Report T-668 Population Characteristics, Food Habits and Spawning Activity of Spotted Seatrout, Cvnoscion nebulosus, in EVE R

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Everglades National Park, South Flor~da Research Center, P.O. Box 279, Homestead, Florida 33030

Population Characteristics, Food Habits and Spawning Activity of Spotted Seatrout, Cynoscion nebulosus, in

Everglades National Park, Florida

Report T-668

Edward Rutherford, Edith Thue and David Buker

National Park Service South Florida Research Center

Everglades National Park Homestead, Florida 33030

June 1982

TABLE OF CONTENTS

. . . . . . . . . . . . . . . . . . . . . . . . . . . LIST OF TABLES ii

LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . iii

. . . . . . . . . . . . . . . . . . . . . . . . . LIST OF APPENDICES v

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ABSTRACT 1

. . . . . . . . . . . . . . . . . . . . . . . . . . . INTRODUCTION 2

Description of the Study Area . . . . . . . . . . . . . . . . . . . 3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . METHODS 3

Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . 3 Aging Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Growth 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Survival 5 Food Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . 5

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RESULTS 5

. . . . . . . . . . . . . . . . . . . . . . . . Length Frequency 6 Verification of Aging Technique . . . . . . . . . . . . . . . . . . 6 Age Composition and Sex Ratio of the Catch . . . . . . . . . . . . 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Growth 8 Growth Equation . . . . . . . . . . . . . . . . . . . . . . . . . 9 Length-weight Relationship . . . . . . . . . . . . . . . . . . . . 9 Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Food Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Spawning Activity . . . . . . . . . . . . . . . . . . . . . . . . 11

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . DISCUSSION 11

. . . . . . . . . . . . . . . . . . . . . . . . LengthFrequency 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . SexRa t io 12 Age. Growth and Mortality . . . . . . . . . . . . . . . . . . . . 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . Food Habits 13 . . . . . . . . . . . . . . . . . . . . . . . . Spawning Activity 14

. . . . . . . . . . . . . . . . . . . . . . . . . . . . CONCLUSIONS 14

ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . 15

. . . . . . . . . . . . . . . . . . . . . . . . . LITERATURE CITED 16

Table

LIST OF TABLES

1. Median lengths at capture of scale aged fish compared with medians of modes of length-frequency distributions for spotted . . . . . . . . . . seat rout males, females, and combined sexes 20

2. Est imates of annual survival and monthly instantaneous fishing and natural mortali ty coefficients, exploitation ratio, and ra t io of conditional fishing mortali ty t o conditional natural mortali ty for spot ted seat rout males, females and combined sexes in . . . . . . . . . . . . . . . . . . Everglades National Park 21

3. Age distribution of r ipe spotted sea t rou t in Everglades National . . . . . . . . . . . . . . . . Park by number and percentage 21

4. Annual survival and mortali ty rates, instantaneous fishing and natural mortali ty coefficients, exploitation ra t io for spot ted seat rout males, females and combined sexes in 1959 and 1979, . . . . . . . . . . . . . . . . . . Everglades National Park 22

LIST OF FIGURES

Figure P a g e

1. Fishing a r e a s in Everglades National Park, Florida. . . . . . . . 23

2. Length-frequency distribution of all spot ted sea t rou t collected f rom sportfishermen c a t c h e s in Everglades National Park, . . . . . . . . . . . . . . . . . . . . . . . . . . Florida 24

3. Length-frequency distributions of male and female spot ted sea t rou t collected from sportf isher men ca tches in Everglades . . . . . . . . . . . . . . . . . . . . National Park, Florida 25

4. Scale margin increment by season of al l a g e 3 and 4 spot ted . . . . . . . . . . seatrou t in Everglades National Park, Florida 26

5. Body length-scale radius regressions for spot ted sea t rou t in . . . . . . . . . . . . . . . Everglades National Park, Florida 27

6 . Mean back-calculated lengths and lengths at cap ture at a g e of al l spot ted sea t rou t in Everglades National Park, Florida . . , . . 28

7. Ca tch curve of al l scale-aged spotted sea t rou t collected f rom sportfishermen c a t c h e s in Everglades National Park, Florida . . . 29

8. Mean back-calculated lengths at a g e of al l spot ted sea t rou t . . . . . . . . . . . . . in Everglades National Park, Florida. 30

9. Mean back-calculated lengths at a g e of male and female spotted . . . . . . . . . . seat rout in Everglades National Park, Florida 31

10. Mean back-calculated lengths at a g e of al l spotted sea t rou t collected among fishing a r e a s in Everglades National Park, . . . . . . . . . . . . . . . . . . . . . . . . . . Florida 32

1 I. Mean back-calculated annual length increment of spotted . . . . sea t rou t year classes in Everglades National Park, Florida 33

12. Regression of instantaneous growth coefficient G on reciprocal of mean back-calculated lengths at a g e for al l spotted sea t rou t in Everglades National Park, Florida. . . . . . . . . . . . . . 34

13. Mean back-calculated lengths at a g e and lengths predicted by t h e von Bertalanffy equation for a l l spot ted sea t rou t in Everglades National Park, Florida . . . . . . . . . . . . . . . . . . . . 35

14. Length-weight relationship for al l spot ted seat rout in Everglades . . . . . . . . . . . . . . . . . . . . National Park, Florida 36

LIST O F FIGURES (cont)

Figure Page

15. Percen t frequency and volume of prey consumed by all spot ted seat rout in Everglades National Park, Florida . . . . . . . . . . 37

16. Percent frequency and volume of prey consumed by size classes of spot ted seat rout in Everglades National Park, Florida . . . . . 38

17. Percen tage of to ta l number of spotted sea t rou t examined t h a t were spawning in Everglades National Park, Florida . . . . . . . 39

18. Percen tage of r ipe male and female spotted sea t rou t among a reas in Everglades National Park, Florida . . . . . . . . . . . 40

19. Mean back-calculated lengths at a g e for park spotted sea t rou t and other se lected populations in eas tern Florida and t h e Gulf of Mexico . . . . . . . . . . . . . . . . . . . . . . . . . . 41

20. Catch curves of all scale-aged spotted sea t rou t taken f rom sportfishermen ca tches in Everglades National Park, Florida . . . 42

LIST O F APPENDICES

Appendix Page

I. Distribution of males, females and combined sexes of spot ted sea t rou t back-calculated lengths, and lengths at cap ture for . . . . . . . . ages I t o VII in Everglades National Park, Florida 43

11. Distribution of male spotted seat rout back-calculated lengths and lengths at capture for ages I t o VII in Everglades National Park, Florida . . . . . . . . . . . . . . . . . . . . . . . . 44

111. Distribution of female spotted seat rout back-calculated lengths and lengths at capture for ages I t o VII in Everglades National Park, Flor ida . . . . . . . . . . . . . . . . . . . . . . . . 45

IV. Von Bertalanffy growth parameters with confidence levels for spot ted sea t rou t males, females and combined sexes in Everglades National Park, Florida . . . . . . . . . . . . . . . . . . . . 46

. . . V. Prey species of spot ted sea t rou t in Everglades National Park 47

ABSTRACT

Age, growth, mortality, stomach content and spawning activity of 570 spotted seat rout taken f rom sportfishermen ca tches in Everglades National Park were studied from November 1978 t o January 1980. Fish ranged in length f rom 220-680 mm and in weight f rom 0.10-2.24 kg. Ages of fish, determined f rom scale readings, were mainly 3, 4 and 5 year olds. Fish were fully recruited by a g e 4. Males lived t o at least a g e 6; females t o at leas t a g e 7. The sex ra t io favored females (1.6711).

