Angler Survey and Walleye Abundance in Fawcett Lake, Alberta, 2003

Transcription

1 Angler Survey and Walleye Abundance in Fawcett Lake, Alberta, 2003 CONSERVATION REPORT SERIES

2 The Alberta Conservation Association is a Delegated Administrative Organization under Alberta s Wildlife Act. CONSERVATION REPORT SERIES 25% Post Consumer Fibre When separated, both the binding and paper in this document are recyclable

3 Angler Survey and Walleye Abundance in Fawcett Lake, Alberta, 2003 Greg Fortier, John Tchir, and Lorraine Sawdon Alberta Conservation Association Bag , Peace River Alberta, Canada T8S 1T4

4 Report Series Editor PETER AKU P.O. Box Baker Centre Postal Outlet Edmonton, AB, T5J 4M9 Conservation Report Series Type Data, Technical ISBN printed: ISBN online: Publication No.: T/137 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., J. Tchir, and L. Sawdon Angler survey and walleye abundance in Fawcett Lake, Alberta, Data Report, Report code number D , produced by Alberta Conservation Association, Peace River, Alberta, Canada. 15 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: Tel: (780) Fax: (780) info@ab conservation.com Website: conservation.com i

5 EXECUTIVE SUMMARY Walleye (Sander vitreus) populations in Alberta experience considerable fishing pressure that has resulted in the overexploitation of most populations. To aid in their recovery Alberta Sustainable Resource Development (ASRD) initiated a province wide management strategy, the Alberta Walleye Management Recovery Plan (WMRP), in The current study was conducted to assess the status of the walleye fishery in Fawcett Lake as part of the province wide walleye recovery program. Although Fawcett Lake is popular among recreational fishermen, limited data exist on the fish populations or fishing pressure on the lake. The main objectives of our study were to 1) estimate the population size and structure of walleye in the lake, and 2) estimate angling pressure on the walleye population. A mark recapture study was used to estimate the walleye population size while an access based creel survey was used to estimate angling pressure, total catch and harvest, and biological characteristics of walleye. Total length (TL) of walleye, from trap netting and angling, ranged from 209 to 744 mm. Of the 5814 fish captured in traps 4103 were males and 1711 were females, resulting in a sex ratio of 2.4 males to 1.0 female. Mean (±SD) size of marked fish was ± 34.8 mm TL (n = 4103) for males and ± 41.9 mm TL (n = 1711) for females. Mean TL of angler harvested fish was ± 31.8 mm (n = 17), 7.9% of which were of sub legal size (TL < 430 mm). Overall, age of walleye ranged from 4 to 18 y but the population was dominated by ages 5 to 13 fish. Mean age of angler harvested fish was 9.9 ± 2.01 y (n = 243). Based on maximum likelihood estimates (MLE), the population of walleye > 300 mm TL was 64,020 (95% CI = 49,020 96,390) with an associated density of 18.7 fish/ha (95% CI = ). Maximum likelihood estimates from the creel survey indicated that anglers exerted a fishing pressure of 23,325 angler h (95% CI = 22,400 30,575) or 7.4 h/ha (95% CI = ) from 16 May to 1 September The mean daily catchper unit effort (CPUE, #fish/angler h) for walleye was (95% CI = ) while the harvest per unit effort (HPUE, #fish kept/angler h) was (95% CI = ). An estimated 22,800 walleye were caught (95% CI = 19,425 27,825) and 1,710 harvested (95% CI = 1,390 2,150). ii

6 Majority (75.4%) of the 2061 anglers surveyed targeted walleye and used baits (77.3%), barbed hooks (83.6%) and depth sounders (54.9%). Most of the anglers (84.6%) that visited Fawcett Lake resided in Edmonton and surrounding area. Key words: Fawcett Lake, walleye, mark-recapture, creel survey, length distribution, population size, angler-harvest, fishing pressure. iii

7 ACKNOWLEDGEMENTS We thank Alberta Sustainable Resource Development staff for their field support. We also thank Jean and Roy Ahlstrom from Anchor Inn Resort, Gerald and Verla Niehaus from Fawcett Lake Resort, for providing accommodations during the creel survey. iv

