Status of the Walleye Fishery at Crawling Valley Reservoir, Alberta, 2004

Transcription

1 Status of the Walleye Fishery at Crawling Valley Reservoir, Alberta, 2004 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 the Walleye Fishery at Crawling Valley Reservoir, Alberta, 2004 Jason K. Blackburn and Jason A. Cooper Alberta Conservation Association 2 nd floor, YPM Place, th Street South Lethbridge, Alberta, Canada T1J 2J8

4 Report Series Co editors PETER AKU KELLEY KISSNER Alberta Conservation Association 59 Tuscany Meadows Cres NW #101, 9 Chippewa Rd Calgary, AB T3L 2T9 Sherwood Park AB T8A 6J7 Conservation Report Series Type Data ISBN printed: ISBN online: ISBN No Publication No.: Pub No. 187 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: Blackburn, J.K., and J.A. Cooper Status of the walleye fishery at Crawling Valley Reservoir, Alberta, Data report, D , produced by Alberta Conservation Association, Lethbridge, Alberta, Canada. 24 pp. 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: Tel: (780) Fax: (780) info@ab conservation.com Website: conservation.com i

5 EXECUTIVE SUMMARY In response to increasing public demand for enhanced angling opportunities, Alberta Sustainable Resource Development (ASRD) initiated walleye stocking programs in the late 1980 s and early 1990 s on many irrigation reservoirs in southern Alberta, including the Crawling Valley Reservoir. Crawling Valley Reservoir was stocked each year from 1990 to 1992 and currently supports one of the most popular walleye fisheries in southern Alberta. However, little data exist on the population structure of walleye or angling pressure for this reservoir. To generate such data, the Alberta Conservation Association (ACA) and ASRD conducted a joint Fall Walleye Index Netting (FWIN) survey from September 2004 to assess the status of the walleye fishery on the reservoir. Data on catch rate and population structure were obtained from gill net catches and growth rates were estimated using the von Bertalanffy growth model. Population status and stability were determined using an ASRD derived regression model and the ASRD Walleye Management and Recovery Plan classification system. A total of 221 walleye were captured during the survey, resulting in a catch rate of 27 fish/net/24 h or 25 fish/100 m 2 /24 h. Of the 144 walleye > 345 mm fork length (the size walleye reach first maturity in the reservoir), 96 were mature. The average catch rate of mature sized fish was 15.8 fish/100 m 2 /24 h. Although nearly twice as many females as males were represented in the overall catch (sex ratio = 1.9 females:1.0 males), the sexes were equally represented among the 96 mature fish (sex ratio = 1.04 females:1.0 males). Overall, the size of walleye captured in 2004 ranged from 104 to 708 mm FL with an average fork length of mm. The population exhibited a multimodal distribution with dominant modes at mm, mm and mm. Thirteen age classes were represented in the catch ranging from age 0 to 14 with a mean age of y. Mean length at age ranged from mm for age 0 fish to mm for age 13 males and mm for age 14 females. Dominant year classes were 1997 (age 7), 1998 (age 6), and 2004 (age 0) with respective catch rates of 5.0, 5.0, and 5.1 fish/net/24 h. These classes comprised 58% of the total catch. In general, growth rates were higher for females than for males, although unpaired t test results showed no significant difference in growth rate between the sexes except for age 13 individuals. Male and female fish reached first maturity by ages 5 and 6, respectively. Estimates of growth rate derived using the von Bertalanffy growth model ii

6 from data collected from 1998 to 2004 and mean length at age data from 1996 to 2004 indicated that annual growth of walleye has generally decreased over the years, suggesting an increase in fish density. One way ANOVA tests among age classes between sampling years also suggest a decrease in growth rates with significant decreases in mean length at age in five age classes when compared to previous years. Walleye density including all size classes was predicted at fish/ha and 9.6 fish/ha for adult sized fish. According to the ASRD Walleye Management and Recovery Plan classification system, the walleye population in Crawling Valley Reservoir is considered vulnerable. Accurate determination of whether a harvestable walleye surplus exists in Crawling Valley Reservoir depends upon a better understanding of the effects of incidental angling mortality, illegal harvest, and water availability on walleye population stability. iii

