Status of Sport Fishes in Gods Lake, Alberta, 2004

Status of Sport Fishes in Gods Lake, Alberta, 2004 CONSERVATION REPORT SERIES

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Status of Sport Fishes in Gods Lake, Alberta, 2004 Greg Fortier, Tyler Johns, and John Tchir Alberta Conservation Association Bag 900 26 Peace River, Alberta, Canada T8S 1T4

Report Series Editor PETER AKU P.O. Box 40027 Baker Centre Postal Outlet Edmonton, AB, T5J 4M9 Conservation Report Series Type Data, Technical ISBN printed: 978 0 7785 5438 7 ISBN online: 978 0 7785 5439 4 Publication No.: T/131 Disclaimer: This document is an independent report prepared by the Alberta Conservation Association. The authors are solely responsible for the interpretations of data and statements made within this report. Reproduction and Availability: This report and its contents may be reproduced in whole, or in part, provided that this title page is included with such reproduction and/or appropriate acknowledgements are provided to the authors and sponsors of this project. Suggested Citation: Fortier G.N., T. Johns, and J.P. Tchir. 2005. Status of sport fishes in Gods Lake, Alberta, 2004. Data report, D 2005 022, produced by Alberta Conservation Association Bag 900 26, Peace River, Alberta, Canada. 19 pp + App. Cover photo credit: David Fairless Digital copies of conservation reports can be obtained from: Alberta Conservation Association P.O. Box 40027, Baker Centre Postal Outlet Edmonton, AB, T5J 4M9 Toll Free: 1 877 969 9091 Tel: (780) 427 5192 Fax: (780) 422 6441 Email: info@ab conservation.com Website: www.ab conservation.com i

EXECUTIVE SUMMARY Increased access in the Red Earth area in the Northwest region of Alberta, resulting from the development of new roads, has raised concerns about impacts of potential increases in angling pressure on sport fish populations of lakes in the region, including Gods Lake. The present study was conducted on Gods Lake to generate quantitative data on abundance, population structure, and growth of four major sport fish species, walleye (Sander vitreus), northern pike (Esox lucius), lake whitefish (Coregonus clupeaformis), and yellow perch (Perca flavescens), that can be used to assess impacts of the increased fishing pressure. A total of 223 sport fish were captured during the survey of which yellow perch was the most abundant, accounting for 30.5% of the catch; walleye, northern pike, and lake whitefish constituted 16.6, 29.1, and 9.0% of the total catch, respectively. Catch per unit effort (CPUE) for walleye ranged from 0.0 to 8.81 fish/100m 2 /24h with a mean (±95% CI) of 1.83 ± 1.86 fish/100m 2 /24h (n = 12). Of the 37 walleye sampled, 59.5% were females and 40.5% were males resulting in a female to male sex ratio of 1.47:1. Length of females ranged from 278 to 679 mm FL with a mean (±SD) of 500.7 ± 72.37 mm (n = 22) while that of males ranged from 406 to 578 mm with a mean of 462.5 ± 37.55 mm (n = 5). Males ranged in age from 7 to 18 y with a mean of 8 ± 2.88 y (n = 15) while age of females ranged from 2 to 17 y with a mean of 8.7 ± 3.50 y (n = 22). Overall mean age of the catch was 8.4 ± 3.24 y (n = 37). CPUE for northern pike ranged from 0.0 to 6.82 fish/100m 2 /24h with a mean of 3.15 ± 2.08 fish/100m 2 /24h (n = 12). Of the 65 northern pike sampled, 47.7% were females and 52.3% were males, resulting in a female to male sex ratio of 0.91:1. Length of females ranged from 479 to 941 mm FL with a mean of 642.4 ± 112.4 mm (n = 31) while that of males ranged from 464 to 809 mm with a mean of 597.7 ± 73.35 mm (n = 34). Males ranged in age from 4 to 11 y with a mean of 6.8 ± 1.16 y (n = 34) while age of females ranged from 4 to 13 y with a mean of 7.3 ± 1.95 y (n = 31). Overall mean age of the catch was 7.0 ± 1.59 y (n = 65). ii

