. J. Fish. Res. Board Can. 30:519-542. Pennak, R.W. 1957. Species Composition of Limnetic Zooplankton Communities.

Limnology and Oceanography 2(3):222-232. Pieters, R. et al. 1998. Arrow Reservoir Limnology and Trophic Status – Year 1

(1997/98) Report. Report RD 67. Fisheries Branch. Ministry of Environment Lands and Parks. Victoria, B.C.

Pieters, R. et al. 2000. Arrow Reservoir Fertilization Experiment Year 1 (1999/2000)

Report. Report RD 82. Fisheries Branch. Ministry of Environment Lands and Parks. Victoria, B.C.

Shepherd, B.G. 1990. Okanagan Lake Management Plan, 1990-95. BC Ministry of

Environment, Lands and Parks, Recreational Fisheries Program, Penticton, BC. Sherman, R.K., D.C. Lasenby and L. Hollett. 1987. Influence of Oxygen

Concentrations on the Distribution of Mysis relicta Lovén in a Eutrophic Temperate Lake. Can. J. Zool. 65:2646-2650.

Smith, W.E. 1970. Tolerance of Mysis relicta to Thermal Shock and Light. Trans. Am.

Fish. Soc. 99:418-422.


Smokorowski, K.E. 1998. The Response of the Freshwater Shrimp, Mysis relicta, to the Partial Fertilization of Kootenay Lake, British Columbia. Ph.D Thesis. Trent University, Peterborough, Ontario.

Smokorowski, K., D. Lasenby and R. Evans. 1998. Quantifying the Uptake and

Release of Cadmium and Copper by the Opossum Shrimp Mysis relicta Preying Upon the Cladoceran Daphnia magna Using Stable Isotope Tracers. Can. J. Fish. Aquat. Sci. 55:909-916.

Spencer, C., D. Potter, R. Bukantis, and J. Stanford. 1991. Impact of Predation by

Mysis relicta on Zooplankton in Fleathead Lake, Montana, USA. J. Plant Res. 21:51-64.

Stockner, J.G., Langston, A,R, and G.A. Wilson. 2001. The Limnology of Williston

Reservoir. Peace/Williston Fish and Wildlife Compensation Program Report No. 242.

Thompson, L.C. 1999. Abundance and Production of Zooplankton and Kokanee

Salmon (Oncorhynchus nerka) in Kootenay Lake, British Columbia during Artificial Fertilization. Ph.D Thesis. Department of Zoology, University of British Columbia, Vancouver, BC.

Thompson, L.C. and L. Vidmanic. 1999. Kootenay Lake Fertilization Experiment –

Year 7 (1998/1990) Report: Responses of Zooplankton, Kokanee Salmon and Rainbow Trout. Prepared for the Fisheries Branch, Ministry of Environment, Lands and Parks, Province of British Columbia. 68p.

Thompson, L.C. and L. Vidmanic. 2000. Kootenay Lake Fertilization Experiment –

Year 8 (1999) Report: Responses of Zooplankton and Mysis relicta. Prepared for the Fisheries Branch, Ministry of Environment, Lands and Parks, Province of British Columbia. 45p.

Truscott, S.J. and B.W. Keslo. 1979. Trophic Changes in Lakes Okanagan, Skaha and

Osoyoos, B.C., Following Implementation of Tertiary Municipal Waste Treatment. Canada – British Columbia Okanagan Basin Implementation Agreement. 159pp.

Whall, J.D. 2000. Comparison of the Trophic Role of the Freshwater Shrimp, Mysis

relicta, in two Okanagan Valley Lakes, British Columbia. Masters Thesis. Trent University, Peterborough, Ontario.

Wilson, G.A. et al. 2002. The Alouette Reservoir Fertilization Project: Years 2000 and

2001 Experiment, Whole Reservoir Fertilization. British Columbia Ministry of Water, Land and Air Protection, Fisheries Project Report No. RD 99.


Major zooplankton groups, OK 1-7, 2005

0%

20%

40%

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Apr May Jun Jul Aug Sep Oct

CladoceraCyclopoidaCalanoida

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Cladocerans only, OK 1-7, 2005

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BosminaDiaphanosomaDaphnia

Figure 1. Percent composition (by density) of major zooplankton groups in Okanagan

Lake for Apr-Oct, 2005. Average of stations OK1-7 (top), Armstrong Arm only (middle), and cladocerans only in stations OK1-7 (bottom).


Cladoceran density

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Figure 2. Density of cladoceran (left) and copepod (right) zooplankton species at five

sampling stations in Okanagan Lake, from May to October, 2005. Note: Y-axis scales differ.

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Figure 3. Biomass of cladoceran (left) and copepod (right) zooplankton species at five

sampling stations in Okanagan Lake, from May to October, 2005. Note: Y-axis scales differ.


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May-05

Sep-05

dens

ity (

anim

als . L-1

) Total Copepods Cladocerans (except Daphnia) Daphnia

OK 3

0102030405060

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

)

OK 6

0102030405060

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

)

OK 7

0102030405060

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

)

Figure 4. Density of cladoceran and copepod zooplankton in Okanagan Lake,

2001-2005.


OK 1

0

25

50

75

100

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

biom

ass

(µg .

L-1

)Copepods Cladocerans (except Daphnia) Daphnia

OK 3

0

25

50

75

100

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

biom

ass

(µg . L

-1)

OK 6

0

25

50

75

100

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

biom

ass

(µg . L

-1)

OK 7

0

25

50

75

100

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

biom

ass

(µg . L

-1)

OK 8

0

100

200

300

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

biom

ass

(µg .

L-1

) Figure 5. Biomass of cladoceran and copepod zooplankton in Okanagan Lake,

2001-2005. Note: Y-axis differs for OK 8.


OK 8

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

)

OK 1

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

) Total calanoida Total cyclopoida

OK 3

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

)

OK 6

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (a

nim

als .

L -1

)

OK 7

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

)

Figure 6. Density of calanoid and cyclopoid copepods in Okanagan Lake 2001-2005.


OK 7

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als .

L-1 )

OK 1

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als

. L -1

)

OK 3

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als .

L-1 )

OK 6

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L

-1 )

OK 8

0

10

20

30

40

50

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L

-1 )

Leptodiaptomus Epishura Diacyclops nauplii Figure 7. Density of copepod species in Okanagan Lake, 2001-2005.


OK 8

0

2

4

6

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

)

OK 1

0

2

4

6

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

Daphnia Diaphanosoma Bosmina

Figure 8. Density of cladoceran species in Okanagan Lake, 2001-2005.

dens

ity (

anim

als . L-1

)

OK 3

0

2

4

6

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

al

s. L-1)

im (

anity

dens

OK 6

0

2

4

6

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als

L)

. -1

OK 7

0

2

4

6

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

dens

ity (

anim

als . L-1

)


0

10

20

30

40

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

# eggs per gravid female Gravid females as % of total # femaleseg

gs /

grav

id fe

mal

e OK 1

0

10

20

30

40

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 3

0

10

20

30

40

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 6

0

10

20

30

40

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 7

0

10

20

30

40

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 8

Figure 9. Fecundity data for copepod Diacyclops bicuspidatus in Okanagan Lake, 2001-2005.


0

5

10

15

20

25

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

# eggs per gravid female Gravid females as % of total # femaleseg

gs /

grav

id fe

mal

e OK 1

0

5

10

15

20

25

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 3

0

5

10

15

20

25

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 6

0

5

10

15

20

25

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 7

0

5

10

15

20

25

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/gra

vid

fem

ale OK 8

Figure 10. Fecundity data for copepod Leptodiaptomus ashlandi in Okanagan Lake,

2001-2005.


0

1

2

3

4

5

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale

OK 1

0

1

2

3

4

5

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 3

0

1

2

3

4

5

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es

.

eggs

/ gr

avid

fem

ale

OK 6

0

1

2

3

4

5

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 7

0

1

2

3

4

5

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale

OK 8

# eggs per gravid female Gravid females as % of total # females Figure 11. Fecundity data for cladoceran Daphnia spp. (includes Daphnia thorata,

D. galeata mendotae, and D. rosea) in Okanagan Lake, 2001-2005.


01234567

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 1

01234567

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale

OK 3

01234567

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 6

01234567

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale OK 7

01234567

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

0%

20%

40%

60%

80%

100%

% g

ravi

d fe

mal

es .

eggs

/ gr

avid

fem

ale

OK 8

# eggs per gravid female Gravid females as % of total # females Figure 12. Fecundity data for cladoceran Bosmina longirostris in Okanagan Lake,

2001-2005.


0%

5%

10%

15%

20%

1971

1978

1979

1980

1991

1992

1993

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

% C

lado

cera

ns

.

OK 1-7OK 8

0

10

20

30

40

50

60

1971

1978

1979

1980

1991

1992

1993

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

Cope

pod

dens

ity (#

. L-1 )

OK 1-7

OK 8

0

2

4

6

8

1971

1978

1979

1980

1991

1992

1993

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

Clad

ocer

an d

ensi

ty (#

. L-1

)

OK 1-7

OK 8

0

10

20

30

40

50

6019

71

1978

1979

1980

1991

1992

1993

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

Tota

l den

sity

(# . L

-1 ) OK 1-7

OK 8 Figure 13. Historical comparison of zooplankton in the main body of Okanagan Lake

(stations OK 1-7), and in the Armstrong Arm (OK 8), from August 1971-2005. Top to bottom graphs show: total zooplankton density, cladoceran density, copepod density, and Cladocerans as a percent of total zooplankton density.


OK 4

0500

100015002000

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

mys

is . m

-2OK 1

0500

100015002000

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

mys

is . m

-2

pelagic near-shore

OK 3

0500

100015002000

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

mys

is . m

-2

OK 5

0500

100015002000

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

mys

is . m

-2

OK 6

0500

100015002000

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

mys

is . m

-2

OK 7

0

2500

5000

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

mys

is . m

-2

OK 8

0

2500

5000

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

mys

is . m

-2

Figure 14. Abundance of Mysis relicta in the pelagic and near-shore sample hauls from

seven stations in Okanagan Lake, 2001-2005. Note: Y-axis scale for OK 7 and OK 8 graphs differs from other stations.


OK 4

02468

10

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

g . m

-2

OK 1

02468

10

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

g . m

-2

OK 3

02468

10

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

g . m

-2

OK 5

02468

10

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

g . m

-2

OK 6

02468

10

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

g . m

-2

OK 7

01020304050

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

g . m

-2

OK 8

01020304050

Jan-01

May-01

Sep-01

Jan-02

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

g . m

-2

pelagic near-shore Figure 15. Areal biomass (g.m-2 dry weight) of male, female, and juvenile Mysis relicta

in pelagic (50-229 m) and near-shore (40 m) hauls from seven stations in Okanagan Lake, 2001-2005. Note: Y-axis scale differs for OK 7 and OK 8.


0

200

400

600

800

1,000

1,20020

01

2003

2005

2001

2003

2005

2001

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2005biom

ass

(g d

ry w

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pelagicnear-shore

OK1 OK7OK6OK5OK4OK3 OK8

Figure 16. Annual May to October abundance (top) and areal biomass (bottom) of

Mysis relicta in the pelagic and near-shore sample hauls of Okanagan Lake, 2001-2005.


Figure 17. Total biomass (metric tons dry weight) of Mysis relicta in two layers of

Okanagan Lake: 10-60 metres and >60 metres. Biomass in each layer is shown for each site, and for the lake as a whole (top graph) from 2001-2005. Note: the graphs for the whole lake, OK 7, and OK 8 have Y-axis scales that differ from the others. For OK 8, both near-shore and pelagic samples are taken in the 10-60 m depth range. [1 metric ton = 1000 kg].

Total for the lake 2,000

0500

1,0001,500

Jan-01

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Depth >60 metres Depth of 10-60 metres

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0200400600

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Met

ric to

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ght)

.


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gravid femalemature femaleimmature femalebreeding malemature maleimmature malejuveniles

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ity (#

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.m -2

)

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ity (#

.m -2

)

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ity (#

.m -2

)

dens

ity (#

.m -2

)

Figure 18. Density of different life stages of Mysis relicta in the pelagic hauls (50-229

m) of Okanagan Lake, Feb-Oct 2005. Note differing Y-axis scales.


0%25%50%75%

100%

Jan-01

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% g

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es .

05101520

Gravid females as % of total # females Eggs per gravid female

OK 1

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100%

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% g

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s / g

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ale

Figure 19. The percentage of gravid females and number of eggs per gravid female

(2002 only) from Mysis relicta captured in pelagic hauls (50-229 m) of Okanagan Lake, 2001-2005.


0

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89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05

Year

OK 1 OK 3 OK 4

OK 6 OK 7 OK 1-7, average

Mys

id a

bund

ance

.(a

nim

als.

m -2

) .

Figure 20. Abundance of Mysis relicta in the main body of Okanagan Lake from

1989-2005. Mysis values are the average of Sept and Oct pelagic data only.


R2 = 0.53

0.0

0.5

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0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014

Spring TP (mg.L-1 )

OK 1, 3, 6, 7OK 8Linear (OK 1, 3, 6, 7)

Sum

mer

cla

doce

ran

dens

ity .

(ani

mal

s.L -1

) Figure 21. The relationship between spring total phosphorus (April, average of 0-10,

20, and 45 m data) and summer cladoceran density (average May to October), 2000-2005. Open symbols represent OK 1, 3, 6, and 7 in the main lake, and the closed symbols represent OK in Armstrong Arm. The regression is for all data points.


OKANAGAN LAKE KOKANEE ABUNDANCE, SIZE AND AGE STRUCTURE BASED ON ACOUSTIC AND TRAWL SURVEYS

1988 to 2005

by

D. C. Sebastian1, G. H. Scholten1, and P.E. Woodruff2

INTRODUCTION Hydroacoustic and trawl net surveys have been conducted annually during the fall period since 1988 in order to monitor trends in the Okanagan Lake kokanee population. Indices of in-lake abundance from the trawl and hydroacoustic data are intended to complement annual shore and stream spawner counts and provide greater insight into the current stock status. Length and scale age information from trawl samples are used to monitor growth and determine age-at-maturity. Acoustic and trawl data have been summarized from 1996 to 2005 as part of the Okanagan Lake Action Plan and comparisons made with data collected since 1988. This report provides an update of previous Okanagan Lake Action Plan and other publications (Sebastian et al. 1995; Sebastian and Scholten in: Ashley et al. 1998, 1999 and in: Andrusak et al. 2000, 2001; and Sebastian et al. in: Andrusak et al. 2002, 2003, 2004, and 2005). METHODS Hydroacoustic Sampling A complete nighttime survey of the limnetic habitat in Okanagan Lake has been conducted each year during the new moon period of either September or October from 1988 through 2004. In 2005, the acoustic survey was done concurrent with the annual trawl survey but slightly earlier than in past years (August 28 to September 11). Acoustic surveys each consisted of 18 transects evenly spaced from the south to the north end of Okanagan Lake (Map 2) using the standard survey design in Sebastian et al. (1995). All surveys were conducted using a Simrad model EY200P operating at 70kHz. The transducer was towed on a planer alongside the boat at a depth of 1.5 m and data was collected continuously along survey lines at 1-2 pings.s-1 while cruising at 2m.s-1. The data was converted to digital format and stored both on a PC computer and backed-up on Sony Digital Audio Tape (DAT). Navigation was by GPS, radar and a 1:50,000 Canadian Hydrographic Services chart. The sounder was field calibrated at depths of 15-40 m using a standard -39.1dB copper calibration sphere. Echosounder specifications and field settings are presented in Appendix 1 and acoustic size classes and fork length equivalents in Appendix 2. 1 Aquatic Ecosystem Science, Biodiversity Branch, Ministry of Environment, Victoria 2 Biological Contractor, British Columbia Conservation Foundation, Surrey, BC


The Simrad survey data were digitized and then analyzed using the Hydroacoustic Data Acquisition System (HADAS) program version 3.98 by Lindem (1991). The HADAS statistical analysis performed a function similar to manual counting to determine the number of targets per unit area by depth stratum. Habitat was stratified by 5 m depth layers and then further stratified into relatively homogeneous zones. Regression through origin of echo counts on areas sampled produced mean density and standard error estimates for each zone and depth stratum. A Monte Carlo Simulation procedure was used to combine all strata and develop maximum likelihood estimates and statistical bounds for each zone and again for the combined zones using 30,000 iterations per run. Average fish densities by transect are shown in Appendix 3 and regression statistics by depth layer and maximum likelihood population estimates with bounds are presented in Appendix 4. Fish size distribution was estimated using a statistical de-convolution algorithm based on Craig and Forbes (1969). The resulting acoustic size distribution was used to proportion the fish population into two size classes representing age 0 fish and age 1-3 fish, respectively. In addition to the standard 70kHz single beam data, some transects were surveyed simultaneously using a Simrad EY500/EP500 split beam echosounding system operating at 120kHz. The size distributions were compared to the single beam data to verify the size cut-off between fry and older fish. Fork lengths of trawl caught fish were converted to the same acoustic scale using Love’s (1977) empirical relation (Appendix 2) and compared to acoustic size distributions in order to verify the age cut-off for the two size groups. Since it was not possible to distinguish between age 1, 2 and 3 fish using acoustic data, the proportions of these age groups were estimated from trawl catches. Kokanee abundance estimates and age 0 proportions were derived from acoustic data while abundance estimates of age 1 and age 2 fish typically relied on acoustic abundance and age proportions in the trawl. Trawl Sampling Trawl gear in 2005 consisted of an opening and closing 3 x 7 m beam trawl utilizing a 20 m long net of graduated mesh size (6 to 92 mm stretched), towed at 0.80-0.95 m.s-1. The trawl net depth was measured with a Notus net depth sensor system and a Lowrance global positioning system (GPS) was used to estimate distances traveled for calculating sampled volumes. The survey design, sampling techniques and trawl gear were similar to 2004. The focus was on capturing sufficient numbers of age 1+ and 2+ fish for determining mean size-at-age while minimizing sampling time. Rather than using the standard stepped oblique trawls as outlined in Sebastian et al. (1995) to sample representatively at all depths where fish were observed, trawling in 2003-2005 was directed at the middle to upper section of the visible fish layer at each station. Two trawls each were done at four of the eight standard stations, with one additional trawl conducted at station 4. The net was fished for 60 minutes covering from 1-3 layers of 7 m depth at each location relying on a Notus depth sensor to indicate approximate trawl net depths and the echosounder to indicate the approximate depth of the fish layer (Appendix 5). Catch numbers were converted to catch per unit effort (number/ha) based on the estimated area covered at


each station with the trawl net (Appendix 6). Captured fish were kept on ice until processed the following morning. The species, fork length, weight, distinguishing marks (e.g., fin clips), scale code, and stage of maturity were recorded. Scales were taken from fish > 75 mm for aging. Fish lengths were adjusted to an October 1 standard using empirical growth data from Rieman and Myers (1992) (Appendix 7). RESULTS AND DISCUSSION Fish Species Verification and Trawl Sampling Trawl catches in the acoustic visible fish layer in September 2005 continue to indicate that the majority (~100%) of fish occupying the limnetic habitat below the thermocline were kokanee (Table 1). Table 1. Species composition from trawl surveys in Okanagan Lake during 1988-2005.

Number Caught by Species Year

Month

No. of Trawls

Kokanee Burbot Lake Whitefish

Pygmy Whitefish

Pike Minnow

Sculpin % Kokanee

1988 10 23 1,014 0 0 0 0 0 100.0 1989 09 24 542 1 0 4 0 0 99.2 1990 10 21 574 0 0 0 1 0 99.8 1991 10 24 559 0 0 1 0 0 99.8 1992 09 24 598 0 0 0 0 0 100.0 1993 10 24 359 0 0 0 0 0 100.0 1994 10 24 316 1 1 2 2 0 98.1 1995 09 26 622 2 0 0 0 0 99.7 1996 10 23 535 0 0 0 0 0 100.0 1997 10 24 437 0 0 0 0 0 100.0 1998 09 24 222 0 0 4 0 0 98.3 1999 09 24 57 0 0 4 0 1 92.0 2000 10 24 216 0 0 20 0 1 91.1 2001 10 2 32 0 0 0 0 0 100.0 2002 09 14 198 0 0 0 0 0 100.0 2003 09 14 911 0 0 0 0 0 100.0 2004 09 12 619 0 0 0 0 0 100.0 2005 09 9 294 0 0 0 0 0 100.0

A total of 294 fish were captured in nine non-standard trawls in September 2005. Although the number of kokanee caught was similar to the early 1990s (Table 2) the non-standard sampling, which targeted only the most dense part of the fish layer, does not allow for direct comparison of catch numbers to earlier sampling. The “directed” trawls should in theory produce similar if not slightly lower estimates of catch per unit effort (CPUE) providing the units are calculated on a catch per “surface area” (i.e., number per hectare) rather than by catch per volume sampled. In fact, the CPUE may be more consistent and reliable given that most, if not all, effort is directed at the layers having the highest densities of fish. Therefore, the reliability of the proportion of fry to larger fish is compromised since fry are known to occur most frequently near the upper


boundary of the fish layer (i.e., nearest the thermocline). Although not used in this discussion, the trawl CPUE (no.ha-1) results are presented in Appendix 6. Table 2. Summary of kokanee catches in Okanagan Lake standard trawl surveys,

1988 to 2005.