Fish lengths at a g e were back calculated from scale annuli. Fish length varied between sexes and among a reas of capture and year classes. Males were larger than females at a g e 1, but smaller at ages 3-6. Calculated fish length and length at capture were g rea tes t in seasonally brackish areas, and smallest in a hypersaline a r e a of t h e park. Calculated lengths of year classes were significantly smaller in 1978 than in 1974-77.

Annual mortali ty of al l fish was 0.77. Annual mortality, exploitation ra t io and conditional fishing mortali ty (0.75) were higher for males than for females.

Spotted seat rout in Everglades National Park were carnivorous, ea t ing shrimp and fish. Their d ie t changed with size; small adults ate proportionately more shrimp than fish while large adults ate more fish than shrimp.

Spotted seat rout spawned nearly year round in Everglades National Park with peaks in spring and l a t e summer. Most r ipe fish were collected in seasonally brackish a reas of t h e Park. Age 2, 3 and 4 fish contributed most t o t h e spawn. Size at f i rs t matur i ty was 230 mm for males and 237 mm for females.

Comparison of t h e results of this study with an earl ier study of park spotted seat rout (Stewart, 1961) showed apparent changes in a g e distribution, age at full recruitment and mortality since 1959, although mean sizes at age of fish have not changed. Dominant ages shifted from 2 and 3 year olds, t o 3 and 4 year old fish. Age at full recrui tment shifted from a g e 3 t o age 4. Annual mortali ty of males decreased slightly since 1959, while annual mortali ty of females increased slightly. Exploitation ratios of both males and females remained constant. Ratios of conditional fishing t o conditional natural mortali ty increased slightly for males and females.

INTRODUCTION

Fishery harvest from Everglades National Park has been monitored through fishermen surveys nearly continuously f rom 1958 t o t he present (Higman, 1966; Davis, 1980). Examination of ca tch and e f for t da ta has shown changes in t h e relative abundance of some gamefish species. Ca tch ra tes of red drum, Sciaenops ocellata, appear t o have increased since 1958 while those of spotted seatrout , Cynoscion nebulosus, have declined.

The t o t a l harvest of major fish and shellfish species from park waters has declined f rom 2.2 million organisms in 1972 t o 1.7 million organisms in 1977 (NPS Fishery Assessment, 1979). The decline in harvest appears t o be related t o a decline in fishing e f for t but may also be environmentally related. Annual fluctuations in temperature and rainfall, hurricane incidence, boating activity and alteration of the historic flow of freshwater in to t he park all may have affected fishery harvest.

Concern over t he decline in fishery harvest from Everglades National Park prompted t he South Florida Research Center t o init iate, in 1978, a study of t h e population biology, spawning activity, and food habits of t h e four most popular gamefish species in the park: spotted seatrout, red drum, snook (Centropomus undecimalis), and gray snapper ( ~ u t j a n u s griseus). Knowledge of t he population biology of these species may offer insight into t he reasons behind t he decline in catchks and provide a basis for measuring future changes in t h e estuary. This paper, the first in a series of reports on t he four gamefishes mentioned above, describes t h e results of these studies for spotted seatrout.

The spotted seatrout is an estuarine sciaenid fish tha t ranges f rom Cape Cod, Massachusetts t o Mexico (Welsh and Breder, 1924). I t is one of t h e most important recreational and commercial fishes in t he Gulf of Mexico (Arnold, Lasswell, Bailey, Williams and Fable, 1976). Spotted seatrout and red drum have always been t h e two most popular gamefish in Everglades National Park as determined by sport- fishermen interviews (Davis, 1980). Spotted seatrout is also fished commercially in t h e park.

Tagging studies conducted elsewhere in Florida indicate t ha t spotted seatrout a r e relatively nonmigratory (Moffett, 1961; Iversen and Tabb, 1962; Beaumariage, 1969). Ninety-five percent of al l recaptured fish tagged at Pine Island, Florida were taken within 30 miles of the tagging site (Moffett, 1961; Iversen and Tabb, 1962). Electrophoretic analyses of spotted seatrou t collected from different locations in Florida and t he Gulf of Mexico have identified dist inct subpopulations (Weinstein and Yerger, 1976). Analysis of calculated length at age da ta has indicated t ha t growth of spotted seatrout varies among estuaries in Florida (Iversen and Tabb, 1962.) I t is therefore important for management purposes t o study each stock of spotted seatrout individually.

Spotted seatrout have been studied previously in Everglades National Park. 'S tewar t (1961) described i ts age, growth, spawning activity and food. Higman (1966) correlated catches of spotted seatrout with rainfall and temperature data. Clark (1970) studied t he distribution of fishes (including spotted seatrout) in

Whitewater Bay in relation t o environmental factors. The relative abundance of fishes (including spotted seatrout) was studied in relation t o environmental variables by Roessler (1967) in Buttonwood Canal, and by Jannke (1971) in Buttonwood Canal and the Shark River. Davis (1980) noted changes in length frequency distributions of spotted seatrout, red drum and gray snapper from 1959-1977. The park spotted seatrout fishery has been described in detail by Higman (1966) and Davis (1980).

Description of t he Study Area

The mainland shoreline of Everglades National Park extends from the Florida Keys t o Everglades City on Florida's west coast. I t contains numerous bays, inlets and rivers which lie at the terminus of the historically immense Everglades and Big Cypress swamp drainages. Price (19541, and Tabb, Dubrow and Manning (1962) have described the animal and plant communities of park waters and identified distinct ecological zones. Their work provided t h e basis for delineating fishing areas used in this study and other Everglades National Park fishery investigations since 1960 (Higman, 1966) (Fig. 1). These areas vary in their topographical, hydrological and biotic characteristics.

METHODS

Data Collection

Data were collected from sportsfishermen catches a t t he Everglades National Park Flamingo boat ramp from November 1978 through June 1980. Flamingo is a central departure point for fishermen in the park (Fig. 1). Samples collected from Flamingo represent the central par t of the fishery but may not adequately represent two other significant areas: the Florida Bay side of the Florida Keys within the park (Areas 1 and 21, and the western par t of the park including Everglades City and the lower 10,000 islands (Area 6) . Special effor t was made t o sample fish caught in the inland waters of the park (Areas 4 and 5) in order t o compare food analysis results with concurrent studies of benthic organism avail- ability in these areas. Therefore, the number of fish sampled from various park areas probably does not ref lect their t rue relative abundance.

Scale samples for age and growth determinations were taken from behind the pectoral fin on the l e f t side of the fish. The scales from each fish were placed in a coin envelope on which the following information was recorded: species, sample number, location of catch, date, t ime collected, t ime caught, gear type used (bait and/or artificial), weight (kg), standard length (mm), sex, reproductive condition and observer.

Aging Methods

Spotted seatrout have previously been successfully aged using scale annuli in Everglades National Park (Stewart, 196 1 ), in eastern Florida (Tabb, 196 I), and elsewhere in the Gulf of Mexico (Pearson, 1928; Klima and Tabb, 1959; Moffett, 1961). In this study, the following cr i ter ia (Bagenal, 1979) were used to evaluate the validity of age determinations from annular marks on spotted seatrout scales:

I. Fish body growth is proportional t o scale growth.

2. Scale annular formation is seasonal and occurs only once each year.

3. Back calculated lengths of fish a t a g e N a r e between observed lengths at capture of fish aged N-1 and N.

4. Lengths at capture of fish aged by scales ag ree with modal lengths of age groups determined by t h e Petersen length frequency method.