7 ACKNOWLEDGEMENTS This study was a collaborative effort between the Alberta Conservation Association (ACA) and Alberta Sustainable Resource Development (ASRD), Fish and Wildlife Division, Southeast Region. We thank Gary Shmorong (ASRD, F&W Officer, Strathmore) and Cam Wallman (ASRD, Fisheries Management, Brooks), for their expertise and assistance in helping conduct the FWIN survey. We also thank the Strathmore Fish and Wildlife Officers who graciously allowed the use of their boat for this survey. The Crawling Valley Recreation Society provided us a seasonal campsite and storage at the reservoir despite the long waiting list. This report benefited from constructive comments offered by Trevor Council, Glen Clements, Cam Wallman and Peter Aku. 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 Reservoir characteristics Fish community METHODS Study design Biological data Data analyses RESULTS Catch results Walleye CUE Age class distribution Size distribution Age at maturity Growth rate and length at age Walleye catch rate comparison Walleye population density and stability Summary LITERATURE CITED APPENDICES v

10 LIST OF FIGURES Figure 1. Map of Crawling Valley Reservoir Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Depth and area stratification of Crawling Valley Reservoir with sample site locations for the 2004 FWIN survey... 5 Catch frequency distribution of all captured walleye from Crawling Valley Reservoir, Catch frequency distribution of walleye > 345 mm FL from Crawling Valley Reservoir, Age class distribution of walleye captured in Crawling Valley Reservoir, Fork length and age frequency distribution of walleye captured in Crawling Valley Reservoir, Age at maturity among male and female walleye in Crawling Valley Reservoir, Figure 8. Length at age of walleye in Crawling Valley Reservoir, Figure 9. Comparison of mean length at age of walleye in Crawling Valley Reservoir in 1996, 1997, 1998, 2003 and Figure 10. Comparison of mean length at age of walleye from Crawling Valley Reservoir in 2004 with populations in 2003 from Newell Reservoir (highest growth rate) and McGregor Reservoir (lowest growth rate) Figure 11. Comparison of mean FWIN catch rate at Crawling Valley Reservoir to other Alberta waterbody FWIN surveys vi

11 LIST OF TABLES Table 1. Summary of mean length at age of walleye in Crawling Valley Reservoir, Table 2. Comparison of mean length at age of female and male walleye Table 3. Table 4. Summary of von Bertalanffy growth indices (L, K, and t 0 ) for walleye collected from Crawling Valley Reservoir in 1998 and in Analysis of variance results for the difference in mean fork length per age class among sample years on Crawling Valley Reservoir vii

12 LIST OF APPENDICES Appendix 1. Appendix 2. Appendix 3. Appendix 4. Catch distribution of walleye by gill net and depth stratum at Crawling Valley Reservoir, Description of population classification criteria from the Alberta Walleye Management and Recovery Plan Catch by mesh size for various fish species from FWIN survey, Crawling Valley Reservoir, von Bertalanffy growth curves and residual plots for walleye from Crawling Valley Reservoir in 1998 and in viii

13 1.0 INTRODUCTION Prior to the late 1990 s, the walleye (Sander vitreus) fishery was minimal in southern Alberta as populations were limited to a small number of rivers and irrigation reservoirs (Council and Clayton 1997, 1998). In response to increasing demands for angling opportunities, Alberta Sustainable Resource Development (ASRD) initiated walleye stocking programs in the late 1980 s and early 1990 s on many irrigation reservoirs in southern Alberta, including the Crawling Valley Reservoir (Alberta Forestry, Lands and Wildlife ). Crawling Valley Reservoir was stocked each year from 1990 to 1992 and currently supports one of the best walleye fisheries in southern Alberta that is fast becoming popular among recreational anglers. To allow stocked walleye sufficient time to establish and reproduce, Crawling Valley Reservoir was managed as a catch and release fishery with an annual angling season from 8 May to 15 March, and an angling closure from 16 March to 7 May during spring spawning (ASRD 2004a). With the increasing popularity of the walleye fishery on the reservoir, anglers are expected to pressure ASRD to change walleye fishing regulations from catch andrelease to an allowable harvest. Although several sportfish inventory studies have been conducted on the reservoir (Council and Clayton 1997, 1998, 1999; Council 2000, 2001, 2002; Council and Cooper 2003; Cooper 2004), little quantitative data exist on angling pressure or walleye population size. In 2004, the Alberta Conservation Association (ACA) and ASRD initiated a five part field study which included a Fall Walleye Index Netting (FWIN) survey to assess the status of the walleye fishery in the reservoir. The quantitative data collected from this survey is intended to help formulate future management guidelines pertaining to walleye harvest in the reservoir. In the current report, data are presented on population structure, growth, density and stability, as part of the larger study. 1