Number of Kokanee Caught Survey Year

Survey Period

No. of Stations

No. of Trawls Age 0 Age 1 Age 2 Age 3 Mature Total

1988 Oct 6-18 8 23 754 206 54 0 3 1,014 1989 Sep 28 - Oct 5 8 24 362 111 69 0 6 542 1990 Oct 16-20 7 21 395 117 62 0 1 574 1991 Oct 4 – 8 8 24 258 110 170 21 29 559 1992 Sep 27 - Oct 1 8 24 349 118 130 1 21 598 1993 Oct 13-19 8 24 191 108 54 6 11 359 1994 Oct 4-8 8 24 167 69 79 1 18 316 1995 Sep 22-28 9 26 331 109 161 21 57 622 1996 Oct 8 – 11 8 23 441 49 31 14 13 535 1997 Oct 2 – 11 8 24 293 97 41 6 13 437 1998 Sep 15-22 8 24 104 86 30 2 11 222 1999 Sep 8-11 8 24 26 9 11 11 12 57 2000 Oct 21-24 8 24 195 7 13 1 1 216 2001 Oct 15 1 2* 21 11 0 0 0 32 2002 Sep 12-15 7 14** 19 98 80 1 44 198 2003 Sep 2-5 7 14*** 823 46 27 15 20 911 2004 Sep 14-17 7 13*** 536 53 24 6 10 619 2005 Sep 9-11 4 9*** 248 23 16 7 6 294

* Two trawls with 3 x 7 m net sampled same volume of habitat as three standard trawls with 5 x 5 m net. Catches by station in 2001 should therefore be directly comparable to previous catches by station.

** Non-standard trawling in 2002 targeted on middle of fish layer. *** Non-standard trawling in 2003, 2004 and 2005 targeted on highest density parts of fish layer. Age interpretations in this report were based on fish length and verified by scale interpretation. The layered sampling suggests an approximate age contribution of 84% age 0+, 8% age 1+, 5% age 2+, and 2% age 3+ kokanee. However it is acknowledged that the fry proportion provided by acoustic sampling is likely more reliable than the proportion suggested by the 2005 trawl results. The layered trawling tends to bias the proportions toward fry since they tend to be more concentrated in a distinct layer than the older age groups which are often more evenly distributed over a wider range of depths. Only 26% of the combined age 2 and 3 fish were mature in 2005 compared with an observed range of 33-55% for previous September trawling. This apparently low proportion of mature fish is more similar to that observed for October trawling which averages 15% (range: 2-29%) since the stream spawning component has left the system and the remaining fish are thought to be shore spawners. The lower proportion in 2005 was probably due to fewer stream spawners in the lake during the September survey since Andrusak and Andrusak (in this OLAP report) noted that Mission Creek spawning occurred two weeks earlier than average (Andrusak and Sebastian in Andrusak et al. 2000). On the other hand, this notion is at odds with the exceptionally large numbers of


shore spawners counted later during the fall of 2005, so it may indicate trawl sample sizes were too small to reliably determine the proportions of mature fish present. Size, Growth and Age-at-Maturity The length-frequency distribution of trawl caught fish in 2005 indicated distinct modes at 70, 120, and 210 mm corresponding to age 0, 1 and 2 fish, respectively (Fig. 1). Scale analysis suggested considerable overlap between age 2 and 3 trawl caught fish, although sample size of age 3 fish was limited. Mean sizes of age 0 and age 1 fish were similar to the two previous years whereas age 2 fish appeared to be slightly larger in 2005 (Fig.2). While the size of age 2 fish increased, the average size of both shore and stream spawners has declined. Combining the length-frequency analyses and mean size-at-age it would appear that the majority of stream spawners were age 3, as in most years, while the shore spawners were most likely age 2 fish (Figs. 2, 3). The relatively strong return of age 3 stream spawners in 2005 is consistent with a larger than average return of stream spawners in 2001. This same logic supports the notion that very strong returns of shore spawners in 2005 were mostly age 2 fish originating from the strong return of shore spawners in 2002. It is less likely that large numbers of shore spawners in 2005 were age 3s originating from a low shore spawner return in 2001. Fish Distribution Age 1-3 kokanee densities in 2004 were fairly evenly distributed over the length of the lake. In 2005, age 1-3 densities were an average of two times higher in the south basin although the fish were fairly evenly distributed within each of the basins (Fig. 4). Fry densities were also approximately two times higher in the south basin although they appeared to be fairly evenly distributed within each basin. The proportion of fry to older kokanee remained low in the north basin in both 2004 and 2005 presumably as a result of lower than average shore spawner returns in 2003 and 2004. With the large shore spawner return in 2005 an increase in the proportion of fry to older fish can be expected to occur in the north basin in 2006. As mentioned in previous OLAP reports, the pattern in south basin fry distribution and abundance is less evident presumably due to a more significant and variable contribution from stream spawners. Genetic tools currently being developed using DNA analysis may help to confirm whether stream spawners are more prevalent in the south basin compared to the north basin. The average kokanee density throughout the lake was 403 fish ha-1 compared with 351 fish ha-1 in 2004 and 455 fish ha-1 in 2003. More importantly, the average age 1-3 densities of 158 fish ha-1 shows a steady annual increase for the last five years since it bottomed out in 2000. These densities have not been observed in Okanagan Lake since the early 1990s. In-Lake Abundance Kokanee abundance (all ages) in 2005 was estimated at 9.72 million (8.76-10.37), a significant increase from 2004, and within statistical bounds of the decade high 2003


abundance estimate (Fig. 5). The 2005 age 1-3 kokanee abundance was estimated at 3.84 million (3.63-4.17) and was significantly higher than the previous eleven years. This increase in larger sized kokanee was particularly encouraging compared with the 2004 results which showed no further increases in age 1-3 abundance following a strong fry year in 2003 (Fig. 6). With another strong fry year anticipated in 2006 due to high escapement levels it should be obvious in 2007 and 2008 if the lake has an ability to support more than the current level of approximately 4 million age 1-3 kokanee. The 2005 hydroacoustic surveys provided key evidence toward estimating the current capacity of Okanagan Lake to support kokanee. Age Proportioning by Acoustic and Trawl Methods Based on fry size in the trawl and on the acoustic size distribution from both single and split beam echo sounders, the size cut-off to separate age 0 from older fish was again at -47dB in 2005 (Fig. 7). Using this cut-off it was estimated that 61% of the kokanee were age 0 and 39% were age 1-3, which is lower than the 2003 fry proportions but similar to 2002 and 2004 (Table 3). Trawl proportions suggested that 84% of the fish may have been age 0, but these results are unreliable due to biases in the trawl sampling as a result of targeting depths where fish are at highest densities to optimize numbers of fish captured. The acoustic proportions were used for final estimates of age 0 and age 1-3 fish abundance. Table 3. Comparison of fry proportions estimated by acoustic and trawl techniques,

1992-2005.

Year Kokanee Abundance

(in millions)

Proportion of Fry from Acoustic Separation1

(%)

Proportion of Fry from Trawling

(%) 1992 10.60 64 58 1993 8.55 58 53 1994 7.36 60 53 1995 7.58 61 53 1996 8.19 71 82 1997 5.09 56 67 1998 5.32 58 47 1999 4.10 46 45 2000 3.11 82 90 2001 5.55 83 662

2002 7.32 65 103

2003 11.20 76 904

2004 7.93 64 874

2005 9.72 61 84 1. Proportions were derived using a –47dB cut-off during 1992-1999 and 2002-2004, and –44dB in

2000-2001. Note: capability for acoustic size separation began in 1992 with acquisition of HADAS system.

2. Trawl proportions in 2001 not reliable as based on only one station (OK6). 3. The upper fry layer appears to have been missed in the non-standard trawls in 2002. 4. Emphasis on sampling the highest density part of fish layer produced biased toward capture of age 0s in

2003 to 2005.


Age Structure and Abundance of Age Groups A combination of trawl and acoustic data has typically been used to analyze trends in abundance and kokanee age structure. Acoustic results are preferred over trawling results for estimating total abundance and proportion of age 0 fish, since the sampling coverage is greater and the variability in estimates lower. The proportions of ages 1, 2, and 3 fish were estimated from trawl catches, although this is known to be somewhat problematic for two reasons: (1) the reliability of proportioning the trawl catch can be compromised by small sample sizes and, (2) a known bias in capture of age 1 fish (Sebastian and Scholten in Andrusak et al. 2001). Despite these problems, trends in abundance within specific age groups should still be valid. To address the trawl bias a multiplier of 1.5 was applied to age 1 trawl catches to ensure that the estimated abundance of age 2 fish was not greater than the abundance of age 1 fish from the same cohort. Length-frequency analysis of trawl captured kokanee combined with some scale analysis has been effective and most reliable in determining age composition (Figs. 1-3). Displaying the age groups by spawning year (brood year) rather than by survey year best illustrates age structure trends (Fig. 8) and most clearly enables a simple cohort analysis. Until the 1998 spawning year (1999 fry year) there had been a general downward trend for all age groups for a decade but an upward inflection began in 1999 for all ages. The age 0 fish continued to increase in abundance until the 2003 fry year. Age 1 fish have mirrored the upward trend in fry but with more modest increases to the current (2003) spawning year. Age 2 fish however, increased considerably the first year following the lowest spawner year, but did not continue to build for the next two years as did the younger age classes. This apparent failure of the year 2000 and 2001 (age 2) cohorts to increase in numbers over previous year classes suggested that lake capacity may have been reached at levels of 600,000 – 800,000 age 2s. A further increase to approximately 1 million age 2 kokanee from the 2002 brood year (i.e., the 2005 sampling year) was encouraging and may indicate the lake could currently have some capacity to support additional numbers of kokanee. The current level of age 2 production has not been observed in Okanagan Lake since the early 1990s (Figs. 6, 8). Limitations to Okanagan Lake kokanee appears to be greatest on age 2+ fish which have the largest energy requirements. The capacity is most likely a function of food quality and/or heavy predation or a combination of the two. Food quality comparisons are underway and it is suggested that some investigations be conducted to assess current predator abundance in Okanagan Lake relative to other lakes and to historic levels, if data exists. Increased numbers of kokanee in recent years appears to be at odds with the limnology data presented by Rae and Wilson and the phytoplankton data presented by Stockner (both reports in this OLAP report). These data reports indicate poor growing conditions for kokanee yet the abundance data clearly shows increased numbers of kokanee. Food habit analysis of kokanee of all ages may be useful to explain the apparent contradictions in the existing data.


Spawner Abundance and Fry Recruitment Despite uncertainty in some of the methods for determining age structure, the analysis of trends in kokanee abundance by age can be quite useful in forecasting future escapements provided in-lake survival remains relatively constant. The inability to reliably estimate total shore spawner numbers limits the prospect of determining whole lake adult kokanee stock size. Because the status of adult size kokanee is of paramount importance to OLAP, some indirect methods have been attempted to estimate future escapements by focusing on the correlation between known in-lake fry abundance and the total number of spawning fish that produced those fry (Sebastian and Scholten in Andrusak et al. 2001). Most of the uncertainty of using this analytical technique has been related to what the peak count of shore spawners represents and what factor should be used to convert the peak count to total count. Andrusak et al. (in Andrusak et al. 2005) discusses this question in some detail. The current analyses applied a conversion rate of 1.5 times to both stream and shore peak counts, except from 1999-2001 where a lower rate of 0.9 was applied to the shore counts based on area under the curve estimates for 2002 (Andrusak et al. in Andrusak et al. 2003). The rationale for using a lower expansion factor (0.9) for those years was that substantially more effort was applied to the shore counts and an area-under-the-curve model suggested the 1.5 factor may have been too high. The 1.5 factor has been applied to the shore spawner data since 2001 because the intensity of shore counts has once again been reduced. Figure 9 suggests that the trend in numbers of spawners and late summer fry has been relatively consistent and parallel from the late 1980s through 2004. This close correlation suggests that egg-to-fry survival and early in-lake fry survival are not the limiting factor(s) for this kokanee population, i.e., more spawners result in more fry yet higher fry numbers have not translated into increasingly higher adult numbers. The limitation to this kokanee population must occur beyond the first summer and likely during the first winter (i.e., between age 0+ and age 1). There is also evidence that age 1 to 2 survival may have declined during the last three years as the numbers of age 1-3 fish increase (Fig. 8). The exceptions to this occurred during the period of time when there were so few spawners (1998 and 1999) that density dependent effects were reduced and numbers of ages 1-3 fish increased disproportionately in 2001 and 2002 (Fig. 6). This upward response by spawners from 2000-2002 was followed by lower returns in 2003 and 2004. Predicted declines in fry numbers in the Year 8 report (Andrusak et al. 2004) as a result of lower spawner numbers in 2003 did in fact occur lending some credibility to this relationship as a predictive tool (Fig. 9). This model predicts a substantial increase in the numbers of kokanee fry for 2006 following the strongest spawner return in sixteen years. With the suspected relatively high numbers of age 2 fish that shore spawned in 2005, a decline in number of age 3 shore spawners returning in 2006 seems likely.


Since the method of estimating shore spawner numbers remains problematic it is believed that new genetic analysis techniques hold the key to improved (future) stock size estimates for Okanagan Lake kokanee. Once reliable genetic markers have been identified they can be used to estimate the proportion of stream vs. shore spawner progeny from trawl caught fish. This proportion can then be applied to the known number of stream spawners to estimate the total number of shore spawners. The only drawback to using genetics for estimating spawner numbers based on proportions of ecotypes by cohort may be our ability to determine the age of spawners. It may also be useful to verify if the north basin is more dependent on shore spawning stocks than the south basin as suggested earlier in this report.


RECOMMENDATIONS 1. Move forward with further research on genetic analytical techniques in 2006 as

funding permits since it appears this is probably the only practical way of establishing actual numbers of shore vs. stream spawners, hence, the relative contribution from each population.

2. Trawl sampling should be scheduled as close to October 1 as possible in order to

minimize length corrections. If the intent is to capture mature shore but not stream spawners, trawling must be scheduled between September 25 and October 15. If the intent is to capture mature fish from both groups, then a second trawl survey should be done in August. It is likely that more trawling effort would be required to attain reliable proportions of mature fish in the population. The genetic analyses in Recommendation #1 would assist in determining the oldest age group which can be used to approximate proportions of the two spawning ecotypes present.

3. Trawl and acoustic surveys should if possible be done from different boats to ensure

both surveys can be completed during the same new moon period. 4. Continue to collect scales from trawl caught fish > 130 mm and use for age

verification. 5. Collect tissue samples and preserve in 95% ethanol for genetic analysis to estimate

the proportions of shore spawning stock to total fish. It is important to keep tissue samples from different age groups separate, as proportions appear to change from year to year. The majority of trawl caught fish can be aged reliably based on their length. However, if age is uncertain, the samples should be stored in separate vials and labeled with scale codes until the age can be determined through scale analysis. Consider also keeping samples from north and south basins separate if practical, as this may help to determine the relative importance of ecotypes to production of kokanee in each basin.

6. Consider collecting additional tissue samples for stock identification from kokanee

by-catch captured in mysis harvesting trials. Since harvesting tends to be concentrated rather than random coverage, the catch location should also be recorded to aid in interpretation of genetic results.


REFERENCES Andrusak, H., D. Sebastian, I. McGregor, S. Matthews, D. Smith, K. Ashley, S. Pollard, G.

Scholten, J. Stockner, P. Ward, R. Kirk, D. Lasenby, J. Webster, J. Whall, G. Wilson and H. Yassien. 2000. Okanagan Lake Action Plan Year 4 (1999) Report. Fisheries Project Report No. RD 83. Fisheries Management Br., Ministry of Agriculture, Food and Fisheries, Province of British Columbia. Victoria, BC. 325p.

Andrusak, H., S. Matthews, I. McGregor, K. Ashley, G. Wilson, L. Vidmanic, J. Stockner,

K. Hall, D. Sebastian, G. Scholten, G. Andrusak, J. Sawada, D. Cassidy and J. Webster. 2001. Okanagan Lake Action Plan Year 5 (2000) Report. Fisheries Project Report No. RD 89. Fisheries Management Br., Ministry of Water, Land and Air Protection, Province of British Columbia. Victoria, BC. 269 p.


D. Sebastian, G. Scholten, P. Woodruff, D. Cassidy, J. Webster, K. Rood, and A. Kay. 2002. Okanagan Lake Action Plan Year 6 (2001) Report with Reference to Results from 1996-2001. Fisheries Project Report No. RD 96. Fisheries Management Br., Ministry of Water, Land and Air Protection, Province of British Columbia. Victoria, BC. 323 p.


D. Sebastian, G. Scholten, P. Woodruff, D. Cassidy, J. Webster, A. Wilson, M. Gaboury, P. Slaney, G. Lawrence, W.K. Oldham, B. Jantz and J. Mitchell. 2003. Okanagan Lake Action Plan Year 7 (2002) Report. Fisheries Project Report No. RD 106. Biodiversity Branch, Ministry of Water, Land and Air Protection, Province of British Columbia. Victoria, BC. 350 p.

Andrusak, H., S. Matthews, I. McGregor, K. Ashley, R. Rae, A. Wilson, D. Sebastian, G.

Scholten, P. Woodruff, L. Vidmanic, J. Stockner, G. Wilson, B. Jantz, J. Webster, H. Wright, C. Walters, J. Korman. 2004. Okanagan Lake Action Plan Year 8 (2003) Report. Fisheries Project Report No. RD 108. Biodiversity Branch, Ministry of Water, Land and Air Protection, Province of British Columbia. Victoria, BC. 372 p.

Andrusak, H., S. Matthews, I. McGregor, K. Ashley, R. Rae, A. Wilson, J. Webster, G.

Andrusak, L. Vidmanic, J. Stockner, D. Sebastian, G. Scholten, P. Woodruff, B. Jantz, D. Bennett, H. Wright, R. Withler, S. Harris. 2005. Okanagan Lake Action Plan Year 9 (2004) Report. Fisheries Project Report No. RD 111. Biodiversity Branch, Ministry of Water, Land and Air Protection, Province of British Columbia. Victoria, BC. 502 p.


Ashley, K., B. Shepherd, D. Sebastian, L. Thompson, L. Vidmanic, Dr. P. Ward, H. Yassien, L. McEachern, R. Nordin, Dr. D. Lasenby, J. Quirt, J.D. Whall, Dr. P. Dill, Dr. E. Taylor, S. Pollard, C. Wong, J. den Dulk and G. Scholten. 1998. Okanagan Lake Action Plan Year 1 (1996-97) and Year 2 (1997-98) Report. Fisheries Project Report No. RD 73. Fisheries Management Branch, Ministry of Fisheries, Victoria, BC. 396p.

Ashley, K. I. McGregor, B. Shepherd, D. Sebastian, S. Matthews, L. Vidmanic, P. Ward,

H. Yassien, L. McEachern, H. Andrusak, D. Lasenby, J. Quirt, J. Whall, E. Taylor, A. Kuiper, P.M. Troffe, C. Wong, G. Scholten, M. Zimmerman, P. Epp, V. Jensen and R. Finnegan. 1999. Okanagan Lake Action Plan Year 3 (1998) Report. Fisheries Project Report No. RD 78, Fisheries Management Branch, Ministry of Fisheries, Victoria, BC. 338p.

Craig, R. E., and S. T. Forbes. 1969. Design of a Sonar for Fish Counting.

Fisheridirektoratets Shrifter. Series Havundersokelser 15: 210-219. Lindem, T. 1991. Hydroacoustic Data Acquisition System HADAS. Instruction Manual.

Lindem Data Acquisition, Lda, Oslo, Norway. Love, R. H. 1977. Target Strength of an Individual Fish at any Aspect. J. Acoust. Soc.

Am. 62(6): 1397-1403. Rieman, B.E. and D.L. Myers. 1992. Influence of Fish Density and Relative Productivity

on Growth of Kokanee in Ten Oligotrophic Lakes and Reservoirs in Idaho. Trans. Am. Fish. Soc. 121:178-191.

Sebastian, D., G. Scholten, D. Addison and D. Green. 1995. Results of the 1985-94

Acoustic and Trawl Surveys on Okanagan Lake. Unpublished MS, Stock Management Unit Report No. 2. Fisheries Branch, Ministry of Environment, Lands and Parks, Victoria, BC, 54p.


n=294

0

10

20

30

40

50

60

70

10 30 50 70 90 110 130 150 170 190 210 230 250 270 290

Fork Length (mm)

Pro

port

ion

(%)

Age 3 n=7

Age 2 n=16

Age 1 n=23

Age 0 n=248

Figure 1. Length-frequency by age for trawl caught fish in September 2005.


0

50

100

150

200

250

300

350

400

85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05

Survey year

Fork

Len

gth

(mm

)Mission spaw ners (mean) age 3 & 4 Mission spaw ners (mode) age 3

Shore spaw ners (mean) age 3 age 2 (traw l)

age 1 (traw l) age 0 (traw l)

Figure 2. Comparison of trends in kokanee mean length-at-age from trawl and

spawner sampling. Length of the first mode of stream spawners from Mission Creek is also reported.


b) 2005

0

15

30

45

60

75

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70

Fork length (cm)

Prop

ortio

n of

age

cla

ss

age 0 (n=248)age 1 (n=23)age 2 (n=16)age 3 (n=7)

Shore spawners (age 3)Stream spawners (age 3-4)

a) 2004

0

15

30

45

60

75

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70

Fork length (cm)

Prop

ortio

n of

age

cla

ss

age 0 (trawl)age 1 (trawl)age 2 (trawl)age 3 (trawl)

Shore spawners (age 3)Stream spawners (age 3-4)

Figure 3. Kokanee length-frequency distributions for ages 1-3 trawl caught fish in

Okanagan Lake and for shore and stream (Mission Creek) spawners in a) 2004 and b) 2005.


a) 2004

0100

200300400

500600

1 2* 3 4* 5* 6 7 8* 9* 10 11 12 13* 14 15* 16 17 18*

Transect number

Den

sity

(no/

ha)

b) 2005

0100

200300

400500

600

1 2* 3 4* 5* 6 7 8* 9* 10 11 12 13* 14 15* 16 17 18*

Transect number

Den

sity

(no/

ha)

Figure 4. Density distribution of age 0 and age 1-3 kokanee in Okanagan Lake based

on acoustic surveys from 2004-2005.


