Status of Sport Fish in Lesser Slave Lake, Alberta, 2005

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CONSERVATION REPORT

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Status of Sport Fish in Lesser Slave Lake, Alberta, 2005

Greg Fortier, Tyler Johns and Nathan Carruthers Alberta Conservation Association Bag 900‐26 Edmonton, Alberta, Canada T8S 1T4

Report Series Editor PETER AKU KELLEY J. KISSNER Alberta Conservation Association 59 Hidden Green NW #101, 9 Chippewa Rd Calgary, AB T3A 5K6 Sherwood Park, AB T8A 6J7

Conservation Report Series Type Data, Technical

ISBN printed: 978‐0‐7785‐6577‐2 ISBN online: 978‐0‐7785‐6578‐9 Publication No.: T/167

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., T. Johns, and N. Carruthers. 2005. Status of sport fish in Lesser Slave Lake, Alberta, 2005. Data Report, D‐2006‐009, produced by Alberta Conservation Association, Peace River, Alberta, Canada. 27 pp. + App.

Cover photo credit: David Fairless

Digital copies of conservation reports can be obtained from: Alberta Conservation Association #101, 9 Chippewa Rd Sherwood Park, AB T8A 6J7 Toll Free: 1‐877‐969‐9091 Tel: (780) 410‐1998 Fax: (780) 464‐0990 Email: info@ab‐conservation.com Website: www.ab‐conservation.com

EXECUTIVE SUMMARY

Lesser Slave Lake, one of the premier sport fishery lakes in Alberta, has experienced increases in angling pressure since 1985. Strategies used by Alberta Sustainable Resource Development (ASRD) to maintain or recover sport fisheries throughout the province include changes to fish size limit, daily bag limits, catch and harvest rates, and fishery closures. To evaluate the effectiveness of such management strategies for Lesser Slave Lake, we conducted gill netting (index netting) surveys on the lake from 12 to 18 September 2005 to quantify population metrics for four major sport fishes, walleye (Sander vitreus), northern pike (Esox lucius), lake whitefish (Corregonus clupeaformis) and yellow perch (Perca flavescens). This information is intended for use by fisheries managers to support management of the fishery at Lesser Slave Lake.

Overall, walleye and lake whitefish were the predominant sport fishes in the lake, constituting 43.0% and 32.7% of the total catch, respectively; northern pike (6.5%) and yellow perch (4.2%) occurred in low numbers. Total catch‐per‐unit‐effort (TCUE) for walleye and lake whitefish was 13.67 and 10.39 fish/100 m2/24 h, respectively, and was 2.06 and 1.33 fish/100 m2/24 h for northern pike and yellow perch, respectively.

Of 761 walleye sampled, 44.7% were females and 55.3% were males resulting in a female to male sex ratio of 0.81:1. Total lengths of males ranged from 127 to 655 mm with a mean (± SD) of 412.7 ± 52.70 mm (n = 421), whereas lengths of females ranged from 184 to 732 mm with a mean of 441.9 ± 76.04 mm (n = 340). Males ranged in age from 1 to 12 y with a mean of 7.5 ± 1.70 y (n = 152), whereas females ranged in age from 1 to 14 y with a mean of 7.5 ± 2.19 y (n = 147). Females reached maturity by age‐6 at 450 mm. In contrast, males reached maturity by age‐5 or by 400 mm. Based on von Bertalanffy growth estimates, walleye in Lesser Slave Lake should reach 43 cm TL in 8.3 years for males and 6.5 years for females.

Of 116 northern pike sampled, 68.1% were females and 31.9% were males resulting in a female to male sex ratio of 2.14:1. Total lengths of males ranged from 233 to 773 mm with a mean of 467.8 ± 101.79 mm (n = 37), whereas lengths of females ranged from 321 to 1,077 mm with a mean of 667.0 ± 175.87 mm (n = 79). Males ranged in age from 1 to 9 y with a mean of 3.4 ± 1.51 y (n = 37), whereas females ranged in age from 2 to 11 y with

ii a mean of 5.7 ± 2.47 y (n = 78). Females reach maturity by age‐3 or by 500 mm. In contrast, males reach maturity by age‐2 or by 350 mm. Based on von Bertalanffy growth estimates, northern pike in Lesser Slave Lake should reach 43 cm TL in 4.0 years.

Of the 466 lake whitefish sampled, 60.7% were females and 39.3% were males resulting in a female to male sex ratio of 1.55:1. Total lengths of males ranged from 243 to 642 mm with a mean of 515.7 ± 67.06 mm (n = 183), whereas lengths of females ranged from 131 to 630 mm with a mean of 513.8 ± 76.30 mm (n = 283). Males ranged in age from 2 to 13 y with a mean of 8.1 ± 2.19 y (n = 111), whereas females ranged in age from 2 to 13 y with a mean of 7.8 ± 2.29 y (n = 112). Both females and males reached maturity by age‐6 or by 500 mm.