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9 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 STUDY AREA MATERIALS AND METHODS Walleye population estimate Creel survey Data analysis RESULTS Water conditions during spawning run Walleye abundance and population structure Creel survey Summary LITERATURE CITED APPENDICES v

10 LIST OF FIGURES Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Map of Fawcett Lake, Alberta, showing the 2003 creel survey access points and trap locations on the inflow Mink River... 3 Fluctuations in water levels and mean daily temperature of the Mink River, Alberta, 9 20 May Mean daily water temperature and number of walleye caught in the upper and lower trap nets from 8 20 May 2003 in Mink River, Alberta... 8 Total length distributions of male and female walleye caught in upper and lower traps, in the Mink River, Alberta, from 8 20 May Maximum likelihood estimates of population size and density of walleye (> 300 mm TL) in Fawcett Lake, Albert, as determined by mark recapture methods in Percentage of anglers interviewed who reside in various locations throughout Alberta, Total length distribution of walleye caught by anglers during the creel survey and test angling in Fawcett Lake, Alberta, Age distribution of walleye caught by anglers during the creel survey and test angling in Fawcett Lake, Alberta, von Bertalanffy growth curve of walleye sampled from Fawcett Lake, Alberta, vi

11 LIST OF TABLES Table 1. Observed and maximum likelihood estimates (MLE) of number of walleye caught and harvested by anglers during the 2003 creel survey on Fawcett Lake, Alberta vii

12 LIST OF APPENDICES Appendix 1. Locations of trap nets in the Mink River during the marking event of the 2003 Fawcett Lake walleye population estimate, Appendix 2. Flow chart outlining the process used to estimate parameters from the angler survey at Fawcett Lake, viii

13 1.0 INTRODUCTION Walleye (Sander vitreus) is one of the most popular sport fishes in the province of Alberta. Because of its popularity walleye populations in Alberta experience considerable fishing pressure that has resulted in the overexploitation of most populations (Berry 1995). To aid in the recovery of walleye populations the Alberta Sustainable Resource Development (ASRD) initiated a province wide management strategy, Alberta s Walleye Management Recovery Plan (WMRP), in 1995 (Berry 1995). The current study was conducted to assess the status of the walleye fishery in Fawcett Lake as part of the province wide walleye recovery program. Limited data exist on the population size or fishing pressure on walleye in Fawcett Lake. For example, during a 1997 study on walleye, population estimates were limited to the outflow Mink River only while creel surveys were conducted at the east end of the lake only (Potter 1998). To address these limitations, our study used a creel survey conducted at multiple access points and a whole lake mark recapture survey to estimate population size. The main objectives of our study were to: 1. Estimate the number of adult walleye in Fawcett Lake. 2. Determine angling pressure, effort, and harvest of walleye during the summer, Determine biological parameters (size, age, condition, growth) of walleye harvested. 2.0 STUDY AREA Fawcett Lake is a 3416 ha lake located approximately 100 km east of Slave Lake and can be accessed by Highway 2 and a gravel road through the town of Smith (Figure 1). It has two basins, a smaller north basin, connected by a narrows to a larger south basin. The Mink River, located on the east side of the northern basin is the major inflow to the lake that also serves as the spawning ground for walleye during the spring. The outflow, Fawcett River, is located in the north west corner of the lake (Figure 1). Two campgrounds, Fawcett Lake Resort on the east end, and Anchor Inn Resort on the west 1

14 end, are located on the lake. In addition, a small community, Broken Paddle, is situated on the south east shore. There are numerous boat launches on the lake, including one at each campground. 2

15 Figure 1. Map of Fawcett Lake, Alberta, showing the 2003 creel survey access points (Fawcett Lake Resort and Anchor Inn Resort) and trap locations on the inflow Mink River. 3