CPUE for lake whitefish ranged from 0.0 to 2.42 fish/100m 2 /24h with a mean of 0.95 ± 1.24 fish/100m 2 /24h (n = 12). Of the 18 lake whitefish sampled, 55.6% were females and 44.4% were males, resulting in a female to male sex ratio of 1.25:1. Length of females ranged from 448 to 618 mm FL with a mean of 534.8 ± 50.90 mm (n = 10) while that of males ranged from 500 to 558 mm with a mean of 529.5 ± 19.11 mm (n = 8). Males ranged in age from 10 to 16 y with a mean of 13.5 ± 2.45 y (n = 8) while age of females ranged from 6 to 17 y with a mean of 12.8 ± 3.58 y (n = 10). Overall mean age of the catch was 12.5 ± 3.92 y (n = 19). CPUE for yellow perch ranged from 0.0 to 8.81 fish/100m 2 /24h with a mean of 1.69 ± 2.10 fish/100m 2 /24h (n = 12). Of the 68 yellow perch sampled, 61.8% were females and 38.2% were males, resulting in a female to male sex ratio of 1.62:1. Length of females ranged from 136 to 172 mm FL with a mean of 146.6 ± 8.51 mm (n = 42) while that of males ranged from 131 to 154 mm with a mean of 140.5 ± 6.54 mm (n = 26). Males ranged in age from 2 to 4 y with a mean of 3.0 ± 0.46 y (n = 24) while age of females ranged from 2 to 5 y with a mean of 3.2 ± 0.52 y (n = 40). Overall mean age of the catch was 3.1 ± 0.51 y (n = 64). The results of the present study provide important baseline information that can be used by resource managers to quantify the effects of anticipated increases in angling pressure on sport fish population in Gods Lake. Key words: Gods Lake, walleye, northern pike, lake whitefish, yellow perch, catch per unit effort, age, growth, size distribution, angler harvest. iii

ACKNOWLEDGEMENTS We thank Kathleen Woodruff (Alberta Conservation Association) for assisting with planning and data collection. We also thank Paul Hvenegaard (Alberta Conservation Association) and Dave DeRosa (Alberta Sustainable Resource Development) for reviewing earlier drafts of this report. iv

CONSERVATION REPORT SERIES

TABLE OF CONTENTS EXECUTIVE SUMMARY...ii ACKNOWLEDGEMENTS...iv TABLE OF CONTENTS...v LIST OF FIGURES...vi LIST OF TABLES...vii LIST OF APPENDICES... viii 1.0 INTRODUCTION... 1 1.1 General introduction...1 1.2 Study objectives...1 2.0 STUDY AREA... 1 3.0 MATERIALS AND METHODS... 3 3.1 Sampling design...3 3.2 Data collection...4 3.3 Data analyses...4 4.0 RESULTS... 5 4.1 Walleye...5 4.2 Northern pike...9 4.3 Lake whitefish...12 4.4 Yellow perch...15 4.5 Summary...17 5.0 LITERATURE CITED... 19 6.0 APPENDIX... 20 v

LIST OF FIGURES Figure 1. Map of Gods Lake showing sampling locations for 2004...2 Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Length distributions of male and female walleye captured in Gods Lake during the 2004 gill net survey...6 Age distributions of male and female walleye captured in Gods Lake during the 2004 gill net survey....7 von Bertalanffy growth curves for male and female walleye from Gods Lake, Alberta, 2004...8 Length distributions of male and female northern pike captured in Gods Lake during the 2004 gill net survey....10 Age distributions of male and female northern pike captured in Gods Lake during the 2004 gill net survey...10 von Bertalanffy growth curves for male and female northern pike from Gods Lake, Alberta, 2004...11 Length distributions of male and female lake whitefish captured in Gods Lake during the 2004 gill net survey....13 Age distributions of male and female lake whitefish captured in Gods Lake during the 2004 gill net survey...13 Figure 10. von Bertalanffy growth curve for male and female lake whitefish from Gods Lake, Alberta, 2004...14 Figure 11. Length distributions of male and female yellow perch captured in Gods Lake during the 2004 gill net survey....16 Figure 12. Age distributions of male and female yellow perch captured in Gods Lake during the 2004 gill net survey...16 Figure 13. von Bertalanffy growth curve for male and female yellow perch from Gods Lake, Alberta. 2004...17 vi