Of the 65 yellow perch sampled, 83.1% were females and 16.9% were males resulting in a female to male sex ratio of 4.91:1. Total lengths of males ranged from 94 to 168 mm with a mean of 108.7 ± 20.56 mm (n = 11), whereas females ranged from 100 to 347 mm with a mean of 245.3 ± 77.59 mm (n = 54). Males ranged in age from 1 to 2 y with a mean of 1.1 ± 0.32 (n = 10), whereas females ranged from 1 to 10 y with a mean of 5.3 ± 2.74 y(n = 51). Females reached maturity by age‐3 or by 250 mm. All males were mature at age‐1 and 100 mm.

The results of this study provide important information that can be used by resource managers to quantify the effects of anticipated increases in angling pressure on sport fish population in Lesser Slave Lake, as well as to evaluate the effects of regulation changes.

Key words: walleye, northern pike, yellow perch, lake whitefish, gill net survey, catch‐per‐unit‐effort, Lesser Slave Lake, Alberta

iii

ACKNOWLEDGEMENTS

We thank Martin Brilling, Dave DeRosa, Brian Lucko, Jim Rosin, Don Schroeder, and John Tchir (Alberta Sustainable Resource Development) and Tom Ernst (Alberta Conservation Association, ACA) for assistance with field work. We also thank Troy Furukawa (ACA) for ageing fish samples and Paul Hvenegaard (ACA) for reviewing earlier drafts of this report.

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 2.0 STUDY AREA ...... 2 2.1 Description...... 2 3.0 MATERIALS AND METHODS...... 4 3.1 Sampling design ...... 4 3.2 Data collection...... 5 3.3 Data analysis ...... 5 4.0 RESULTS...... 7 4.1 Overall species composition...... 7 4.2 Walleye...... 8 4.3 Northern pike...... 13 4.4 Lake whitefish...... 17 4.5 Yellow perch...... 22 4.6 Summary...... 26 5.0 LITERATURE CITED...... 27 6.0 APPENDICES...... 28

LIST OF FIGURES

Figure 1. Map of Lesser Slave Lake showing gill net locations for 2005...... 3 Figure 2. Length distributions of male and female walleye captured in Lesser Slave Lake during the 2005 gill net survey...... 9 Figure 3. Age distributions of male and female walleye captured in Lesser Slave Lake during the 2005 gill net survey...... 10 Figure 4. von Bertalanffy growth curves for male and female walleye from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 11 Figure 5. Length distributions of male and female northern pike captured in Lesser Slave Lake during the 2005 gill net survey...... 14 Figure 6. Age distributions of male and female northern pike captured in Lesser Slave Lake during the 2005 gill net survey...... 14 Figure 7. von Bertalanffy growth curve for northern pike from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 15 Figure 8. Length distributions of male and female lake whitefish captured in Lesser Slave Lake during the 2005 gill net survey...... 18 Figure 9. Age distributions of male and female lake whitefish captured in Lesser Slave Lake during the 2005 gill net survey...... 19 Figure 10. von Bertalanffy growth curve for lake whitefish from the 2005 gill net survey at Lesser Slave Lake, Alberta ...... 20 Figure 11. Length distributions of male and female yellow perch captured in Lesser Slave Lake during the 2005 gill net survey...... 22 Figure 12. Age distributions of male and female yellow perch captured in Lesser Slave Lake during the 2005 gill net survey...... 23 Figure 13. von Bertalanffy growth curve for yellow perch from the 2005 gill net survey at Lesser Slave Lake, Alberta ...... 24

LIST OF TABLES

Table 1. Distribution of fish sampling effort using stratified sampling design in Lesser Slave Lake, Alberta in 2005...... 4 Table 2. Abundance of fish species captured in Lesser Slave Lake, Alberta during the 2005 gill net survey...... 7 Table 3. Total catch‐per‐unit‐effort (TCUE, fish/100 m2/24 h) of fish captured during the 2005 gill net survey at Lesser Slave Lake, Alberta...... 8 Table 4. Proportion of mature walleye in each age class from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 12 Table 5. Proportion of mature walleye in each length class from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 13 Table 6. Proportion of mature northern pike in each age class from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 16 Table 7. Proportion of mature northern pike in each length class from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 17 Table 8. Proportion of mature lake whitefish in each age class from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 21 Table 9. Proportion of mature lake whitefish in each length class from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 21 Table 10. Proportion of mature yellow perch in each age class from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 25 Table 11. Proportion of mature yellow perch in each length class from the 2005 gill net survey at Lesser Slave Lake, Alberta...... 25