14 2.0 STUDY AREA Crawling Valley Reservoir (Townships 22 and 23, Ranges 17 and 18, west of the Fourth Meridian) is located approximately 140 km east of Calgary, near Bassano, Alberta. Construction was completed in October 1984 with the filling of the reservoir, and it was officially opened on 10 June Water levels first reached full supply level (FSL) in 1987 (English 1988). The reservoir is owned and operated by the Eastern Irrigation District (EID). Primary access to the reservoir is located at the southwest corner of the Crawling Valley Reservoir campground near the south dam and inlet canal (Figure 1). Access can also be gained via oil and gas roads at various points along the shoreline, but these access points limit anglers to hand launched boats or fishing from shore. 2.1 Reservoir characteristics Crawling Valley Reservoir at FSL has a surface area of 2,315 ha, a maximum length of 15.5 km, and a maximum width of 4.9 km. The reservoir has a mean depth of 5.7 m and a maximum depth of 16.8 m (ASRD 2004b). When Crawling Valley Reservoir was constructed and filled, it flooded a valley and integrated two natural water bodies, Barkenhouse Lake and South Reservoir, as well as numerous side coulees. As a result, the reservoir has approximately 150 km of shoreline, and a shoreline development factor of 7.9 (Mitchell and Prepas 1990). The canal (North Branch) supplying water to Crawling Valley Reservoir originates at Bassano Reservoir on the Bow River and has four water control structures located along its length. The inlet canal enters the reservoir in the southwest corner and the outlet canal is situated at the southeast corner. The close proximity of the inlet and outlet canals limits the exchange of water to the south end, leaving the remainder of the reservoir with little mixing action and a longer residence time. The mean annual drawdown is 0.6 m, and residence time of the water averages 1.4 y (Mitchell and Prepas 1990). 2

15 DAM Alberta Crawling Valley Reservoir Edmonton Calgary Lethbridge N W E Campground & Boatlaunch MAIN DAM OUTLET CANAL S INLET CANAL SCALE IN KILOMETRES Figure 1. Map of Crawling Valley Reservoir. Inset is a map of Alberta indicating the location of the reservoir within the province. 3

16 2.2 Fish community Crawling Valley Reservoir currently supports a diverse fish assemblage. Immediately after construction, northern pike (Esox lucius) and rainbow trout (Oncorhynchus mykiss) migrated from the Bow River to the reservoir via the North Branch Canal. The reservoir was also stocked with brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout during its first year of operation in 1985, and later with walleye over a three year period from 1990 to Additional species in the reservoir include cisco (Coregonus artedi) which were accidentally introduced during the 1992 walleye stocking program, and lake whitefish (Coregonus clupeaformis) which migrated from connecting reservoir canals. Several other species in the reservoir were residents of the two waterbodies incorporated into Crawling Valley Reservoir. These species include: white sucker (Catostomus commersoni), longnose sucker (Catostomus catostomus), shorthead redhorse (Moxostoma macrolepidotum), burbot (Lota lota), fathead minnow (Pimephales promelas), spottail shiner (Notropis hudsonius), trout perch (Percopsis omiscomaycus), and brook stickleback (Culaea inconstans) (Mitchell and Prepas 1990). 3.0 METHODS 3.1 Study design The surface area of the reservoir was divided into 1 km 2 sample units (based on a Universal Transverse Mercator (UTM) grid). Each sample unit was further divided into four 0.25 km 2 quadrats. Sampling sites were randomly selected from the pool of quadrats (phone book method) as described in Morgan (2000). Once a quadrat was selected, it could not be selected again (sampling without replacement). The reservoir was divided into two depth strata. The shallow stratum ranged from 2 to 5 m in depth and the deep stratum ranged from 5 to 15 m in depth. Sampling effort was allocated among the two depth strata in proportion to the area within each stratum (Morgan 2000). The ratio of surface area within the 2 to 5 m stratum (684 ha) to that of the deep stratum (1,024 ha) was 1:1.15. Based on this ratio, three nets were set in the shallow stratum and five in the deep stratum (Figure 2). 4