Table 1. LIST OF TABLES Distribution of fish sampling effort by depth strata in Gods Lake, Alberta, 2004.... 3 Table 2. Mean catch per unit effort (CPUE) of walleye in gill nets during the 2004 stock assessment at Gods Lake, Alberta... 6 Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Proportion of mature walleye in each age class from gill nets during the 2004 stock assessment at Gods Lake, Alberta... 8 Proportion of mature walleye in each length class from gill nets during the 2004 stock assessment at Gods Lake, Alberta... 9 Mean catch per unit effort (CPUE) of northern pike in gill nets during the 2004 stock assessment at Gods Lake, Alberta... 9 Proportion of mature northern pike in each age class from gill nets during the 2004 stock assessment at Gods Lake, Alberta.... 11 Proportion of mature northern pike in each length class from gill nets during the 2004 stock assessment at Gods Lake, Alberta.... 12 Mean catch per unit effort (CPUE) of lake whitefish in gill nets during the 2004 stock assessment at Gods Lake, Alberta... 12 Proportion of mature lake whitefish in each age class from gill nets during the 2004 stock assessment at Gods Lake, Alberta.... 14 Proportion of mature lake whitefish in each length class from gill nets during the 2004 stock assessment at Gods Lake, Alberta.... 15 Mean catch per unit effort (CPUE) of yellow perch in gill nets during the 2004 stock assessment at Gods Lake, Alberta... 15 vii

LIST OF APPENDICES Appendix 1. Universal transverse mercator (UTM) coordinates (NAD 83, UTM zone 11) of gill net locations in Gods Lake, Alberta 2004...20 viii

1.0 INTRODUCTION 1.1 General introduction Increased access in the Red Earth area in the Northwest region of Alberta, resulting from the development of new roads, has raised concerns about impacts of potential increases in angling pressure on sport fish populations of lakes in the region, including Gods Lake. Currently the roads used to access Gods Lake are of poor quality and are not regularly maintained. Future development in the Red Earth area may result in improvement of these roads which can lead to additional angling pressure. 1.2 Study objectives To assess impacts of the anticipated increased accessibility on Gods Lake sport fishery, we conducted a stock assessment survey between 12 and 16 September 2004 to generate baseline data on abundance, population structure, and growth of four major sport species, walleye (Sander vitreus), northern pike (Esox lucius), lake whitefish (Coregonus clupeaformis), and yellow perch (Perca flavescens) in the lake. The data generated in our study will aid in formulating management guidelines for the sports fishery on the lake. 2.0 STUDY AREA Gods Lake is located approximately 66 km northeast of Red Earth, Alberta (Figure 1). It has a surface area of 680 ha, an average depth of 13.0 m, and a maximum depth of 25.0 m. A gravel/earth road is used to access the lake. The lake supports natural populations of white sucker (Catostomus commersoni), longnose sucker (Catostomus catostomus), cisco (Coregonus artedi), lake whitefish, northern pike, burbot (Lota lota), yellow perch, and walleye. 1

Figure 1. Map of Gods Lake showing sampling locations for 2004. Inset is map of the province of Alberta. 2

3.0 MATERIALS AND METHODS 3.1 Sampling design We used multi mesh benthic gill nets to capture fish. Each net comprised of five 15 x 2.4 m panels of different mesh sizes 38, 63, 89, 114, and 140 mm (stretch measure) and connected in sequential order. Sampling sites were selected in a stratified random fashion using five depth strata, set at 5 m intervals. Table 1 shows the stratification and the proportion of lake surface area represented by each stratum. Sampling effort was allocated proportionately to surface area of the five depth strata (Table 1). A total of 12 gill nets were deployed and their locations were geo reference using a Garmin 12 handheld GPS unit. Sample sites were randomly selected using Arcview GIS version 3.1, with a minimum distance of 500 m between sites. Nets were set at depths 2 m for approximately 24 h. Nets were set perpendicular to the shoreline; if a net extended beyond its depth stratum then it was reset at an angle. The orientation of the largest or smallest mesh of each net in relation to the shore was random. Table 1. Distribution of fish sampling effort by depth strata in Gods Lake, Alberta, 2004. One net was set at each site thus, the total number of nets equals the total number of sampling sites. Depth stratum (m) Proportion of lake surface area (%) Number of sites 0 5 29.2 4 5 10 10.8 1 10 15 15.3 2 15 20 27.7 3 >20 17 2 3

