Status of Walleye Stock at Lac Bellevue, Alberta, 2003 CONSERVATION REPORT SERIES
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Status of Walleye Stock in Lac Bellevue, Alberta, 2003. Bill Patterson and Stephanie R. Grossman Alberta Conservation Association #111, 4999-98 Avenue Twin Atria Building Edmonton, Alberta, Canada T5R-2X3.
Report Series Co editors PETER K.M AKU GARRY J. SCRIMGEOUR Alberta Conservation Association Alberta Conservation Twin Atria Building P.O. Box 40027 #111, 4999 98 Avenue Baker Centre Postal Outlet Edmonton, AB, T6B 2X3 Edmonton, AB, T5J 4M9 Conservation Report Series Types: Data, Technical ISBN printed: 0 7785 4113 4 ISBN online: 0 7785 4114 2 ISSN printed: ISSN online: Publication 0 7785 4114 2 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. 2005. Status of walleye stock in Lac Bellevue, Alberta, 2003. Data Report, (D 2005 003) 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: 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 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 16.8 25.0 walleye/100 m 2 /24 h (95% CI); n = 158. ii
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
TABLE OF CONTENTS EXECUTIVE SUMMARY...ii ACKNOWLEDGEMENTS...iii TABLE OF CONTENTS...iv LIST OF FIGURES...v LIST OF TABLES...vi 1.0 INTRODUCTION... 1 1.1 General introduction... 1 1.2 Study rationale... 1 2.0 STUDY AREA... 1 3.0 MATERIALS AND METHODS... 3 3.1 Survey method... 3 3.2 Biological data... 4 3.3 Data analysis... 4 4.0 RESULTS... 5 4.1 Catch rate... 5 4.2 Age class distribution and stability... 6 4.3 Length at age... 8 4.4 Age at maturity... 8 4.5 Stock assessment summary... 10 5.0 REFERENCES... 11 6.0 APPENDICES... 13 iv
LIST OF FIGURES Figure 1. Map of Lac Bellevue and the Fall Walleye Index Netting locations.... 2 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 2003... 6 Age class distribution of walleye sampled from Fall Walleye Index Netting survey of Lac Bellevue, 2003..... 7 Length at age of walleye captured during the Fall Walleye Index Netting survey at Lac Bellevue, 2003..... 8 Age at maturity of male walleye from the Fall Walleye Index Netting survey at Lac Bellevue in 2003... 9 Age at maturity of female walleye from the Fall Walleye Index Netting survey at Lac Bellevue in 2003... 9 v
LIST OF TABLES Table 1. Summary of methods for 2003 Fall Walleye Index Netting survey at Lac Bellevue, Alberta.... 3 Table 2. Stocking history of walleye at Lac Bellevue, Alberta... 7 vi
CONSERVATION REPORT SERIES
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
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
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 2003. 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 21 27 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
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 = 26.0 29.8 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
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 = 16.8 25.0 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
1.0 <5 >30 Standardized Probability Density 0.8 0.6 0.4 0.2 0.0 0 10 20 30 40 50 60 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 = 16.8 25.0; 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
CUE (Walleye/100m 2 /24h) 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Age (years) Figure 3. Age class distribution of walleye sampled from Fall Walleye Index Netting survey of Lac Bellevue, 2003. 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 1991 1992 1994 21,285 21,417 20,109 Fingerlings Fingerlings Fingerlings 7
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) 800 700 600 500 400 300 200 100 0 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 Age (y) Figure 4. Length at age of walleye captured during the Fall Walleye Index Netting survey at Lac Bellevue, 2003. 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
Catch (Walleye/100m 2 /24h) 4 3 2 1 0 Mature male, n=46 Immature male, n=19 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Age (y) Figure 2. Age at maturity of male walleye from the Fall Walleye Index Netting survey at Lac Bellevue in 2003. Catch (Walleye/100m 2 /24h) 4 3 2 1 0 Mature female, n=24 Immature female, n=20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Age (y) Figure 3. Age at maturity of female walleye from the Fall Walleye Index Netting survey at Lac Bellevue in 2003. 9
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 16.8 25.0 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
5.0 REFERENCES Berry, D. 1995. 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. 2000. 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. 2004. A primer of ecological statistics. Sinauer Associates Inc., Sutherland, Massachusetts, USA. 510 pp. Haddon, M. 2001. 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.). 1990. 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. 2000. 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. 2003. Can anglers influence the abundance of native and nonnative salmonids in a stream from the Canadian Rocky Mountains? North American Journal of Fisheries Management 23:109 119. Sullivan, M.G. 2004. Computer simulation of sport fishery parameters. Unpublished memorandum of Alberta Fish and Wildlife Division, Edmonton, Alberta, Canada. 16 pp. 11
