Status of Walleye Stock at Lac Bellevue, Alberta, 2003

Transcription

1 Status of Walleye Stock at Lac Bellevue, 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 Status of Walleye Stock in Lac Bellevue, Alberta, Bill Patterson and Stephanie R. Grossman Alberta Conservation Association #111, Avenue Twin Atria Building Edmonton, Alberta, Canada T5R-2X3.

4 Report Series Co editors PETER K.M AKU GARRY J. SCRIMGEOUR Alberta Conservation Association Alberta Conservation Twin Atria Building P.O. Box #111, Avenue Baker Centre Postal Outlet Edmonton, AB, T6B 2X3 Edmonton, AB, T5J 4M9 Conservation Report Series Types: Data, Technical ISBN printed: ISBN online: ISSN printed: ISSN online: Publication 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: Patterson, B. and Stephanie R. Grossman Status of walleye stock in Lac Bellevue, Alberta, Data Report, (D ) produced by Alberta Conservation Association, Edmonton, Alberta, Canada. 12 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 To aid in the management and recovery of Alberta s walleye (Sander vitreus) stock at Lac Bellevue, the Alberta Conservation Association conducted a Fall Walleye Index Netting (FWIN) survey on 23 September 2003 to collect data for the ongoing assessment of the walleye fishery at Lac Bellevue. Fall Walleye Index Netting provides both abundance and population structure information, and is used to assist Alberta Sustainable Resource Development in formulating sustainable management guidelines for the sport fishery. Results from this survey indicate that walleye in Lac Bellevue had a moderately broad age class distribution with 11 year classes. The age class distribution was unstable, with several weak or absent year classes. Although Lac Bellevue was stocked with walleye fingerlings in 1991, 1992 and 1994, only individuals from the 1992 year class (age 11) were captured during our survey suggesting that the 1991 (age 12) and 1994 (age 14) year classes make up little or no portion of the current fishery. The walleye fishery was composed of moderately fast growing fish, with both males and females reaching 500 mm FL by age 7. Both male and female walleye were mature by age 7, indicating a moderate maturation schedule. The estimated catch rate ranged from walleye/100 m 2 /24 h (95% CI); n = 158. ii

6 ACKNOWLEDGEMENTS The Alberta Conservation Association (ACA) funded this work. In addition, The ACA received in kind support from Alberta Sustainable Resource Development, in Edmonton and St. Paul. iii

7 TABLE OF CONTENTS EXECUTIVE SUMMARY...ii ACKNOWLEDGEMENTS...iii TABLE OF CONTENTS...iv LIST OF FIGURES...v LIST OF TABLES...vi 1.0 INTRODUCTION General introduction Study rationale STUDY AREA MATERIALS AND METHODS Survey method Biological data Data analysis RESULTS Catch rate Age class distribution and stability Length at age Age at maturity Stock assessment summary REFERENCES APPENDICES iv

8 LIST OF FIGURES Figure 1. Map of Lac Bellevue and the Fall Walleye Index Netting locations Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Standardized probability density function of Fall Walleye Index Netting catch rate at Lac Bellevue in Age class distribution of walleye sampled from Fall Walleye Index Netting survey of Lac Bellevue, Length at age of walleye captured during the Fall Walleye Index Netting survey at Lac Bellevue, Age at maturity of male walleye from the Fall Walleye Index Netting survey at Lac Bellevue in Age at maturity of female walleye from the Fall Walleye Index Netting survey at Lac Bellevue in v

9 LIST OF TABLES Table 1. Summary of methods for 2003 Fall Walleye Index Netting survey at Lac Bellevue, Alberta Table 2. Stocking history of walleye at Lac Bellevue, Alberta... 7 vi

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11 1.0 INTRODUCTION 1.1 General introduction Alberta Conservation Association (ACA) conducted a Fall Walleye Index Netting (FWIN) survey at Lac Bellevue on 23 September 2003 to obtain information regarding the abundance and population structure of walleye (Sander vitreus) in the lake. Using population density estimates and angler total catch rate data, FWIN catch rates (catch/net) were recently validated as an appropriate index of walleye abundance estimates (Sullivan and Park 2004); the metric catch/net, was highly correlated with catch/angling hour and therefore, can be used to describe the abundance of walleye. Because surveys are completed within a narrow time frame and under selected environmental conditions (3 days, water temperature ranging from 10 to 15 o C), information collected from FWIN surveys provide precise snapshots of the population structure by minimizing variations associated with growth and age of fish. 1.2 Study rationale The purpose of the current FWIN survey was to provide Alberta Sustainable Resource Development (ASRD) with information on the status of the walleye fishery at Lac Bellevue, Alberta, as part of an ongoing assessment and management of the walleye fishery on the lake. In 1971, 250 adult walleye were introduced into the lake from Beaver River (Dick Brown, ASRD Fisheries Biologist, pers. comm.). Lac Bellevue was also stocked during 1991, 1992, and 1994 with a total of 62,811 walleye fingerlings. In 1996 the lake was categorized as having a collapsed (stocked) walleye fishery and since that time, the sport fishery regulation has been modified to a catch and release (zero daily bag limit) angling only. Our survey provides the data necessary to re assess the status of this walleye fishery after a number of years of restricted angler harvest. 2.0 STUDY AREA Lac Bellevue is located approximately 180 km northeast of Edmonton, Alberta and 25 km south of St. Paul, Alberta (Figure 1). The lake has a surface area of 461 ha (ASRD 1