3.2 Data collection Biological data collected from all captured fish included fork length (FL), total length (TL), and weight. Sex, maturity, and stomach contents were determined through internal examination of sacrificed fish. Stomach content data were collected and archived as requested by Alberta Sustainable Resource Development but not included in this report. Ageing structures were also removed from sacrificed fish and aged following methods in Mackay et al. (1990). Left pelvic fin rays were collected for ageing walleye and yellow perch, cleithra were collected to age northern pike, and scales were collected for ageing lake whitefish. All data on sport fish, as well as non sport fish species (number caught, fork length, and weight) were entered into the Provincial Governments Fisheries Management Information System (FMIS). 3.3 Data analyses The abundance of each species, expressed as catch per unit effort (CPUE, fish/100m 2 of net/24h) was calculated at each sampling site and used to estimate the mean CPUE (+ 95% confidence interval (95% CI)). CPUE values were reported for each depth stratum, as well as a grand mean for all depth strata combined (whole lake). Total catch per unit effort (TCUE) is the total catch of each fish species over the total effort applied. Length frequency and age frequency distributions were used to examine the population structure of each species. Distributions of length and age were shown in relation to CPUE (y axis). We established relationships between FL and TL for walleye and northern pike from fish captured in this study, as well as those captured during a parallel angler survey on the lake (FMIS project location ID 6374). In order to reduce sampling time, TL was not measured for all fish. Plotting FL and TL measurements of individual fish, where both were recorded, we fitted the following linear regression models to walleye and northern pike. Walleye: TL = 1.038 FL + 10.25; (R 2 = 0.993, n = 111). Northern pike: TL = 1.051 FL + 6.39; (R 2 = 0.994, n = 142). 4

Fish maturity was described as the age at which 50% of the fish are mature. The length at which 50% of fish were mature was also reported. Fish growth rate was described using the von Bertalanffy (1938) growth model: L t = L (1 e K (t t 0 ) ) where: Lt = length at age t L = the asymptote or final maximum size K = the rate at which the growth curve approaches the asymptote t = age t0 = a time scaler, the hypothetical time when the fish was size zero To account for sexual variations in growth rate, the von Bertalanffy model was fitted separately for male and female fish. The parameter used to estimate growth in the von Bertalanffy model is K i.e., the rate at which the fish approaches maximum size (L ). Higher values of K represent faster growth and are usually associated with low L. Due to small sample sizes of small fish, t0 was fixed at zero to reduce bias in the growth function. 4.0 RESULTS 4.1 Walleye Walleye accounted for 16.6% of the total catch (i.e., 37 individuals of the 223 fish captured). TCUE was 1.75 fish/100m 2 /24h. Mean CPUE for depth intervals ranged from 0.00 to 8.81 fish/100m 2 /24h with a whole lake mean of 1.83 fish/100m 2 /24h (Table 2). 5