17 Figure 2. Depth and area stratification of Crawling Valley Reservoir with sample site locations for the 2004 FWIN survey. 5

18 We sampled fish using the fall walleye index gill netting (FWIN) protocol (Morgan 2000). Each FWIN gill net was 61 m long and consisted of eight 7.6 x 1.8 m monofilament panels of different mesh sizes (25, 38, 51, 64, 76, 102, 127, and 152 mm, stretched mesh) sewn together in ascending order. Nets were set perpendicular to reservoir contours from shallow to deep water for a duration of 24 h (± 3 h). Nets were set for an average duration of 22.8 h, ranging from 20.5 to 28.5 h. When adjacent quadrats from different grids were scheduled to be sampled on the same day, nets were set no less than 500 m apart to ensure sites were independent of one another. Areas with steep gradients or abundant aquatic vegetation were avoided. Surface water temperatures (0.5 m below water surface) were measured at each site to ensure sampling was conducted within the FWIN guideline range of 10 to 15 C (Appendix 1); when the water column is equally mixed and fish are randomly distributed (Morgan 2000). 3.2 Biological data As nets were lifted, fish were removed and placed in plastic bags labelled with corresponding sample site and panel mesh size. The number, species and fork length (FL, mm) were recorded for each fish, mesh size panel, and net. Fish that escaped or fell out of the net during retrieval were also recorded and included in overall catch. Additional data were collected on captured walleye including total length (TL, mm), weight (± 5 g), sex, maturity and age. Weight was determined using a Pelouze 5000 g capacity electronic scale that was regularly calibrated with standard weights. Sex was determined by examination of internal organs and maturity level was recorded as immature or mature based on whether the fish appeared able to spawn the next spawning season. The left pelvic fin and scales were used to determine age of adult and juvenile fish, respectively, following procedures in MacKay et al. (1990). All data collected were entered into the provincial government Fisheries Management Information System database administered by ASRD. 6

19 3.3 Data analyses Data analyses and production of graphs were done using Microsoft Excel. Bootstrapping methods described by Haddon (2001) were used to calculate confidence intervals (95%, based on 2,000 replicates with replacement) for FWIN walleye catch (walleye per net). One way ANOVA analyses were performed using JMP IN version 4.0 statistical software and unpaired students t tests were performed using Microsoft Excel Catch per unit effort Catch per unit effort (CUE) was calculated based on the catch per FWIN net, per 24 h period (fish/net/24 h). Walleye CUE estimates from Crawling Valley Reservoir were compared to those from other southern region reservoirs and those from lakes in the northern region of the province to assess the relative walleye abundance. Catch per unit effort was calculated as fish/net to compare with these existing data Length at age and growth We used mean length at age to estimate fish growth using the von Bertalanffy (1938) growth model: Lt = L (1 e K (t t 0 ) ) where, Lt = length at age t, L = the asymptote or final maximum size, K = the rate at which the growth curve approaches the asymptote, and t0 = a time scaler, the hypothetical time when the fish was size zero. Parameter estimates of the growth model were made using Fisheries Analysis and Simulation Tools (FAST 2.0) software (Slipke and Maceina 2001). The 2004 growth 7