Scales were prepared for a g e analysis by pressing t h e m into plast ic slides with an Ann Arbor fish scale press and photographing t h e slide impressions with a Model 500 3 M microfilm reader printer. The enlarged (20x1 scale pictures were examined for number of annuli. The distance from t h e focus was measured for each annulus and for t h e t o t a l sca le radius. Fish body length was regressed on t o t a l sca le radius for each a r e a of cap tu re and sex t o determine t h e proportionality of fish body growth t o scale growth. The y in tercept of this regression was used a s t h e correction fac tor "a" in t h e Dahl-Lea (Bagenal, 1979) formula t o back ca lcu la te fish length at each annulus. The Dahl-Lea formula is:

where 1 is length at a g e t, S t is t h e distance (mm) t o annulus t, S is t h e t o t a l sca le t radius and L is t h e observed fish length (mm) at capture.

Seasonality of scale annulus formation was es t imated by plotting scale radius marginal increment against month of capture. Year class of fish was determined by subtracting t h e number of annuli f rom the d a t e of capture.

Sex was determined by inspection of t h e gonads. Developmental s tages of t h e gonads were classified according t o Lagler (1956).

Growth

Possible differences in back calculated fish lengths and lengths a t cap tu re among sexes and a reas of capture were analyzed using two factor Analysis of Variance (Zar, 1974). Differences in calculated annual f ish growth among year classes were analyzed using th ree fac to r (year class, sex, a r e a of capture) Analysis of Variance. A student Neuman-Keuls t e s t was used t o determine which specific differences were significant. Growth d a t a (mean back calculated lengths a t age) were f i t t ed t o t h e von Bertalanffy growth equation (Bayley, 1977). Length-weight relationships were calculated for each sex according t o t h e formula:

where W = weight (decagrams), L= length (mm S.L.), and a,b a r e empirically deter- mined constants. The lengthcweight regressions were logarithmically (base 10) transformed and compared using analysis of covariance (Zar, 1974).

Survival

Annual survival was es t imated for fully recruited fish from t h e age distribution of t h e c a t c h (Robson and Chapman, 1961). Age at full recrui tment was determined according t o Robson and Chapman's (1 961) method. Total instantaneous mortali ty coeff ic ients (2) were calculated f rom t h e es t imates of annual survival (S) using t h e relationship Z = -1nS. Natural mortali ty coefficients (M) were es t imated from variables obtained from t h e von Bertalanffy equation and f rom mean water temperatures (T c ) recorded in t h e study a r e a according t o Pauly's (1980) equation:

log 10 M = -0.0066 - 0.2790 log 10 Lw + 0.6543 log 10 K + 0.4634 log 10 T

Estimates of fishing mortali ty coefficients (F) were then obtained by subtracting t h e es t imated natural mortali ty coefficient f rom t h e coeff ic ient of to ta l mortality. These mortali ty coefficients also permit ted calculation of exploitation ratios (El, conditional fishing mortali t ies (m), and conditional natura l (n) mortalities.

Exploitation ratios measure t h e fraction of t o t a l mortali ty in a stock due t o fishing when fishing and natural mortali ty occur simultaneously. Conditional mortali t ies measure t h e mortali ty due t o e i ther fishing or natura l causes in a stock assuming i t is t h e only form of mortali ty occurring at t h a t t i m e (Ricker, 1975).

Food Analvses

Stomach samples for t h e food study were removed by cut t ing open t h e body cavity f rom t h e th roa t t o t h e anal pore. The s tomach was removed by clamping the esophagus and cut t ing above t h e clamp. Stomachs were immediately placed in 10% buffered formalin for la ter examination.

Food i tems of s tomach samples were identified t o t h e species level when possible. For analysis of percent frequency and percent volume, prey species were grouped into six categories: shrimp, fish, crabs, mollusks, a lgae + plants and other. The percent volume of each food i tem was taken by blotting dry t h e i tem, measuring i t s volume (mL) by water displacement and expressing this a s a percentage of t h e to ta l volume of food in a designated series (individuals of a species; by area , sex and month). The percent frequency of a food i t em was calculated as t h e number of stomachs in which it occurred, divided by t h e to ta l number of stomachs in t h e series.

RESULTS

Seven hundred and for ty eight spot ted seat rout were collected for analysis from Florida Bay (Areas 1, 2, 3) and t h e Whitewater Bay-Shark River a reas (Areas 4, 5). No fish f rom t h e lower Ten Thousand Islands a reas (Area 6 ) were sampled. Five hundred and seventy of t h e fish were examined for information on age and growth, reproductive condition and stomach content. An additional 178 spotted seat rout were measured for length frequency information and 154 fish examined for s tomach content. Fish ranged in length from 220-680 mm (S.L.) (2 = 330 - + 4 mm) and in weight from 0.10-2.24 kg (2 = 0.57 - + .02 kg).

Length Frequency

The mean length of al l fish in t h e ca tch was 330 mm (Fig. 2). Females (x = 341 + 6 mm) were significantly larger (p5001) than males (x = 314 + 6 mm). ~ e m a l e s r a n g e d in length from 220-530 mm, while males ranged in length from 230-465 mm (Fig. 3).

2 Significant (x = 21.53; P<.05) seasonal differences in length frequency distri- butions were noted for spotted seat rout (combined sexes). Small fish (-=280 mm) occurred proportionately more o f ten in winter than in other seasons. The mean length of fish was greates t in spring and declined steadily in ?ummer, fa l l and winter. Female length distributions also differed significantly (x = 22.993; P<.05) among seasons. Large females (>400 mm) occurred proportionately more of ten in spring than in summer, fal l or winter. Mean length of females was g rea tes t in spring and leas t in fal l and winter. Male length distributions were no t significantly di f ferent among seasons. Because no consistent seasonal progression in mean length of fish or length modes was noticed, recrui tment into t h e fishery was considered continuous.

Significant (.01<P<.025) differences were found in length frequency distributions of male spot ted seat rout among a reas of capture. Mean fish length was significantly larger (Pc.025) and sample size smaller in North Florida Bay than in t h e Whitewater Bay and Cape Sable areas. Fish f rom south Florida Bay (Area 2) were not included in t h e analysis of variance because of inadequate sample s i ze (n = 4) although their mean length was largest (? = 412 mm) of all. Length frequency distributions of females and combined sexes, considered separately, were not significantly di f ferent among areas.

Verification of Aging Technique

Scales f rom 570 spotted seat rout were analyzed for annular marks. Tabb (1956) gives an excellent description of spotted seat rout scales and their annuli which proved t o be invaluable in finding annular marks:

"The circuli and normal checks a r e concentric with t h e scale margin. There is no appreciable crowding of circuli in t h e zones designated as annuli. Annuli a r e characterized by a slight dip in t h e scale surface and a discon- formity of t h e circuli in t h e la tera l posterior angle of t h e scale. New radii of ten originate in t h e immediate vicinity of annuli, hence a r e useful in locating an annulus in large scales with coarsened surface features. The c teni i inside and outside t h e first annulus differ in s ize and regularity, and form t h e best single clue t o t h e location of t h e f i rs t annulus, a mark t h a t may be overlooked."

We verified a g e analysis of spotted seat rout by scale annuli by meeting a l l cr i ter ia listed in t h e Methods section except age analysis by t h e Petersen length frequency

. method.