12 unpublished data). It has two access points, one each on the north and south ends. The shoreline of Lac Bellevue is developed, with summer villages, a recreation area campground and a municipal campground. The surrounding area is mostly agricultural, consisting of both cattle and annual crop. Legend: FWIN net locations: Deep set Shallow set St. Paul Edmonton Lac Bellevue Red Deer Calgary Figure 1. Map of Lac Bellevue and the Fall Walleye Index Netting locations. Alberta map indicates location of Lac Bellevue. The red dots and blue triangles represent deep (5 15 m depth) and shallow (2 5 m depth) net locations, respectively. Grid lines indicate 0.25 km 2 quadrats based on a Universal Transverse Mercator (UTM) grid. 2

13 3.0 MATERIALS AND METHODS 3.1 Survey method The FWIN survey methods described by the Ontario Ministry of Natural Resources (Morgan 2000) were followed in this study. Table 1 summarizes the basic sampling methods employed at Lac Bellevue in We used a standard, 1.8 m deep by 61 m long, monofilament gill net, consisting of eight panels of different mesh sizes (25, 38, 51, 64, 76, 102, 127, and 152 mm, stretched mesh) sewn together in ascending order of size. Table 1. Summary of methods for 2003 Fall Walleye Index Netting survey at Lac Bellevue, Alberta. Modified from Morgan (2000). Criteria Target Season Fall; when surface temperature is between 10 and 15 C Set duration 24 hours (acceptable range hrs) Gear Orientation Depth Gillnet gang 8 mesh sizes (25 mm to 152 mm) Each mesh 1.8 m deep x 7.6 m long Perpendicular to shore contour Two strata, 2 5 m and 5 15 m Stratification Sampling was stratified across shallow (2 5 m) and deep (5 15 m) quadrats proportional to the area within each stratum across the whole lake. The surface area of the lake was divided into 0.25 km 2 quadrats using a Universal Transverse Mercator (UTM) grid. To minimize bias in locating sites, we sequentially numbered the quadrats and selected sampling sites randomly (without replacement) using these numbers (Figure 1). Bathymetric data was used to calculate a ratio of surface area for the depth strata i) 2 5 m and ii) 5 15 m. We stratified the number of nets set in both shallow and deep quadrats based on this ratio of shallow:deep quadrats 3

14 throughout the lake. Nets were located in the centre of each randomly selected quadrat if possible, or within 250 m of the centre. If the desired depth or suitable topography was not found within 250 m of a quadrat centre, it was replaced with the next randomly selected quadrat in the sequence following Morgan (2000). Six nets, three each in deep and shallow water quadrats, were set in Lac Bellevue on 23 September 2003 (Appendix 6.1). The average soak time per net was 27.6 hours (range = hours). 3.2 Biological data In the field, all fish caught were collected, bagged and recorded separately by species and mesh size (i.e., by panel) for each net. We collected data on fork length (FL, ± 1 mm), total weight (± 10 g), sex, and state of maturity as well as ageing structures from each fish. Fish were described as sexually mature if they appeared able to spawn during the next spawning season (Duffy et al. 2000). The left operculum and the first three rays of the left pelvic fin were collected for age determinations according to Mackay et al. (1990). 3.3 Data analysis We used age composition, length frequency distributions, length at age and age atmaturity to assess the population structure for walleye in the lake. Weight length and length age graphs were plotted to identify and verify any outliers. Outliers were omitted if a measurement or recording error was suspected. We used a bootstrap technique to calculate an estimate of walleye catch per net, as well as the associated confidence intervals for this metric. Sullivan (2004) summarized that bootstrapping is a statistical procedure whereby an original sample of the population is subsequently re sampled and a new mean calculated. Bootstrap samples are assumed to approximate the distribution of values that would have arisen from repeatedly sampling the original sampled population (Haddon 2001). Re sampling thousands of times provides a distribution of possible means describing the likelihood of the true (population) mean being within that distribution (Sullivan 2004). This group of means represents the distribution of possible means from data with the same scale of variation as observed in the original data set. Frequentist parameter estimates (e.g., means) are typically equal to maximum likelihood estimates (MLE) for the parameters of the 4