20 models were compared to data collected from previous surveys (1998, 2002, and 2003). One way ANOVAs were performed on walleye length at age data from previous sample years to determine whether growth rates changed over time. Unpaired students t tests were performed on walleye length at age data to determine whether growth rate differed between the sexes and ANOVA was used to determine whether length at age varied between sexes Density and stability Walleye population density (y) was predicted using a regression equation (y = x , where x = mean CUE) developed by M. Sullivan based on population estimates and angler creel data from 17 Alberta lakes (M. Sullivan, ASRD Fish and Wildlife Division, pers. comm.). Population stability was based on current total allowable catch (TOC) risk analysis (Sullivan 2003; M. Sullivan, pers. comm. 2005) and on criteria used to classify stability from the ASRD Walleye Management and Recovery Plan (Appendix 2). A standardized probability of CUE was calculated as fish/100 m 2 /24 h using bootstrapping in order to determine the status category in which the walleye population at Crawling Valley Reservoir in 2004 should be classified based on the ASRD Walleye Management and Recovery Plan. Two separate catch rates were used to determine population status and density. One included the mean CUE of all walleye captured in the FWIN, whereas the other included the mean CUE of walleye > 345 mm FL (adult sized walleye; Cooper and Blackburn 2005; unpubl. data). The latter catch rate correction was made because development of the linear regression equation for calculating density was based on angling and trapping data of primarily adult (spawning) walleye. 8

21 4.0 RESULTS Subsurface water temperatures averaged 13.1 C (range 12.5 to 14.0 C) and were all within the FWIN temperature range guidelines of 10 to 15 C. 4.1 Catch results A total of 312 fish comprising seven species were captured during the survey. The mean catch per set was 39.0 fish/net/24 h. More fish were captured per net in deep water (42.2 fish/net/24 h) than in shallow water (33.7 fish/net/24 h). Of the 312 individuals captured, 221 were walleye, with the remaining catch (91 fish) comprised of cisco, white sucker, northern pike, lake whitefish, spottail shiner, and longnose sucker (Appendix 3). 4.2 Walleye CUE Walleye were captured in all mesh sizes with an average catch of 27.2 fish/net/24 h (95% CI = fish/net/24 h) or 24.5 fish/100 m 2 /24 h (95% CI = fish/100 m 2 /24 h) (Figure 3). More walleye were captured in deep water (32.6 fish/net/24 h) than in shallow water (18.4 fish/net/24 h). The 76 mm mesh gill net panel was most efficient at catching walleye (n = 52, 24%) and the 152 mm panel the least efficient (n = 1, < 1%, Appendix 3). Of the 221 walleye captured in the survey, 144 were > 345 mm resulting in an average adult walleye catch rate of 17.9 fish/net/24 h or 15.8 fish/100 m 2 /24 h and 95% CI of fish/100 m 2 /24 h (Figure 4). 9

22 Standardized Probability Lower 95 % CI Upper 95 % CI C U E (walleye/100m 2 /24h) Figure 3. Catch frequency distribution of all captured walleye from Crawling Valley Reservoir, CUE and 95% confidence intervals (24.5 walleye/100 m 2 /24 h; 95% CI = ) calculated using bootstrapping methodology. Standardized Probability Lower 95 % CI Upper 95 % CI C U E (adult walleye/100m 2 /24h) Figure 4. Catch frequency distribution of walleye > 345 mm FL from Crawling Valley Reservoir, CUE and 95% confidence intervals (15.8 walleye/100 m 2 /24 h; 95% CI = ) calculated using bootstrapping methodology. 10

23 4.3 Age class distribution Overall, 13 age classes, ranging from age 0 (young of the year) to age 14 fish with a mean age of y were represented in the catch (Figure 5). Dominant year classes were 1997 (age 7), 1998 (age 6), and 2004 (age 0) with respective catch rates of 5.1, 5.0, and 5.0 fish/net. Collectively, these three age classes accounted for more than half (58%) of the total catch. The 2000 and 2001 year classes, with combined catch rates of < 1 fish/net, were the weakest year classes. Individuals of all three initial stocking yearclasses in 1990, 1991 and 1992 (ages 12 to 14) were represented in the 2004 catch. There was an absence of 1993 and 1994 year classes suggesting stocked walleye did not successfully reproduce until The overall age class distribution suggests recruitment has occurred annually since N = 220 CUE (walleye per net) yoy Age (y) Initial stocking years Figure 5. Age class distribution of walleye captured in Crawling Valley Reservoir, Size distribution Size (FL) of walleye in Crawling Valley Reservoir ranged from mm with an average FL of mm (Figure 6). The population exhibited a multimodal 11