16 3.0 MATERIALS AND METHODS 3.1 Walleye population estimate A mark recapture study was used to estimate the size of the walleye population in Fawcett Lake. Two trap nets were set in the Mink River from 8 to 20 May 2003 to capture spawning walleye migrating upstream from Fawcett Lake. The trap nets were set approximately 1 km apart, starting from the confluence of the Mink River to Fawcett Lake. A maximum minimum thermometer and a temperature data logger were installed in the Mink River and used to monitor and record fluctuations of water temperature during the spawning run. The nets were set when the water reached 4.5 O C, the approximate temperature at which walleye spawning occurs (Nelson and Paetz 1992). Both traps were visited daily for 12 consecutive days. All walleye caught were removed, sexed, measured, and tagged with T bar anchor Floy tags and released upstream of the traps. The upstream and downstream traps were checked in the morning and afternoon, respectively. Trap locations were georeferenced using a handheld Garmin GPS unit (Appendix 1). Walleye were recaptured during a stock assessment gill netting survey conducted on the lake from 2 to 5 September 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 mesh) and connected in sequential order. Sampling sites were selected in a stratified random fashion using three depth strata, set at 5 m intervals. A total of 18 gill nets were deployed and their locations were geo reference using a Garmin 12 handheld GPS unit. Sample sites were randomly selected with a minimum distance of 500 m between sites using Arcview GIS version 3.1. 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 in relation to the shore was random. 4

17 3.2 Creel survey The creel survey on Fawcett Lake was conducted from 16 May to 1 September Each survey session lasted 10 days and included all weekends, with a 4 day interval between sessions. Five days of each session were spent on either end of the lake (Anchor Inn Resort on the west and Fawcett Lake Resort on the east); initiations of the 10 day shifts were alternated between sites to ensure equitable distribution of effort. Boat counts were conducted to account for anglers using access sites other than the ones surveyed. Counts were stratified by time of day as AM (morning = 1000 to 1300) and PM (evening = 1645 to 2345), 60% of the counts were conducted in the PM as more people angled in the evenings than in the morning. Twenty six days were randomly selected for PM boat counts and 18 were selected for AM counts for a total of 44 boat counts. Creel technicians interviewed all anglers returning to access site upon completion of their fishing trips. Data recorded included length of fishing trip, number of fish harvested, and released (legal and sub legal), the fish species targeted, electronics used, use of bait and barbed hooks, and angler residence. When possible, creel clerks collected biological data including, fork length (FL), total length (TL), weight, sex, stomach contents, and ageing structures from fish harvested by anglers. Left pelvic fin rays and operculum were used to age walleye according to Mackay et al. (1990). 3.3 Data analysis Boat counts were used to determine a ratio of use (ROU) for each of the surveyed access sites. The ROU was used to extrapolate the information, collected from anglers at the access sites, to all anglers on the lake. Ratio of use (ROU) = # boats from boat count # boats using surveyed site A binomial maximum likelihood estimate (MLE) (Haddon 2001) was used to estimate the adult walleye population size from trapping and gill netting events. An MLE was 5

18 generated using the number of marked, captured, and recaptured walleye. The mode of the distribution and associated 97.5% confidence intervals (97.5% CI) were used as estimates of population size following Haddon (2001) and Sullivan (2004). Bootstrap methods (Haddon 2001) were used to calculate the maximum likelihood estimates for the following parameters: number of angler interviews, angling effort, catch and harvest of walleye, and ROU. Samples were stratified by weekdays (Monday Thursday) and weekend days (Friday Sunday, including statutory holidays). Daily totals of each parameter were bootstrapped for each day type, generating a distribution of 10,000 bootstrap samples. The distributions from bootstrapping were used to extrapolate to days that were not surveyed. A flow chart describing the bootstrapping procedure is presented in Appendix 2. Daily catch per unit effort (CPUE) was calculated using the total number of fish caught for a give day divided by the total effort (daily total of angler hours). Total catch perunit effort (TCUE) was calculated from the total observed catch divided by the total number of angler hours observed during the entire study period. Fish growth rate was described using the von Bertalanffy (1938) growth model: L t = L (1 e K (t t 0 ) ) where: L t = length at age t L = the asymptote or final maximum size K = the rate at which the growth curve approaches the asymptote t = age t 0 = 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. 6