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LIST OF APPENDICES

Appendix 1. Universal transverse mercator (UTM) coordinates of gill netting locations on Lesser Slave Lake, Alberta in 2005...... 28

viii

1.0 INTRODUCTION

High angling pressure on most fish populations in Alberta, including walleye (Sander vitreus) and northern pike (Esox lucius), has raised concerns about the sustainability of these sport fisheries in the province. Strategies implemented by Alberta Sustainable Resource Development (ASRD) to maintain or recover sport fisheries throughout the province include changes in angling regulations (see Berry 1995, 1999). Such regulation changes are made in response to changes in angling pressure, catch and harvest rates, as well as sport fish population parameters.

Lesser Slave Lake, one of the premier walleye lakes in Alberta, has experienced increases in angling pressure since 1985 (Buchwald 1985; Hildebrand 1986; Lucko 1999). Other major sport fishes in the lake include northern pike, lake whitefish (Corregonus clupeaformis) and yellow perch (Perca flavescens). Current regulations for Lesser Slave Lake state that each angler may keep one walleye ≥ 43 cm total length (TL) per day between 20 May and 15 June, and two from 16 June to 31 March (Alberta Sustainable Resource Development 2005). From 20 May to 31 March, three northern pike ≥ 55 cm TL may be kept each day. Daily bag limits are used for yellow perch (15 per day) and lake whitefish (10 per day). A closure to angling is in effect for the whole lake from 1 April to 19 May. In addition, a section of the lake which lies west of a line drawn from Shaw Point to Little Grassy Point is closed from 1 March to 15 June.

To evaluate the effectiveness of these management strategies, Alberta Conservation Association conducted gill netting (index netting) surveys on the lake from 12 to 18 September 2005 to quantify population metrics for walleye, northern pike, lake whitefish and yellow perch. This information is intended for use by fisheries managers to support management of the sport fishery at Lesser Slave Lake.

2.0 STUDY AREA

2.1 Description

Lesser Slave Lake is located approximately 250 km northwest of Edmonton (Figure 1). It is a eutrophic lake with a total surface area of 118,659 ha and an average depth of 11.4 m (Mitchell and Prepas 1990). It is comprised of two basins with an east‐west orientation. Many creeks and rivers flow into the lake, with much of the inflowing water entering from the west end via the South Heart River / Buffalo Bay system. The three largest inflows on the south shores of Lesser Slave Lake are the Driftpile, Swan and Assineau rivers. The single outflow is the Lesser Slave River located at the eastern end of the lake in the town of Slave Lake. A more detailed description of the physical, chemical and biological characteristics may be found in Mitchell and Prepas (1990).

Figure 1. Map of Lesser Slave Lake showing gill net locations for 2005. Inset is a map of Alberta showing the location of the lake within the province.

3.0 MATERIALS AND METHODS

3.1 Sampling design

Sampling sites were selected in a stratified random sampling design, with two depth strata (2 – 5 and 5 – 15 m) as outlined in the Fall Walleye Index Netting (FWIN) methodology. Timing of the gill net survey was determined by temperature; FWIN protocol requires netting to occur in the fall when water temperatures are between 15OC and 10OC. As such, netting was conducted between 12 September and 18 September 2005. Sampling effort was allocated proportionately to surface area of the two depth strata in each basin (Table 1). A total of 33 nets were deployed in the west basin and 17 in the east (Table 1; Appendix 1). Locations of individual nets are shown in Figure 1. Sample sites were randomly selected with a minimum distance of 500 m between all sites.

Nets were set perpendicular to the shoreline, where possible, without crossing depth intervals. The orientation of the largest or smallest mesh in relation to the shore was random. Set duration was as close to 24 hours as logistically possible.

Table 1. Distribution of fish sampling effort using stratified sampling design in Lesser Slave Lake, Alberta in 2005.

Depth stratum Proportion of lake Number of sites Basin (m) surface area (%) (nets) 2 ‐ 5 13.2 7 East 5 ‐ 15 20.3 10 2 ‐ 5 18.1 9 West 5 ‐ 15 48.4 24 2 ‐ 5 31.3 16 Total 5 ‐ 15 68.7 34

3.2 Data collection

Fork length (FL), TL, and weights were measured for all fish captured. Sex and maturity were determined through dissection of deceased fish. Ageing structures were removed from deceased fish and were aged following methods in Mackay et al. (1990). Ageing structures collected were the left pelvic fin rays for walleye, anal fin rays for yellow perch, cleithra for northern pike, and scales for lake whitefish. All data on sport fish as well as non‐sport fish species (number caught, FL, and weight) were entered into the provincial government Fisheries Management Information System (FMIS) maintained by ASRD.