0

2

4

6

8

10

12

14

16

88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05

Year

No.

of K

okan

ee (i

n m

illio

ns)

Figure 5. Kokanee abundance in Okanagan Lake based on acoustic surveys,

1988-2005. Error bars represent 95% confidence limits.

0

1

2

3

4

5

6

7

8

9

10

88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05

Survey year

No.

of k

okan

ee (m

illio

ns) age 0

age 1-3

Figure 6. Abundance trends in age 0 and age 1-3 kokanee in Okanagan Lake based

on acoustic surveys, 1988-2005.


0

5

10

15

20

25

30

-62 -59 -56 -53 -50 -47 -44 -41 -38 -35

Target strength (dB)

Pro

porti

on (%

)70kHz

120kHz

Age 0

Age 1-3

Figure 7. Comparison of acoustic size distributions (in 3 decibel intervals) for pelagic

fish in Okanagan Lake, using the 70kHz single beam and 120kHz split beam echosounders.

0

1

2

3

4

5

6

7

8

9

10

87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04

Spaw ning year

Abun

danc

e (m

illion

s)

age 0

age 1

age 2

Figure 8. Trends in kokanee abundance by age and spawning year based on

combined acoustic and trawl results from 1988-2005. Note: data is presented by spawning years.


0

100

200

300

400

500

87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05

Spawning year

Num

ber

of S

paw

ners

(th

ousa

nds)

0

2

4

6

8

10

Num

ber o

f Fry

(mill

ions

)

combined stream & shorespawners*

age 0+ abundance (year following)

Figure 9. Trends in combined spawner numbers and following year fry abundance

presented by spawning year for 1987-2004 (X denotes years where an expansion factor of 0.9 was applied to shore spawner counts; 1.5 was used for all other years).


Appendix 1. Equipment and Data Processing Specifications

Echosounder Specifications and Field Settings Description SIMRAD EY200P-P Transducer type Single beam 70 kHz beam angle 11.6 degree5 receiver gain 3 (O dB) pulse width (msec) 0.3 ping rate (p/sec) medium (1.5) time varied gain 40 log r TVG range (m) 2 to 66 Attenuation -15 dB Power 1/1 Calibration 2 min. AC tone Tape recorder Sony TCD-D10 Record volume 3.5 fixed

Data Processing Specifications Description HADAS version 3.98

Interface gain Calibration tone to intersect 2 volts at 50 milliseconds

Threshold Minimum detectable target approximately - 65 dB

Voltage and threshold used for survey 4100mV, threshold 240mV

Lab calibration July 8 1998, Applied Physics Laboratory UWA

Field calibration August 28, 2005 Appendix 2. Love’s (1977) empirical relation of fish length to acoustic target strength.

TS = 19.1 log10 (L) – 0.9 log10 (F) - 62

where TS = target strength in decibels (dB)

L = length in cm and

F = frequency in kHz

HADAS size class (db)1

Acoustic size range (dB)

Fish length range2 (mm)

-35 -35 -33.1 317 500+-38 -38 -35.1 221 317 -41 -41 -38.1 154 221 -44 -44 -41.1 107 154 -47 -47 -44.1 75 107 -50 -50 -47.1 52 75 -53 -53 -50.1 36 52 -56 -56 -53.1 25 36 -59 -59 -56.1 18 25 -62 -62 -59.1 12 18

1 HADAS was set up to view 30 dB range in 10 size classes of 3 dB. 2 From Love’s (1977) empirical formula (Dorsal aspect).


Appendix 3. Summary of fish density (number.ha-1) by transect based on acoustic surveys, September 2005.

Transect Number

All Ages Age 0 Age 1-3

1 441 247 194 2 523 332 191 3 499 300 199 4 624 372 252 5 493 273 220 6 536 351 185 7 535 280 255 8 503 323 180 9 462 271 190

10 536 373 163 11 389 320 68 12 209 140 68 13 205 113 92 14 239 118 121 15 348 211 138 16 273 167 107 17 243 107 136 18 189 112 77

South Basin 515 312 203 North Basin 262 161 101


Appendix 4. Maximum likelihood abundance estimates (MLE) and bounds for Okanagan Lake kokanee during September 2005 based on regression analyses and Monte Carlo Simulations.

a) Kokanee All Ages

September 2005 statistics for fish >-62 dB in 2 zones (transects: 1-10, 11-18) Zone Depth N R2 Density

(no/ha) Std Dev

Area (ha)

Stratum Population

Statistic2

Abundance

1 5 9 0.18 1.76 1.32 13,674 24,080 South Basin 1 10 10 0.59 71.16 19.94 13,674 973,028 LB= 6,008,0001 15 9 0.96 204.35 13.99 13,674 2,794,227 MLE= 6,561,0001 20 9 0.97 84.98 4.96 13,327 1,132,419 UB= 7,389,0001 25 10 0.94 73.27 6.22 12,979 950,971 1 30 10 0.96 40.41 2.92 12,370 499,851 North Basin 1 35 9 0.93 15.93 1.57 11,760 187,325 LB= 2,455,0001 40 9 0.87 7.96 1.09 11,199 89,106 MLE= 2,942,0001 45 9 0.92 3.02 0.33 10,637 32,071 UB= 3,287,0001 50 9 0.90 1.59 0.19 10,124 16,106 2 5 7 0.58 6.23 2.15 11,714 73,002 Total Lake 2 10 7 0.89 4.13 0.61 11,714 48,379 LB= 8,759,0002 15 8 0.80 79.11 14.90 11,714 926,695 MLE= 9,720,0002 20 8 0.90 49.89 6.20 11,502 573,858 UB= 10,371,0002 25 8 0.91 58.05 6.78 11,290 655,328 2 30 8 0.91 33.65 4.05 10,764 362,138 2 35 7 0.96 13.49 1.09 10,237 138,087 2 40 8 0.96 5.48 0.42 9,783 53,650 2 45 7 0.93 2.77 0.30 9,329 25,813 2 50 7 0.84 1.00 0.18 8,949 8,931

2 Key: LB = Lower bounds, UB = Upper bounds, MLE = Maximum likelihood estimate.


Appendix 4 - continued b) Age 1-3 Kokanee

September 2005 statistics for fish >-47 dB in 2 zones (transects: 1-10, 11-18) Zone Depth N R2 Density

(no/ha) Std Dev Area

(ha) Stratum

Population Statistic

Abundance

1 10 9 0.71 8.13 1.85 13,674 111,129 South Basin 1 15 9 0.95 54.31 4.25 13,674 742,635 LB= 2,469,0001 20 9 0.98 48.81 2.75 13,327 650,440 MLE= 2,680,0001 25 10 0.90 52.49 5.79 12,979 681,203 UB= 2,901,0001 30 10 0.93 26.74 2.46 12,370 330,748 1 35 10 0.93 8.15 0.74 11,760 95,832 North Basin 1 40 9 0.81 4.62 0.80 11,199 51,692 LB= 1,040,0001 45 9 0.83 1.21 0.19 10,637 12,871 MLE= 1,234,0001 50 9 0.86 0.90 0.13 10,124 9,152 UB= 1,384,0002 10 7 0.69 1.05 0.29 11,714 12,347 2 15 7 0.95 12.72 1.18 11,714 149,049 Total Lake 2 20 8 0.82 28.83 5.08 11,502 331,603 LB= 3,620,0002 25 7 0.90 33.10 4.40 11,290 373,710 MLE= 3,838,0002 30 8 0.84 21.06 3.49 10,764 226,669 UB= 4,170,0002 35 7 0.95 8.37 0.82 10,237 85,725 2 40 7 0.95 1.93 0.19 9,783 18,920 2 45 7 0.66 0.79 0.23 9,329 7,342 2 50 7 0.73 0.56 0.14 8,949 5,020


Appendix 5. Kokanee trawl logs for September 2005 showing time, distance, depth and number of layers targeted.

Trawl

Number Station Name

Date Time In Time Out

Distance (m)

Fish Depth

Trawl Depth

(m)

Number of

Layers T1-1 TRT 11-Sep 21:13 22:13 3000 15-34 15-33 3 T1-2 TRT 11-Sep 22:35 23:35 3000 15-34 15-35 3 T4-1 GEL 10-Sep 20:50 21:50 3000 13-34 14-27 2 T4-2 GEL 10-Sep 22:10 23:10 3000 13-34 13-32 3 T4-3 GEL 10-Sep 23:50 01:20 4500 13-34 14-36 3 T6-1 OLR 9-Sep 23:45 00:45 3000 15-35 15-35 3 T6-2 OLR 9-Sep 01:12 02:12 3000 15-35 16-36 3 T7-1 WHI 9-Sep 20:43 21:43 3000 15-36 16-36 3 T7-2 WHI 9-Sep 22:05 23:05 3000 15-36 15-36 3

Appendix 6. Kokanee trawl catch and catch per unit effort (CPUE) by age and trawl

location for Okanagan Lake during September 2005. Station Kokanee Catch (no) Area1 Trawl CPUE (no/ha)

No. age 0 age 1 age 2 age 3 Total (ha) age 0 age 1 age 2 age 3 Total1 87 4 6 1 98 0.60 173 6 10 2 163 4 43 3 3 2 51 0.75 57 4 4 3 68 6 55 10 3 1 69 0.60 91 17 5 2 115 7 63 6 4 3 76 0.60 105 10 7 5 127

Total 248 23 16 7 294 2.55 97 9 6 3 115 1 Area sampled was based on trawl distance, width of the net and the number of layers sampled.


Appendix 7. Kokanee length correction factors for Okanagan Lake. Correction factors for > 180 mm fish and for 100-180 mm fish are from Rieman and Myers (1992). Correction factors for < 100 mm fish were derived from Okanagan Lake trawl samples collected during 1988-1993.

Date > 180 mm 100 – 180 mm < 100 mm Date > 180 mm 100 – 180 mm < 100 mm1-Sep 1.025 1.064 1.090 7-Oct 1.000 1.000 0.982 2-Sep 1.023 1.061 1.087 8-Oct 1.000 1.000 0.979 3-Sep 1.021 1.058 1.084 9-Oct 1.000 1.000 0.976 4-Sep 1.020 1.056 1.081 10-Oct 1.000 1.000 0.973 5-Sep 1.018 1.053 1.078 11-Oct 1.000 1.000 0.970 6-Sep 1.016 1.050 1.075 12-Oct 1.000 1.000 0.967 7-Sep 1.014 1.047 1.072 13-Oct 1.000 1.000 0.964 8-Sep 1.012 1.044 1.069 14-Oct 1.000 1.000 0.961 9-Sep 1.011 1.042 1.066 15-Oct 1.000 1.000 0.958 10-Sep 1.009 1.039 1.063 16-Oct 1.000 1.000 0.955 11-Sep 1.007 1.036 1.060 17-Oct 1.000 1.000 0.952 12-Sep 1.005 1.033 1.057 18-Oct 1.000 1.000 0.949 13-Sep 1.003 1.030 1.054 19-Oct 1.000 1.000 0.946 14-Sep 1.002 1.028 1.051 20-Oct 1.000 1.000 0.943 15-Sep 1.000 1.025 1.048 21-Oct 1.000 1.000 0.940 16-Sep 1.000 1.023 1.045 22-Oct 1.000 1.000 0.936 17-Sep 1.000 1.022 1.042 23-Oct 1.000 1.000 0.933 18-Sep 1.000 1.020 1.039 24-Oct 1.000 1.000 0.930 19-Sep 1.000 1.018 1.036 25-Oct 1.000 1.000 0.927 20-Sep 1.000 1.017 1.033 26-Oct 1.000 1.000 0.924 21-Sep 1.000 1.015 1.030 27-Oct 1.000 1.000 0.921 22-Sep 1.000 1.013 1.027 28-Oct 1.000 1.000 0.918 23-Sep 1.000 1.011 1.024 29-Oct 1.000 1.000 0.915 24-Sep 1.000 1.010 1.021 30-Oct 1.000 1.000 0.912 25-Sep 1.000 1.008 1.018 31-Oct 1.000 1.000 0.909 26-Sep 1.000 1.006 1.015 1-Nov 1.000 1.000 0.906 27-Sep 1.000 1.005 1.012 2-Nov 1.000 1.000 0.903 28-Sep 1.000 1.003 1.009 3-Nov 1.000 1.000 0.900 29-Sep 1.000 1.001 1.006 4-Nov 1.000 1.000 0.897 30-Sep 1.000 1.000 1.003 5-Nov 1.000 1.000 0.894 1-Oct 1.000 1.000 1.000 6-Nov 1.000 1.000 0.891 2-Oct 1.000 1.000 0.997 7-Nov 1.000 1.000 0.888 3-Oct 1.000 1.000 0.994 8-Nov 1.000 1.000 0.885 4-Oct 1.000 1.000 0.991 9-Nov 1.000 1.000 0.882 5-Oct 1.000 1.000 0.988 10-Nov 1.000 1.000 0.879 6-Oct 1.000 1.000 0.985 11-Nov 1.000 1.000 0.876


MISSION CREEK KOKANEE SPAWNING CHANNEL PRODUCTION AND 2005 ESCAPEMENT

by

H. Andrusak1 and G Andrusak2

INTRODUCTION Monitoring of stream spawning kokanee is a key activity associated with OLAP’s long term objective of restoring kokanee in Okanagan Lake. Mission Creek is the largest and most important tributary since it supports the majority of the stream spawning population of kokanee (Oncorhynchus nerka). This system has been monitored for kokanee escapements for well over three decades and the data provides the best trend information available for the stream spawning component of the lakes’ population. Also, this system is also known to be highly important for Okanagan Lake spawning rainbow trout [Oncorhynchus mykiss] (Wightman and Sebastian 1979). In general, total kokanee in Okanagan Lake have declined from approximately 12 million to 3.1 million by 2000 with modest increases noted since then (Sebastian et al. in this OLAP report). Many studies, particularly the Okanagan Lake Action Plan (OLAP), have been conducted to determine and identify the causes of the kokanee decline in Okanagan Lake (Northcote et al. 1972, Smith 1978, Mathews and Bull 1981, Andrusak and Sebastian in Andrusak et al. 2000). A continuous decline in Okanagan Lake kokanee has been observed for over 30 years with Mission Creek escapements falling to an unprecedented low of ~1,000 recorded in 1998. This decline was initially attributed to habitat loss since over the past 30 years much of the lower 10 km has been channelized for flood control purposes. The incremental loss of fish habitat in this stream led OLAP to conduct a complete review of habitat restoration opportunities reported by Gaboury and Slaney (in Andrusak et al. 2003). However, the downward trend in kokanee numbers has not been restricted to Mission Creek alone, as other smaller tributary stream escapements also have declined (Webster in this OLAP report) indicating a common problem involving an in-lake bottleneck. The cause(s) of this limitation is the subject of much research reported by others in this OLAP report. At one time Mission Creek spawning kokanee ascended Mission Creek for some 19 km (Shepherd in Ashley et al. 1998), but owing to smaller numbers today most spawning occurs in the lower 10 km. The evolution of the Mission Creek spawning channel has been described in previous OLAP reports (Andrusak in Ashley et al. 1999). The final configuration and operation of this channel is somewhat different from other kokanee spawning channels because of private property constraints and priority for flood control. 1 Redfish Consulting Ltd., 5244 HWY 3A, Nelson, BC V1L 6N6 2 Redfish Consulting Ltd., 5240 HWY 3A, Nelson, BC V1L 6N6


In terms of overall performance, Mission Creek channel ranked much lower compared to five other provincial kokanee spawning channels, although it still produces kokanee fry at a much higher rate than natural stream production (Redfish Consulting Ltd. 1999). More importantly, fry production has increased in recent years possibly due to modifications to the water intake at the upper end of the channel (Webster 2005a). Biological data obtained from samples of the fall 2005 kokanee spawners and spring 2004 kokanee fry production estimates are summarized in this report. Data from a sample of the 2005 fish are analyzed for sex ratio, spawner size, age composition, and fecundity. Fry production estimates in the spring 2005 are used to estimate fry-to-adult survival rates. Estimates of 2005 egg deposition for the spawning channel and stream are made from known fecundity and egg retention and these estimates will in turn be used for determining 2006 egg-to-fry survival rates. BACKGROUND Concern regarding Okanagan Lake fish and particularly kokanee can be traced back as far as the late 1960s. In 1969, due to the continual and increasing demand for water for agricultural and domestic use, a Canada-British Columbia Okanagan Basin Agreement was reached between the two levels of government to integrate and manage water resources in the Okanagan Basin (Shepherd 1990b). The main report (Canada-British Columbia Okanagan Basin Agreement 1974) contained several key recommendations for fish including specific stream flows to protect Mission Creek fish and fish habitat. In addition, the work recommended design and implementation of a habitat improvement program for Mission Creek. Over the last three decades some minor improvements have been made to the stream and recently some major restoration projects were proposed by Gaboury and Slaney (in Andrusak et al. 2003). Decline in Okanagan Lake kokanee abundance was initially believed to be due to poor stream spawning success resulting from stream channelization and severe water withdrawals for agriculture. Some limited success in kokanee stocking of the lake from 1987 to 1991 (Shepherd 1994) and some specific stream stockings with hatchery reared fed-fry probably masked the continued downward trend of wild kokanee numbers. Aside from stream habitat deterioration, the impact of Mysis relicta on kokanee fry survival was recognized as a problem by Shepherd (1990a) but the degree of impact was poorly understood. Recently, the question of primary nutrient imbalance between N:P has also been identified as a major reason for the kokanee decline (Stockner in this OLAP report). Competition between mysids and kokanee for zooplankton and/or deterioration of spawning habitat has also been identified as limitations to kokanee (Andrusak et al. 2000). At one time, Okanagan Lake supported a very productive sport fishery for kokanee and rainbow trout. An estimate of fishing effort in 1971 was 188,000 angler hours resulting in a catch of 178,000 kokanee (Shepherd 1994). By the early 1990s, annual effort had increased to approximately 250,000 hours but kokanee catch had declined to only 37,000 (Shepherd 1994). By the mid 1990s the collapse of kokanee was very evident and a fishing closure for kokanee was imposed in 1995. Since then the fishery has


remained closed but with the realization that the lake carrying capacity has been reduced perhaps permanently, the question has been raised as to whether or not the kokanee can support a modest sport fishery at a much reduced level of harvest. Wilson and Webster (in Andrusak et al. 2005) conducted a test fishery in 2005 to obtain updated biological data and catch statistics. Johnston (in this OLAP report) has developed a science based harvest control model that indicates a small harvest can be permitted albeit much less than that recorded in the 1970s. A limited sport fishery has been proposed for the summer, 2006. Critical to the analysis by Johnston was the data available from the stream and shore spawner estimates. Enumeration and biological sampling of Okanagan Lake’s stream spawning kokanee have been on-going since the early 1970s (Northcote et al. 1972). Kokanee enumerations on Mission Creek date back to the early 1970s; therefore, a well established long-term data set is available for trend analysis and estimation of a sustainable harvest via the fishery. SITE DESCRIPTION Mission Creek is the primary drainage of the local Midway Mountains on the western slope of the Monashee Mountain range encompassing an area of approximately 880 km2. The lower 19 km of Mission Creek is accessible to spawning rainbow trout and kokanee from Okanagan Lake (Wightman and Sebastian 1979). At this point, there is an impassable set of waterfalls and cascades known as Gallagher’s Falls. The lower 13 km of Mission Creek has been channelized to varying degrees for flood control purposes as it flows through agricultural and residential areas adjacent to and within the City of Kelowna. Despite the numerous impacts to this system, it remains the primary system utilized by stream spawning kokanee. The lower end of present day Mission Creek spawning channel is located approximately 7 km upstream of Okanagan Lake within the City of Kelowna. The channel (Fig. 1) is now ~900 m long and 3.6 m wide and has an average reach gradient of 0.05% (Redfish Consulting Ltd. 1999). It is located on the south side of Mission Creek in the Sutherland Regional Park, Kelowna, BC. The channel is readily accessible to the public and there is a great deal of interest in its operation as well as providing ideal viewing opportunities for watching spawning kokanee. METHODS Escapements Until 2003, the standard method of enumerating spawners in the channel has involved estimating numbers using the area-under-the curve (AUC) methodology (Hill and Irvine 2001). The description for estimating a parameter of the AUC, residence time, can be found in Dill and Larsen (1995). The development of standard methods and variations used up to 2002 for estimating Mission Creek spawner numbers are described in Dill (1990 to 1993, 1996, and 1998) as well as in annual data reports on escapements and fry production on file in the BC Fisheries Office, Penticton, BC.