Sullivan, M. G. and D. Park. 2004. 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. 1994. 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. 2005. Calling Lake fall walleye index netting survey in 2004. Alberta Sustainable Resource Development, Fish and Wildlife Division, Edmonton, Alberta, Canada. 25 pp. 12
6.0 APPENDICES 6.1 Appendix 1. Catch of walleye from the Fall Walleye Index Netting survey of Lac Bellevue, 2003. Set number Depth strata Walleye catch Net set date Net pull date 1D Shallow 32 23 Sept 24 Sept 29.75 7A Shallow 25 23 Sept 24 Sept 26.5 8A Shallow 39 23 Sept 24 Sept 28.5 6B Deep 20 23 Sept 24 Sept 27 5B Deep 25 23 Sept 24 Sept 26 9A Deep 17 23 Sept 24 Sept 27.75 Net deployment (hours) 13
6.2 Appendix 6.2. Biological data collected from the walleye captured during Fall Walleye Index Netting at Lac Bellevue, 2003. Sex code: U = unidentifiable, M = male, F = female. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) 1 121 16 U Immature 2 123 18 U Immature 3 142 28 U Immature 4 145 34 U Immature 5 127 18 U Immature 6 120 16 U Immature 7 511 1588 F Mature 10 8 291 280 F Immature 3 9 291 226 M Immature 3 10 303 320 M Immature 4 11 315 320 M Immature 3 12 413 804 M Mature 4 13 396 668 4 14 476 1310 M Mature 10 15 509 1530 F Mature 10 16 492 1322 M Mature 10 17 615 2175 F Mature 15 18 520 1808 F Mature 7 19 395 726 M Mature 5 20 507 1624 M Mature 10 21 391 694 M Mature 4 22 295 256 F Mature 3 23 421 864 M Mature 5 24 496 1280 F Mature 7 25 442 1070 F Mature 5 26 583 1980 F Mature 15 27 489 1368 M Mature 7 28 526 1666 M Mature 10 29 515 1702 F Mature 7 30 516 1610 F Mature 8 31 505 1578 F Mature 7 32 492 1486 M Mature 8 14
6.2 Appendix 2. Continued. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) 33 114 14 U Immature 34 140 18 U Immature 35 123 16 U Immature 36 120 16 U Immature 37 120 16 U Immature 38 122 18 U Immature 39 112 14 U Immature 40 161 48 U Immature 1 41 401 764 M Mature 5 42 305 286 F Immature 3 43 411 790 M Mature 5 44 302 264 F Immature 3 45 436 898 F Immature 5 46 273 244 M Immature 3 47 575 2258 M Mature 13 48 390 700 M Mature 4 49 403 810 M Mature 5 50 433 896 F Immature 5 51 410 784 M Mature 5 52 393 752 M Mature 5 53 425 898 M Mature 5 54 468 1176 M Mature 8 55 433 956 M Mature 5 56 424 952 F Mature 5 57 517 1644 M Mature 10 58 122 16 U Immature 59 118 14 U Immature 60 114 14 U Immature 61 127 16 U Immature 62 120 16 U Immature 63 123 18 U Immature 64 509 1624 F Mature 7 65 423 886 M Mature 5 66 438 1042 M Mature 5 67 523 1502 F Mature 8 68 234 126 M Immature 2 15
6.2 Appendix 2. Continued. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) 69 230 126 F Immature 2 71 472 1360 M Mature 7 72 471 1336 M Mature 7 73 482 1200 M Mature 8 74 463 1290 M Mature 7 75 498 1568 F Mature 7 76 501 1542 M Mature 10 77 398 776 M Mature 5 78 385 586 F Immature 4 79 410 782 F Mature 5 80 378 610 M Mature 4 81 365 500 M Mature 4 82 439 1052 M Mature 7 83 403 758 M Mature 5 84 396 644 M Mature 5 85 472 1480 M Mature 11 86 372 608 F Immature 4 87 392 702 M Mature 5 88 490 1320 M Mature 8 89 415 938 F Immature 5 90 541 1940 F Mature 10 91 565 2078 F Mature 10 92 435 1012 M Mature 5 93 438 996 M Mature 4 94 435 940 F Immature 4 95 578 2500 M Mature 13 96 498 1560 F Mature 8 97 115 14 U Immature 98 121 16 U Immature 99 123 18 U Immature 100 120 16 U Immature 101 113 14 U Immature 102 120 16 U Immature 103 133 22 U Immature 104 132 20 U Immature 105 117 16 U Immature 16
6.2 Appendix 2. Continued. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) 106 127 18 U Immature 107 126 18 U Immature 109 231 124 F Immature 2 110 304 262 M Immature 3 111 289 244 F Immature 3 112 280 226 M Immature 3 113 300 294 M Immature 4 114 305 314 M Immature 4 115 319 356 F Immature 4 116 293 276 M Immature 3 117 625 2664 13 118 122 16 U Immature 119 128 20 U Immature 120 123 18 U Immature 121 127 18 U Immature 122 109 12 U Immature 123 120 18 U Immature 124 112 14 U Immature 125 125 20 U Immature 126 125 18 U Immature 127 132 20 U Immature 128 234 138 F Immature 2 129 226 118 2 130 225 116 M Immature 2 131 400 802 M Mature 5 132 288 254 M Immature 3 133 300 276 M Immature 3 134 305 340 M Immature 3 135 305 332 F Immature 3 136 402 730 M Immature 5 137 407 788 M Mature 5 138 319 372 F Immature 3 139 381 710 M Mature 4 140 538 1768 F Mature 8 141 524 1552 M Mature 10 142 117 14 U Immature 143 127 18 U Immature 17
6.2 Appendix 2. Continued. Sample number Fork length (mm) Weight (g) Sex Maturity Age (yrs) 144 125 18 U Immature 145 120 16 U Immature 146 128 20 U Immature 147 212 110 M Immature 2 148 206 94 M Immature 2 149 230 122 F Immature 2 150 389 666 M Mature 5 151 307 298 F Immature 3 152 305 298 M Immature 3 153 422 906 F Mature 5 154 425 868 F Mature 5 155 359 494 M Immature 4 156 325 392 F Immature 4 157 568 2112 F Mature 10 158 472 1242 F Mature 5 18
CONSERVATION REPORT SERIES
The Alberta Conservation Association acknowledges the following partner for their generous support of this project