3.3 Data analysis

3.3.1 Catch‐per‐unit‐effort

We quantified the relative abundance of each fish species caught at each sampling site as catch‐per‐unit‐effort (CPUE), with effort standardized to 100 m2 of net per 24‐h period (fish/100 m2/24 h). CPUE was reported as the mean ± 95% confidence interval (CI) of all sample sites for each species. Mean CPUE (± 95% CI) for each depth stratum was reported as well as whole lake overall mean. Whole lake total catch‐per‐unit‐effort (TCUE) was also reported (total number of fish/100 m2/24 h) for each species.

3.3.2 Maturity

Maturity was reported in terms of the age and length at which 50% of fish are likely to be mature. Total lengths were divided into 50‐mm size classes in order to maintain adequate sample sizes in each category.

3.3.3 Length and age distribution

Length‐frequency and age‐frequency distributions were used to examine the population structure of each species. Distributions of length were examined in relation to CPUE (y‐axis) and distributions of age were indicated as percent of the total sample.

We established relations between FL and TL for walleye, northern pike, lake whitefish, and yellow perch from fish captured in this study. In order to reduce sampling time TL

5 was not measured for all fish; thus, the relationship between FL and TL was established using data from fish where both were measured. The following linear regression models were fit for each species.

Walleye: TL = 1.048 FL + 7.267; (R2 = 0.998, n = 465). Northern pike: TL = 1.039 FL + 11.497; (R2 = 0.999, n = 74). Lake Whitefish: TL = 1.091 FL + 10.780; (R2 = 0.992, n = 38). Yellow perch: TL = 1.040 FL + 0.874; (R2 = 0.999, n = 29).

3.3.4 Growth rate

Growth rate of each species was examined using the von Bertalanffy growth function (von Bertalanffy 1938):

‐K (t‐ )t L = (1L ‐ 0 )e t ∞ where:

Lt = length at age t

L∞ = the asymptote or final maximum size, K = the rate at which the growth curve approaches the asymptote, and t = age

t0 = a time scaler, the hypothetical time when the fish was size zero

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 a lower L∞. Due to small sample sizes of small fish t0 was fixed at zero to reduce bias in the growth function. To account for sexual variation in growth rate, age and length data were fitted for males and females separately.

4.0 RESULTS

4.1 Overall species composition

Overall, walleye and lake whitefish were the predominant fish species constituting 43.0% and 32.7% of the total catch respectively; northern pike (6.5%) and yellow perch (4.2%) occurred in low numbers (Table 2). Corresponding TCUEs were 13.67 and 10.39 fish/100 m2/24 h for walleye and lake whitefish, respectively, and 2.06 and 1.33 fish/100 m2/24 h for northern pike and yellow perch, respectively (Table 3). Lake whitefish was the most abundant species in the 2 ‐ 5 m depth, constituting 66% of the catch in this stratum, whereas walleye was the most abundant species in the 5 ‐ 15 m stratum, constituting 56% of the catch. Other species encountered include cisco (Coregonus artedi), longnose sucker (Catostomus catostomus), white sucker (Catostomus commersoni), spot tail shiner (Notropis hudsonius), mountain whitefish (Prosopium willimsoni), and burbot (Lota lota), all of which made up less than 14% of the total catch (Table 2).

Table 2. Abundance of fish species captured in Lesser Slave Lake, Alberta during the 2005 gill net survey.

Number Captured Percent of Species 2 ‐ 5 m 5 ‐ 15 m Strata total catch stratum stratum combined Walleye 86 685 771 43.0 Lake whitefish 373 213 586 32.7 Northern pike 64 52 116 6.5 Yellow perch 17 58 75 4.2 Others species1 23 222 245 13.7 Total 563 1230 1793 100 1Include cisco, longnose sucker, white sucker, spottail shiner, mountain whitefish, and burbot.

Table 3. Total catch‐per‐unit‐effort (TCUE, fish/100 m2/24 h) of fish captured during the 2005 gill net survey at Lesser Slave Lake, Alberta.

TCUE (fish/100 m2/24 h) Species 2 ‐ 5 m 5 ‐ 15 m Strata Stratum stratum Combined Walleye 4.84 17.72 13.67 Lake whitefish 21.00 5.51 10.39 Northern pike 3.60 1.35 2.06 Yellow perch 0.96 1.50 1.33

4.2 Walleye

Mean (± 95% CI) CPUE of walleye was 4.92 ± 1.9 fish/100 m2/24 h for the 2 ‐ 5‐m stratum and 18.83 ± 3.02 fish/100 m2/24 h for the 5 ‐ 15‐m stratum resulting in a whole‐lake CPUE of 14.38 ± 2.81 fish/100 m2/24 h.