19 4.0 RESULTS 4.1. Water conditions during spawning run Water levels fluctuated very little (< 3 cm/d) throughout the course of the spawning run (Figure 2). Highest recorded depth of the Mink River was 32 cm on 17 May, and the lowest was 27 cm on 20 May. Water temperature ranged from 2.5 O C on 8 May to 12.0 O C on 13 May (Figure 2). Water level (cm) Water lev el Water tem p eratu re Average water temperature ( o C) Date Figure 2. Fluctuations in water levels and mean daily temperature of the Mink River, Alberta, 9 20 May Walleye abundance and population structure A total of 6115 walleye were captured in both trap nets over the 12 day period from 8 to 20 May. Overall, catch was higher in the upper trap net (n = 3694) than in the lower trap (n = 2421). Catch in both trap nets were highest from 12 to 18 May, when mean daily water temperatures ranged 8 11 O C (Figure 3). 7

20 Figure 3. Number of walleye captured Date Upper trap Lower trap Mean daily water temperature and number of walleye caught in the upper and lower trap nets from 8 20 May 2003 in Mink River, Alberta Water temperature ( o C) Male walleye were more prevalent than females throughout the study period. The upper trap captured 2674 males and 659 females, resulting in a male to female sex ratio of 4.1:1. In the lower trap 1433 males and 782 females were captured for a 1.8:1 sex ratio. Where maturity could be determined, 54% of females were immature, 34% were ripe and 12% were spent (n = 1440). In contrast, 98% of males were ripe, 2% were spent and < 1% were immature (n = 4103). Total length of male walleye captured in the upper and lower trap nets, ranged from 308 to 616 mm (mean ± SD = ± mm; n = 4103) and females from 301 to 744 mm (mean = ± mm; n = 1440) (Figure 4). 8

21 Relative abundance (%) M a le s (n = 4103) Fem ales (n = 1440) Total len g th (m m ) Figure 4. Length distributions of male and female walleye caught in upper and lower traps, in the Mink River, Alberta, from 8 20 May A total of 664 mature female and 4100 mature male walleye > 300 mm TL were marked. Of the 339 fish (189 males and 150 females) captured during test netting, 21 males and 11 females were recaptures. Based on these recapture numbers, the MLE population size was 39,450 males (95% CI = 28,580 66,190) and 23,330 females (95% CI = 15,330 52,380) resulting in a total of = 64,560 fish (95% CI = 49,020 96,390) (Figure 5). Associated densities were male fish/ha (95% CI = ), 6.83 female fish/ha (95% CI = ), and a total of 18.9 fish/ha (95% CI = ) (Figure 5). 100 Population size (x 1000) M ales Fem alescom bined Density (fish/ha) Figure 5. Maximum likelihood estimates (± 95% CI) of population size and density of walleye (> 300 mm TL) in Fawcett Lake, Albert, as determined by mark recapture methods in

22 4.3 Creel survey Majority (75.4%) of the 2061 anglers surveyed targeted walleye and used baits (77.3%), barbed hooks (83.6%), and depth sounders (54.9%). The majority of anglers (84.6%) resided in Edmonton and surrounding area (Figure 6). The two access sites (Fawcett Lake Resort and Anchor Inn Resort) were used by 64% of boating anglers. Fawcett Lake Resort accounted for 40.3% of anglers and Anchor Inn Resort for 24% Percentage (%) Pigeon Lake Red D eer & area B a rh e a d E d so n / H in to n A th a b a sca / L a c L a B ich e C a lg a ry & a re a Residence E d m o n to n & a re a O th e r Figure 6. Percentage of anglers interviewed (n = 2061) who reside in various locations throughout Alberta, Total estimated fishing effort was 23,325 angler hours (angler h; 95% CI = 22,400 30,575) or 7.4 h/ha (95% CI = ). Observed and estimated values of walleye catch and harvest are shown in Table 1. Total CPUE was 1.14 fish/h. Daily CPUE was fish/h (95% CI = ) in the angler survey and fish/h (95% CI = ) for test angling. Harvest per unit effort was fish/h (95% CI = ) in the angler survey. 10