Scale margin increments were plotted by season for a g e 3 and 4 fish in t h e ca tch t o determine t i m e of annulus formation (Fig. 4). Most minimal scale increments (0-2 mm) occurred in spring (March, April and May), indicating t h a t spotted seat rout form annuli at this t i m e (Fig. 4). The mean marginal increment increased during t h e year. I t was lowest in spring and rose steadily t o a peak in winter. The occurrence of a f e w fish with minimal scale margin increments in fal l may be due t o mistaking spawning checks on t h e scales of these fish for annular marks.

Fish body length was significantly (P<.001) corre la ted with scale growth for each sex in each a r e a of capture. The regressions of fish body length on to ta l scale radius were found t o b e significantly (P<.OOl) d i f ferent among sexes and a reas by analysis of covariance. Regression plot elevations of males and females in t h e Cape Sable a r e a (Area 3) d i f fered significantly f rom each other and from al l o ther fish. Therefore, th ree groups were formed: males f rom Cape Sable, females f rom Cape Sable, and males and females f rom North Florida Bay, South Florida Bay, Whitewater Bay and t h e Shark River Area (Areas 1, 2, 4, 5) (Fig. 5). The y inter- c e p t of each group was used as t h e standard correction factor "a" t o back calcula te lengths at previous ages.

Figure 6 and Appendices 1-3 show t h e distribution of back calculated lengths and observed lengths at capture fo r 539 spot ted seatrout. Mean observed lengths at annulus a r e similar to, but larger than, back calculated lengths because of growth since annulus for mation.

To compare t h e age-length key derived f rom t h e Petersen method with the age- length key derived from scale readings, modal lengths of fish in t h e length frequency distributions were separated by Cassie's (1954) method and compared with lengths at capture of scale-aged fish (Table 1). Only at a g e 3 were lengths at capture of scale aged fish and modal lengths of t h e length distributions similar. No modal lengths were observed below 280 mm S.L. because of t h e 12 inch T.L. (258 mm S.L.) minimum size limit. Based upon lengths at a g e reported for o ther spotted seat rout stocks (Pearson, 1928; Tabb, 19611, young of t h e year and a g e 1 fish were underrepresented in t h e catch. I t was therefore impossible t o determine ages of spotted seat rout f rom length frequency analysis without a representative sample of small fish.

Age Composition and Sex Ra t io of t h e Ca tch

The sportfish ca tch in Everglades National Park consisted mainly of 3 and 4 year old fish, which comprised 45% and 29% of t h e catch, respectively (Fig. 7). Recruitment t o t h e fishery began at age 1 and was complete by age 4 as determined by a Robson and Chapman (1961) chi square analysis. The number of fish caught dropped sharply a f t e r a g e 4; no males over 6 years old and no females over 7 years old were observed. The small number of a g e 1 fish examined (4) was primarily due t o t h e minimum legal size limit of 12 inches (305 mm T.L.); sport- fishermen repor t catching small fish frequently and releasing them.

The mean a g e of al l fish in t h e ca tch was 3.3 + .l yrs. The mean a g e (x = 3.4 2 .1 yrs.) of females was significantly (.005<P<.01) older than mean a g e (2 = 3.1 4.1 yrs.) of males. Mean ages of males, females and combined sexes did not vary among areas.

The overall sex ra t io of t h e ca tch favored females by 1.6711. The sex ra t io remained constant with age as indicated by chi square tests for heterogeneity. The sex ra t io appeared t o be different at ages 1 (0.3311) and 6 (3.511) because sample size was small; t h e ra t io remained constant at ages 2 through 5 where sample s ize was larger. No significant differences were found in sex ra t io among areas.

Growth

Back calculated lengths based on scale annuli indicate t h a t growth of spotted seat rout is g rea tes t in t h e f irst year of l ife when growth averages 212 mm (Fig. 8). Yearly growth increments a r e smaller (40-50 mm) f rom ages 1-5 but a r e uniform from year t o year. The smallest mean length increment (22 mm) occurred in t h e sixth year. The large increase in growth in t h e seventh year (71 mm) may be an a r t i f ac t of t h e small sample s ize of large fish available for back calculation in th is year.

Significant sexual differences in length at cap ture and back calculated length were found for spot ted seatrout. Females were significantly (P<.001) larger in observed length at cap ture at ages 3, 4 and 5. Males were larger (Pc.05) in back calculated length than females at age 1 but were again smaller (P<.01) at ages 3, 4 and 5, indicating t h a t females grew significantly (P< .001) more than males in t h e second, third, fourth and f i f th growth years (Fig. 9).

Significant (P< .025) a r e a differences in fish length were found at ages 1 through 4. Mean lengths at capture of fish in t h e Shark River a r e a were largest and lengths of fish in t h e C a p e Sable a r e a smallest a t a g e 4. Mean back calcula ted lengths of fish in t h e Cape Sable a r e a were smallest at ages 1-4 (Fig. lo), although these differences in fish length were de tec ted by a SNK test only at ages 3 and 4. Back calculated growth r a t e of fish differed significantly (Pc.025) between a reas in t h e f irst , third and f i f th growth years. In t h e f irst and f i f th growth years, fish in North Florida Bay grew most and fish in Cape Sable grew least. In t h e third growth year fish in t h e Shark River a r e a grew most and fish in Whitewater Bay grew least. Fish taken f rom South Florida Bay were excluded from t h e analyses because of small sample s ize (N = 10).

Differences in calculated annual growth r a t e of year classes were noticed for spotted seatrout. Year classes of fish increased in length at significantly (P<.001) di f ferent r a t e s in t h e second, third and fourth growth years (Fig. 11). In these growth years, year classes grew significantly less in calendar year 1978 than in any other calendar year.

Interaction e f f e c t s between a rea of capture, sex and year class on fish length were examined but no c lear differences were found.

Growth Equation

The regression of G, t h e instantaneous growth coefficient , on t h e reciprocal of mean length was significant (.025< P < .05) fo r both males, females and combined sexes (Fig. 12). The von Bertalanffy equations derived from this regression appeared t o f i t calculated length d a t a at ages 1-6 well. Figure 13 compares lengths es t imated by t h e von Bertalanffy equation with mean back calculated length data . The von Beralanffy equations were:

males Lt = 591 (1 - e - .12 ( t + 2.95))

females Lt = 656 (1 - e - .13 ( t + 2.04))

combined sexes Lt = 774 (1 -e - .09(t + 2.54))

Confidence intervals (95%) around K, L, and to for males, females and combined sexes a r e listed in Appendix IV. Confidence intervals calculated for L, were negative because of t h e poor f i t , and subsequent high variance, of t h e length weight regression t o very small (age 1) and very large (age 7) fish. The high variance created wide confidence intervals around 1/L,, and thus L,; confidence intervals around k and to were smaller.

The von Bertalanffy es t imates of L,, t h e maximum theoret ica l length of a species, a r e smaller than t h e s ize of t h e largest spotted seat rout reported for Florida, a 860 mm (15 Ib, 6 oz) fish (Lorio and Perre t , 1980).

Length-weight relationship

Figure 14 shows a length-weight relationship calculated for 567 spotted seatrout. A logarithmic (base 10) transformation of t h e d a t a provided t h e best f i t (Pc.001) t o t h e relationship for males, females and combined sexes. There was no difference in length-weight relationship between sexes or among a reas of capture.

Survival

Survival r a t e s of spotted seat rout were calculated from t h e age composition of t h e catch. All fish were fully recruited by age 4 (as determined by t h e Robson and Chapman (1961) method, therefore survival e s t imates were calculated for spotted seat rout older than age 3.