Of the 761 walleye sampled where sex could be determined, 44.7% (n = 340) were females and 55.3% (n = 421) were males resulting in a female:male sex ratio of 0.81:1. Male and female walleye length distributions are shown in Figure 2. Lengths of males ranged from 127 to 655 mm with a mean (± SD) of 412.7 ± 52.70 mm (n = 421), whereas lengths of females ranged from 184 to 732 mm with a mean of 441.9 ± 76.04 mm (n = 340).

2.5 Males, n = 431

2 Females, n = 340 effort ‐ 1.5 ‐ unit

per 1 ‐

(fish/100m^2/24h) 0.5 Catch

0 120 180 240 300 360 420 480 540 600 660 720 Total Length (mm)

Figure 2. Length distributions of male and female walleye captured in Lesser Slave Lake during the 2005 gill net survey.

Males ranged in age from 1 to 12 y with a mean of 7.5 ± 1.70 y (n = 152), whereas females ranged in age from 1 to 14 y with a mean of 7.5 ± 2.19 y (n = 147) (Figure 3). Both male and female age distributions show normality with the largest age class being 8 y. Age‐8 males had a mean length of 412.6 mm ± 25.70 mm (n = 66) and age‐8 females had a mean length of 444.3 mm ± 29.70 mm (n = 54).

50 45 Males, n = 152 40 Females, n = 147 35 (%)

Total 25

20 15 Percent 10 5 0 1234567891011121314

Age (y)

Figure 3. Age distributions of male and female walleye captured in Lesser Slave Lake during the 2005 gill net survey.

The theoretical maximum length (L∞) of male walleye was 460.2 mm FL with a growth

coefficient (K) of 0.328 (n = 151) (Figure 4). The theoretical maximum length (L∞) of female walleye was 518.8 mm FL with a growth coefficient K of 0.272 (n = 143) (Figure 4). On average, females should reach 43 cm TL between six and seven years, whereas males take eight to nine years to attain this size.

600

500

400 Min. harvest length (mm)

300 Length Males Male growth curve Total 200 Females Female growth curve 100

0 012345678910111213141516

Age (y)

Figure 4. von Bertalanffy growth curves for male and female walleye from the 2005 gill net survey at Lesser Slave Lake, Alberta. von Bertalanffy growth parameters: Males: L∞ = 460.2, K = 0.328, n = 151; Females: L∞ = 518.8, K = 0.272, n = 143.

The proportion of mature walleye in each age and length class is shown in Table 4 and 5. Half (50%) of females are mature by age‐6 or 450 mm, whereas 50% of males reach maturity by age‐5 or earlier and by 400 mm.

Table 4. Proportion of mature walleye in each age class from the 2005 gill net survey at Lesser Slave Lake, Alberta.

Age Males Females (y) % mature n % mature n 1 0 1 0 2 2 0 4 0 2 3 0 1 0 6 4 100 2 0 5 5 100 6 37.5 8 6 100 15 63.6 11 7 100 33 66.7 27 8 98.5 66 70.4 54 9 100 12 66.7 12 10 100 8 75.0 12 11 100 3 100 4 12 100 1 100 2 13 ‐ ‐ ‐ ‐ 14 ‐ ‐ 100 2

Table 5. Proportion of mature walleye in each length class from the 2005 gill net survey at Lesser Slave Lake, Alberta.

Total length Males Females (mm) % mature n % mature n 150 0 1 ‐ ‐ 200 0 2 0 4 250 0 6 0 2 300 14.3 7 0 8 350 0 3 0 16 400 98.5 132 21.1 38 450 99.5 197 60.5 129 500 100 53 87.9 91 550 94.7 19 81.8 33 600 ‐ ‐ 90.0 10 650 ‐ ‐ 100 2 700 100 1 100 4 750 ‐ ‐ 100 3

4.3 Northern pike

Mean (± 95% CI) CPUE of northern pike was 3.66 ± 1.24 fish/100 m2/24 h for the 2 ‐ 5 m stratum and 1.46 ± 0.56 fish/100 m2/24 h in the 5 – 15 m stratum resulting in a whole‐ lake CPUE of 2.16 ± 0.60 fish/100 m2/24 h.

Of the 116 northern pike sampled where sex could be determined, 68.1% (n = 79) were females and 31.9% (n = 37) were males resulting in a female:male sex ratio of 2.14:1. Male and female northern pike length distributions are shown in Figure 5. Lengths of males ranged from 233 to 773 mm with a mean (± SD) of 467.8 ± 101.79 mm (n = 37), whereas lengths of females ranged from 321 to 1,077 mm with a mean of 667.0 ± 175.87 mm (n = 79).