Commencing in 2003, the total adult escapement estimate was derived by multiplying the peak number of fish counted during the daily live counts by an expansion factor of 1.5 (Andrusak and Sebastian in Andrusak et al. 2000). This conversion is based on daily counts of spawners captured in fish traps at three spawning channels over a number of years and comparing the cumulative counts with the date of peak numbers. A regression of peak counts on the cumulative total at the peak results in a conversion factor of 1.5. Kokanee spawner counts are also made on several other streams including Mission Creek as part of the annual Okanagan Lake stream survey work. These counts are made independent of the spawning channel estimates. Annually, a two-person crew walks the stream and visually estimates spawner numbers. Until 1998, these counts were conducted at least once every 10 days at the beginning of the spawning season with frequency increased to once every 5 days prior to and just after the peak of the run. In 1998, the stream counts were modified to ensure the peak was accounted for. The frequency of days counted has been increased to a count every third day during the expected peak with counts made only every 5 days on either side of the peak. Since 2000, daily counts are made immediately around the peak, usually every second day. More detail on methods used to estimate stream spawners and results for 2005 are described by Webster (in this OLAP report). Spawner Size and Sex Ratio In 2005, 201 kokanee samples were collected between September 20-30 from the spawning channel and from the stream (Webster 2005a). These samples were used to determine length, sex ratio, and egg retention. Both otoliths were removed from a total of 100 sampled kokanee. Commencing in 2004, average egg retention of spawned out females was determined for both the spawning channel and the natural stream. It should be noted that in the past, fecundity and egg retention data collected from the natural stream during the course of stream enumerations had not been included, hence, some minor differences exist between this and previous reports. Fecundity In most years, a regression formula has been used to derive fecundity from known female lengths. Dill (1992) initially developed a length-fecundity equation using pre-spawning mortalities (eggs still in skeins) randomly collected from the Mission Creek spawning channel in 1991 and 1992. Andrusak and Sebastian (in Andrusak et al. 2000) included more data from 1998 and 1999 to refine Dill’s formula. The slightly revised equation is:

Log10 (Eggs) = 3.289 x Log10 (female length in mm) - 5.275 (r2 = 0.823; n = 101) As mentioned, fecundity estimates in this report vary somewhat from those reported by Andrusak and Sebastian (in Andrusak et al. 2000) because the database (female length) has been expanded in recent years to include stream samples as well as those


from the channel. Consequently, egg deposition and egg-to-fry survival rates may also vary slightly from earlier reports but the overall trend has not been affected due to these small changes. Prior to 2000, the mean length from the total sample was used to derive the fecundity, which resulted in an underestimate of egg deposition since the larger fish with much higher numbers of eggs per female were under represented. Since 2000, individual female lengths have been used to generate fecundity estimates using the regression formula. Separate egg deposition estimates were made for the channel compared to the stream since egg retention was determined for both. In 2005 the derived mean fecundity minus the average retention for the channel was determined from 92 female samples. Egg retention estimates were made separately for the stream and channel and these were subtracted from the derived fecundity estimate for egg deposition estimates shown in Appendix 1. Fry Enumeration Methodology for fry enumeration remains unchanged since this work began in 1991. The onset of kokanee fry out-migration is determined with a single 60 cm wide fyke net that is initially fished overnight. Once fry out-migration commences, a standard sub-sampling netting procedure starts at the lower end of the channel (Andolfatto and Dill 1997). Fry sampling consists of placing three box traps each 31 cm wide, 31 cm high and 61 cm deep equidistant across the 3.6 m wide channel. At the sampling site the channel bed is level, therefore, the cross sectional area is fully sub-sampled. The traps are typically placed in the channel at dusk and fished for a designated period each hour every hour until dawn. On a weekly basis, five nights were sampled for four hours, whereas for two nights the entire time period from dusk to dawn was sampled hourly. Incidentally, if fishing ceases prior to dawn a correction factor is employed to estimate the entire night out-migration. Fishing times of 1 to 20 minutes per hour are used and adjusted within the night to catch 15 to 25 fry per net per sampling hour. The number of fry passing by the sampling site per night is extrapolated from the hourly sub sample and the number over the entire spring period is then extrapolated from the estimates on sample nights (Andolfatto and Dill 1997). In most years, fry sampling occurred every night over the period of fry migration until no fry are caught over several hours of sampling. The 2005 fry production estimates can be found in Webster (2005b). RESULTS AND DISCUSSION Escapement, egg deposition and subsequent fry production estimates at the Mission Creek Channel have been sufficiently consistent to allow for comparisons from 1991 to 2005. Reconstruction of the channel during 1995 and 1996 precluded fry production estimates for 1994 and 1995 and the 1999 data is considered unreliable due to low spawner numbers. The most reliable data is that from 2000 onward because of higher


escapements resulting in much higher egg depositions and therefore larger sample sizes for estimating fry production. Escapements Annually, visual estimates of spawn kokanee have been made since 1974 in the main stream as well as the spawning channel in relatively the same manner thus providing good time series information. 2005 For the second year in a row Mission Creek escapements increased significantly with a total estimate of 32,587 compared to 27,442 (2004) and 13,644 (2003). The spawning channel continues to attract and or retain approximately 20-25% of the total Mission Creek escapement with ~ 6,400 spawning in the channel in 2005 (Fig. 2, Table 1). The low percentage of use reflects the passive manner in which the channel is operated, (no attempt is made to contain upstreaming fish in the channel). A one-way fish fence at the lower end of the channel would likely increase the use, and subsequently fry production. As noted, Mission Creek is the largest tributary on Okanagan Lake utilized by spawning kokanee. Slightly over 61% of the total 2005 stream spawning kokanee escapement were enumerated in Mission Creek (see Webster in this OLAP report). Since 1989, Mission Creek has supported between 30-60 % of the total stream spawners when compared to the other seven primary spawning streams (Fig. 3). The only exceptions to this were in 1998 and 1999, the years of lowest Mission Creek escapements (Fig. 2). Peak of spawning in the channel was observed on September 16, 2005, whereas the stream peak count occurred on September 20th. Most other stream peak counts were observed nearly 10 days later between September 29-30, 2005 (Webster 2005b). Spawner Size Mean size of spawners has been decreasing during the last three years. In 2005, mean fork length of Mission Creek spawners was 258 mm based on 201 samples obtained from the stream and the channel. Recently, the mean size of females has declined from 329 mm (2003), 262 (2004) to 258 (2005), close to the lowest estimate in 1993 when the mean was 249 mm (Fig 4; Table 2). The 2005 spawners were primarily comprised of what appears to be a single mode between 230-275 mm with very few fish exceeding 300 mm (Fig. 5). As recent as 2003 and certainly during the 1980s a high proportion (> 40%) of the spawners was > 300 mm, presumably representing several older age groups. Age Composition Accurate and consistent age determination of Okanagan Lake spawners remains near impossible to achieve and OLAP biologists have concluded that length-frequency


analysis combined with age determination of trawl caught fish are more accurate. Analysis of length-frequency histograms (Fig. 5) and age of trawl caught fish (Sebastian et al., in this OLAP report) suggests the first mode are age 3+ with older fish > 300 mm ranging from age 4+ to age 6+. Table 1. Mission Creek kokanee escapements estimated by BC Fisheries field crews

and contractors. All estimates except 1971 have been adjusted by 1.5. YEAR Stream Peak Count x 1.5 Channel Peak Count (x 1.5) Stream + Channel

1971 312,100 312,100 1972 1973 1974 136,304 1975 40,435 1976 31,956 1977 33,913 1978 90,653 1979 117,391 1980 78,261 1981 61,957 1982 1983 37,826 1984 76,304 1985 98,625 1986 84,000 1987 16,200 1988 21,525 1989 13,043 4,566 17,609 1990 16,304 3,913 20,217 1991 61,500 14,022 75,522 1992 41,153 23,478 64,630 1993 20,870 9,783 30,653 1994 12,783 3,783 16,566 1995 7,043 3,261 10,304 1996 14,804 7,826 22,630 1997 8,283 3,653 11,935 1998 1,028 708 1,735 1999 1,271 342 1,613 2000 16,482 7,938 24,420 2001 31,509 6,702 38,847 2002 17,936 2,267 20,203 2003 9,358 4,286 13,644 2004 20,494 6,948 27,442 2005 26,196 6391 32,587

1 From Northcote et al. 1972 (actual count from fence operation).


Table 2. Mission Creek kokanee lengths: mean female, male, and combined lengths, 1970, 1974 and 1986 to 20052.

# Female Sample

Female Mean SD SE # Male

Sample Mean SD SE # Sample Mean M/F

1970 10 266 10 268 20 267 1971 25 259 53 264 78 262 1974 49 255 61 268 110 262 1986 72 261 21 3 28 275 19 4 100 265 1987 115 341 83 8 86 367 85 9 201 352 1988 52 266 26 4 48 273 24 3 100 270 1989 77 293 57 6 20 257 12 3 97 285 1990 326 289 53 3 260 303 69 4 587 295 1991 364 277 57 3 260 304 82 5 626 289 1992 468 258 47 2 453 262 48 2 921 260 1993 257 249 30 2 141 266 42 4 398 255 1994 323 262 55 3 322 271 71 4 645 267 1995 124 280 55 5 160 303 70 6 284 293 1996 105 290 51 7 130 309 72 9 235 300 1997 135 263 60 4 191 272 56 5 327 268 1998 13 369 36 396 49 389 1999 43 324 48 351 91 339 2000 59 278 46 6 42 294 68 10 101 284 2001 131 278 31 3 117 295 47 4 248 286 2002 106 309 68 7 116 319 69 6 222 314 2003 77 329 72 8.2 83 333 89 9.8 160 331 2004 177 262 26 2 126 287 57 5 303 273 2005 102 258 36 4 99 259 39 4 201 258

2 Data from Penticton Fisheries OKFISH files. Fecundity As would be expected, given the small size of 2005 females, the calculated fecundity was the lowest in over a decade (Table 3) at 488 eggs•female (N=92). The last year fecundity was < 500 was in 1993. As noted earlier, there were very few fish > 300 mm. The sex ratio for fish sampled in the channel (only) was exactly 1:1.


Table 3. Derived fecundity estimates1 for Mission Creek kokanee 19712, 1989-2005.

Year Sample Size Female Mean Length Derived Fecundity

1971 50 259 480 1989 47 318 1,021 1990 307 289 762 1991 278 283 737 1992 468 258 525 1993 257 249 425 1994 275 266 578 1995 124 280 687 1996 105 290 755 1997 135 263 546 1998 13 369 1,592 1999 43 284 1,185 2000 59 267 643 2001 131 278 608 2002 106 309 818 2003 77 329 1,009 2004 160 262 501 2005 102 258 488

1 All data from OKFISH file; regression formula Log10 (fecundity) = 3.289* log10 (length in mm) – 5.275 used to derive fecundity estimates for all years except 1971.

2 Direct measurements as reported by Northcote et al. (1972). Egg Deposition In 2004 and again in 2005, egg deposition was estimated separately for the channel and the stream. Egg retention was higher in the natural stream (mean = 15) than in the channel (mean = 8). Derived mean fecundity minus retention was 480 eggs per female for the channel while the derived mean fecundity minus retention was 473 eggs per female for the stream. Therefore, it was calculated that the channel egg deposition was approximately 1.53 million eggs compared to the stream egg deposition of 6.2 million eggs. Egg deposition in the channel estimates have ranged from a high in 2.5 million (1992) to a low of only 0.11 million in 1999 (Table 4). Fry Production The spawning channel produced nearly one million fry in 2004 and the 2005 estimate was just slightly lower at 854,618 (Table 4). The estimated egg-to-fry survival rate for 2005 of 49.1 % was virtually identical to the rate calculated for 2004 (47%). It should be noted that there was a small difference in the 2004 egg deposition estimate report by Andrusak and Andrusak (in Andrusak et al. 2005) that has been revised downward in Table 4 resulting in a slightly higher egg-to-fry survival estimate. It is believed that continual minor improvements to the channel and more diligent gravel scarification techniques most likely accounts for the higher survival rates during the last five years (Webster 2005b).


Table 4. Estimates of kokanee egg deposition, fry production and egg-to-fry survival rates from Mission Creek spawning channel 1990 to 2004*.

Adult Year Channel

Numbers Female

Mean Length (mm)

Fecundity Egg Deposition

x 106

Fry Year Fry Production

% Egg/Fry Survival

Rate 1990 9,200 289 500 1.6 1991 484,324 30.3 1991 11,765 277 595 2.46 1992 203,146 8.3 1992 25,541 258 559 2.51 1993 890,361 35.5 1993 9,003 249 392 1.64 1994 1994 3,881 262 471 0.92 1995 1995 6,021 280 609 1.35 1996 574,456 42.6 1996 7,030 290 649 1.28 1997 509,873 39.8 1997 3,422 263 429 0.57 1998 45,648 8 1998 708 369 1,586 0.8 1999 136,970 17 1999 322 284 1,185 0.11 2000 22,091 20.8 2000 7,358 267 643 2.27 2001 679,802 30 2001 4,659 278 562 1.33 2002 814,201 61.4 2002 3,132 309 818 1.07 2003 384,640 35.9 2003 4,285 329 1,009 1.97 2004 929,412 47 2004 6,948 262 513 1.74 2005 854,618 49.1 2005 6391 258 488 1.53 2006

* Data from various contractor reports cited elsewhere have been used for these estimates; data on file BC Fisheries, Penticton OKFISH file.

Fry-to-Adult Survival Rates Survival rates of the fry that move into Okanagan Lake to grow and then return four or more summers later as adults cannot be determined directly since there have been no fry production estimates made from the main stream. However, there has been sufficient spawner use and fry production data collected from the spawning channel and spawner numbers in the stream that some crude estimates of fry-to-adult survival rates can be constructed for the whole stream (Appendix 1). While these estimates are based on a number of reasonable assumptions supported by data from other kokanee spawning channels, they should not be considered as accurate estimates but rather only as trend indicators. One change that has occurred in 2004 was an estimate made egg deposition for both the channel and the natural stream since separate egg retentions were determined for each. Data, assumptions and calculations used to construct theoretical fry-to-adult survival rates for Mission Creek are shown in Appendix 1. The early years (prior to 1998) data was not considered as reliable as the data from the 2000s since far more assumptions had to be made. For example, when sex ratio data was unavailable it was assumed to be 1:1. Slight variations in this ratio actually make little difference to the calculated survival rates. This assumption has been supported by more recent actual sex ratio determinations from 2002-2005 that have been very close to 1:1. Based on Dill’s work on the spawning channel, a 20% pre-spawn mortality was assigned prior to 2000 since


Dill (1996) and Taylor and Dill (1997) often noted high mortality probably due to very warm water (>15°C). No significant spawner mortality has been observed in 2000s and onward, although Webster (2005b) does make the observation that human activity such as children throwing rocks at the spawners and dogs running freely into the channel were probably responsible for some spawner mortality. In the absence of real data, a spawning channel mean fecundity of 412 eggs (reduced by 108 eggs due to retention) from Dill (1990 to 1993, 1996, 1998 and Taylor and Dill 1997) was assigned to the years 1984 to 1989 to determine stream egg deposition for those years. Since 1990, actual data has been used to estimate egg deposition. To estimate natural stream fry production a conservative 5% egg-to-fry survival rate was applied based on natural stream production estimates of 6% (range 1.4 to 17%) in Meadow, Hill, and Redfish creeks (Redfish Consulting Ltd. 1999). Since there appear to be problems with the quality of the natural spawning habitat in Mission Creek (Gaboury and Slaney in Andrusak et al. 2003), use of the lower value of 5% is deemed reasonable. For those two years (1994 and 1995) when the spawning channel was not evaluated for fry production a conservative value of 20% egg-to-fry survival was assigned to the channel. This value is considered reasonable and very conservative given the much higher survival rates experienced in recent years. Because there was a sport fishery prior to 1995, the annual harvest has to be factored in to the abundance estimates (Appendix 1). Kokanee harvest on Okanagan Lake was estimated to be 178,000 in 1971 and the fishery was monitored from 1988 to 1992. Based upon the data in Shepherd (1994), a harvest level of 150,000 was assigned to 1974 and 85,000 was assigned for 1984. Harvests were then extrapolated for 1974 to 1977 and 1984 to 1987. The fishery has been closed since 1995 although a very limited test fishery was conducted in 2004 involving < 500 fish being harvested. There was no estimate of the number of shore vs stream spawners but as Shepherd (1994) and more recently Andrusak (in Andrusak et al. 2005) pointed out stream spawners are much larger in size than shore spawners, and therefore, more vulnerable to fishing. It has been assumed for this analysis that 60% of the annual harvest was stream-origin fish. It is known that 70% of all the stream spawners during those years spawned in Mission Creek (Shepherd in Ashley et al. 1998) and this factor was used in the final determination of harvest of Mission Creek (only) fish. Based on the constructed data for Mission Creek shown in Appendix 1, fry-to-adult survival rates have been derived using scenarios of dominance of age 2+ and or age 3+ at maturity. The on-going problem of definitive age determination of the spawners is the rationale for generating two scenarios. Until 2000, the derived survival rates were very similar regardless of assigned age-at-maturity (Fig. 6). Commencing in 2000, the survival rates began to increase, especially if the majority of fish were in fact age 2+. From 2001-2004, the survival rates were very high regardless of assigned age-at-maturity. This was not surprising since adult numbers were so low in 1998 and 1999 that recruitment was also undoubtedly low but juvenile fish in the lake survived at very high rates due to such low lake densities. However by 2003 the lake densities had increased (Sebastian et al. in this OLAP report) and a density dependent growth


response was evident as the age 2+ scenario survival rate fell to 2.4 % while age 3+ was only slightly > at 3.1%. In 2005, the rate increased slightly to 4.6% for the age 2+ scenario and decreased slightly to 2.9% for age 3+. The derived survival rates for either age scenario may be leveling off at ~ 3%. This analysis is meant only to illustrate that a change did occur within the lake in the late 1990s and early 2000s since during most of the 1990s the survival rates employing either of the age-at-maturity scenario analysis resulted in relatively low but comparable survival rates (~3-5%). The 2000-2003 generated fry-to-adult survival rates for Mission Creek were far higher than what has been observed in Kootenay Lake and Arrow Reservoir since lake fertilization began. During initial years of fertilization, kokanee survival rates on these two systems increased as high as 15 and 10% respectively. Arrow Reservoir survival rates remain high (Hill Creek stock) at > 10% whereas in Kootenay Lake, the trend is downward to around 5% as the population has again completely rebuilt (Andrusak et al. 2004). The large increase in fry-to-adult survival rates in Okanagan Lake from 2000-2003 was unexpected since there has been no obvious change in lake growing conditions (see Stockner in this OLAP report). The 2003-2005 data indicates that the Mission Creek spawners have recovered from the low numbers recorded in 1998 and 1999. The higher survival rates in the 2000s suggest that there must have been some improvement in the rearing conditions in the lake or more likely a density growth response considering the low numbers in the lake during the late 1990s (see Sebastian et al. in this OLAP report). Numbers of recruits from either age 2+ or 3+ parents from 1994-2000 were less than parental numbers (Fig. 7). The spawner-recruit relationship changed starting in 2000 when the number of recruits began to exceed parental numbers. For example, in 1997, the Mission Creek escapement was only ≈12,000 while in 2001 returning progeny (assuming the 3+ scenario) were nearly 39,000. Despite the larger escapement (~33,000) in 2005 these numbers were actually less than the parental numbers in 2001 (~39,000) assuming most were age 3+. Most of the 2005 fish were suspected to have been age 3+ based on length-frequency analysis (Fig. 5). These crude calculations of spawner recruit ratios provide further evidence that in-lake survival during the last 5 years must have improved albeit probably only temporarily. Unfortunately, without a clear understanding of the age composition of the spawners interpretation of annual escapements is limited and somewhat speculative. It would appear that age determination for Okanagan Lake spawners may only be accomplished by capturing adult size fish during the summer months to obtain good readable scale samples. It should be noted that recent years of increased kokanee escapements conflict with the interpretations of the phytoplankton data (see Stockner in this OLAP report), with the suggestion that poor algal species composition and low biomass of “good” algae represents poor growing conditions for kokanee is not supported by the escapement data. If anything, growing conditions must have improved somewhat during the 2000s as in the evidence of improved in-lake survival rates (Fig. 6) and improvement in the spawner-recruit relationship (Fig. 7). Differences in nutritional value of various zooplanktors have been implicated in the demise of Okanagan Lake kokanee.


Unusually high biovolumes of blue-greens that offer low nutritional value to zooplankton has been theorized as a primary cause of poor survival of kokanee (see Rae and Vidmanic in this OLAP report). However, Clarke and Bennett (2004) point out that species composition and size of prey as well as densities may all be important in survival and growth of juvenile kokanee. Cladoceran densities in Okanagan Lake are comparable to Kootenay Lake (post fertilization) but are lower than lakes without mysids (Rae and Vidmanic in Andrusak et al. 2005), meaning there has been no obvious improvement in zooplankton densities in recent years. It is plausible that increased survival of Okanagan Lake kokanee juveniles implied by increased escapements during the 2000s is due to the gradual decline in mysid densities (Rae and Vidmanic in this OLAP report) over the last decade. Juvenile kokanee may be the beneficiaries of the mysid decline, utilizing zooplankton that in the past has been consumed by mysids. This would explain why zooplankton densities have remained fairly constant yet kokanee numbers have increased. If this theory is correct then the hypothesis that poor food quality due to dominance of blue-greens in the lake is the cause of the kokanee decline needs to be re-examined. It is more likely that the competitive interaction between kokanee and mysids is the root cause of the decline exacerbated by poor quality food in some years.