24 distribution. A dominant peak at the mm range represented age 0 walleye. Other peaks at mm consisted primarily of yearling walleye with a few age 2 and 3 fish. The mm range represented fish ranging from age 4 to 12 y, but was dominated by age 6 and 7 fish. There were few fish within the mm size range representing age 4 fish. Although there were differences in gear used among years, the size range of walleye captured in 2004 was similar to those of previous surveys in 1998 and 2003 (Council and Clayton 1999; Council and Cooper 2003). 5.0 N = CUE (walleye per net) Fork Length (mm) Figure 6. Fork length and age frequency distribution of walleye captured in Crawling Valley Reservoir,

25 4.5 Age at maturity Of the 144 adult walleye captured, 96 were mature. Of the mature fish, 47 were females and 49 were males resulting in a female to male sex ratio of 1.0:1.04. Although nearly twice as many females as males were represented in the overall catch (sex ratio = 1.9 females:1.0 males), sexes were equally represented among mature fish. Males and females reached maturity by ages 5 and 6, respectively (Figure 7). By age 7 (473 mm FL), 50% of walleye had reached maturity. CUE (walleye per net) Immature unknowns, n=58 Immature males, n=8 Immature females, n=59 Mature males, n=49 Mature females, n= Age (y) Figure 7. Age at maturity among male and female walleye in Crawling Valley Reservoir, Growth rate and length at age Overall, mean length at age of the walleye population in Crawling Valley Reservoir ranged from mm for age 0 fish to mm for age 14 fish (Table 1). Male walleye younger than age 5 were not captured, therefore comparisons of growth rate between the sexes were limited to ages 5 through 13. In general, growth rate tended to be higher for females than for males; however, unpaired t test results showed a significant sex difference in mean length at age only for age 13 fish (Table 2 and Figure 8). 13

26 Table 1. Summary of mean (± SE) length at age of walleye in Crawling Valley Reservoir, Age Mean length (mm) ± SE (y) All fish n Males n Females n ± Table 2. Comparison of mean (± SE) length at age of female and male walleye. Age Mean FL of females (mm) Mean FL of males (mm) ANOVA t test F df p t df p

27 Females Males Fork length (mm) Males: FL = (Ln Age) ; R 2 = 0.867, n = 106 Females :FL = (Ln Age) ; R 2 = , n = Age (y) Figure 8. Length at age of walleye in Crawling Valley Reservoir, Equations are natural log transformed values. The von Bertalanffy K values (rate at which the fish growth approaches maximum size) showed an overall decrease in walleye growth from 2002 to 2004 (Table 3 and Appendix 4). Results of one way ANOVA analyses showed that overall growth rates significantly decreased among 2, 5, 6, 7 and 12 y age classes across years (Table 4). Mean length at age of walleye from 1996 to 2004 also indicated an overall decreasing trend in growth rate (Figure 9). In comparison to other reservoirs, growth rates of 2004 walleye in Crawling Valley Reservoir were similar to those from the 2003 Lake McGregor population (Figure 10), which was the slowest growing of the southern reservoir walleye populations sampled that year (Cooper 2004). 15

28 Table 3. Summary of von Bertalanffy growth indices (L, K, and t 0 ) for walleye collected from Crawling Valley Reservoir in 1998, and in Age L K t R p < < < < n Lt = length at age t, L = the asymptote or final maximum size, K = the rate at which the growth curve approaches the asymptote, t0 = the theoretical time when fork length = 0. 16

29 Table 4. Analysis of variance results for the difference in mean fork length per age class among sample years on Crawling Valley Reservoir. Age Class Sample Year Mean FL (mm) ± SE n df F ratio p ± ± ± ± ± ± ± ± < ± ± ± ± < ± ± ± ± < ± ± ± ± ± ± ± ± ± ± ± ± ±