23 Table 1. Observed and maximum likelihood estimates (MLE) of number of walleye caught and harvested by anglers during the 2003 creel survey on Fawcett Lake, Alberta. In brackets are 95% CI for the MLE estimates. Observed MLE (95% CI) Number caught 5,458 22,800 ( ,825) Number harvested 418 1,710 ( ) Angler harvested walleye ranged between 361 and 602 mm TL and was dominated by individuals in the mm size range. Test angled walleye ranged between 209 and 525 mm TL. The length frequency distributions from the angler harvest (creel survey) and test angling are shown in (Figure 7). 60 Relative abundance (%) Test Angling (n = 253) Creel (n = 245) Total length (mm) Figure 7. Length distribution of walleye caught by anglers during the creel survey and test angling in Fawcett Lake, Alberta, Mean (±SD) length (TL) was mm (n = 246) for angler harvested fish and 349 ± mm (n = 257) for test angled fish. Sub legal (TL < 430 mm) fish accounted 11

24 for 7.35% (n = 18) of the reported angler harvested fish. Mean length of sub legal was harvest 415 ± mm (n = 18). Age of walleye ranged from 7 to 18 y for angler harvested fish and 4 to 12 y for test angled fish (Figure 8). Mean age of angler harvested fish was 9.92 ± 2.01 y (n = 242) while that of fish from test angling was 7.18 ± 1.47 y (n = 188). Relative abundance (%) Creel (n = 242) Test angling (n = 188) Age (y) Figure 8. Age distribution of walleye caught by anglers during the creel survey and test angling in Fawcett Lake, Alberta, Length at age data from angler harvested walleye were fitted to the von Bertalanffy growth curve (Figure 9). Walleye showed an L of 569 mm TL and a growth coefficient K of

25 Total length (mm) Age (y) Figure 9. von Bertalanffy growth curve of walleye sampled from Fawcett Lake, Alberta, von Bertalanffy growth parameters: L = 569, K = 0.156; n = Summary Based on MLEs, adult walleye (> 300 mm TL) population in Fawcett Lake was 64,020 (95% CI = 49,020 96,390), consisting of 39,450 (95% CI = 28,580 66,190) males and 23,330 (95% CI = 15,330 52,380) females. Corresponding densities were 18.7 fish/ha (95% CI = ), 11.5 males/ha (95% CI = ), and 6.8 females/ha (95% CI = ). Anglers exerted a fishing pressure of 23,325 angler h (95% CI = 22,400 30,575) or 7.4 h/ha (95% CI ) from 16 May to 1 September The mean daily CPUE for walleye was fish/angler h (95% CI = ) while the HPUE, was fish/angler h (95% CI = ). An estimated 22,800 walleye were caught (95% CI = 19,425 27,825) and 1710 harvested (95% CI = ). 13

26 5.0 LITERATURE CITED Berry D.K Alberta s walleye management and recovery plan. Alberta Environmental Protection, Natural Resources Service. Number T/310. Edmonton, Alberta. 32 pp. Haddon, M Modelling and quantitative methods in fisheries. Chapman Hall/CRC, Boca Raton, Florida. 406 pp. Mackay, W.C., G.R. Ash, and H.J. Norris 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. 113pp. Nelson, J. S., and M. J. Paetz The Fishes of Alberta. 2 nd edition. The University of Alberta Press, University of Alberta, Edmonton, Alberta, Canada. 437pp. Potter, K.L Fawcett Lake walleye (Stizostedion vitreum vitreum) population assessment and angler creel survey. Alberta Conservation Association, Northwest Boreal Region, Slave Lake. 55pp + 8 app. Sullivan, M.G Computer simulation of sport fish parameters. Alberta Sustainable Resource Development. 13 pp. von Bertalanffy, L A quantitative theory of organic growth. Human Biology, 10:

27 6.0 APPENDICES Appendix 1. Locations of trap nets in the Mink River during the marking event of the 2003 Fawcett Lake walleye population estimate. Location UTM Easting UTM Northing Upstream trap (trap #1) Downstream trap (trap #2)

28 Appendix 2. Flow chart outlining the process used to estimate parameters from the angler survey at Fawcett Lake, Circles represent values with no variance while rectangles represent likelihood distributions of 10,000 replicates from bootstrapping. Bold outline represents derived parameters used in the assessment of the sport fishery (e.g., total effort, total walleye harvest). The two access points were surveyed were Anchor Inn Resort (AIR) and Fawcett Lake Resort (FLR). The ratio of use (ROU) is the number of boats from aerial boat count/number of boats in the angler survey 16

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