SUMMARY Kokanee escapements to Mission Creek in 2005 once again increased following on improved numbers in 2004 and 2003. In fact, the 2005 return was the second highest since 1993. The highest escapement in the last decade was in 2001 and these represent the parents (age 3+) of the 2005 returns. Mean size and fecundity in 2005 was similar to 2004, (low and comparable to the lowest recorded since 1993, Table 2; Fig. 4). There were very few fish that exceeded 300 mm a major change from a number of years ago (1987, Fig. 5) when >25% of the spawners were >400 mm. Total fry production from the channel in 2005 was comparatively high close to the record high determined in 2004. The 2005 egg-to-fry survival rate was almost identical to the 2004 estimate, with the second highest (47%) having years much higher than the 13 year average of 32.5%. Escapements in the 2000s have increased considerably compared to the late 1990s and the data indicates high replacement values for three of the four or five cycles. The very high fry-to-adult survival rates for the 1997-2000 broods are of particular interest and suggest a much improved lake environment for some or all the years that their progeny grew in the lake. The lower survival rate and <1 spawner-recruit ratio estimated for the 2001-2005 cycle may be a signal that these fish experienced lower in-lake survival because the lake abundance levels (2003-2005) were much higher than before (see Sebastian et al., in this OLAP report). It is speculated that the escapement levels in 2004 and 2005 probably reflect a plateau commensurate with the current and much lower lake carrying capacity. The increase in kokanee numbers during the 2000s is at odds with the interpretation by OLAP biologists who have analyzed the phytoplankton data. Stockner (in this OLAP report) and Rae and Vidmanic (in this OLAP report) both suggest that poor quality phytoplankton due to nutrient imbalance may be the reason why Okanagan Lake kokanee have declined. This may be partially correct but it is also likely that declining mysid densities (Rae and Vidmanic in this OLAP report) are also responsible for improved kokanee survival rates. Overall the use of the Mission Creek spawning channel by kokanee spawners has been less than expected, primarily because no effort is made to farm and contain the fish in the channel. Declining escapements and the distance of the channel from the lake are also factors that appear to limit the numbers of fish using the channel. For these reasons, egg deposition densities have been well below the designed optimum. The range of estimated egg-to-fry survival rates suggests the channel is capable of consistently good fry production (> 30% egg-to-fry survival). A word of caution though about future production from this channel; if fry production were to significantly increase it could create a weak-strong stock scenario between Mission Creek vs other streams as has been the case on Kootenay Lake. It may be prudent to permit fry production only at current levels (< 1 million) until lake productivity improves.


RECOMMENDATIONS 1. Use a conversion factor of 1.5 times the peak count of adult kokanee to estimate

stream and channel spawner populations. 2. All Mission Creek data should be used to determine mean size, sex ratio, and

fecundity. A minimum 200 fish should be randomly collected from the stream and lower fence trap and measured for fork length, and the sex determined. Of the 200, a minimum of 60 pre-spawn females should be captured at the beginning (10), mid point (40), and near end (10) of spawning run for direct egg counts. Otoliths should continue to be collected from these fish for age determination.

3. To determine egg deposition in the spawning channel, egg retention counts should

be conducted on dead females found in the channel. The same should be done for the stream spawners.

4. Escapement enumeration in the Mission Creek spawning channel should ideally be

changed to daily trapping (using a one-way trap), counting, and release of spawning fish. This would ensure more fish utilize the channel and would eliminate uncertainty and bias related to length and fecundity measurements.

5. To achieve maximum production potential of kokanee the fish should be diverted

into the spawning channel using a full mainstem fence until design or target densities have been achieved. Within the channel they should also be “farmed’ using additional one way fences to improve spawner distribution.

6. Increasing fry production >1-1.5 million should not occur until lake productivity

improves. 7. Fry enumeration methods should continue to be conducted as in previous years.

Fry length measurements should be discontinued as they provide no valuable information for the management of the kokanee resource of Okanagan Lake.


REFERENCES Andolfatto, D.D., and P.A. Dill, P.A. 1997. Outmigration of Kokanee Salmon fry From

Mission Creek Spawning Channel and Estimate of Egg-to-Fry Survival, 1997. Contractor Rept. Prep. for Min. Env. Fish Sect, Penticton.

Andrusak, H. 2003. Response of Arrow Reservoir Kokanee to Experimental

Fertilization in 2002. Report prepared for the Ministry of Water, Land and Air Protection, Nelson, BC.

Andrusak, H., D. Sebastian, I. McGregor, S. Matthews, D. Smith, K. Ashley, S. Pollard,

G. Scholten, J. Stockner, P. Ward, R. Kirk, D. Lasenby, J. Webster, J. Whall, G. Wilson, H. Yassien. 2000. Okanagan Lake Action Plan Year 4 (1999) Report. Fisheries Project Report No. RD 83. Fisheries Management Branch, Ministry of Agriculture, Food and Fisheries, Province of British Columbia.


D. Sebastian, G. Scholten, P. Woodruff, D. Cassidy, J. Webster, A. Wilson, M. Gaboury, P. Slaney, G. Lawrence, W.K. Oldham, B. Janz and J. Mitchell. 2003. Okanagan Lake Action Plan Year 7 (2002) Report. Fisheries Project Report No. RD 106. 2003. Fisheries Management Branch, Ministry of Water, Land and Air Protection, Province of British Columbia.


G. Scholten, P. Woodruff, D. L. Vidmanic, J. Stockner, G. Wilson, , B. Janz, J. Webster, H. Wright, C. Walters and J. Korman. 2004a. Okanagan Lake Action Plan Year 8 (2003) Report. Fisheries Project Report No. RD 108. 2004. Fisheries Management Branch, Ministry of Water, Land and Air Protection, Province of British Columbia.

Andrusak, H., S. Matthews I. McGregor, K. Ashley, R. Rae, A. Wilson, J. Webster, G.

Andrusak, L. Vidmanic, J. Stockner, D. Sebastian, G. Scholten, P. Woodruff, B. Jantz, D. Bennett, H. Wright R. Withler and S. Harris 2005. Okanagan Lake Action Plan Year 9 (2004) Report. Fisheries Project Report No. RD 111. 2005. Fisheries Management Branch, Ministry of Environment, Province of British Columbia




Andrusak, H., D. Sebastian, G. Scholten, and P. Woodruff. 2004b. Response of Kokanee and Gerrard Rainbow Trout to Experimental Fertilization of the North Arm of Kootenay Lake, 2002 and 2003. Redfish Consulting Ltd. Contract Report for the Columbia Basin Fish and Wildlife Compensation Program, Nelson, BC.

Ashley, K., B. Shepherd, D. Sebastian, L. Thompson, L. Vidmanic, Dr. P. Ward,

H.A. Yassien, L. McEachern, R. Nordin, Dr. D. Lasenby, J. Quirt, J.D. Whall, Dr. P. Dill, Dr. E. Taylor, S. Pollard, C. Wong, J. den Dulk, G. Scholten. 1998. Okanagan Lake Action Plan Year 1 (1996-1997) and Year 2 (1997-1998) Report. Fisheries Project Report No. RD 73. Province of British Columbia, Ministry of Fisheries, Fisheries Management Branch.

Ashley, K., I. McGregor, B. Shepherd, D. Sebastian, S. Matthews, L. Vidmanic,

P. Ward, H. Yassien, L. McEachern, H. Andrusak, D. Lasenby, J. Quirt, J. Whall, E. Taylor, A. Kuiper, P.M. Troffe, C. Wong, G. Scholten, M. Zimmerman, P. Epp, V. Jensen, R. Finnegan. 1999. Okanagan Lake Action Plan Year 3 (1998-99) Report. Fisheries Project Report No. RD 78. Province of British Columbia, Ministry of Fisheries, Fisheries Management Branch, Victoria, BC.

Canada-British Columbia Okanagan Basin Agreement. 1974. Main Report of the

Consultative Board including the Comprehensive Framework Plan. Office of the Study Director. Penticton, BC. 536 pp.

Clarke, L. R., and D. H. Bennett. 2004. Zooplankton Community Changes at Pend

Oreille Lake, Idaho: Testing Implications for Age-0 Kokanee Prey Selection, Digestion, and Growth. Transactions of the American fisheries Society 133: 1221-1234

Dill, P.A. 1990-1993, 1996, 1998 MS. Series of Technical reports on Mission Creek

Spawning Channel Kokanee Adult and Fry Enumerations on file Ministry of Lands, Water and Air Protection, Penticton Office.

Dill, P.A. and D. Larsen. 1995. Migration of Kokanee Salmon Adults into Mission Creek

Spawning Channel and Estimate of Egg Deposition, 1995. Contractor Rep. Prep. for Min. Env,. Fish. Sect, Penticton, BC.

Hill, R. A. and J.R. Irvine. 2001. Standardizing Spawner Escapement Data: A Case

Study of the Nechako River Chinook Salmon North American Journal of Fisheries Management 21:651-655, 2001.

Matthews, S. and C.J. Bull. 1981. Effect of Water Level Fluctuations on Shore

Spawning Kokanee in Okanagan Lake Ministry of Environment Fish and Wildlife Program 20p.

Northcote, T.G., T.G. Halsey, and S.J. MacDonald. 1972. Fish as Indicators of Water

Quality in the Okanagan Basin Lakes, British Columbia. Okanagan Basin Study Comm. Prelim. Rep. No. 22.


Redfish Consulting Ltd. 1999. Performance Evaluation of Six British Columbia

Kokanee Spawning Channels. Unpubl. Contractor Report Prepared for the Ministry of Fisheries, Province of British Columbia, Victoria, BC.

Shepherd, B.G. 1990a. Kokanee Fry Production Assessment of Mission Spawning

Channel and Peachland Creek, 1990. Min. Env., OK Sub-Reg. Tech. Rept., Penticton.

Shepherd, B.G. 1990b. Okanagan Lake Management Plan, 1990 - 1995. BC Min.

Env., Recreational Fish. Progr., Penticton, BC. Shepherd, B.G. 1994. Angler Surveys of Okanagan Main Valley Lakes, 1982 - 1992.

Fish. Proj. Rep. No. OK -17, Okanagan Sub-Reg., S. Int. Reg., Penticton, BC. Smith, D.R. 1978. A Summary of Existing Data on Kokanee (O. nerka) in Okanagan

Lake. Fish. Sect., Tech. Rep., Okanagan Sub-Reg., S. Int. Reg., BC Min. Env., Penticton, BC.

Taylor, D., and P.A. Dill. 1997. Migration of Kokanee Salmon Adults into Mission Creek

Spawning Channel and Estimate of Egg Deposition, 1997. Contractor rept. prep. for Min. Env. Fish. Sect., Penticton, BC.

Webster, J. 2005a. Estimation of Kokanee Escapement and Egg Deposition at Mission

Creek Spawning Channel 2005. Contractor Rep. Prep. for Min. Water Air and Land Protection, Penticton, BC.

Webster, J. 2005b. 2005 Kokanee Fry Out-migration, Mission Creek Spawning

Channel, 2004 Brood. Contractor Rept. Prep. for Min. Water Air and Land Protection, Penticton, BC.

Wightman, J.C. and D.C. Sebastian. 1979, MS. Assessment of Mission Creek

Rainbow Trout Carrying Capacity (August 1978), with Reference to Enhancement Opportunities under the Okanagan Basin Implementation Program.


Figure 1. Okanagan Lake and location of Mission Creek and Mission Creek spawning

channel.


0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

71 75 77 79 81 84 86 88 90 92 94 96 98 00 02 04

Year

Esca

pem

ent n

umbe

rMission Creek Channel

Mission Creek

Figure 2. Mission Creek escapement numbers illustrating the numbers in the stream

and the numbers estimated in the spawning channel.

0

20000

40000

60000

80000

100000

120000

89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05

Year

Esca

pem

ent n

umbe

r

Total 7 streams

Total Mission

Figure 3. Numbers of spawning kokanee contributing to Mission Creek compared to

the total of seven index streams.


0

50

100

150

200

250

300

350

400

450

70 71 74 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04

Year

Mea

n le

ngth

(mm

)

0

200

400

600

800

1000

1200

1400

1600

1800

Mea

n fe

cund

ity

Female Male Fecundity

Figure 4. Mean size (mm) of male and female kokanee spawners from Mission Creek

and derived fecundity for those years data available1970s-2005.


1987n=200

02468

10

175 205 235 265 295 325 355 385 415 445 475 505 535 565 595Length (mm)

% fr

eque

ncy

1992n=921

0

10

20

30

175 205 235 265 295 325 355 385 415 445 475 505 535 565 595

Length (mm)

% fr

eque

ncy

2003n=222

0

5

10

15

175 205 235 265 295 325 355 385 415 445 475 505 535 565 595

Length (mm)

% fr

eque

ncy

2004n=303

0

10

20

30

175 205 235 265 295 325 355 385 415 445 475 505 535 565 595

Length (mm)

% fr

eque

ncy

2005n=201

05

1015202530

175 195 215 235 255 275 295 315 335 355 375 395 415 435 455 475 495 515 535 555 575 595

Length (mm)

% fr

eque

ncy

Figure 5. Percent length-frequency of Mission Creek kokanee for select years,

1980s-2005.



0

5

10

15

20

25

30

35

40

45

94 95 96 97 98 99 00 01 02 03 04 05

Adult Year

Fry-

to-A

dult

Surv

ival

Rat

e

74 75 86 87 88 89 90 91 92 93

Age 3+

Age 2+

Figure 6. Mission Creek kokanee fry-to-adult survival rates derived from constructed

data shown in Appendix 1. Numerous assumptions made for years prior to 1990 to construct probable survival rates but since 1990 fry production estimates from the spawning channel have been used. Scenarios shown assume dominant ages 2+, or age 3+ at maturity.

Mission Creek kokanee fry-to-adult survival rates derived from constructed data shown in Appendix 1. Numerous assumptions made for years prior to 1990 to construct probable survival rates but since 1990 fry production estimates from the spawning channel have been used. Scenarios shown assume dominant ages 2+, or age 3+ at maturity.

Figure 7. Spawner-recruit ratios generated for Mission Creek kokanee under age 2+

and age 3+ scenarios. Note: 2004 values identical @ 0.7. Figure 7. Spawner-recruit ratios generated for Mission Creek kokanee under age 2+

and age 3+ scenarios. Note: 2004 values identical @ 0.7.

0

2

4

6

8

10

12

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Adult Year

Spaw

ner-R

ecru

it Ra

tio 3+ sp/r

Replacement Level

2+ sp/r

Okanagan Lake A

ction Plan – Y

ear 10 Chapter 2 – P

age 214

Appendix 1. Estimates of kokanee fry production from Mission Creek by extrapolation of data from the spawning channel (data from Dill technical reports 1990-1993, 1996, 1998; Taylor and Dill 1997 and Chara Consulting Inc. 2003a) and fry-to-adult survival rate estimates using three age group scenarios. Harvest data from Shepherd (1994).

Stream+channel

Adult Year Fecundity Less egg Stream Egg Fry Year Stream fry Channel Fry Fed Fry Fry Year Total Fry Adult Total Harvest Abundance Adult

Retention Deposition Production (5%) Production Production Year Escapement Year

1971 480 368 57,426,400 1972 2,871,320 1972 2,871,320 1974 136,304 65,000 201,304 age 2+ age 3+ age 4+

1975 40,434 63,000 103,434

1984 526* 414 15,794,928 1985 789,746 1985 789,747 1984 76,304 35,700* 117,091 1974 7

1985 526* 414 20,384,907 1986 1,019,245 1986 1,019,245 1985 98,478 33,600 132,078 1975 3.6

1986 526* 414 17,388,000 1987 869,400 20,000 1987 889,400 1986 84,000 31,500 115,500 1986

1987 526* 414 3,353,400 1988 167,670 616,456 1988 784,126 1987 16,200 29,400 45,600 1987 5.8

1988 526* 414 4,455,675 1989 222,784 868,000 1989 1,090,784 1988 21,525 26,460 47,985 1988 4.7 6.1

1989 526* 414 2,699,992 1990 135,000 173,000 972,300 1990 1,280,300 1989 17,609 21,840 39,449 1989 4.4 3.91990 500 400 3,260,813 1991 163,041 484,324 1,053,930 1991 1,701,295 1990 20,217 8,820 29,037 1990 3.7 3.3 2.81991 595 422 12,976,500 1992 648,825 203,146 1992 851,971 1991 75,522 9,660 85,182 1991 7.8 10.9 9.6

1992 559 388 7,983,585 1993 399,179 890,361 1993 1,289,540 1992 64,630 7,980 72,610 1992 5.7 6.7 9.3

1993 377 314 3,276,541 1994 163,827 328,000 1994 491,827 1993 30,653 5,040 35,693 1993 2.1 2.8 3.31994 463 410 2,620,477 1995 131,024 184,000 1995 315,024 1994 16,566 2,520 19,086 1994 2.2 1.1 1.51995 609 524 1,848,381 1996 92,269 574,456 1996 666,725 1995 10,304 0 10,304 1995 0.8 1.2 0.6

1996 649 444 3,286,502 1997 164,325 509,873 1997 674,198 1996 22,630 0 22,630 1996 4.6 1.8 2.7

1997 429 406 1,681,411 1998 84,071 45,648 1998 129,719 1997 11,935 0 11,935 1997 3.8 2.4 0.91998 1,586 1,269 652,163 1999 32,608 136,970 1999 169,578 1998 1,735 0 1,735 1998 0.3 0.6 0.41999 1,185 948 602,454 2000 30,123 22,091 2000 52,214 1999 1,613 0 1,613 1999 0.2 0.2 0.52000 643 514 4,235,874 2001 211,794 679,802 2001 891,596 2000 24,420 0 24,420 2000 18.8 3.6 3.72001 562 539 8,491,676 2002 321,503 814,201 2002 1,135,704 2001 38,847 0 38,847 2001 22.9 29.9 5.82002 818 717 6,430,056 2003 321,503 384,640 2003 706,143 2002 20,203 0 20,203 2002 38.7 11.9 15.62003 1,009 961 4,316,812 2004 215,841 929,412 2004 1,145,253 2003 13,644 0 13,644 2003 1.5 26.1 8.02004 473 458 5,482,718 2005 274,136 854,618 2005 1,128,754 2004 27,442 351 27,442 2004 2.4 3.1 52.62005 488 473 6,195,354 2006 2006 2005 32,587 0 32,587 2005 4.6 2.9 3.7

2007 2006

Stream (except channel) Channel only

Age-at-Spawning

% Fry/Adult Survival Rate

Notes and Assumptions 1. Fecundity and retention assumed the same in the stream as measured in the channel. 2. Bold and italicized indicates years where data was derived using mean values from Dill (1991-1998). 3. 1993-1994 harvest was extrapolated from last census in 1992 (Shepherd 1994, MS) and assumes a harvest level of 85,000 in 1984. 4. Bold and italicized indicates years where fecundity and egg deposition data was derived using mean values from Dill (1991-1998). 5. Fecundity of 526 less 108 for retention also used for stream deposition estimates. 6. Spawner mortality assumed to be 20% for 1984-1989; 1998-2000. 7. Conversion from peak to total count = 1.5. 8. Sex ratio assumed to be 50:50 for 1998-2002.