30 Fork length (mm) CVR 1996 CVR 1997 CVR 1998 CVR 2003 CVR Age (yrs) Figure 9. Comparison of mean length at age of walleye in Crawling Valley Reservoir in 1996, 1997, 1998, 2003 and 2004 (Cooper 2004) Fork Length (mm) CVR 2004 Newell 2003 McGregor Age (yrs) Figure 10. Comparison of mean length at age of walleye from Crawling Valley Reservoir in 2004 with populations in 2003 from Newell Reservoir (highest growth rate) and McGregor Reservoir (lowest growth rate) (Cooper 2004). 18

31 4.7 Walleye catch rate comparison A catch rate of 17.9 mature fish/net was observed in Crawling Valley Reservoir in 2004, and was higher than those reported for two other southern region reservoirs in the same year, Milk River Ridge (16.0 fish/net) and Forty Mile Coulee (11.1 fish/net) using similar sampling gear and protocol (ASRD 2004c). Relative to other waterbodies in Alberta, FWIN catch rates for Crawling Valley were moderate to high for total walleye and moderate to low for adult walleye (Figure 11) CUE (walleye per net) Heart ʹ00 Release ʹ01 Seibert ʹ00 Milk River Ridge ʹ04 40 Mile ʹ04 Gregoire ʹ02 Bourque ʹ00 CV Adult 04 Calling ʹ02 Long ʹ03 Calling ʹ01 LS Anne ʹ01 Crawling Valley ʹ04 Garner ʹ01 Lakes and Reservoirs in Alberta LS Anne ʹ02 Pigeon ʹ04 Vincent ʹ00 Pigeon ʹ03 Figure 11. Comparison of mean FWIN catch rate (walleye/net) at Crawling Valley Reservoir to other Alberta waterbody FWIN surveys. Graph and data from Watters (2004). 19

32 4.8 Walleye population density and stability An initial walleye density of fish/ha was predicted for Crawling Valley Reservoir using the regression equation. When juveniles were excluded, the corrected walleye density was 9.6 fish/ha, consistent with data from an angler survey on the reservoir that estimated walleye density at 9.67 fish/ha (Cooper and Blackburn 2005). According to the ASRD Walleye Management and Recovery Plan classification (Appendix 2), the status of the walleye population in Crawling Valley Reservoir was determined to be vulnerable. Of the five criteria used to classify Alberta walleye populations, three clearly indicated a vulnerable status (age class stability, length atage, and age at maturity). The remaining two criteria, age class distribution and mean CUE, fell within more than one status range but both had variables within the vulnerable category. Age class stability indicated vulnerable status because the population exhibits considerable variation in year class strength with poor representation from 1999 to 2002 (severe drought years), even though several age classes were present (13 classes) it was the variation in year class strength that suggests a vulnerable population. Length atage was moderate as fish reached 50 cm FL within 6 to 9 years. Age at maturity matched very closely to the vulnerable status category with mean age at maturity ranging between 6 9 y for females and 5 9 y for males. Walleye age class distribution was considered wide with 13 age classes present, indicative of either a stable or a collapsed population. However, the mean age of walleye was 5.2 y, leading to the classification of vulnerable for the age class distribution criterion. Mean catch rate indicated a population that borders between a status of stable and vulnerable with a wide confidence range of walleye/100 m 2 /24 h. However, when only adult fish were included, catch rates were unambiguously within the vulnerable category at walleye/100 m 2 /24 h. 20