Table 2. Mean catch per unit effort (CPUE) of walleye in gill nets during the 2004 stock assessment at Gods Lake, Alberta. n = number of nets. Depth stratum (m) CPUE (fish/100m 2 /24h) Mean 95% CI (±) 0 5 4.55 4.79 4 5 10 0.49 1 10 15 0.61 7.79 2 15 20 0.00 3 >20 0.00 2 Whole lake 1.83 1.86 12 n Of the 37 walleye sampled where sex could be determined, 59.5% were females and 40.5% were males, resulting in a female:male sex ratio of 1.47:1. Male and female walleye length distributions are shown in Figure 2. Length of males ranged from 406 to 578 mm FL with a mean of 462.5 ± 37.55 mm (n = 15), while that of females ranged from 278 to 679 mm with a mean of 500.7 ± 72.37 mm (n = 22). Walleye size distribution does not appear to be truncated at the minimum size limit (50 cm TL or 47.2 cm FL) for angler harvest. 0.5 Males n = 15 Catch per unit effort (fish/100m 2 /24h) 0.4 0.3 0.2 0.1 Females n = 22 0 280 320 360 400 440 480 520 560 600 640 680 Fork length (mm) Figure 2. Length distributions of male and female walleye captured in Gods Lake during the 2004 gill net survey. 6

Males ranged in age from 7 to 18 y with a mean of 8.0 ± 2.88 y (n = 15) while age of females ranged from 2 to 17 y with a mean of 8.7 ± 3.50 y (n = 22; Figure 3). The overall mean age of the catch was 8.4 ± 3.24 y (n = 37). The age 7 cohort was the most abundant year class for both male and female walleye, representing 80% of all males and 50% of all females. Age 7 males showed a mean of 452.1 ± 20.74 mm FL (n =12) or 479.5 mm TL. Age 7 females showed a mean of 490.0 ± 12.49 mm FL (n = 11) or 518.9 mm TL. Therefore, most female and some male 7 y old walleye are susceptible to angler harvest. The low representation of fish less than age 7 suggests several years of low recruitment of younger age classes. This highlights the vulnerability of walleye in Gods Lake. With an average FL of 490.0 ± 12.49 mm (n = 11) or 518.9 cm TL, 7 y old females have recently surpassed the legal harvest size of 50 cm TL and become susceptible to angler harvest. With an average FL of 452.1 ± 20.74 mm (n =12) or 479.5 mm TL, the 7 y old males will surpass the legal harvest size within a year. 0.6 Catch per unit effort (fish/100m 2 /24h) 0.5 0.4 0.3 0.2 0.1 Males n = 15 Females n = 22 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Age (y) Figure 3. Age distributions of male and female walleye captured in Gods Lake during the 2004 gill net survey. When fitted to the von Bertalanffy growth function, male walleye showed an L of 551.7 mm FL and a growth coefficient K of 0.253 (Figure 4). Females showed an L of 598.6 mm FL and a growth coefficient K of 0.231 (Figure 4) thereby, attaining larger sizes and at a slower rate than males. 7

800 700 Fork length (mm) 600 500 400 300 200 100 0 0 5 10 15 20 25 Age (y) Figure 4. von Bertalanffy growth curves for male and female walleye from Gods Lake, Alberta, 2004. von Bertalanffy growth parameters: a) Males: L = 551.7, K = 0.253, n = 25; b) Females: L = 598.6, K= 0.231, n = 45. The proportion of mature walleye in each age and length class is shown in Tables 3 and 4. While only one female and no male walleye were found to be immature the data shows that males and females likely reach 50% maturity by age 7. Males appear to reach 50% maturity by 450 mm and females by 500 mm. Table 3. Proportion of mature walleye in each age class from gill nets during the 2004 stock assessment at Gods Lake, Alberta. Age (y) Males Females % mature n % mature n 2 0 1 7 100 12 100 11 8 100 1 100 4 10 100 1 100 1 11 100 2 14 100 1 17 100 2 18 100 1 8