0.14 Males, n = 37 0.12 Females, n = 79 0.1 ‐ effort 0.08 unit ‐ 0.06 per ‐ 0.04 (fish/100m^2/24h) Catch 0.02 0 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 Total Length (mm)

Figure 5. Length distributions of male and female northern pike captured in Lesser Slave Lake during the 2005 gill net survey.

Males ranged in age from 1 to 9 y with a mean of 3.35 ± 1.51 y (n = 37), whereas females ranged in age from 2 to 11 y with a mean of 5.7 ± 2.47 y (n = 78) (Figure 6). There was no prominent age class in either the male or female distribution.

40 Males, n = 37 35 Females, n = 78 30 (%) 25

Total 20

Percent 10

5 0 123456789101112

Age (y)

Figure 6. Age distributions of male and female northern pike captured in Lesser Slave Lake during the 2005 gill net survey.

Male and female length and age data were combined to estimate one growth curve due to small sample size of males. The theoretical maximum length (L∞) of northern pike was 1100.0 mm FL with a growth coefficient K of 0.175 (Figure 7).

1200

1000

800 Min. harvest (mm) length 600 ≤ 2004

Length 2005

Total 400

200 Males and Females growth curve

0 0123456789101112

Age (y)

Figure 7. von Bertalanffy growth curve for northern pike from the 2005 gill net survey at Lesser Slave Lake, Alberta. von Bertalanffy growth parameters: L∞ = 1100.0, K = 0.175, n = 115. Estimated age at new (2005) and previous (≤ 2004) angling regulation minimum harvestable lengths are shown.

The proportion of mature northern pike in each age and length class is shown in Tables 6 and 7. The data suggest that 50% of males were mature by age‐2 or 350 mm, whereas 50% of females were mature by age‐3 or before 500 mm.

Table 6. Proportion of mature northern pike in each age class from the 2005 gill net survey at Lesser Slave Lake, Alberta.

Age Males Females (y) % mature n % mature n 1 33.3 3 ‐ ‐ 2 75 8 0 5 3 100 8 72.7 11 4 100 14 88.2 17 5 100 2 100 9 6 100 1 100 1 7 ‐ ‐ 100 15 8 ‐ ‐ 100 11 9 100 1 100 4 10 ‐ ‐ ‐ ‐ 11 ‐ ‐ 100 5

Table 7. Proportion of mature northern pike in each length class from the 2005 gill net survey at Lesser Slave Lake, Alberta.

Total length Males Females (mm) % mature n % mature n 250 0 1 ‐ ‐ 300 0 1 ‐ ‐ 350 66.7 3 0 1 400 66.7 3 ‐ ‐ 450 100 6 0 5 500 100 10 66.7 6 550 100 5 94.1 17 600 100 7 87.5 8 650 ‐ ‐ 100 5 700 ‐ ‐ 100 1 750 ‐ ‐ 100 3 800 100 1 100 9 850 ‐ ‐ 100 13 900 ‐ ‐ 100 4 950 ‐ ‐ 100 1 1000 ‐ ‐ 100 4 1050 ‐ ‐ 100 1 1100 ‐ ‐ 100 1

4.4 Lake whitefish

Mean (± 95% CI) CPUE of lake whitefish was 21.49 ± 4.43 fish/100 m2/24 h for the 2 – 5 m stratum and 5.98 ± 2.68 fish/100 m2/24 h for the 5 – 15 m stratum resulting in a whole‐ lake CPUE of 10.94 ± 3.04 fish/100 m2/24 h.

Of 466 lake whitefish sampled where sex could be determined, 60.7% (n = 283) were females and 39.3% (n = 183) were males resulting in a female:male sex ratio of 1.55:1. Male and female lake whitefish length distributions are shown in Figure 8. Lengths of males ranged from 243 to 642 mm with a mean (± SD) of 515.7 ± 67.06 mm (n = 183), whereas lengths of females ranged from 131 to 630 mm with a mean of 245.3 ± 77.59 mm (n = 54).

1.4 Males, n = 192

1.2 Females, n = 283 1 effort ‐ 0.8 ‐ unit 0.6 per ‐ 0.4 (fish/100m^2/24h) Catch 0.2 0 140 180 220 260 300 340 380 420 460 500 540 580 620 660 Total Length (mm)

Figure 8. Length distributions of male and female lake whitefish captured in Lesser Slave Lake during the 2005 gill net survey.

Males ranged in age from 2 to 13 y with a mean of 8.1 ± 2.19 y (n = 112), whereas females ranged in age from 2 to 13 y with a mean of 7.8 ± 2.29 y (n = 112) (Figure 9). Both male and female age distributions appear to follow a normal distribution with no predominant age classes.