OKANAGAN LAKE KOKANEE STREAM SPAWNING ENUMERATION 2005

by

Jason Webster1

INTRODUCTION Routine monitoring of Okanagan Lake kokanee (Oncorhynchus nerka) escapements has spanned nearly four decades with the first comprehensive enumeration conducted by Northcote et al. (1972). Enumeration and biological sampling of the stream spawning population are two very important components of the long-term monitoring program. Even though stream population estimates before the 1980s are less reliable because often only a single count was made and peak spawning numbers were probably missed, it is clear that there were substantially more stream spawners in the 1970s and 1980s than in the 1990s and early 2000s (Andrusak and Sebastian in Andrusak et al. 2000). Enumeration of kokanee is based on visual counts and the accuracy of the counts is subject to variables such as high flows, water clarity and light conditions. In spite of these limitations, the long-term data set provides fisheries management with a valuable index of population trends. Since the inception of OLAP estimation methods used to determine spawner numbers has been standardized (Matthews and Shepherd in Ashley et al. 1999; Andrusak and Sebastian in Andrusak et al. 2000). This report summarizes 2005 escapement data with comparisons made with the long-term data set. METHODS Enumerations In 2005, 19 tributaries of Okanagan Lake were surveyed to determine spawner numbers. They included: Vernon Creek; Shorts Creek; Lambly Creek; Kelowna (Mill) Creek; Mission Creek (and spawning channel); McDougal Creek; Powers Creek; Smith Creek; Trepanier Creek; Peachland Creek; Eneas Creek; Prairie Valley Creek; Naramata Creek; Robinson Creek; Trout Creek; Penticton Creek; Nashwito Creek; Six Mile Creek; and Whitemans Creek. The basic enumeration schedule did not change from previous years described by Andrusak and Sebastian (in Andrusak et al. 2000). Although duration of the survey period was longer in 2005, the procedures remained the same. In the first part of the survey, each stream was assessed every five days. As the period of expected peak spawning approached, the sampling periodicity was reduced to every three days. Once the numbers of fish in the system began to decrease, the frequency of enumeration reverted to every five days. More counts were performed on Mission, Powers, 1 BCCF Contract Biologist, Kelowna, BC


Peachland, Penticton, Trepanier and Kelowna Creeks since these streams have historically supported larger kokanee escapements. In Mission Creek, traditionally with the largest numbers of all tributaries, enumerations occurred every second day during the peak of spawning. Kokanee enumerations in all streams were performed by ground counts. Polaroid sunglasses and brimmed hats were worn on all counts to increase visibility and to decrease the glare effect off the water surface. Keeping the sun at the counter’s back whenever possible proved to be most effective. Because fish tend to move upstream when frightened, counting while moving downstream also proved to work well. When possible, counters walked along the stream banks and looked from a higher vantage point down onto the water surface. Although staying out of the creek bed may have prevented the disturbance of redds, it sometimes could not be avoided. In these situations, foot placement was deliberate. Hand counters (tally whackers) were used to count live and dead kokanee, and chest or thigh waders were worn in all the streams. On most occasions, kokanee were tallied as individual fish. During some of the counts performed on Mission Creek and Peachland Creek, kokanee were counted 10 at a time due to relatively high densities. As mentioned, the largest number of Okanagan Lake kokanee stream spawners is usually found in Mission Creek. This system is an atypical kokanee spawning stream compared to other Okanagan lake tributaries because it is accessible for a considerable length (18.9 km). All other streams average only 2.6 km of accessible water and most provide only a few hundred meters of preferred spawning habitat. For Mission Creek, the 2005 escapement estimate was modified to include the entire accessible length of stream. Mission Creek escapement estimates over a number of years in the past (1990s) have only included that portion from the lake upstream to the East Kelowna Rd Bridge (≈ 9 km) due to access limitations and budget constraints. In the 1970s and 1980s, the upper reach of Mission Creek from the East Kelowna Road Bridge upstream to Gallagher’s Falls was included in the escapement estimate when the survey was conducted but this did not occur every year. This section was not surveyed in the 1990s because of very low numbers and budget constraints. In 2000, this section was again enumerated using a helicopter. The helicopter estimate for this section was then applied to the ground count estimate for the section of stream downstream of the spawning channel intake (upstream limit for enumerations) in order to derive a representative proportion of kokanee that spawned in the section upstream of the channel. This proportion has then been used to calculate the number of fish spawning in the upstream section of creek for those years when aerial or ground surveys were not possible. In 2000, the Mission Creek helicopter survey indicated that 31% of the total fish counted in the downstream section was a reasonable correction factor used to estimate the number of fish upstream of the channel. This factor was used for the 2005 estimate.


Using a hand held thermometer water temperature was recorded slightly upstream of the mouth of all the streams enumerated in 2005. The temperature data was collected in an attempt to develop a better means of predicting timing of peak spawning. All 2005 information from Six Mile, Nashwito, and Whitemans creeks was provided by the Okanagan Nations Alliance. The 2005 enumerations on Robinson and Prairie Valley creeks were provided by Monashee Environmental and Lora Nield respectively. Biological Sampling A target of 100 kokanee samples was set for each of Peachland, Powers and Penticton creeks and at least 200 samples from Mission Creek. All fish (dead) were collected by hand or with a dip net and had to be in good physical condition. Carcasses were also sampled if in good condition, therefore, live samples were not always required to achieve the target of 100 samples/stream. Once collected, the samples were placed on a portable measuring board where fork length was measured. Kokanee were sexed by identification of external features and by internal examination. Maturity was recorded as “spent” for both males and females. The only exceptions were if a significant number of retained eggs (in relation to the size of the female) were counted. In this case, maturity was noted as “ripe” or “mature”. Any retained eggs from the female samples were counted individually after an incision of the body wall. Data was added to the OKFISH database located in the Penticton Ministry of Environment (MOE) office. DNA samples were collected from as many of the kokanee samples as possible. A small 1 cm by 1 cm portion of flesh was cut from the opercula of each kokanee sample and placed in a container of non-denatured ethanol in order to preserve them for later DNA analysis. The containers were labelled by creek name and only samples from that specific creek were placed inside. Results of the DNA analysis may help in identifying the origins of Okanagan Lake kokanee (i.e., Fraser River or Columbia River) along with identifying differences in stream spawning and shore spawning populations. Otoliths were collected from 50 of the samples from Mission Creek, Peachland Creek, Penticton Creek and Powers Creek. An incision was made through the top of the head bisecting it as closely as possible. An otolith was then removed from the lower portion of the brain cavity with a pair of tweezers, dipped in water and placed in a scale sample envelope. In most cases both of the otoliths were kept. RESULTS Escapements The estimated total number of kokanee stream-spawners for Okanagan Lake in 2005 was 60,998 (Table 1). The estimated number for each creek is calculated by multiplying the peak count of live fish by a conversion factor of 1.5 (Andrusak and Sebastian in


Andrusak et. al. 2000). The 2005 escapement estimate represents a sizeable increase of about 14,000 spawners when compared with the 2004 estimate of 46,167. However, the 2005 estimate was slightly lower than the parental numbers in 2001 (see below). As in previous years, the highest number of stream spawners in 2005 was estimated at ~ 34,000 in Mission Creek. Powers, Peachland and Trepanier Creeks recorded the next highest amount of spawners in 2005 (Table 1). For most streams the peak of spawning activity occurred from September 20 to September 30. Time series escapement data for eight streams with data extending back to the 1980s is illustrated in Figure 1. The eight streams represent 91% of the total 2005 escapement. The 2005 escapement estimate total is the second highest return over the past 10 years and is the sixth consecutive year of encouraging returns since 1999 (Fig. 1; Appendix 1). Note however, that the 2000s estimates remain far lower than those recorded in the 1970s through to the early 1990s. Highlights of the 2005 spawner escapement were the excellent returns estimated in Mission, Six Mile, and Eneas Creeks along with the reappearance of kokanee in Prairie Valley Creek after five years of no returns. Table 1. Summary of Enumeration Results 2005 – Okanagan Lake CREEK TEMP(C) COUNTS PEAK DATE ADJ TOTAL Vernon 11 2 505 10/04/2005 757 Mission (not inc. Sp Chan) 12.5 12 22,878 9/20/2005 34,317 Mission Spawning Channel 33 4,261 9/16/2005 6,391 Powers 11 8 2,579 9/23/2005 3,868 Trepanier 11 8 2,040 9/26/2005 3,060 Peachland 10.5 8 2,085 9/20/2005 3,127 Eneas 11 2 84 9/29/2005 126 McDougal 12 2 0 9/29/2005 0 Naramata 9 2 114 9/29/2005 171 Penticton 11 8 1,916 9/29/2005 2,874 Shorts n/a 2 dry 9/22/2005 0 Kelowna (Mill) 11 5 1,127 9/30/2005 1,690 Lambly 11 2 152 9/22/2005 228 Six Mile (Equesis) n/a n/a 1,283 n/a 1,925 Nashwito n/a n/a 484 n/a 726 Whiteman n/a n/a 665 n/a 998 Trout 12 3 429 9/29/2005 643 Prairie Valley n/a n/a 25 n/a 38 Robinson n/a n/a 31 n/a 47 Smith 11 2 8 9/28/2005 12 Total 60,998 * Includes estimate of kokanee utilising creek upstream of the East Kelowna Bridge. (See methods

section for a description of how this estimate was derived.) Poor viewing/counting conditions due to high amounts of suspended sediments occurred in Trout Creek on September 19th and 29th and in Mill (Kelowna) Creek on


September 18th and 24th and again on October 6th. On these dates it is possible that a larger number of kokanee (up to 50% more) may have been present than were actually counted. Biological Data The target number of one hundred carcasses was obtained in each Penticton and Peachland Creeks. A total of 191 carcasses were processed from Mission Creek and 99 were collected from Powers Creek. Length-at-Maturity The length-frequency distributions of kokanee spawners from Powers, Mission, Penticton, and Peachland creeks are illustrated in Figure 2. There is a considerable difference in the mean lengths observed between males and females within the four Okanagan Lake streams sampled. Females in Peachland Creek averaged 301 mm, 42 mm longer than the average female length in Mission Creek (258 mm). Males in Peachland Creek (324 mm) were 65 mm longer on average than the males in Mission Creek (259 mm). The dominant length mode for all four Okanagan Lake streams appears to be close to 240 mm. An additional prominent length mode is apparent at 300 mm for Peachland Creek and to a lesser extent there appears to be a mode around 320 mm in the Penticton Creek histogram. Based on data analysis from the 1980s and 1990s on these same spawners, Andrusak and Sebastian (in Andrusak et al. 2000) concluded that the smaller mode was age 3+. The mode evident around 300 mm-320 mm in the 2005 frequency probably represents age 4+ fish and modes at 420-440 mm and > 500 mm are likely a mix of ages 5-7+. Age analysis of otoliths collected in 2005 was not completed at time of writing. Mean sizes of the 2005 samples from the four streams were smaller than the means recorded in 2004 and close to the smallest mean sizes (~260 mm) recorded in the early 1990s (Fig. 3). Fecundity estimates was derived using the Okanagan Lake regression formula determined by Andrusak and Sebastian (in Andrusak et al. 2000):

Log Egg # = 3.289 Log length (mm) – 5.275. Given the large range in fish size, there was a considerable variability in estimated fecundities amongst the four streams.


Table 2. Summary of kokanee spawner data collected during September and October 2005 from selected Okanagan Lake streams.

Creek No. Male Fem

Male Mean

Length (mm)

Female Mean

Length (mm)

Egg Retent.

(%)

Mean Fecund minus

retention

Total Est.

Females

Estimated egg deposition

2005 Penticton 100 69 31 311 283 3.1 593 890 527,770 S.E. 7.9 8 Powers 99 51 48 271 265 6.1 465 1856 863,040 S.E. 7.2 7.5 Peachland 100 58 42 324 301 8.4 686 1313 900,718 S.E. 12 7.3 Mission 201 99 102 259 258 3.1 437 17,501 7,647,937 S.E. 3.9 3.6 Mission Chan. 1.8 445 3,195 1,421,775 Totals 11,361,240

It should be noted that all carcass sampling performed should be considered as non-random sampling, due to the fact that only carcasses deemed to be in good shape were collected. However, it is believed that all of the tributaries' carcass samples are reasonably representative of the actual size distribution. DISCUSSION The total (adjusted) number of kokanee that were estimated in the 19 Okanagan Lake streams in 2005 was 60,998 of which over half were in Mission Creek. By way of comparison, the escapement in 2004 was 46,167, in 2003 was 23,725, in 2002 was 44,488, 67,077 (2001), 42,700 (2000), 6,991 (1999) and in 1998 it was 8,300 (data on file Ministry of Environment, Penticton, BC. Despite some recent (and encouraging) increases in escapements the overall trend in the last two decades continues to track downward (Fig. 1) and the numbers are far less than the 1970s when ~ 0.5 million spawners were present in some years (Northcote et al. 1972; Andrusak and Sebastian in Andrusak et al. 2000). Similar to 2004, adequate or above average stream flows occurred during the 2005 spawning period. High water and poor viewing conditions was not an issue during any of the counts on Mission Creek. As was observed in 2003, flows in Shorts Creek did not allow any migration upstream in 2005. The creek bed went dry approximately 200 meters upstream of the mouth. Flows continued underground, until the confluence with Okanagan Lake. There was considerable variation in the sizes of spawners measured in 2005 between sexes both within and between the streams sampled (Table 2). Both females and males in Peachland Creek averaged the longest. The largest fish were found in Peachland Creek whereas the smallest were found in Mission Creek. In fact, the


average size of 2005 Mission Creek kokanee was the second smallest average size recorded since 1986. Overall, the 2005 mean lengths were quite small compared to the last 10 years (Fig. 3) but were close to the average of ~ 260 mm recorded during the last three decades. Figure 2 shows that the majority of spawners ranged in size form 220-280 mm. Length-frequency histograms for the 2005 samples illustrate that multiple modes are present that represent several age groups. It is known from the trawl data (Sebastian et al. in this OLAP report) that the fish in the 200-280 mm mode are age 3+ while those > 300 mm are probably a mix of ages 4-7+ (Fig. 2). As in previous years a few fish were sampled that were > 500 mm with the largest recorded at 614 mm. A note of caution regarding the Penticton Creek samples should be mentioned. Due to the fact that most of the accessible portion of Penticton Creek is a concrete flume, the majority of carcasses were collected from the section of the creek close to the mouth, where the stream flow is slow. It was observed that the larger, hence possibly older fish, tended to get caught up in the rocks more easily than the smaller ones at this location. This sample of fish is probably bias towards larger fish. With such a large variation in fish size in 2005 the estimated fecundity ranged from 437-686 (less retention). Mission Creek fecundity in 2005 was quite low with a mean of 488 (see Andrusak and Andrusak in this OLAP report). Okanagan Lake kokanee are relatively fecund compared to other similar nearby lakes such as Arrow Lakes Reservoir and Kootenay and Shuswap lakes where the average fecundity ranges from 200-350 (H. Andrusak, Fisheries Biologist, Nelson, BC, pers. comm.). There is also a considerable difference between the fecundities of Penticton and Peachland Creek fish compared to Mission creek fish (Table 2). Estimated egg deposition for the four streams illustrates the importance of Mission Creek. The number of recruits produced by their parents that survived in the lake provides some insight into the current status of the population as well as in-lake survival conditions. The numbers of spawners returning to Mission Creek and the seven index streams can be used to generate crude replacement values (ratio of recruits/spawners). Assuming the majority of fish spawn at age 3+ the 2005 spawner numbers for both Mission Creek and the seven index streams failed to equal the numbers of parents that produced them (R/S < 1.0). The 2004 R/S ratio was just slightly > 1.0 whereas this value was much higher than 1.0 from 2000-2003 (Fig. 4). During the 1990s the R/S values were < 1.0 indicative of in-lake survival problems since there has been no sport fish harvest since 1994. Despite higher fry production from the Mission Creek spawning channel in recent years (see Andrusak and Andrusak in this OLAP report) there has not been an improvement in replacement. This lack of increase is attributed to poor growing conditions and or survival rates in the lake. Construction was noted around some of the enumerated streams in 2005. In most cases, no damage to the streams was observed. The only exception was in Powers Creek where road crews were de-watering a dig site immediately north of the creek and pumping the water to a location where it filtered back into the creek. The road crew was shown the problem and changed the location of the outlet hose to a more suitable


location. Because the construction area was only 75 meters upstream of the mouth of Powers Creek, it is believed that very little sedimentation of spawning gravels occurred (practically no spawning kokanee are observed within 75 meters of the mouth of Powers Creek). High sediment loads were observed in Trout Creek during the 2005 enumerations. The source of the sediment loading in Trout Creek is believed to be a perpetually eroding bank in the canyon section of the creek. ACKNOWLEDGEMENTS A special thanks to Randy Erbacker for his substantial involvement in this project.


LITERATURE CITED Andrusak, H. 2003. Response of Arrow Reservoir Kokanee to Experimental

Fertilization in 2002. Report prepared for the Ministry of Water, Land and Air Protection, Nelson, BC.

Andrusak, H., D. Sebastian, I. McGregor, S. Matthews, D. Smith, K. Ashley, S. Pollard,

G. Scholten, J. Stockner, P. Ward, R. Kirk, D. Lasenby, J. Webster, J. Whall, G. Wilson, H. Yassien. 2000. Okanagan Lake Action Plan Year 4 (1999) Report. Fisheries Project Report No. RD 83. Fisheries Management Branch, Ministry of Agriculture, Food and Fisheries, Province of British Columbia.

Andrusak, H., D. Sebastian, G. Scholten, and P. Woodruff. 2005. Response of

Kokanee and Gerrard Rainbow Trout to Experimental Fertilization of the North Arm of Kootenay Lake, 2002 and 2003. Redfish Consulting Ltd. Contract Report for the Columbia Basin Fish and Wildlife Compensation Program, Nelson, BC.



Ashley, K., I. McGregor, D. Sebastian, B. Shepherd, Lidija Vidmanic, P. Ward,

H. Yassien, L. McEachern, H. Andrusak, D. Lasenby, J. Quirt, J. Whall, E. Taylor, A. Kuiper, P. Troffe, C. Wong, S. Matthews, G. Scholten, M. Zimmerman, P. Epp, V. Jensen, and R. Finnegan. 1999. Okanagan Lake Action Plan, Year 3 (1998) Report. Fisheries Project Report No. RD 78. Fisheries Management Branch, Ministry of Fisheries, Province of British Columbia.

Northcote, T.G., T.G. Halsey, and S.J. Macdonald. 1972. Fish as Indicators of Water



0

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imat

ed #

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wne

rs

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Figure 1. Escapement estimates for Mission Creek and the total of seven index

streams that include: Powers, Peachland, Penticton, Trepanier, Lambly, Naramata, and Mill creeks (1989-2005). Mission Creek and the seven stream estimates combined are illustrated with the cross hatch pattern bars.


Mission Creek 2005

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Figure 2. Percent length-frequency distribution of 2005 kokanee female and male

spawners from Mission, Powers, Peachland, and Penticton creeks.


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Figure 3. Mean size (mm) of kokanee spawners from Mission Creek, Peachland and

Powers creeks, 1986-2005.

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Figure 4. Replacement values of each cycle of kokanee since 1990 for (a) Mission

Creek, and (b) the seven major spawning index streams excluding Mission Creek. This analysis assumes a dominance of age 3+ spawners.


Appendix 1. Total escapement for all eight streams, 1971-2005.

Year Mission Total of 7 Streams

Total of all 8 Streams

1971 312,000 39,293 351,293 1974 136,304 3,000 139,304 1975 40,435 3,495 43,930 1976 31,956 3,471 35,427 1977 33,913 3,913 37,826 1978 90,652 9,125 99,777 1979 117,391 14,296 131,687 1980 78,261 18,261 96,522 1981 61,957 11,726 73,683 1983 37,500 7,073 44,573 1984 76,220 27,499 103,719 1985 98,625 41,158 139,783 1986 84,000 20,952 104,952 1987 16,200 25,575 41,775 1988 21,525 18,787 40,312 1989 17,609 22,814 40,423 1990 20,217 26,944 47,161 1991 75,522 22,516 98,038 1992 64,631 29,806 94,437 1993 30,653 21,521 52,174 1994 16,566 25,240 41,806 1995 10,304 19,811 30,115 1996 22,630 15,392 38,022 1997 11,936 9,265 21,201 1998 1,735 5,454 7,189 1999 1,613 4,670 6,283 2000 24,420 13,093 37,513 2001 38,847 24,606 63,453 2002 20,203 20,060 40,263 2003 13,644 8,799 22,443 2004 27,442 11,757 39,199 2005 40,708 15,018 55,726


OKANAGAN LAKE SHORE SPAWNING ENUMERATION AND DISTRIBUTION STUDY

2005

by

G. Andrusak1 and H. Andrusak2

INTRODUCTION Shore spawning kokanee (Onchorynchus nerka) are one of two ecotypes found in Okanagan Lake that usually spawn in mid-October. The second form spawn in a number of tributaries usually in early September and are generally much larger than the shoreline spawners (Andrusak et al. in Andrusak et al. 2004a). Microsatellite DNA analysis has been used to confirm genetic differences between these two types of spawners (Pollard in Andrusak et al. 2000; Withler in Andrusak et al. 2004a). Okanagan Lake kokanee numbers have been in a prolonged decline since the 1970s. The reasons for the decline have been the subject of primary concern for the Okanagan Lake Action Plan (OLAP). OLAP workers believe that a combination of reduced lake productivity, loss of spawning habitat and competition for food between kokanee and Mysis relicta all are contributing factors that have led to greatly reduced kokanee numbers. Causal factors responsible for the decline in kokanee shore spawners have also been attributed to lake level regulation. In particular, lake level drawdown in some years has resulted in more than 30% of deposited eggs dewatered (Halsey and Lea 1973). Okanagan Lake shore spawners are known to utilize specific areas of the shoreline to spawn and tend to select a very narrow range within the water column, usually < 1 m in depth (Halsey and Lea 1973; Matthews and Bull 1981; Dill in Ashley et al. 1998, Andrusak et al. 2004b). Remedial action was initiated in 2000 to minimize the lake level drawdown impacts on Okanagan Lake shore spawners as well as sockeye salmon spawning in the Okanagan River downstream of McIntyre Dam. Completion of a computer model, based on a set of interrelated sub models, has assisted in optimizing regulation of Okanagan Lake levels for both kokanee and sockeye management. Each year since initial model development data has been collected on the shore spawners to improve the model. Improvement of the kokanee sub-model through inclusion of recent data (2001-2004) on shore spawner egg development and fry emergence ensures that all fish resources are considered in water management decision making. This report summarizes Okanagan Lake shore spawning enumeration and distribution for 2005. The 2005 field work was very much reduced owing to budget constraints so additional data is quite limited. This report does include a summary of 2005 egg