Table 4. Proportion of mature walleye in each length class from gill nets during the 2004 stock assessment at Gods Lake, Alberta. Fork length (mm) Males Females % mature n % mature n 300 100 1 450 100 5 100 1 500 100 9 100 10 550 100 6 600 100 1 100 2 650 100 1 700 100 1 4.2 Northern pike Northern pike accounted for 29.1% of the total catch (i.e., 65 individuals of the 223 fish captured. TCUE was 3.07 fish/100m 2 /24h. Mean CPUE for depth intervals ranged from 0.00 to 6.82 fish/100m 2 /24h with a whole lake mean of 3.15 fish/100m 2 /24h (Table 5). Table 5. Mean catch per unit effort (CPUE) of northern pike in gill nets during the 2004 stock assessment at Gods Lake, Alberta. n = number of nets. Depth stratum (m) CPUE (fish/100m 2 /24h) Mean 95% CI (±) 0 5 6.82 2.72 4 5 10 5.38 1 10 15 2.57 6.32 2 15 20 0.00 3 >20 0.00 2 Whole lake 3.15 2.08 12 n Of the 65 northern pike sampled where sex could be determined, 47.7% were females and 52.3% were males, resulting in a female:male sex ratio of 0.91:1. Male and female northern pike length distributions are shown in Figure 5. Length of males ranged from 464 to 809 mm FL with a mean of 597.7 ± 73.35 mm (n = 34), while that of females ranged from 479 to 941 mm with a mean of 642.4 ± 112.4 mm (n = 31). Northern pike 9

size distribution has not been truncated at the minimum size limit (i.e., 63 cm TL or 59.7 cm) for angler harvest. 0.25 Males n = 34 Catch per unit effort (fish/100m 2 /24h) 0.20 0.15 0.10 0.05 Females n = 31 0.00 480 520 560 600 640 680 720 760 800 840 880 920 960 Fork le ngth (mm) Figure 5. Length distributions of male and female northern pike captured in Gods Lake during the 2004 gill net survey. Males ranged in age from 4 to 11 y with a mean of 6.8 ± 1.16 y (n = 34) while females ranged from 4 to 13 y with a mean of 7.3 ± 1.95 y (n = 31; Figure 6). The overall mean age of the catch was 7.0 ± 1.59 y (n = 65). 0.8 Males n = 34 Catch per unit effort (fish/100m 2 /24h) 0.6 0.4 0.2 Females n = 31 0 3 4 5 6 7 8 9 10 11 12 13 14 Age (y) Figure 6. Age distributions of male and female northern pike captured in Gods Lake during the 2004 gill net survey. 10

When fitted to the von Bertalanffy growth function, female northern pike showed an L of 989.5 mm FL and a growth coefficient K of 0.148 (Figure 7). Females showed an L of 1029.0 mm FL and a growth coefficient K of 0.13 (Figure 7) thereby, attaining larger sizes and at a slower rate than males. 1000 900 800 Fork length (mm) 700 600 500 400 300 200 100 0 0 2 4 6 8 10 12 14 Age (y) Figure 7. von Bertalanffy growth curves for male and female northern pike from Gods Lake, Alberta, 2004. von Bertalanffy growth parameters: a) Males: L = 1029.0, K = 0.13, n = 34; b) Females: L = 989.5, K = 0.148, n = 30. All captured northern pike were mature i.e., individuals of both sexes 4 y and 500 mm FL (Tables 6 and 7). Table 6. Proportion of mature northern pike in each age class from gill nets during the 2004 stock assessment at Gods Lake, Alberta. Age (y) Males Females % mature n % mature n 4 100 1 100 1 5 100 1 100 4 6 100 12 100 3 7 100 14 100 14 8 100 5 100 4 9 100 3 11 100 1 13 2 11

Table 7. Proportion of mature northern pike in each length class from gill nets during the 2004 stock assessment at Gods Lake, Alberta. Fork length (mm) Males Females % mature n % mature n 500 100 3 100 3 550 100 5 100 4 600 100 11 100 5 650 100 6 100 4 700 100 7 100 5 750 100 1 100 6 800 100 2 850 100 1 900 100 1 950 100 1 4.3 Lake whitefish Lake whitefish accounted for 9.0 % of the total catch (i.e., 20 individuals of the 223 fish captured). TCUE was 0.95 fish/100m 2 /24h. Mean CPUE for depth intervals ranged from 0.00 to 2.42 fish/100m 2 /24h with a whole lake mean of 0.95 fish/100m 2 /24h (Table 8). Table 8. Mean catch per unit effort (CPUE) of lake whitefish in gill nets during the 2004 stock assessment at Gods Lake, Alberta. n = number of nets. Depth stratum (m) CPUE (fish/100m 2 /24h) Mean 95% CI (±) 0 5 2.42 4.79 4 5 10 0.49 1 10 15 0.61 7.79 2 15 20 0.00 3 >20 0.00 2 Whole lake 0.95 1.24 12 n Of the 18 lake whitefish sampled where sex could be determined, 55.6% were females and 44.4% were males, resulting in a female:male sex ratio of 1.25:1. Male and female lake whitefish length distributions are shown in Figure 8. Length of males ranged from 12