Annual survival of a l l fish was S = 0.23 + 0.05. Male survival (S = 0.18 + . lo) was lower than female survival (S = 0.25 +3.07) (Table 2). The natural m o r t a l i t y coefficients calculated from Paulyls equation for males (M = 0.35) and females (M = 0.36) were nearly identical; natura l mortali ty coefficient of both sexes combined was 0.27. These coefficients, when subtracted from to ta l mortali ty coefficients es t imated by t h e Robson and Chapman method, yielded fishing mortali ty coefficients t h a t were higher for males (F = 1.37) than for females (F = 1.02). Consequently, t h e exploitation ra t io (E) and ratios of conditional fishing t o natura l mortali ty (m/n) were higher for males than for females (Table 2). Conditional fishing mortality ra tes were at least twice as high as conditional natura l mortali t ies for each sex.

Food Analyses

Figure 15 shows t h e results of the analysis of 724 seat rout stomachs. Two hundred thirty e ight (32.5%) of t h e fish analyzed contained food items. A species list of a l l identif iable food i tems is given in Appendix V.

Spotted seat rout consumed mainly shrimp of t h e family Penaeidae, primarily Penaeus duorarum. Shrimp appeared in 72.7% of al l s tomachs and totalled 53.8% of t h e food volume. Other common shrimp species in t h e die t were Alphaeus heterochaelis and - A. armillatus.

Fish were the next most important prey, occurring in 42.4% of t h e stomachs and comprising 43.5% of t h e volume. The most common identifiable families were Sparidae, particularly Archosargus rhomboides, Batrachoidadae and Gerreidae, particularly Eucinostomus spp.

Algae and marine plants ranked third in frequency (17.2%) and volume (2.0%) in t h e die t but may have been consumed accidentally along with other food items. Commonly consumed marine plants were Thalassia testudinum, Halodule wrightii, Ruppia marit ima, and Udotea flabellum.

Molluscs and crabs consti tuted a very small portion of t h e diet, occurring in 8.8% and 3.8% of t h e stomachs and comprising 0.3% and 0.07% of t h e volume, respect- ively. Molluscan prey included ~ e r i t h e u m eburneum, Modulus modulus, Brachidontes exustus, Marginella apicina, and Bulla str iata. The most commonly consumed c r a b species was Pagures annulipes.

The las t prey category, "other", contained tunicates, serpulid worms, amphipods and unidentifiable organic matter .

Differences in food consumption by a r e a of capture, season, sex and s ize (length) of t h e predator were tes ted by chi-square analysis of prey frequencies in t h e diet. There were no significant differences in food consumption by area , season or sex.

Food consumption did differ significantly (P<.01) by s ize of predator (Fig. 16). The percentage frequency and volume of fish prey species increased with t h e size of t h e predator. Fish prey species occurred in stomachs of small (<271 mm) spotted seat rout only 20% of t h e t i m e and occupied 11.6% of t h e volume, whereas in large (>371 mm) spotted seatrout, fish were predominant (58.3% frequency, 64.2% volume) in t h e diet. Conversely, shrimp were most common (88.3%) and occupied t h e most volume (87.2%) in the die t of small spotted seat rout but were less prevalent (58.3% frequency, 35.2% volume) in t h e diet of large predators. The consumption of o ther prey categories did not change with predator size.

The use of shrimp (Penaeus duorarum) and fish (Mugil cephalus) as bait did not significantly distort their relat ive abundance a s food i tems in the analyses. The frequencies of a l l prey categor ies consumed by fish caught on all bait types was not

significantly di f ferent f rom those consumed by fish caught on art if icial bait. The size of fish caught on all bai t types and on art if icial lures was approximately t h e same, discounting the possibility of s ize influence on food consumption by t h e 5 groups.

Spawning Activity

Spotted seat rout were found t o spawn nearly every month of t h e year in Everglades National Park. However, spawning peaks occurred in spring and l a t e summer. Most females examined (46%) spawned in l a te summer with a secondary peak (37%) in spring. Most males examined (33%) spawned in spring with a secondary peak (29%) in summer (Fig. 17). The seasonal difference in spawning peaks among males and females was slight and probably does not represent distinctly different spawning peaks by sexes.

Ripe fish of both sexes were collected in al l a r e a s of t h e park. Most fish in spawning condition were caught in t h e Shark River and Whitewater Bay a reas during t h e year (Fig. 18); in Shark River and North Florida Bay during t h e l a t e summer peak, and in Shark River, Whitewater Bay and North Florida Bay during t h e spring peak.

The smallest r ipe male spotted seat rout collected was 237 mm; t h e smallest r ipe female collected was 230 mm. The age distribution of a l l ripe fish (Table 3) shows t h a t a g e 3 and a g e 4 fish numerically contributed most t o female spawning effort , while male spawning e f f o r t c a m e primarily from age 2, 3 and 4 fish.

DISCUSSION

Length Frequency

Distinct annual modes in length frequency distributions of the park spotted seat rout population were difficult t o discern because of t h e species' extended spawning season; fish spawned in April grow almost a full season more than fish spawned in October, creat ing a bimodal distribution (Guest and Gunter, 1958). After 2 years, when most fish s t a r t recruiting into t h e fishery, modes become even less distinct. The lack of distinct modes in t h e length distributions make a g e analysis by length frequency difficult, if not impossible. Therefore, in Everglades National Park, as has been shown for spotted seat rout in o ther a reas (Pearson, 1928; Klima and Tabb, 1959; Moffett, 1961; Stewart , 1961; Tabb, 1961), scales or otoliths should be used t o accurate ly age t h e fish.

Seasonal differences observed for mean spotted seat rout length may indicate greater availability of large fish in spring than in other seasons. Fish length decreased steadily a f t e r spring, suggesting t h a t these large fish move out of t h e park during the year. Seasonal inshore-offshore movements have been reported for spotted seat rout in Georgia (Mahood, 1974), Florida (Tabb, 1966), and Texas (Simmons, 195 1; Guest and Gunter, 1958).

Sex Rat io

Our findings of an overall sex ra t io favoring females agrees with those reported previously (Pearson, 1928; Klima and Tabb, 1959; Moffett , 1961; Stewart , 1961; Tabb, 1961). The sex ra t io remained constant with age in this study. However, t h e sex ratio of park spotted seat rout reported by Stewart in 1961 favored females by a lesser amount (1.310, and changed with age, going from near unity at ages 1 and 2 t o favor females at ages 3, 4 and 5. Stewart made a special e f f o r t t o obtain small (young) fish, perhaps making his ra t io more representative of t h e park population.

Age. Growth and Mortalitv

All studies of spotted seat rout in east Florida and in t h e Gulf t o d a t e have shown sexual differences in growth and longevity (Pearson, 1928; Klima and Tabb, 1959; Moffett , 1961; Stewart , 1961; Tabb, 1961). In some populations, females live longer than males and a r e larger at every a g e (Pearson, 1928; Klima and Tabb, 1959; Stewart , 1961; Tabb, 1961). In this study, males were larger than females at age 1, and smaller a f t e r age 2. Females lived longer than males. The di f ference in longevity between t h e sexes in Everglades National Park might b e explained by differences in fishing mortality. Our observations suggest tha t males experience higher r a t e s of annual mortali ty and conditional fishing mortali ty than females but equivalent r a tes of conditional natura l mortality. No es t imates of longevity have been made for unfished populations.