15 specified probability density function (Gotelli and Ellison 2004). Empirical confidence intervals (95% CI) were calculated following Haddon (2001). The final proportions (i.e., probability densities) were standardized to range between 0 and 1 (Paul et al. 2003). All data were stored in the Fisheries Management Information System (FMIS) of ASRD. 4.0 RESULTS The following subsections are listed according to biological characteristics used by the ASRD in assigning management categories (i.e., stable, vulnerable, and collapsed) to walleye fisheries. These categories are described in detail in the ASRD Walleye Management and Recovery Plan (WMRP; Berry (1995). 4.1 Catch rate A total of 156 walleye were capture in the FWIN nets during our study period. The maximum likelihood estimate (MLE) of walleye catch rate was 20.8 fish/100 m 2 /24 h (95% CI = fish/100 m 2 /24 h; n = 158; Figure 2). This catch rate is moderate, compared to other Alberta lakes surveyed in the 1980s and 1990s and is indicative of a vulnerable walleye fishery (Sullivan 1994; Watters 2005). 5

16 1.0 <5 >30 Standardized Probability Density Catch (walleye/100m 2 /24h) Figure 2. Standardized probability density function of Fall Walleye Index Netting catch rate at Lac Bellevue in 2003 (MLE = 20.8 fish/100 m 2 /24 h; 95% CI = ; n = 158). The catch rates (i.e., < 5, 5 30 and > 30 fish/100 m 2 /24 h), indicated by the heavy vertical bars, specify the setpoints of ASRD management categories (i.e., collapsed, vulnerable, stable). 4.2 Age class distribution and stability The walleye catch in Lac Bellevue displayed a moderately broad age class distribution with 11 age classes from ages 1 to 15 being represented, with a mean age of 5.6 years (Figure 3). Few walleye older than age 10 were caught. The age class distribution was unstable, with several weak year classes and four age classes (ages 6, 9, 12, and 14) not represented, suggesting multiple year class failures. The sample size for age class analysis, n = 113, is lower than the total number of fish caught (n = 158), as many fish could not accurately be aged, and therefore were excluded from the analysis. 6

17 CUE (Walleye/100m 2 /24h) Age (years) Figure 3. Age class distribution of walleye sampled from Fall Walleye Index Netting survey of Lac Bellevue, The mean age was 5.6, n = 113. Although Lac Bellevue was stocked with 62,811 walleye fingerlings in 1991, 1992 and 1994 (Table 2), only individuals from the 1992 year class (age 11) were captured during our survey suggesting that the 1991 (age 12) and 1994 (age 14) year classes make up little or no portion of the current fishery. Table 2. Stocking history of walleye at Lac Bellevue, Alberta. Stocking year Number stocked Approximate size ,285 21,417 20,109 Fingerlings Fingerlings Fingerlings 7

18 4.3 Length at age Walleye typically reached 500 mm FL by age 7 (Figure 4). Based on this length at age information, the walleye population at Lac Bellevue was classified as having moderate to fast growth according to the WMRP (Berry 1995). Fork Length (mm) Age (y) Figure 4. Length at age of walleye captured during the Fall Walleye Index Netting survey at Lac Bellevue, The black line represents the logarithmic lineof best fit (r 2 = 0.92, n = 113) and the blue crosses represent the real data. The dark horizontal line indicates the 500 mm fork length. 4.4 Age at maturity Overall, 71% (n = 46) and 55% (n = 24) of males and females, respectively, were mature in 2003 (Figures 5 and 6). At age 5, 95% of males (n = 19) and 67% of females (n = 9) were mature; all individuals of both sexes were mature by age 7. Because none was captured, we were unable to determine maturity of age 6 fish. 8

19 Catch (Walleye/100m 2 /24h) Mature male, n=46 Immature male, n= Age (y) Figure 2. Age at maturity of male walleye from the Fall Walleye Index Netting survey at Lac Bellevue in Catch (Walleye/100m 2 /24h) Mature female, n=24 Immature female, n= Age (y) Figure 3. Age at maturity of female walleye from the Fall Walleye Index Netting survey at Lac Bellevue in

20 4.5 Stock assessment summary In general, Lac Bellevue had a moderately broad age class distribution with 11 year classes being represented. The age class distribution was unstable with several weak year classes, possibly indicating multiple year class failure. The walleye fishery was composed of moderately fast growing fish and all fish sampled over age 7 were mature; a moderate maturation schedule relative to Alberta walleye fisheries surveyed in the 1980s and 1990s (Sullivan 1994). Catch of walleye ranged from fish/100 m 2 /24 h (MLE = 20.8 fish/100 m 2 /24 h); this moderate catch rate is indicative of a vulnerable walleye fishery (Sullivan 1994). 10