30 Males, n = 112 25 Females, n = 112 (%) 20

Totals 15

10 Percent 5

0 12345678910111213

Age (y)

Figure 9. Age distributions of male and female lake whitefish captured in Lesser Slave Lake during the 2005 gill net survey.

The theoretical maximum length (L∞) of male lake whitefish was 589.9 mm with a growth coefficient (K) of 0.271 (n = 147) ( Figure 10). The theoretical maximum length of female lake whitefish was 589.8 mm with a growth coefficient of 0.276 ( Figure 10), thereby showing a virtually identical growth curve to males.

700

600

500 (mm) 400 Length 300 Female growth curve Total 200 Male growth curve Males 100 Females

0 0123456789101112

Age (y)

Figure 10. von Bertalanffy growth curve for lake whitefish from the 2005 gill net survey at Lesser Slave Lake, Alberta. von Bertalanffy growth parameters: Males: L∞ = 589.9, K = 0.271, n = 147; Females: L∞ = 589.8, K = 0.276, n = 149

By age‐6 and 500 mm, 50% of male and female lake whitefish had reached maturity. The proportion of mature lake whitefish in each age and length class is shown in Tables 8 and 9.

Table 8. Proportion of mature lake whitefish in each age class from the 2005 gill net survey at Lesser Slave Lake, Alberta.

Age Males Females (y) % mature N % mature n 2 0 3 0 5 3 20.0 5 0 5 4 0 4 16.7 6 5 33.3 3 25.0 4 6 73.3 15 100 12 7 100 24 86.4 22 8 100 23 97.6 41 9 100 28 100 28 10 100 28 100 16 11 92.9 14 100 10 12 100 1 ‐ ‐ 13 100 1 100 2

Table 9. Proportion of mature lake whitefish in each length class from the 2005 gill net survey at Lesser Slave Lake, Alberta.

Total length Males Females (mm) % mature N % mature n 150 ‐ ‐ 100 1 200 ‐ ‐ ‐ ‐ 250 0 1 0 4 300 0 4 0 7 350 14.3 7 0 8 400 0 3 37.5 8 450 25.0 12 25.0 16 500 100 38 89.5 38 550 99.0 97 98.1 161 600 100 64 100 90 650 100 4 100 7

4.5 Yellow perch

Mean (± 95% CI) CPUE of yellow perch was 0.94 ± 0.77 fish/100 m2/24 h (n = 16) for the 2 – 5 m stratum and 1.56 ± 0.59 fish/100 m2/24 h (n = 34) in the 5 – 15 m stratum resulting in a whole‐lake CPUE of 1.36 ± 0.46 fish/100 m2/24 h (n = 50).

Of 65 yellow perch sampled where sex could be determined, 83.1% (n = 54) were females and 16.9% (n = 11) were males resulting in a female:male sex ratio of 4.9:1. Male and female yellow perch length distributions are shown in Figure 11. Lengths of males ranged from 94 to 168 mm with a mean (±SD) of 108.7 ± 20.56 mm (n = 11), whereas lengths of females ranged from 100 to 347 mm with a mean of 245.3 ± 77.59 mm (n = 54).

0.25 Males, n = 11

0.2 Females, n = 54 effort ‐ 0.15 unit ‐

per 0.1 ‐ (fish/100m^2/24h)

Catch 0.05

0 100 120 140 160 180 200 220 240 260 280 300 320 340 360 Total Length (mm)

Figure 11. Length distributions of male and female yellow perch captured in Lesser Slave Lake during the 2005 gill net survey.

Males ranged in age from 1 to 2 y with a mean of 1.1 ± 0.32 y (n = 10), whereas females ranged in age from 1 to 10 y with a mean of 5.3 ± 2.74 y (n = 51) (Figure 12).

100 90 Males, n = 10 80 Females, n = 51 70 (%)

Total 50

40 30 Percent 20 10 0 123456789101112

Age (y)

Figure 12. Age distributions of male and female yellow perch captured in Lesser Slave Lake during the 2005 gill net survey.

Male and female length and age data were combined to estimate one growth curve due

to small sample size of males. The theoretical maximum length (L∞) of yellow perch was 327.8 mm FL with a growth coefficient (K) of 0.343 (Figure 13).

400

350

300

250 (mm)

200 Length

150 Total

100

Males and Females 50 growth curve

0 0123456789101112

Age (y)

Figure 13. von Bertalanffy growth curve for yellow perch from the 2005 gill net survey at Lesser Slave Lake, Alberta. von Bertalanffy growth parameters: L∞ = 327.8, K = 0.343, n = 61

The proportion of mature yellow perch in each age and length class is shown in Tables 10 and 11. All male yellow perch sampled were mature and the data suggest that the point of 50% maturity for females occurs at around age‐3 and before 250 mm.