Mortality ra tes of spotted seat rout have been es t imated only twice before. Iversen and Moffett (1962), in a tagging study of a Pine Island, Florida population, es t imated t h e t o t a l annual mortali ty r a t e of a l l fish t o be 41.6%. Conditional natural mortali ty was 1.3 t imes greater than conditional fishing mortality. Tatum (1980) es t imated t h e mean t o t a l mortali ty r a t e of an Alabama population by length frequency analysis t o be 50%. Both studies sampled fish of t h e same length range as t h e park population.

The calculated growth curve derived for t h e 1979 Everglades National Park spotted seat rout population was similar at ages 3-7 t o those reported for t h e 1959 park population and other populations in Florida's east coast and t h e Gulf of Mexico (Fig. 19). Spotted seat rout in t h e present study were larger at ages 1 and 2 than other populations studied because of t h e back calculation formula used. Previous investigators back calculated lengths at nnulus directly without a correction s? fac to r according t o t h e formula Lt = - L, where Lt = length at annulus t , L = length of fish at capture, st = scale raaius at annulus t, S = to ta l scale radius (Bagenal, 1979). The difference in length resulting from t h e type of back calculation formula used becomes negligible a f t e r age 2 when lengths of t h e park spot ted seat rout population closely parallel lengths reported for o ther Gulf populations.

Varying growth of spotted seat rout among ecologically different a reas in t h e park may be due t o environmental differences among these areas. Fish grew less in t h e hypersaline Cape Sable a r e a than in t h e seasonally brackish a reas (Whitewater Bay,

Shark River, North Florida Bay) of t h e park. Salinities in Cape Sable a r e generally t h e highest of a l l park areas, ranging f rom 26-47'100 and averaging 35O/oo (Tabb, Dubrow and Manning, 1962). They exceed optimal salinities reported for growth and survival of larval spotted sea t rou t (20-35~/00) and for metabolic activity and sustained swimming speed of juvenile and adult fish (20°/oo) (Wakeman and Wohlschlag, 1977; Taniguchi, 1980). Since tagging studies have shown t h a t spotted sea t rou t a r e relatively nonmigratory (Iversen and Tabb, 1962; Beaumariage, 1969), it is likely t h a t local environmental conditions could have a f fec ted their growth.

The y in tercepts of t h e scale radius body length relationships of males and females in Cape Sable were significantly di f ferent from each other and from fish in other areas. The di f ferences in y in tercepts were probably an a r t i f a c t of having sampled adult fish. I t is unlikely t h a t sexual differences in size at scale formation would exist in t h e Cape Sable a r e a and not in o ther areas.

Observed di f ferences in calculated growth of seat rout year classes may be a r t i f ac t s of Rosa Lee's phenomenon (Bagenal, 1979), in which lengths of a given a g e group a r e larger t h e older t h e fish f rom which they were calculated (i.e., fish in thei r third growing season in 1975 (year class 1973) were largest, and fish in their third growing season in 1978 (year class 1976) were smallest). Lee's phenomenon may be caused by s ize selective mortality eliminating t h e smaller members of an age group, leaving a pool of large individuals from which t o back calcula te fish lengths (Bagenal, 1979). I t is also possible t h a t t h e poor growth of year classes in 1978 may have been caused by unfavorable c l imat ic conditions in t h a t year.

Temperature is one of t h e most important parameters influencing growth of fish, (Webb, 1978; Bret t , 1979). Although spotted seat rout ohave been observed t o survive and feed actively at temperatures between 4-33 C when allowed t ime t o acc l imate (Simpons, 19571, they survive and grow best at temperatures ranging f rom 23.1-32.9 C for larvae (Taniguchi, 1980) and 1 5 - 2 7 ' ~ for adults (Tabb, 1966). W e examined a i r t empera tu re d a t a for 1978 for Everglades National Park t o see if unusually cold weather had occurred which might have influenced growth. The winter of 1978 was not unusually cold. Mea: t empera tu re of 2 0 . 5 ' ~ for t h e period November 1980 through March 197; was 3.7 C warmer than t h e long-term average and temperatures dropped below 4 C fo r only 2 days (NOAA, 1978, 1979). Other factors , including salinity and food availability, may have caused the poor growth of year classes in t h a t year.

Food Habits

Results of this food study confirm findings of o ther food studies of spotted seat rout in t h e Gulf of Mexico (Pearson, 1928; Moody, 1950; Stewart , 1961; Tabb, 1961; Seagle, 1969). Spotted seat rout a r e carnivorous, ea t ing mainly fish and shrimp. Their d ie t changes with size. Seasonal differences found in other investigations (Gunter, 1945; Moody, 1950) of spotted seat rout stomach content were not found in th is study.

Spawning Activity

Stewart (1961) also found t h a t park spotted sea t rou t spawn throughout t h e year with peaks in spring and fall. S tewart corre la ted t h e spawning peaks t o a surface water temperature range of 25-30'~. H e collected most r ipe fish f rom north Florida Bay and Cape Sable. Over 70% of t h e r ipe fish collected in t h e present study c a m e from t h e seasonally brackish Whitewater-Coot Bay and Shark River a reas (Areas 4 and 5 combined), although this may ref lect sampling bias ra ther than ac tua l location of spawning activity. Roessler (1967) and Jannke (1971) collected larval and juvenile spotted seat rout in passes and canals leading t o t h e inland waters of t h e park. They both postulated t h a t spotted seat rout spawn near ocean passes or channels which lead t o brackish water. Taniguchi (1980) reported t h a t survival and growth of laboratory reared spotted seat rout larvae were optimal at 23.1-32.9'~ and 20-35 O/oo, conditions commonly found in Whitewater Bay and t h e Shark River area. The ability of spotted seat rout t o use the estuarine environment a s a nursery a r e a is thought t o afford protection from stenohaline compet i tors and predators (Tabb, 1966).

Elsewhere in t h e Gulf of Mexico, spotted seat rout spawn from February through October with a peak in May (Pearson, 1928; Klima and Tabb, 1959; Fontenot and Rogilio, 1970). They a r e known t o mature at 1 t o 3 years, with t h e majority of fish reaching maturi ty in t h e third year (Miles, 1950; Guest and Gunter, 1958; Klima and Tabb, 1959).

CONCLUSIONS

Comparison of our results with those of Stewart 's (1961) earl ier study of park spotted seat rout indicates a change in age distribution, age at full recrui tment and mortali ty r a t e since 1959. Although Stewart did not provide specific figures, e s t imates f rom Figure 12 of his thesis indicate t h a t mean lengths at cap ture at a g e of males and females do not appear t o have changed.

The age distribution of t h e ca tch appears t o have shifted f rom a pre&minance of 2 and 3, t o 3 and 4 year old fish (Fig. 20). Age at full recrui tment switched f rom a g e 3 in 1959 t o age 4 in 1979. The apparent shift in age s t ructure may be an a r t i f a c t of sample bias. S tewar t (1961) s t a ted t h a t h e made a special e f fo r t t o collect juvenile fish in t h e 1959 study. Therefore, t h e relat ive proportions of 1 and 2 year old fish in his study may not re f l ec t their t r u e abundance in t h e recreational catch.

Mortality ra tes of fully recruited spotted seat rout have also changed f rom 1959 t o 1979. Annual mortali ty r a t e s of all fish and of females taken separately increased slightly. These changes in mortali ty ra tes were not a f fec ted by sample bias. If one assumes t h a t spotted seat rout were fully recruited at age 4 in 1959, thereby eliminating Stewart 's sample bias for smaller fish, mortali ty ra tes still increased f rom 1959 t o 1979. These changes in mortali ty r a t e s were due t o corresponding changes in both fishing mortali ty and natural mortali ty (Table 4).