1 Redfish Consulting Ltd., 5240 HWY 3A, Nelson, BC, V8L 6N6 2 Redfish Consulting Ltd., 5244 HWY 3A, Nelson, BC, V8L 6N6


development to time of writing based on accumulated thermal units (ATU’s) derived from lake temperature recorders. OBJECTIVES The purpose of this report is to: 1. Summarize the 2005 estimates of Okanagan Lake shore spawning kokanee. 2. Summarize egg development from the 2005 brood based on accumulated thermal

units (ATU’s). 3. Summarize current status and understanding of the biology of Okanagan Lake shore

spawning kokanee as it pertains to the kokanee sub model. BACKGROUND Decline in Okanagan Lake kokanee has been well documented in a number of publications with the most recent summary found in Andrusak et al. (in Andrusak et al. 2005). For well over 70 years there have been a number of problems associated with Okanagan Lake and its fish populations. In an area that has a very dry climate and where water is in such high demand due to urban and agricultural development it should be no surprise that Okanagan Lake fish and fish habitat have constantly been threatened. In late summer, many of the smaller streams are either completely dry or have below minimum flows required to sustain fish life. Anglers and fisheries biologists have observed a gradual decline of Okanagan Lake fish populations since the late 1960s. In 1996, the Okanagan Lake Action Plan (OLAP) was initiated to facilitate the recovery of kokanee (stream and shore) through a series of studies that were designed to provide information that could lead to improvements to kokanee production. Valuable information gathered by OLAP concluded that a variety of confounding factors have led to the decline in both stream and shore spawning kokanee. Specifically, reduced carrying capacity (N:P problems) and/or Mysis relicta have been identified as the most likely causes for the precipitous decline in kokanee numbers. This conclusion was formulated based on a kokanee population dynamics model used by Walters (1995) and updated in 2004 (Walters and Korman in Andrusak et al. 2004a). Recent studies of the shore spawners have re-affirmed the older investigations (Halsey and Lea 1973, Matthews and Bull 1981, Dill in Ashley et al. 1998) that survival of shore spawning kokanee in Okanagan Lake can be negatively impacted by inappropriate winter time lake level drawdowns. In the early 2000s, an initiative was launched to minimize the impacts of lake level drawdown on shore spawning kokanee in Okanagan Lake as well as sockeye salmon spawning in the Okanagan River. ESSA Technologies Ltd. was retained by the Okanagan Basin Technical Working Group (OBTWBG) with funding from the Douglas County Public Utility District to develop a computer model that


links water management decisions with impacts to fisheries and other resources (e.g., water intakes). OBTWBG is a formal working committee comprised of Federal Department of Fisheries and Oceans Canada (DFO), the Okanagan Nation Fisheries Commission (ONFC), and the Ministry of Environment (MOE). The model was completed by late 2003 and was immediately used to assist water and fisheries managers in decision making on water storage and release scenarios from Okanagan Lake that should be more “fish friendly”. The model was based on a set of interrelated sub models that included temperature, hydrology, sockeye, and kokanee development. The kokanee sub model was initially developed in 2001 (Redfish Consulting Ltd. 2002) as part of the overall modeling project to ensure that all fish resources were considered in water management decision making. However, a number of assumptions about Okanagan Lake shore spawning kokanee life history and sensitivity to lake level fluctuations were initially included in the sub model. Subsequent work has been undertaken to verify the assumptions made and provide updated information that can be used to refine the model. Survey work from 2001-2004 has revealed that shore spawning kokanee numbers are highly variable from year to year. In 2001 and 2003 there were ideal drawdown patterns but relatively few fish, whereas in 2002, the drawdown was again optimal with far more fish observed. In all years, most of the spawning occurred in preferred water depths of 0.25-0.75 m resulting in little or no impact from lowered lake elevation (≈0.25 m) during the winter months. Despite larger numbers of spawner in 2002 the distribution remained tightly associated with the one meter zone with some lateral extension in areas spawned. Moreover, these studies concluded that the limited lake drawdown in 2001-2004 had little impact on kokanee egg development and survival. Shore spawner estimates have been made periodically since 1972 but as reported by Andrusak and Sebastian (in Andrusak et al. 2000) there had been little consistency in the number of days and/or sites enumerated until the late 1980s. Spawning estimates from 1974-1997 demonstrated differences in peak spawning times based on lake quadrants (Shepherd, 1998 draft report). During the last 10 years there have been far more consistent methods and frequency of shoreline counts. In 2004 and again in 2005, a reduced field program was undertaken to assess spawner numbers and distribution with greater emphasis placed on biological data collection. SITE DESCRIPTION Dominating the Okanagan Valley is Okanagan Lake located in the southern interior of BC near the 49th parallel positioned in a north-south axis between the Monashee and Cascade mountain ranges. The lake is located entirely within the warm, dry southern interior and receives an average annual precipitation annually of only 315 mm (Ward et al. in Ashley et al. 1999). The lake is approximately 135 km long, but only 4-5 km wide with a surface area of about 35,112 hectares. Despite this size, the lake has a maximum depth of 242 m and a mean depth of only 76 m. Figure 1 illustrates the longitudinal profile of the lake that is divided into three basins created by underwater sills located at Squally Point and at the site of the Kelowna Bridge.


There are no major river systems that flows into Okanagan Lake, with inflow limited to a few tributary streams of any size the largest being Mission Creek. The Okanagan River flows out of the south end of the lake near Penticton, British Columbia into Skaha Lake, then south through Osoyoos Lake and eventually joins the Columbia River in northern Washington. At the outlet located near Penticton is a small dam that effectively regulates the lake between elevations 341 m to 342.5 m (see Ward et al. in Ashley et al. 1999 for more detail). The average through flow of water is relatively small because of the arid climate and low annual runoff of the Okanagan Valley. Lake residence time has been calculated at 52 years (Shepherd 1990) but in dry years with little inflow the residence time can be > 90 years (K. Ashley, BC Fisheries Biologist, UBC, Vancouver, BC, pers. comm.). METHODS In the late 1980s, Okanagan Lake fish and fisheries information were consolidated into computer databases for boat counts (BOATSP.dbf), catch success (OKCREELP.dbf), fish samples (OKFISHP.dbf), and enumeration of stream and shore spawning kokanee runs (KO_ENUMP.dbf and KO_SHORE.dbf, respectively). These databases are updated annually and are the primary source of Okanagan Lake fish data. Historic Shore Spawning Escapement Estimates Prior to 2001 Counts of kokanee spawning along the shoreline of Okanagan Lake have been made since 1971. The standard method has been to run a boat parallel to the shoreline at 800-1,200 rpm along the 3-4 m depth contour. The numbers of spawners inshore of this point were estimated visually by BC Fisheries staff with previous survey experience. The lake has been divided into four quadrants (Fig. 2) with reach breaks defined for each quadrant based on landmarks taken from aerial photographs. Each reach estimate is recorded separately and then, summed by quadrant as outlined in Table 1. Table 1. Shoreline habitat reach descriptions. Note: reach numbering runs

counterclockwise, beginning in the SE quadrant.

Quadrant Name Quadrant (Reach) Boundaries Reaches Landmark Reach No's1

SE (southeast) Penticton to Kelowna Bridge (Commando Bay to Lebanon Creek).

1 - 22a Bertram Park 22 Rattlesnake Island 9

NE (northeast) Kelowna to Armstrong Arm (Alder Pt to opp. Nashwito Creek).

23 - 49b Paul’s Tomb 24

NW (northwest) Armstrong Arm to Kelowna Bridge (Whiteman Creek to Trader’s Cove).

50 – 77 Bear Creek 74-75

SW (southwest) Kelowna Bridge to Penticton (Gellatly to Peachland).

78

1 Details of location of reach numbers can be found in Wong (in Ashley et al. 1998). Reaches were only assigned numbers if kokanee spawning had been observed there during the Okanagan Basin studies in the 1970s (see details in Northcote et al. 1972).


Numbered reaches not known to support shore spawners prior to 1988 were at most spot-checked in subsequent years; for example, only a small section of the SW Quadrant (Kelowna Bridge - Penticton) was checked each year. Local residents within this quadrant continue to report the presence of shore spawning kokanee, but the small numbers involved do not warrant annual enumeration. In 2005, a single survey was conducted along the SW quadrant to re-confirm minimal spawner activity. Each year since 1998, a temperature logger has been placed at the Bertram Park site, as well as, one site at each of the NE and NW quadrants to record daily surface water temperatures over the spawning and incubation period. A permanent temperature probe was established by the federal government near the Kelowna Bridge in 2002. In most years, counts routinely began in the SE Quadrant (Squally Point - Bertram Creek area) in the third week of October. Prior to the first count, reach 22 is initially checked either by boat or aircraft until spawners were sighted (Squally Point area consistently has high numbers of kokanee). Also, in recent years, waterfront residents advised fisheries staff when kokanee were initially observed. Annual enumerations begin shortly following the first kokanee sighting and continued each week until it was obvious that numbers had peaked and were declining, usually by early November. Usually shoreline enumerations by boat have been supported by visual observations made by experienced provincial government fisheries observers using fixed-wing aircraft or helicopter. These flights were used to verify general spawner distributions throughout the lake, confirm low or nil numbers in stretches not surveyed by boat, and also to direct subsequent boat surveys to the areas utilized by spawners. Estimates determined for all reaches surveyed were summed to produce a total peak estimate for that day for each quadrant. In years when surveys are conducted for a number of days per quadrant, the highest cumulative count on a given date is considered the “peak” count. Sources of error in estimating shore spawners are numerous. Over the years of record, temporal and spatial coverage, as well as, the quality of boat based counts have been significantly affected by weather conditions, especially wave action. In some years, quadrant counts were incomplete for all reaches at the estimated peak date, and were adjusted using the proportions observed between reaches on the closest days that complete counts were made. Thompson (in Ashley et al. 1998) reviewed the methods employed over the years and discusses the biases inherent in the methods. The value of the shore counts is as an index of abundance and not as an estimate of total spawner numbers. Recent Survey Modifications Since 2003 A slight change in methodology was made effective after the 2002 shore spawner survey. It was observed in 2001 and 2002 that most spawners did not appear on the spawning sites until 10:00 hr and that by 15:00 hr most had move to deeper water. Consequently, the boat counts were initiated one hour later (@ 10:00 hr rather than 9:00 hr) and areas of documented low use (or no use) were deleted to ensure good


counts on the preferred sites during the optimal time (10:00-15:00 hr). Adjustment in start time was made with the time change to day light saving time. Since 1995 multiple day counts have been conducted rather than only one day per quadrant. 2005 Shore Spawning Estimates Due to budget constraints no overview flights were conducted in 2005 to confirm the presence of shore spawning kokanee prior to boat survey enumerations. Commencement of the 2005 boat count surveys was initiated based on presence of shore spawners reported by local lakeshore residents. Boat surveys started approximately at 10:30 hr in each of the three quadrants. Kokanee shore spawner enumerations were initiated as early as October 12th in the SE quadrant and were completed by October 26th in the NW. However, only three days of counts were made in the NE and NW, while four counts were made in the SE quadrant in 2005 (Fig. 2). A single survey was also conducted in the SW quadrant. Weather over the period of shore spawning kokanee enumeration is a key variable that can have a profound impact on the quality of counts. In 2005, relatively good viewing conditions prevailed for counts in all quadrants. Shore Based Observations of Shore Spawners No shore based observations of shore spawners were conducted in 2005. Andrusak et al. (in Andrusak et al. 2004a) provides a description of methods used and results of shore based counts that were compared to the boat counts. 2005 Biological Data Fish samples were collected in 2005 at Rattlesnake Island (SE), Paul’s Tomb (NE) and Cars Landing (NE). They were collected from either dead or near dead kokanee captured using dipnets or by hand. All samples were collected on October 24-25, 2005. Samples were also obtained for fecundity determination. Captured females were examined to ascertain if the eggs were still in intact skeins or not. Only those samples where it was clear that all eggs remained in the skein were considered for fecundity counts, i.e., “green fish”. All captured fish were measured for fork length and sexed. Additionally, otoliths and scales were removed for later age determination. RESULTS Historical Review Historically, shore spawner estimates have been made periodically since 1971 although there has been little consistency in the number of days and/or sites enumerated until the late 1980s. Shepherd (1998, draft report) indicated that average peak spawning from


1974-1997 occurred earlier in the SE (October 23rd) compared to the NE (October 25th) and NW (October 26th) quadrants. In addition, he also indicated that there was considerable variation in timing with a range extending over two weeks for each quadrant and that in some years only single counts were conducted which were assumed to reflect peak of spawning. As well, in some years’ shore counts were supported by aerial over flight counts while in other years they were not. Consequently, information on date of peak spawning is quite limited with the most reliable data collected in the last few years. Table 2 summarizes the number of counts and peak of spawning for the three quadrants that have been consistently monitored in the 1990s and 2000s. Over the years very little spawning activity has been observed in the SW quadrant, consequently, it has not been included in the shore counts. Historically, the third week of October appears to be when peak spawning takes place in the SE quadrant (Table 2). In addition, with the exception of the 1993 Bertram Park data (Dill 1996b), the SE quadrant also appears to experience peak spawning activity earlier that the northern quadrants. There does not appear to be much difference in timing between the NE and NW quadrants with peak spawning usually occurring in the last week of October. On average, the peak of spawning for the SE quadrant is most likely October 18th while it is probably October 25th for the NE and October 26th for the NW quadrant based on data from 1974-2004. Water temperature and length of day likely combine to set the period of kokanee spawning. Water temperature has been identified as a key determinant for spawn timing in other nerkid populations. For example, Okanagan River sockeye spawning tends to peak as water temperatures fall below 12°C (Alexander et. al 2003). Typically, surface water temperatures in Okanagan Lake fall rapidly through the month of October, with the lake becoming isothermal by mid November (see Rae and Wilson, in this OLAP report). This pattern appears to be consistent through time with the temperature usually falling below 13°C in the 2nd or 3rd week of October (e.g., 2002 and 2004). However, in some years temperatures do not fall below this threshold until the beginning of November (e.g., 2003). The impact of this delay in temperature decrease is not clear but it is conceivable that it could delay the onset and peak of shore spawning by a number of weeks. Presence of spawners on the shoreline usually spans the last three weeks of October and the first week of November. However, this information only reflects the time period that boat counts were conducted, not the entire length of time spawners were present.


Table 2. Okanagan Lake boat survey shore spawning counts and dates indicating range of time of spawning and peak of spawning for the SE, NE, and NW quadrants.

Area # Counts Peak Range* Reference

SE 1993 (Bertram) 6 Nov. 2 Oct. 24-Nov. 9 Dill (1996a) 1994 (Bertram) 9 Oct. 17 Oct. 16-28 Dill (1996a) 1995 (Bertram) 22 Oct. 18 Oct. 11-Nov. 3 Dill (1996a) 1995 4 Oct. 18 Oct. 12-23 Penticton file data** 1996 6 Oct. 19 Oct. 19-Nov. 12 1999 2 Oct. 27 Oct. 19-27 2000 4 Oct. 10 Oct. 2-18 2001 6 Oct. 15 Oct. 15-26 Andrusak et al. 2002 2002 4 Oct. 24 Oct. 18-Nov. 4 Andrusak et al. 2003 2003 4 Nov. 1 Oct 23-Nov. 3 Andrusak et al. 2004a2004 4 Oct. 24 Oct. 20-30 Andrusak et al. 2004a2005 4 Oct 14 October 12-24 In this OLAP report NE 1995 3 Oct. 19 Oct. 18-25 1996 2 Oct. 31 Oct. 5-31 1999 2 Oct. 26 Oct. 26 2000 3 Oct. 11 Oct. 2-17 2001 4 Oct. 24 Oct. 19-Oct. 27 Andrusak et al. 2002 2002 4 Oct. 25 Oct. 19-Nov. 5 2003 3 Oct. 29 Oct. 27-Nov. 8 Andrusak et al. 2004a2004 4 Oct. 29 Oct. 21-Nov. 1 Andrusak et al. 2004a2005 3 Oct.20 Oct. 16-Oct. 25 In this OLAP report NW 1995 5 Oct. 23 Oct. 16-25 1996 4 Oct. 31 Oct. 30-Nov.5 1999 3 Oct. 26 Oct. 18-26 2000 3 Oct. 7 Oct. 2-18 2001 4 Oct. 25 Oct. 22-Nov. 5 Andrusak et al. 2002 2002 3 Oct. 30 Oct. 23-Nov. 5 Andrusak et al. 2003 2003 3 Oct. 31 Oct. 27-Nov. 8 Andrusak et al. 2004a2004 4 Oct. 25 Oct. 21-Oct. 31 Andrusak et al. 2004a2005 3 Oct. 21 Oct. 18-26 In this OLAP report * Range indicates when spawning fish were initially observed and the date when they were last observed. ** All data obtained from Ministry of Environment Penticton office files.


2005 Estimates of Shore Spawners by Boat Reported presence of shore spawners by the public triggered initial boat surveys as early as October 12, 2005 in the SE quadrant. As indicated above, three surveys were completed in the NE and NW quadrants while four surveys were done on the SE quadrant. One survey was conducted in the SW quadrant. The final survey was completed on October 26 in the NW quadrant. As an index of abundance, it was estimated that ~162,120 shore spawners occupied the shores of Okanagan Lake in 2005, based on all quadrants (Fig 3). As in previous years, kokanee spawners initially appeared in the SE quadrant and then became visible in a progressive fashion from south to north. In support of this trend, excluding the SW quadrant where only one count was done, the daily peak estimates also demonstrated that there was a south to north gradient. The single day survey of the SW quadrant served to re-confirm that few fish spawn in this area of the lake as only 600 fish were counted. The SE quadrant peaked on October 14th (58,205) while the NE (53,645)and NW (49,670) peaked approximately one week later, October 20th and October 21st respectively (Table 3). The weather was considered to be moderate to very good for all surveys in 2005. 2005 Temperatures Lake Levels and ATUs Similar to 2003 and 2004, declining surface water temperatures appeared to trigger commencement of spawning in 2005 (Figs. 4, 5, 6). Lake temperatures declined from October 1st at 15.7°C to October 31st at 12°C. Data indicated that on October 26, 2005, temperatures declined below 13°C at which time the last survey was being conducted at the NW quadrant (Table 3). Temperatures dropped below 6°C on December 12th, 2005, and maintained a range between 4-6°C until of March 23, 2006, before increasing. Lake levels declined at the beginning of October 2005 from 341.871 m to the lowest level on December 19th at 341.737 m before some refilling occurred (Figs. 7, 8). During the spawning period lake levels declined only 0.05 m from October 1-31, 2005. This drawdown pattern was generated using the model to ensure minimal impact on eggs deposited in the gravel. Although it was slightly more severe than that for 2004-2005 this modest draw down was still very good from a kokanee spawning perspective. The lake only dropped 5 cm during the spawning period and only a maximum of 13 cm during the egg incubation period. ATUs were calculated from October 20, 2005 through to March 20, 2006 at 870 (data on file). Andrusak et al. (in Andrusak et al. 2005) have determined that free swimming fry required 950 ATUs therefore fully developed fry would be present by the first week of April assuming water temperatures were a constant 5 °C for the remainder of March 2006.


Table 3. Daily boat count estimates of Okanagan Lake shore spawners 2005 for NE, NW, SW, and SE quadrants.

2005 Temp

°C Total Numbers of Fish per Quadrant

(not expanded) SE NE NW SW

Peak Estimate

October 12 14.6 57,720 October 14 14.3 58,205 58,205 October 19 13.3 56,181 October 24 13.3 1,577

October 16 14.0 30,877 October 20 13.4 53,645 53,645 October 25 13.2 42,340

October 18 134 40,718 October 21 13.3 49,670 49,670 October 26 13.0 22,250

October 24 13.3 600 600

Total 162,120

2005 Biological Data A total of 265 samples were collected from Rattlesnake Island (SE), Paul’s Tomb (NE) and Cars Landing (NE) on October 25th and 26th , 2005. No analysis of fecundity or age from 2005 data had been completed at time of writing. Of the 265 samples, 131 females and 134 males were collected which resulted in a male:female ratio of 1.0:0.97. Based on the 265 samples, mean size for male and female combined was 227.8 (SE±0.65) (Table 4). Average length of females was 226.8 (SE±0.92) mm while males’ average length was 228.7 mm (SE±0.90). Length-frequency distribution (Fig. 9) for 2005 shore spawners shows only a single mode suggesting a single age of the spawners. It is acknowledged that some sample bias may be introduced (e.g., selectivity) but this is not considered to be a serious problem. Table 4. Mean length, minimum and maximum lengths of Okanagan Lake shore

spawners from 2001-2005 (± SE).

Range Year Sample(N) Mean Length (mm) Min (mm) Max (mm)

Male:Female Ratio

2001 204 263 (± 0.74) 206 294 1.0:0.79 2002 201 206 (± 1.00) 177 303 0.96:1.0 2003 213 238 (± 1.63) 206 485 1.0:0.80 2004 69 245 (± 3.2) 184 430 1.0:0.93 2005 265 228 (± 0.65) 199 258 1.0:0.97


Fecundity for the 2005 females can be derived from the length-fecundity regression formula derived from 2003 and 2004 data (Figs. 9, 10) reported by Andrusak et al. (in Andrusak et al. 2005).

Log10(fecundity) = 0.6075*Log10(length) + 1.062

From this formula, it was estimated that the mean fecundity was ~311 eggs/female based on a 131 female lengths measured in 2005. However, this length-fecundity relationship for shore spawning kokanee describes < 1% of the variation (R2=0.010) between the variables because of a very narrow defined range of lengths at spawning. A regression of length-fecundity relationship from Mission Creek stream spawners combined with the 2005 shore spawners’ data explains approximately 82% of the variation (Fig. 11). This formula should be used and the predicted fecundity based on it results in an estimated 301 eggs/female.