Table 10. Proportion of mature yellow perch in each age class from the 2005 gill net survey at Lesser Slave Lake, Alberta.

Age Males Females (y) % mature n % mature n 1 100 9 0 6 2 100 1 0 7 3 ‐ ‐ 100 2 4 ‐ ‐ 100 6 5 ‐ ‐ 100 2 6 ‐ ‐ 100 4 7 ‐ ‐ 100 15 8 ‐ ‐ 100 4 9 ‐ ‐ 100 2 10 ‐ ‐ 100 3

Table 11. Proportion of mature yellow perch in each length class from the 2005 gill net survey at Lesser Slave Lake, Alberta.

Total length Males Females (mm) % mature n % mature n 100 100 4 0 1 150 100 6 0 9 200 100 1 0 4 250 ‐ ‐ 100 5 300 ‐ ‐ 100 18 350 ‐ ‐ 100 17

4.6 Summary

In Lesser Slave Lake, the size distribution of walleye does not suggest a truncation at the minimum size limit of 43 cm TL. Instead, the CPUE values for fish larger than 43 cm showed a steady decline as fish length increases.

The minimum size limit for northern pike was reduced from ≥ 63 cm TL in 2004 to ≥ 55 cm TL in 2005. Our data suggest that angler‐mediated mortality of northern pike may be minimal and has not truncated the size distribution. There was strong representation of northern pike above both the 2004 minimum size limit (≥ 63 cm TL) and the 2005 limit (≥ 55 cm TL). There was significant representation of large class sizes beginning around 740 mm. Both male and female lake whitefish showed relatively normal length distributions. Female yellow perch showed a bimodal length distribution, whereas males were not well represented.

The results of the present study provide important information that can be used by resource managers to quantify the effects of changes in angling regulations on Lesser Slave Lake.

5.0 LITERATURE CITED

Alberta Sustainable Resource Development. 2005. 2005 Alberta Guide to Sportfishing Regulations 2005. Sport Scene Publication, Edmonton, Alberta. 92 pp.

Berry, D.K. 1995. Alberta’s walleye management and recovery plan. Alberta Environmental Protection, Natural Resources Service, Edmonton, Alberta. 32 pp.

Berry D.K. 1999. Alberta’s northern pike management and recovery plan. Alberta Environmental Protection, Natural Resources Service, Edmonton, Alberta. 22 pp.

Buchwald, V. 1985. Lesser Slave Lake – 1985 summer creel survey. Alberta Energy and Natural Resources, Fish and Wildlife Division, Slave Lake, Alberta. 11 pp.

Hildebrand, L., and G. Ash. 1986. A summer creel survey of the west end of Lesser Slave Lake, 1986. R.L. & L. Environmental Services Ltd. 46 pp. + App.

Lucko, B. 1999. Lake monitoring program 1999 results Lesser Slave Lake. Technical report. Prepared by Alberta Conservation Association, Peace River, Alberta. 59 pp.

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.

Mitchell, P., and E. Prepas. 1990. Atlas of Alberta lakes. University of Alberta Press, Edmonton, Alberta, Canada. 675 pp.

von Bertalanffy, L. 1938. A quantitative theory of organic growth. Human Biology 10: 181‐213.

6.0 APPENDICES

Appendix 1. Universal transverse mercator (UTM) coordinates (NAD 83, UTM zone 11) of gill netting locations on Lesser Slave Lake, Alberta in 2005.

East Basin West Basin Depth UTM UTM Depth UTM UTM Stratum Easting Northing Stratum Easting Northing 639567 6133072 560705 6148455 627642 6137282 586208 6132165 603532 6144975 561653 6141911 2‐5 m 641248 6137766 561357 6148253 611381 6138481 2‐5 m 585141 6132726 639480 6130716 563442 6141851 638820 6132025 580818 6140686 636559 6141806 566114 6141950 639717 6135136 574818 6139547 625266 6154128 571993 6150824 635844 6136436 585101 6150008 635720 6142970 578292 6150518 5‐15 m 634566 6143802 584193 6140588 615113 6154400 592634 6148415 629382 6138971 572937 6143955 604518 6146887 572319 6142840 631079 6139765 599049 6144200 593439 6145603 576769 6147800 595451 6145515 589382 6135352 5‐15 m 563848 6147791 594457 6140724 577502 6144741 570541 6142451 565436 6147594 571186 6142121 591177 6135970 579583 6151582 599582 6147017 598396 6146553 564930 6148443 567128 6148837

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