ACKNOWLEDGEMENTS

W e wish t o thank the following people for their help in this project. Gary Davis proposed the study and made valuable suggestions. Dr. Edward Houde helped with statist ical analyses. Julio Garcia Gomez and Robert Work helped t o identify food items. Enid Sisskin drew the figures. Fay Schattner, Dee Childs and Dottie Anderson typed the manuscript. W e especially thank the sportfishermen at Flamingo for their cooperation and Jim Tilmant for his guidance and critical review of t h e manuscript.

LITERATURE CITED

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Table 1. Median lengths at capture of scale aged fish compared with medians of modes of length frequency (L - F) distributions for spot ted sea t rou t males, females, and combined sexes.

Males

Median lengths a t 231 283 305 340 394 4 15 capture of scale aged fish

'Lledian of 257 302 348 L - F Modes ( ~ n m )

Females

Median lengths at 237 280 32 1 36 9 427 capture of sca le aged fish

Median of 25 5 3 12 383 45 1 L - F Modes (mm)

Combined Sexes

Median lengths at 233 282 314 359 416 . 420 505 capture of sca le aged fish

Median of 250 305 37 7 L - F Modes (mm)

Table 2. Est imates of annual survival (S) and monthly (A), instantaneous fishing (F) and natural mortali ty (MI coefficients, exploitation ra t io (El, and ra t io of conditional fishing mortail ty (m) t o conditional natural mortality (n) for spot ted seat rout males, f emales and combined sexes in Everglades National Park.

~ ~- - -

Combined Sexes .23 - + .05 .77 .27 1.21 2.92 .82

Males .18 - + .10 .82 .35 1.37 2.52 .80

Females .25 - + .07 .75 .36 1.02 2.11 .74

Survival r a t e s with 95% confidence intervals.

Table 3. Age distribution of r ipe spotted seat rout in Everglades National Park by number and percentage.

Males Females All Fish

Age N % N % N %

Total 2 8 100.1 9 1 100.1 119 99.9

Table 4. Annual survival (S), and mor ta l i ty (A) r a t e s , ins tan taneous fishing (F) and na tu ra l (M) mor ta l i t y coef f ic ien ts , exploi tat ion r a t i o (E) and r a t i o of condit ional f ishing (m) t o condit ional na tu ra l (n) mor t a l i t y for spo t t ed s e a t r o u t males, f e m a l e s and combined sexes in 1959 and 1979, Everglades National Park.

S A M 1 F 1 .- -- m/n - E~

Combined Sexes

Males

Fernales

or purposes of comparison t h e s e e s t i m a t e s were made f rom lengths back ca lcula ted f r o m t h e s a m e formula , wi thout a correc t ion f ac to r .

Ti $4 a m O n H

m z m cd -a

1 ALL FISH N=748

200 R=330f 4mm

LENGTH (mrn SL)

Figure 2. Length-frequency distribution of all spotted seatrout collected from sportfishermen catches in Everglades National Park, Florida. Means with - + 95% confidence intervals.

I LENGTH (mm S.L.)

1 j B. FEMALES N1345

LENGTH (mm SL)

Figure 3. Length-frequency distributions of male and female spotted seatrout collected from sportfishermen catches in Everglades National Park, Florida. Means with - + 95% con£ idence intervals.

. . k

h aJ ; 2 .5 a pc; a d a M a 3 0 -d k r l M a k 0s

-I m m

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rl a d

M M h 0 aJ F-

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C 6 0 .d $4

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$4 M a c .d [I) C rd m aJ

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1 2

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60

80

10

6 12

0 14

0

SC

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I 2

0

40

60

80

100

12

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140

SC

AL

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S

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Fig

ure

5.

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y le

ng

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sc

ale

ra

diu

s r

eg

res

sio

ns

f

or

sp

ott

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se

atr

ou

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ve

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de

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ati

on

al

Pa

rk,

Flo

rid

a : M

ale

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Cap

e S

ab

le

(le

ng

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1

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ale

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=

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9

(A))

; F

em

ale

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Cap

e S

ab

le

(le

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th =

7

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+ 3

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ale

ra

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=

8

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r =

0

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(B));

Ma

les

and

fe

ma

les,

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oo

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ite

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ter

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ark

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ive

r.

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rth

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So

uth

Flo

rid

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ays

(le

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2.9

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ca

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).

n =

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5

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.

o MEAN LENGTHS at CAPTURE

MEAN BACK CALCULATED LENGTHS

i

1 2 3 4 5 6 7

AGE lyrsl

F i g u r e 6 . Mean b a c k - c a l c u l a t e d l e n g t h s and l e n g t h s a t c a p t u r e a t a g e o f a l l s p o t t e d s e a t r o u t i n E v e r g l a d e s N a t i o n a l P a r k , F l o r i d a . B a r s i n d i c a t e 95% c o n f i d e n c e i n t e r v a l s .

AGE I y r s I

F i g u r e 7 . Catch c u r v e of a l l s c a l e - a g e d s p o t t e d s e a t r o u t c o l l e c t e d from s p o r t f i s h e r m e n c a t c h e s i n Everg lades N a t i o n a l Park , F l o r i d a .

F i g u r e 8. Mean back-ca lcu la ted l e n g t h s a t age of a l l s p o t t e d s e a t r o u t i n Everg lades N a t i o n a l Park , F l o r i d a . E a r s i n d i c a t e 95% conf idence i n t e r v a l s .

700- - -4 U, 600- E E V

U,

500- C3 z Y e3 F 400- a 1 2 0 J

8 300- Y 0 a m = 200- 3 2

100 -

N= 539

1 2 3 4 5 6 7

AGE l y r s l

0 MALES N=205

A FEMALES N=326

1 2 3 4 5 6 7

AGE Iyrs l

F i g u r e 9 . Mean back-ca lcu la ted l e n g t h s a t age of male and female s p o t t e d s e a t r o u t i n Everglades N a t i o n a l Park , F l o r i d a . Bars i n d i c a t e 95% conf idence i n t e r v a l s .

A NORTH FLORIDA BAY

o SHARK RIVER

COOT & WHITEWATER BAYS

CAPE SABLE

AGE lyrsl

F i g u r e 10 . Mean back-ca lcu la ted l e n g t h s a t age of a l l s p o t t e d s e a t r o u t c o l l e c t e d among f i s h i n g a r e a s i n Everglades N a t i o n a l Park , F l o r i d a . Bars i n d i c a t e 95% conf idence i n t e r v a l s .

YEAR CLASSES 1973 N = 2 0

0 1974 N=40 A 1975 N=173

1976 N=218 V 1977 N=75

1 2 3 4

GROWTH YEAR

F i g u r e 11. Mean back-ca lcu la ted a n n u a l l e n g t h increment of s p o t t e d s e a t r o u t y e a r c l a s s e s i n Everglades N a t i o n a l Park , F l o r i d a . Bars i n d i c a t e 9 5 % conf idence i n t e r v a l s .