21 5.0 REFERENCES Berry, D Alberta s walleye management and recovery plan. Publication T/310 of Alberta Fish and Wildlife Division, Edmonton, Alberta, Canada. 32 pp. Duffy, M., J. McNulty and T. Mosindy Identification of sex, maturity and gonad condition of walleye Stizostedion vitreum vitreum. Ontario Ministry of Natural Resources, Thunder Bay, Ontario, Canada. 33 pp. Gotelli, N. J. and A. M. Ellison A primer of ecological statistics. Sinauer Associates Inc., Sutherland, Massachusetts, USA. 510 pp. Haddon, M Modeling and quantitative methods in fisheries. Chapman and Hall/CRC, Boca Raton, Florida. 406 pp Mackay, W. C., G. R. Ash, and H. J. Norris (eds.) Fish ageing methods for Alberta. R.L. & R. Environmental Services Ltd. in association with Alberta Fish and Wildlife Division and University of Alberta, Edmonton, Alberta, Canada. 113 pp. Morgan, G. E Manual of instructions: Fall Walleye Index Netting (FWIN). Ontario Ministry of Natural Resources, Fish and Wildlife Division. Peterborough, Ontario, Canada. 34 pp. Paul, A. J., J. R. Post, and J. D. Stelfox Can anglers influence the abundance of native and nonnative salmonids in a stream from the Canadian Rocky Mountains? North American Journal of Fisheries Management 23: Sullivan, M.G Computer simulation of sport fishery parameters. Unpublished memorandum of Alberta Fish and Wildlife Division, Edmonton, Alberta, Canada. 16 pp. 11

22 Sullivan, M. G. and D. Park Alberta walleye index netting protocols: summary of joint ACA/SRD index netting subcommittee. Alberta Fish and Wildlife Division and Alberta Conservation Association. 13 pp. Sullivan, M. G A model of walleye management based on stock recruitment characteristics. Unpublished report of Alberta environmental Protection, Fish and Wildlife Service, Edmonton, Alberta, Canada. Watters, D Calling Lake fall walleye index netting survey in Alberta Sustainable Resource Development, Fish and Wildlife Division, Edmonton, Alberta, Canada. 25 pp. 12

23 6.0 APPENDICES 6.1 Appendix 1. Catch of walleye from the Fall Walleye Index Netting survey of Lac Bellevue, Set number Depth strata Walleye catch Net set date Net pull date 1D Shallow Sept 24 Sept A Shallow Sept 24 Sept A Shallow Sept 24 Sept B Deep Sept 24 Sept 27 5B Deep Sept 24 Sept 26 9A Deep Sept 24 Sept Net deployment (hours) 13

24 6.2 Appendix 6.2. Biological data collected from the walleye captured during Fall Walleye Index Netting at Lac Bellevue, Sex code: U = unidentifiable, M = male, F = female. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) U Immature U Immature U Immature U Immature U Immature U Immature F Mature F Immature M Immature M Immature M Immature M Mature M Mature F Mature M Mature F Mature F Mature M Mature M Mature M Mature F Mature M Mature F Mature F Mature F Mature M Mature M Mature F Mature F Mature F Mature M Mature 8 14

25 6.2 Appendix 2. Continued. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) U Immature U Immature U Immature U Immature U Immature U Immature U Immature U Immature M Mature F Immature M Mature F Immature F Immature M Immature M Mature M Mature M Mature F Immature M Mature M Mature M Mature M Mature M Mature F Mature M Mature U Immature U Immature U Immature U Immature U Immature U Immature F Mature M Mature M Mature F Mature M Immature 2 15

26 6.2 Appendix 2. Continued. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) F Immature M Mature M Mature M Mature M Mature F Mature M Mature M Mature F Immature F Mature M Mature M Mature M Mature M Mature M Mature M Mature F Immature M Mature M Mature F Immature F Mature F Mature M Mature M Mature F Immature M Mature F Mature U Immature U Immature U Immature U Immature U Immature U Immature U Immature U Immature U Immature 16

27 6.2 Appendix 2. Continued. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) U Immature U Immature F Immature M Immature F Immature M Immature M Immature M Immature F Immature M Immature U Immature U Immature U Immature U Immature U Immature U Immature U Immature U Immature U Immature U Immature F Immature M Immature M Mature M Immature M Immature M Immature F Immature M Immature M Mature F Immature M Mature F Mature M Mature U Immature U Immature 17

28 6.2 Appendix 2. Continued. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) U Immature U Immature U Immature M Immature M Immature F Immature M Mature F Immature M Immature F Mature F Mature M Immature F Immature F Mature F Mature 5 18

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