Log10(fecundity) = 3.2895*Log10(length) - 5.2748 DISCUSSION The shore spawning kokanee estimates represent an index of abundance and provide trend data but are limited to detection of only large changes in abundance. It was estimated that ~162,120 shore spawners occupied the shores of Okanagan Lake in 2005, based on all quadrants, a substantial increase compared to the last four years. This escapement level has not been observed since 2000 when ~139,000 were estimated to have spawned. Assuming the brood year for the 2005 spawners was in 2001 (i.e., age 3+ spawners) there appears to be just over an eight fold increase for this cycle. It can only be speculated to which of the many factors have resulted in the apparent increase in shore spawner abundance. Certainly, the improved lake level regulation due to use of the model has likely had a positive affect. Estimating total numbers of shore spawners has proven to be elusive. The most promising method is believed to be the AUC methodology described by Hill and Irvine (2001). However, this method relies on estimation of residence time that is known to be highly variable from year to year (Schwarz and Manske 1999; Hill and Irvine, 2001). Because it is important to have accurate and precise estimates of residence time when determining an escapement number by using the AUC method, residence time would have to be estimated for a number of years. Residence time information from Okanagan Lake kokanee shore spawners has proven to be fairly difficult to define owing to uncertainty as to when fish appear on the spawning sites. Based on previous year’s data (2003 and 2004), it was estimated that residence times varied from 4-6 days. The 2004 data did show a smooth decay-type relationship was evident and all females were gone within 9 days of tagging (Andrusak et al. in Andrusak et al. 2005). While the 2004 data is useful, far more work is required if the AUC method is to be used to estimate total numbers.


Shore spawning kokanee in Okanagan Lake have historically had variable spawning times (Table 2). Earlier presence of shore spawners in 2005 initiated surveys commencing October 12th compared to October 20th in 2004 and October 23rd in 2003. Based on data from 2001-2005, kokanee spawners have demonstrated a consistent south to north gradient in arrival timing and peak counts. It has been postulated that the arrival timing and subsequent peak is correlated with temperature in Okanagan Lake. In past years, lake temperatures near or below 13°C were considered cues for peak spawning in Okanagan Lake. Wilson and Andrusak (2005) analyzed the differences in shore spawning egg development and subsequent fry emergence for 2001, 2002 and 2003 brood years. Very early spawning in 2001 resulted in early fry emergence in 2002. In comparison, the 2002 and 2003 brood egg developments were much later and fry emergence was over a month later. Implications of the temperature differences between years and the understanding of optimal fry emergence time are not well understood and require further investigation. Peak spawning in 2005 occurred above 13°C suggesting that a slightly wider temperature range (±1°C) may be cueing shore spawning. Although not assessed in 2005 depth distribution of the spawners was consistent with previous years’ observations; all of the 2005 shore spawners that could be observed clustered within the 1 m depth zone along the shoreline. Historical analysis of kokanee shore spawning data and the Okanagan Lake drawdown pattern suggested that a > 25 cm drawdown experienced over the period of egg and alevin incubation could impact survival of eggs deposited in very shallow water (< 0.25 m) (Andrusak et al. in Andrusak et al. 2004a). The total drop in lake level elevation in 2005-2006 was only 13 cm, and therefore, it is reasonable to conclude that there was little impact on the 2005 brood. Biological data demonstrated that there was a decline in mean length of kokanee shore spawners in 2005 whereas escapement numbers greatly increased. The 2005 length frequency histogram indicates a decline in mean size (227 mm) compared to the 2004 and 2003 data (Fig .9). A prominent feature for all Okanagan Lake kokanee shore spawners has been the single mode (age) usually falling between 240-270 mm (Andrusak and Sebastian in Andrusak et al. 2000). In 2005, a single age mode again was represented ranging from 199 mm to 258 mm well below the average range of 240-270 mm. This smaller size was similar to the 2002 spawner size, when the single mode ranged from only 180-240 mm with a mean of 206 mm. The 2005 data indicated a male:female ratio of 1.0:0.97 similar to that found in 2004 but higher than in 2001 and 2002 (Table 4). Fecundity samples were obtained in 2005 but analysis was not conducted at the time of preparing this report. Based on the smaller mean size of the 2005 fish it would be expected that fecundity would also be lower. Determination of 2005 fecundity using the regression of length-fecundity for the shore spawning kokanee data alone results in a linear relationship with a very weak correlation (Fig. 10), i.e., there appears to be no relationship. This is due to the very narrow size range of shore spawners (~20-26 cm). Andrusak et al. (in Andrusak et al. 2004a) demonstrated there was only a 10.5% difference between actual numbers of eggs counted and predicted numbers based on a


regression when combining shore and stream spawner data. Therefore, based on the combined data regression formula, the estimated fecundity was 301 eggs/female in 2005 (Fig. 11). This estimated fecundity is below the estimate for 2004 of 333 eggs/female (mean size of 242 mm) but slightly higher than in 2003 of 293 eggs/female (mean size of 245 mm). It should be noted that there was only about ~3% difference in fecundity between the predicted fecundity based on either regression formula. Results from intensive sampling of shore spawners over the years have confirmed some key differences compared to the stream spawners. Mission Creek stream spawners are always larger than shore spawning kokanee (Fig. 12). A parallel reduction in both kokanee shore and stream spawner size was evident in 2005. The mean lengths of the two populations have increased or decreased in a parallel manner, with the exception of 2002 and 2004. Unlike the length-frequency histograms for shore spawners which demonstrate a single mode, stream spawner histograms display multiple modes as a result a larger variation in length (Andrusak et al. in this OLAP report). To date, no age determination had been done for the 2005 data. Based on previous year’s data, except for 2002, the majority of shore spawners have been age 3+. In 2002, shore spawners length-frequency analysis of these fish suggested they were predominately age 2+ rather than expected age 3+ as reported by Andrusak and Sebastian (in Andrusak et al. 2000). The majority of stream spawners have been age 3+ but unlike the shore spawners there are also older age groups represented. The 2005 shore spawners were most likely age 3+. The shore spawning kokanee numbers increased dramatically in 2005, they were considerably greater in number than their parents in 2001. Kokanee, similar to sockeye, are known to display density dependency as a result of an increase in abundance which manifests itself in reduced growth and fecundity (Levy and Wood 1992, Myers et al. 1997, Ricker 1997, Myers 2001). An increase in competition for resources between cohorts and the two distinct kokanee ecotypes may alone account for the reduced growth. However, it should be recognized that effects of kokanee abundance can be masked by interactions with Mysis relicta, which are considered competitors for selective zooplankton within Okanagan Lake. Mysis have the ability to significantly alter the zooplankton assemblages which have direct negative impacts to kokanee populations (Chipps and Bennett 2000). The 2005 survey work was quite limited due to budget constraints. The data obtained does contribute to the ever improving data base that has been accumulating for a number of years. Certainly the last five years of data collection on the shore spawners has greatly improved the understanding of the inter-relationship between lake level regulation and survival of incubating kokanee eggs.


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S. Matthews, K. Hyatt, M. Stockwell, and H. Andrusak. 2003. Development of Decision Support Software for Fish/Water Management in Okanagan Basin Lakes and River System Draft Design Document as of February 7, 2003, for Canadian Okanagan Basin Technical Working Group, 170 pp.


K. Hall, D. Sebastian, G. Scholten, G. Andrusak, J. Sawada, D. Cassidy, J. Webster, 2001. Okanagan Lake Action Plan Year 5 (2000) Report. Fisheries Project Report No. RD 89. 2001. Fisheries Management Branch, Ministry of Water, Land and Air Protection, Province of British Columbia.


D. Sebastian, G. Scholten, P. Woodruff, D. Cassidy J. Webster, K. Rood, A. Kay. 2002. Okanagan Lake Action Plan Year 6 (2001) Report. Fisheries Project Report No. RD 96. 2002. Fisheries Management Branch, Ministry of Water, land and Air Protection, Province of British Columbia.


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Okanagan Lake Kokanee Shore Spawning Enumeration and Distribution Study, 2003. Contract report for Douglas County Public Utility District in Washington State.

Andrusak, H., S. Matthews I. McGregor, K. Ashley, R. Rae, A. Wilson, J. Webster, G.

Andrusak, L. Vidmanic, J. Stockner, D. Sebastian, G. Scholten, P. Woodruff, B. Jantz, D. Bennett, H. Wright R. Withler and S. Harris. 2005. Okanagan Lake Action Plan Year 9 (2004) Report. Fisheries Project Report No. RD 111. 2005. Fisheries Management Branch, Ministry of Environment, Province of British Columbia.


Andrusak, H., S. Matthews, R. Rae, A. Wilson, J. Webster, G. Andrusak, L. Vidmanic,

J. Stockner, D. Sebastian, G. Scholten, P. Woodruff, B. Jantz, R. Withler and S. Harris. 2006. Okanagan Lake Action Plan Year 10 (2005) Report. Fisheries Project Report No. RD 115. 2006. Fisheries Management Branch, Ministry of Environment, Province of British Columbia.

Ashley, K., Bruce Shepherd, Dale Sebastian, Lisa Thompson, Lidija Vidmanic, Dr. Peter

Ward, Hansen A. Yassien, Laurie McEachern, Rick Nordin, Dr. Dave Lasenby, Janice Quirt, J.D. Whall, Dr. Peter Dill, Dr. Eric Taylor, Susan Pollard, Cecilia Wong, Jan den Dulk, George Scholten. 1998. Okanagan Lake Action Plan Year 1 (1996-97) and Year 2 (1997-98) Report. Fisheries Project Report No. RD 73. Province of British Columbia, Ministry of Fisheries, Fisheries Management Branch.

Ashley, K.A., I. McGregor, B. Shepherd, D. Sebastian, S. Matthews, L. Vidmanic, P.

Ward, H. Yassien, L. McEachern, H. Andrusak, D. Lasenby, J. Quirt, J. Whall, E. Taylor, A. Kuiper, P.M. Troffe, C. Wong, and G. Scholten. 1999. Okanagan Lake Action Plan Year 3 (1998) Report. Fisheries Project Report No. 78. Province of British Columbia, Ministry of Fisheries, Fisheries Management Branch. Canada-British Columbia Okanagan Basin Agreement. 1974. Main Report of the Consultative Board Including the Comprehensive Framework Plan. Office of the Study Director. Penticton, BC. 536 pp.

Chipps, S.R. and D.H. Bennett. 2000. Zooplanktivory and Nutrient Regeneration by

Invertebrate (Mysis relicta) and Vertebrate (Oncorhynchus nerka) Planktivores: Implications for Trophic Interactions in Oligotrophic Lakes. Transactions of the American Fisheries Society 129:569-583.

Dill, P.A. 1996a. Migration of Kokanee Salmon Adults into Mission Creek Spawning

Channel and Estimate of Egg Deposition, 1996. Contractor rep. prep. for Min. Env. Fish. Sect., Penticton, BC.

Dill, P.A. 1996b. A Study of Shore-Spawning Kokanee Salmon (Oncorhynchus nerka)

at Bertram Creek Park, Okanagan Lake, BC, 1992-1996. Contractor rep. prep. for BC Min. Env., Penticton, BC.

Halsey, T.G. and B.N. Lea. 1973. The Shore Spawning Habitat of Kokanee in

Okanagan Lake and the Effect of Lake Level Changes on Reproductive Success. British Columbia Fish and Wildlife Branch Department of Recreation and Conservation.

Hill, R. A. and J.R. Irvine. 2001. Standardizing Spawner Escapement Data: A Case

Study of the Nechako River Chinook Salmon. North American Journal of Fisheries Management 21:651-655, 2001.


Levy, D.A., and Wood, C.C. 1992. Review of Proposed Mechanisms for Sockeye Salmon Population Cycles in the Fraser River. Bull. Math. Biol. 54:241-261.

Matthews, S. and C.J. Bull. 1981. Effect of Water Level Fluctuations on Shore

Spawning Kokanee in Okanagan Lake. Ministry of Environment Fish and Wildlife Program, 20p.

Myers, R.A, Bradford, M.J., Bridson, J.M., Mertz, G. 1997. Estimating Delayed

Density-Dependent Mortality in Sockeye Salmon (Oncorhynchus nerka): A Meta-Analytic Approach. Can. J. Fish. Aquat. Sci. 54: 2449-2462 (1997).

Myers, R.A. 2001. Stock and Recruitment: Generalizations about Maximum

Reproductive Rate, Density Dependence, and Variability Using Meta-Analytic Approaches. ICES Journal of Marine Science, 58: 937-951.

Northcote, T.G., T.G. Halsey, and S.J. MacDonald. 1972. Fish as Indicators of Water


Redfish Consulting Ltd. 2002. Freshwater Management Tools Project (FWMTP)

Kokanee Sub Model. Contract Report for the Douglas County Public Utility District Washington State. 22 p.

Ricker, W.E. 1997. Cycles of Abundance Among Fraser River Sockeye Salmon.

Canadian Journal of Fisheries and Aquatic Sciences, 54: 950-968. Schwarz, C.J. and M. Manske 1999. Estimates of stream residence time and

escapement based on capture-recapture data. Can. J. Fish. Aquat. Sci. 57:241-246 (2000).

Shepherd, B.G. 1990. Okanagan Lake Management Plan, 1990 - 1995. BC Min. Env.,

Recreational Fish. Progr., Penticton, BC. Shepherd, B. G. 1998. Draft Report Okanagan Kokanee (Oncorhynchus nerka)

Spawner Surveys 1982-1997. Ministry of Environment, Lands and Parks, Fisheries Section, Penticton, BC.

Walters, C. J. 1995. Model for Kokanee Populations Responses to Changes in Lake

Carrying Capacity. Contract report to the Fisheries Research and Development Section, Fisheries Branch, Province of BC. 5 pp.

Wilson, A, and H. Andrusak. 2005. Egg development and Fry Emergence of Okanagan

Lake 2004 Shore Spawning Kokanee with Reference to 2001-2003 Brood Year Results. Report prepared for the Okanagan Nation Alliance and the Ministry of Environment BC..


Lim

nolo

gica

l Sta

tion

Oka

naga

n La

ke

OK1

- O

K8

Kala

mal

ka L

ake

K

A1

- KA2

- tem

pera

ture

/oxy

gen

prof

ile- w

ater

sam

plin

g- p

hyto

plan

kton

- zoo

plan

kton

- mys

is

Traw

l Sta

tions

T1 -

Trou

t Cre

ek (

TRT)

T2 -

Sum

mer

land

(S

UM

)T3

- S

qual

ly P

oint

(S

QL)

T4 -

Gel

latly

(G

EL)

T5 -

Mis

sion

Cre

ek (

MIS

)T6

- O

kana

gan

Res

ort

(OK

R)

T7 -

Whi

skey

Isla

nd (

WH

I)T8

- C

amer

on P

oint

(C

AM

)

traw

l lin

es

Hyd

roac

oust

ic T

rans

ects

Sout

h ba

sin

Pow

ers

Cr.

Trep

anie

r Cr.

Peac

hlan

d C

r.En

eas

Cr.

Trou

t Cr.

Pent

icto

n C

r.N

aram

ata

Cr.

Mis

sion

Cr.

Mis

sion

Cha

nnel

Kelo

wna

Cr.

Nor

th b

asin

Lam

bly

Cr.

Sho

rts C

r.W

hite

man

Cr.

Nas

whi

to C

r.E

ques

is C

r.Ve

rnon

Cr.

Stre

am S

paw

ner E

num

erat

ions

loca

tions

1

- 18

13

45

1011

1217

1516

187

89

6O

K6

OK

3O

K2O

K1

OK

4O

K5

OK

7

Figure 1. Okanagan Lake Action Plan sampling stations and key kokanee spawning

locations.

OK

8

depth (m)

0 50 100

150

200

250

Oka

naga

n la

ke lo

ngitu

dina

l dep

th p

rofil

e

2

GH

S99

0309

Sho

rE

num

Lake

Sim

rad

70 k

Hz

and

Bio

soni

cs 4

20 k

Hz

data

col

lect

ions

e Sp

awne

r er

atio

ns

sho

re s

urve

yed

plan

view prof

ile v

iew

T#

Pen

ticto

n

Sum

mer

land

Pea

chla

nd

Wes

tban

k

Vern

on

Woo

d La

ke

Naswhito Cr.

Equesi

s Cr.

Vern

on C

r.

Kel

owna

Trepanie

r Cr.

Trou

t Cr.

KA

1

OK8

OK

6

OK

3

OK

2

OK

1

OK

4O

K5

OK

7

KA2

05

10 k

m

Eneas

Cr.

Mis

sion

Cre

ekS

paw

ning

Cha

nnel

T8T7

T6T5

T4

T3

T2

T1B

ertr

am P

ark

KA

1K

A2

depth (m)

0 50 100

150

Woo

d an

d K

alam

alka

Lak

e lo

ngitu

dina

l dep

th p

rofil

e

Pow

ers

Cr.

Lam

bly

Cr.

Shorts C

r.

Whiteman Cr.

Kala

mal

ka L

ake

Kelo

wna

Cr.

Mission

Cr.

Nara

mat

a Cr

.

Pent

icton

Cr.

Peac

hlan

d C

r.


Figure 2. Location of four quadrants and reach numbers used in estimating

Okanagan Lake kokanee shore spawners.


0

100

200

300

400

500

600

700

800

71 74 75 76 77 78 79 80 81 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05

Year

Spaw

ners

(x1,

000)

Figure 3. Indices of abundance of shoreline spawning kokanee, Okanagan Lake,

1971, 1974, 1975-81 and 1983-2005.


2003

0

2

4

6

8

10

12

14

16

Oct

. 20

Nov

. 1

Dec

.

Jan.

1

Date

Tem

pera

ture

(C)

Period ofspaw ning

13 C Figure 4. Daily surface water temperature (°C) recorded at Paul's Tomb, Okanagan

Lake 2003. Note: kokanee shore spawning illustrated from October 27 to November 9, 2003.

Figure 5. Daily surface water temperature (°C) recorded at Kelowna Bridge 2004.

Note: kokanee shore spawning illustrated from Oct. 20 - Nov. 1, 2004.

2004

02468

1012141618

1-O

ct

1-N

ov

1-D

ec

1-Ja

n

Date

Tem

pera

ture

(C)

Period of spaw ning

13 C

2005

02468

1012141618

1-O

ct

1-N

ov

1-D

ec

1-Ja

n

Date

Tem

pera

ture

(C)

Period of spaw ning

13 C

Figure 6. Daily surface water temperature (°C) recorded at Kelowna Bridge 2005.

Note: kokanee shore spawning illustrated from October 12 - October 26, 2005.


2004

341.65

341.7

341.75

341.8

341.85

341.9

341.95

1-O

ct

1-N

ov

1-D

ec

1-Ja

n

Month

Lake

ele

vatio

n (m

)

Initialspaw ning

End ofspaw ning

Lake level at commencment of spaw ning Figure 7. Timing of Okanagan Lake shore spawning kokanee relative to receding

lake levels 2004.

2005

341.650

341.700

341.750

341.800

341.850

341.900

1-O

ct

1-N

ov

1-D

ec

1-Ja

n

1-Fe

b

Month

Lake

ele

vatio

n (m

)

Initial Spaw ning

End of Spaw ning

Lake level at commencement of spaw ning Figure 8. Timing of Okanagan Lake shore spawning kokanee relative to receding

lake levels 2005.


2001

0

10

20

30

40

50

170 190 210 230 250 270 290 310 330 350 370 390 410 430Length (mm)

% fr

eque

ncy N=204

2002

0

10

20

30

40

170 190 210 230 250 270 290 310 330 350 370 390 410 430

Length (mm)

% fr

eque

ncy

N=201

2003

0

10

20

30

40

170 190 210 230 250 270 290 310 330 350 370 390 410 430

Length (mm)

% fr

eque

ncy N=213

2004

0

10

20

30

40

170 190 210 230 250 270 290 310 330 350 370 390 410 430Length (mm)

% fr

eque

ncy

N=69

2005

01020304050

170 190 210 230 250 270 290 310 330 350 370 390 410 430Length (mm)

% fr

eque

ncy

N=265

Figure 9. Percent length-frequency distribution of captured Okanagan lake shore

spawning kokanee 2001-2005. Arrows denote variable age modes in 2002, 2003 and 2004.


Okanagan Lake shore spawners (2003-2004 data)

y = 0.6075x + 1.062R2 = 0.0102

0

0.5

1

1.5

2

2.5

3

3.5

2.35 2.36 2.37 2.38 2.39 2.4 2.41 2.42 2.43

Log 10 length (mm)

Log

10 e

ggs

Figure 10. Mean length of Okanagan Lake shore spawning kokanee and Mission

Creek kokanee for years where data available. Minimum sample size = 49 fish per year.

y = 3.2895x - 5.2748R2 = 0.8235

0

0.51

1.52

2.5

33.5

4

2.3 2.35 2.4 2.45 2.5 2.55 2.6 2.65

Log 10 length (mm)

Log

10 e

ggs

Mission Creek fecundity (N=101)

Shore sp fecundity (N=50)

Linear (Mission Creek fecundity(N=101))

Figure 11. Regression of fecundity to female fish length for Mission Creek kokanee

spawners vs. shore spawners captured in 2003 and 2004.


18

20

22

24

26

28

30

32

34

36

1987 1988 1989 1990 1991 1992 1993 1994 1995 1997 2001 2002 2003 2004 2005

Year

Mea

n Le

ngth

(cm

)Shore Mission Creek

Figure 12. Preliminary regression model of fecundity vs. length (mm) of Okanagan

Lake shore spawning kokanee captured at shore based observation sites in 2003 and 2004.


CHAPTER 2 MONITORING PROGRAM

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