500 to 558 mm FL with a mean of 529.5 ± 19.11 mm (n = 8), while that of females ranged from 448 to 618 mm with a mean of 534.8 ± 50.9 mm (n = 10). Catch per unit effort (fish/100m 2 /24h) 0.150 0.125 0.100 0.075 0.050 0.025 Males n = 8 Females n = 10 0.000 440 460 480 500 520 540 560 580 600 620 640 Fork length (mm) Figure 8. Length distributions of male and female lake whitefish captured in Gods Lake during the 2004 gill net survey. Males ranged in age from 10 to 16 y with a mean of 13.5 ± 2.45 (n = 8) while age of females ranged from 6 to 17 y with a mean of 12.8 ± 3.58 y (n = 10; Figure 9). The overall mean age of the catch was 12.5 ± 3.92 y (n = 19). 0.150 Catch per unit effort (fish/100m 2 /24h) 0.125 0.100 0.075 0.050 0.025 Males n = 8 Females n = 10 0.000 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Age (y) Figure 9. Age distributions of male and female lake whitefish captured in Gods Lake during the 2004 gill net survey. 13

When fitted to the von Bertalanffy growth function, male lake whitefish showed an L of 551.7 mm FL and a growth coefficient K of 0.250 (Figure 10). Females showed an L of 559.2 mm FL and a growth coefficient K of 0.285 (Figure 10) thereby, attaining similar sizes as males. 700 600 Fork length (mm) 500 400 300 200 100 0 0 5 10 15 20 Age (y) Figure 10. von Bertalanffy growth curve for male and female lake whitefish from Gods Lake, Alberta, 2004. von Bertalanffy growth parameters: a) Males: L = 551.7, K= 0.250, n = 8; b) Females: L = 559.2, K = 0.285, n = 10). All captured lake whitefish were mature i.e., males 10 y and 500 mm FL and females 6 y and 450 mm FL (Tables 9 and 10). Table 9. Proportion of mature lake whitefish in each age class from gill nets during the 2004 stock assessment at Gods Lake, Alberta. Age (y) Males Females % mature n % mature n 6 100 1 9 100 1 10 100 1 100 1 11 100 2 100 1 14 100 1 100 1 15 100 2 100 3 16 100 2 100 1 17 100 1 14

Table 10. Proportion of mature lake whitefish in each length class from gill nets during the 2004 stock assessment at Gods Lake, Alberta. Fork length (mm) Males Females % mature n % mature n 450 100 1 500 100 1 100 1 550 100 6 100 4 600 100 1 100 3 650 100 1 4.4 Yellow perch Yellow perch accounted for 30.5% of the total catch (i.e., 68 individuals of the 223 fish captured). TCUE was 3.22 fish/100m 2 /24h. Mean CPUE for depth intervals ranged from 0.00 to 8.81 fish/100m 2 /24h with a whole lake mean of 1.69 fish/100m 2 /24h (Table 11). Table 11. Mean catch per unit effort (CPUE) of yellow perch in gill nets during the 2004 stock assessment at Gods Lake, Alberta. n = number of nets. Depth stratum (m) CPUE (fish/100m 2 /24h) Mean 95% CI (±) 0 5 0.71 0.86 4 5 10 8.81 1 10 15 4.29 54.53 2 15 20 0.00 3 >20 0.00 2 Whole lake 1.69 2.10 12 n Of the 68 yellow perch sampled where sex could be determined, 61.8% were females and 38.2% were males, resulting in a female:male sex ratio of 1.62:1. Male and female yellow perch length distributions are shown in Figure 11. Length of males ranged from 131 to 154 mm FL with a mean of 140.5 ± 6.54 mm (n = 26), while that of females ranged from 136 to 172 mm with a mean of 146.6 ± 8.51 mm (n = 42). 15