F i g u r e 12. Regress ion of i n s t a n t a n e o u s growth c o e f f i c i e n t G on r e c i p r o c a l of mean b a c k - c a l c u l a t e d l e n g t h s a t age f o r a l l s p o t t e d s e a t r o u t i n Everglades N a t i q n a l Park , F l o r i d a . G = -0.2501 + 0.1936(1/L

MEAN BACK CALCULATED LENGTHS

0 PREDICTED LENGTHS

1 2 3 4 5 6 7

AGE (yrs )

F i g u r e 13. Mean back-ca lcu la ted l e n g t h s a t age and l e n g t h s p r e d i c t e d by t h e von B e r t a l a n f f y e q u a t i o n f o r a l l s p o t t e d s e a t r o u t i n Everg lades N a t i o n a l Pa rk , F l o r i d a :

LENGTH (mm S U

F i g u r e 14 . Length-weight r e l a t i o n s h i p f o r a l l s p o t t e d s e a t r o u t i n Everg lades N a t i o n a l Park , F l o r i d a . Dashed l i n e s i n d i c a t e 95% conf idence i n t e r v a l s . Weight p r e d i c t e d by t h i s equa t ion i s i n decagrams.

SHRIMP FISH CRABS MOLLUSCS ALGAE & OTHER

PLANTS

FOOD GROUPS

TOTAL V0LUME~888.63

SHRIMP FISH CRABS MOLLUSCS ALGAE & OTHER PLANTS

FOOD GROUPS

F i g u r e 15. P e r c e n t f requency and volume of p rey consumed by a l l s p o t t e d s e a t r o u t i n Everglades N a t i o n a l Park , F l o r i d a .

SHRIMP FISH CRABS MOLLUSCS *pLLi:y:f OTHER

FOOD GROUPS.

SHRIMP FISH CRABS MOLLU8CS ALGAE & OTHER PLANTS

FOOD GROUPS

F i g u r e 16 . P e r c e n t f requency and volume of p rey consumed by s i z e c l a s s o f s p o t t e d s e a t r o u t i n Everglades N a t i o n a l Park , F l o r i d a .

6oi . FEMALES

DEC-FEB -MAR-MAY JUNE-AUG S EPT- NOV

F i g u r e 17. Percen tage of t o t a l number of s p o t t e d s e a t r o u t examined t h a t were spawning i n Everglades N a t i o n a l Park , F l o r i d a . Numbers above g raphs a r e t o t a l numbers of f i s h examined i n a season .

I FEMALES N.99

50 - 40-

30-

20-

10- I G LL

BAY BAY S A B L E C O O T B A Y S RIVER

AREA

Figure 18. Percentage of ripe male and female spotted seatrout among areas in Everglades National Park, Florida.

(3 N. FLA. S. FLA. C A P E WHITEWATER SHARK

f BAY BAY S A B L E C O O T B A Y S R IVER

a n AREA V> - 0

MALES N=29

r

.

I I

FLORIDA BAY (E.N.P.) 1979 M 3 9

A FLORDA BAY (ENP.) 1959 M 9 5

0 M A N RIVER, FL 1957 k 7 6 8

CENTRAL TEXAS 1928 W 6

1 2 3 4 5 6 7 8

AGE ly rs l

F i g u r e 1 9 . Mean b a c k - c a l c u l a t e d l e n g t h s a t a g e f o r p a r k s p o t t e d s e a t r o u t and o t h e r s e l e c t e d p o p u l a t i o n s i n e a s t e r n F l o r i d a and t h e Gulf of Mexico. B a r s i n d i c a t e 95% c o n f i d e n c e i n t e r v a l s . Da ta t a k e n from Tabb (1961) f o r I n d i a n River , F l o r i d a ; f rom P e a r s o n (1928) f o r c e n t r a l Texas : and from S t e w a r t (1961) f o r F l o r i d a Bay, 1959.

1 2 3 4 5 6 7

AGE lyrsl

Figure 20. Catch curves of all scale-aged spotted seatrout taken from sportfishermen catches in Everglades National Park, Florida, 1959 (Stewart, 1961) and 1979.

App

endi

x I.

Dis

trib

utio

n of

mal

es,

fem

ales

and

com

bine

d se

xes

of

spo

tted

sea

tro

ut

back

-cal

cula

ted

len

gth

s (C

) an

d le

ng

ths

at

cap

ture

(0

) fo

r ag

es I

to V

II i

n E

verg

lade

s N

atio

nal

Par

k,

Flo

rida

.

Age

I

I1

111

IV

--

v V

I V

II -- -

0

C

0

C

0

C

0

C

0

C

0

C

0

Le

ng

th_

rnrn

!C

- ---- -

- -

-- -- - ------

---

o m I -2 m L IOi 5 2 MLL c .. 2 2 >i"i -0 (0 QJ CL C,

I 2 7-d I 3 !=

2 .2 101 I I

2 2 Y z >/ : V " rd a)

L I -0 rd

IUi I

C, 4 I 3 M 0 L L QJ + > 191 I I

g w I ) I vl .5 1 -0 QJ =: z >

10: I

App

endi

x 11

1. D

istr

ibut

ion

of f

erna

le s

po

tted

sea

tro

ut

back

-cal

cula

ted

len

gth

s (C

) and

len

gths

at

cap

ture

(0)

for

ages

I to

VII

in

Eve

rgla

des

Nat

iona

l P

ark,

Flo

rida

.

Age

I

I1

--- 11

1 .-

I V

v v I

--

-- -

VII

--

-

C

0

C

0

C

0

C

0

C

0

C

0

Le

ng

thn

nm -c

-- -- -0 --

- - - - _

- - - - -- - - - -- - - - -

- - - - - - - - -- - -- - ------ --

-

- ----

Appendix IV. Von Bertalanffy growth p a r a m e t e r s K , L, and to with conf idence levels (95%) for spo t t ed s e a t r o u t males, f e m a l e s and combined sexes in Everglades National Park , Florida.

hlales

Females

Combined Sexes

Appendix V. Prey species o f spot ted sea t rou t in Everglades National Park. Occurrence of prey in g rea te r than 5% of t h e s tomachs is noted as common (C) and less than 5% as r a r e (R).

MARINE PLANTS

Algae

Chlorophyta

Udotea flabellum Caulerpa spp.

Rhodophyta

Acanthophora speci fera Bostrychia spp.

Phanerograms

Thalassia testudinurn Halodule wr igh t i i Ruppia rnaritirna Cyrnodacea manatorum

Polychaeta

Serpulidae spp.

Gastropoda

Modulus modulus Ceri thium eburneum Ceritheurn muscarurn Marginella apicina Bulla s t r i a t a --

MARINE ANIMALS

Pelecypoda

Brachidontes exustus Anomalocardia cumimeris Lucinidae SPD.

Arthropoda

Crus tacea

Corophidae ~ p e . Parapenacus longirastris Penacus a t t e c u s Dynamene spp. Penaeus duorarum Penaeus se t i ferus Alpheus armillatus Alpheus heterochaelis Tozeuma carolinensis Leander tenuicornis Thor floridanus Periclimenes longicaudatus Pagurus spp. Sesarsma spp. Petrolistes galathinus

Tunicata ( ~ r o c h o r d a t a )

Ascidiacea

Molgula spp.

Ver tebra ta (Chordata - Pisces)

Unknown spp.

Perciformes

Lutjanus griseus Eucinostomus spp. Bairdiella chrysura Micro~obius SPP. ~ r c h & a r g u s rhornboidales Opsanus beta

Rutherford, Edward, Edith Thue, and David Buker. 1982. Population Character- istics, Food Habits and Spawning Activity of Spotted Seatrout, Cynoscion nebulosus, in Everglades National Park, Florida. South Florida Research Center Report T-668. 48 pp.