Catch per unit effort (fish/100m 2 /24h) 1.0 0.8 0.6 0.4 0.2 Males n = 26 Females n = 42 0.0 130 140 150 160 170 180 190 Fork le ngth (mm) Figure 11. Length distributions of male and female yellow perch captured in Gods Lake during the 2004 gill net survey. Males ranged in age from 2 to 4 y with a mean of 3.0 ± 0.46 y (n = 24) while age of females ranged from 2 to 5 y with a mean of 3.2 ± 0.52 y (n = 40; Figure 12). The overall mean age of the catch was 3.1 ± 0.51 y (n = 64). Catch per unit effort (fish/100m 2 /24h) 1.6 1.2 0.8 0.4 Males n = 24 Females n = 40 0.0 1 2 3 4 5 6 Age (y) Figure 12. Age distributions of male and female yellow perch captured in Gods Lake during the 2004 gill net survey. 16

When fitted to the von Bertalanffy growth function, male yellow perch showed an L of 142.9 mm FL and a growth coefficient K of 1.586 (Figure 13). Females showed an L of 158.2 mm FL and a growth coefficient K of 0.832 (Figure 13) thereby, attaining larger sizes and at a slower rate than males. 200 Fork length (mm) 150 100 50 0 0 1 2 3 4 5 6 Age (y) Figure 13. von Bertalanffy growth curve for male and female yellow perch from Gods Lake, Alberta, 2004. von Bertalanffy growth parameters: a) Males: L = 142.9, K = 1.586, n = 24; b) Females: L = 158.2, K= 0.832, n = 40). 4.5 Summary In Gods Lake, the walleye size distribution does not appear to be truncated at the minimum size limit (50 cm TL or 47.2 cm FL) for angler harvest. In deed, CPUE of fish greater than the 50 cm TL size limit does not appear to be substantially lower than the length classes below it. While truncation of the size distribution is not of concern, the age 7 cohort represent 62.2% of walleye captured (50.0% of females and 80.0% of males). Most female and some male walleye with mean FLs of 452.1 mm (479.5 mm TL) and 490.0 mm (518.9 mm TL), respectively, are susceptible to anger harvest. There is very little representation of age classes younger than age 7 suggesting very low recruitment of upcoming age classes. This highlights the vulnerability of walleye in Gods Lake. 17

Our data also suggests that the northern pike size distribution has not been truncated at the minimum size limit (i.e., 63 cm TL or 59.7 cm) for angler harvest. Catch per uniteffort of northern pike > 63 cm was also not greatly lower than that for smaller fish. Improved access (upgraded and new roads) into lakes in the Red Earth area, including Gods Lake, in recent years has raised concern about the potential for increased angling pressure. The results of the present study provide important baseline information that can be used by resource managers to quantify the effects of anticipated increases in angling pressure on sport fish population in Gods Lake. 18

5.0 LITERATURE CITED Mackay, W.C., G.R. Ash, and H.J. Norris. 1990. Fish ageing methods for Alberta. R.L. & L. Environmental Services Ltd. In association with Alberta Fish and Wildlife Division and University of Alberta, Edmonton, Alberta. 113 pp. von Bertalanffy, L. 1938. A quantitative theory of organic growth. Human Biology, 10: 181 213. 19

6.0 APPENDIX Appendix 1. Universal transverse mercator (UTM) coordinates (NAD 83, UTM zone 11) of gill net locations in Gods Lake, Alberta 2004. Depth interval (m) UTM Easting UTM Northing 664075.80 6300600.49 0 5 666096.20 6301107.70 664802.81 6299738.22 666358.26 6298368.74 5 10 666620.32 6298799.88 10 15 666265.27 6299163.38 664828.17 6301665.64 664819.71 6300194.72 15 20 665377.65 6299467.71 665529.81 6301090.80 >20 664684.46 6300727.29 665090.23 6301141.52 20

CONSERVATION REPORT SERIES

The Alberta Conservation Association acknowledges the following partner for their generous support of this project