33 4.9 Summary When considering all criteria in the Alberta Walleye Management and Recovery Plan, the walleye population in Crawling Valley Reservoir may be designated as vulnerable. Although classified as vulnerable, the walleye population in Crawling Valley Reservoir shows indications of increasing stability with high recent recruitment and ten consecutive years of natural recruitment. Certain year classes are stronger than others, but generally the age structure of Crawling Valley Reservoir appears to be approaching a normalized, more stable level. In addition, K values derived from the von Bertalanffy growth model suggest overall decreased growth rates, indicating a potential increase in density. A similar trend was observed in overall mean length at age comparisons from 1996 to Comparison of mean length at age among age classes between sampling years also suggest decreasing growth rates with significant decreases observed in five age classes. Uncertainty still exists surrounding the Crawling Valley Reservoir walleye population as to whether it will attain a more stabilized state or if current pressures such as incidental angling mortality and illegal harvest will keep the population in varying states of vulnerability, or lead to collapse. A greater degree of certainty is needed regarding the effects of these negative pressures and to what extent environmental effects such as drought have on population stability. Future studies addressing these factors may provide better insight as to whether a harvestable surplus of walleye persists in Crawling Valley Reservoir. 21

34 5.0 LITERATURE CITED Alberta Forestry, Lands and Wildlife Fish planting list. Fish and Wildlife Division, Edmonton, Alberta. Alberta Sustainable Resource Development. 2004a Alberta guide to sport fishing regulations. Queens Printer Bookstore, Edmonton, Alberta, Canada. 92 pp. Alberta Sustainable Resource Development. 2004b. Unpublished lake files on Crawling Valley Reservoir stockings and bathymetric mapping. Alberta Sustainable Resource Development, Fish and Wildlife Division, Brooks, Alberta. Alberta Sustainable Resource Development. 2004c. Unpublished lake files on Forty Mile Coulee and Milk River Ridge reservoirs FWIN sampling program. Alberta Sustainable Resource Development, Fish and Wildlife Division, Lethbridge, Alberta. Berry, D.K Alberta s walleye management and recovery plan. No. T/310, Alberta Environmental Protection, Natural Resources Service, Edmonton, Alberta. 32 pp. Cooper, J.A Walleye (Stizostedion vitreum) recruitment in southern region reservoirs, Alberta, 2003 studies. Alberta Conservation Association, Lethbridge, Alberta. Unpublished. 117 pp. Cooper, J.A., and J.K. Blackburn Population estimate of walleye (Sander vitreus) in Crawling Valley Reservoir, Alberta Conservation Association, Lethbridge, Alberta. Unpublished. 33 pp. Council, T.F Investigations into northern pike (Esox lucius) status in prairie region reservoirs, Alberta, 1999 studies. Alberta Conservation Association, Lethbridge, Alberta. 128 pp. 22

35 Council, T.F Investigations into northern pike (Esox lucius) status in prairie region reservoirs, Alberta, 2000 studies. Alberta Conservation Association, Lethbridge, Alberta. 142 pp. Council, T.F Walleye (Stizostedion vitreum) recruitment in prairie region reservoirs, Alberta, 2001 studies. Alberta Conservation Association, Lethbridge, Alberta. 100 pp. Council, T.F., and J.A. Cooper Sport fish inventory in southern region reservoirs, Alberta 2002 studies. Alberta Conservation Association, Lethbridge, Alberta. 152 pp. Council, T.F., and T.B. Clayton Walleye (Stizostedion vitreum) recruitment in prairie region reservoirs, Alberta, 1996 studies. Alberta Conservation Association, Lethbridge, Alberta. 167 pp. Council, T.F., and T.B. Clayton Walleye (Stizostedion vitreum) recruitment in prairie region reservoirs, Alberta, 1997 studies. Alberta Conservation Association, Lethbridge, Alberta. Unpublished. 183 pp. Council, T.F., and T.B. Clayton Walleye (Stizostedion vitreum) recruitment in prairie region reservoirs, Alberta, 1998 studies. Alberta Conservation Association, Lethbridge, Alberta. 205 pp. English, W.G Lake inventory survey: Crawling Valley Reservoir. Alberta Forestry Lands and Wildlife, Fish and Wildlife Division, Lethbridge, Alberta. Unpublished. 29 pp. Haddon M Modelling and quantitative methods in fisheries. Chapman and Hall/CRC Press, Washington, D.C. 405 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, Canada. 113 pp. 23

36 Mitchell, P., and E. Prepas Atlas of Alberta lakes. University of Alberta Press, Edmonton, Alberta. 675 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. Patterson, B Stock status assessment of walleye (Sander vitreus) at Touchwood Lake, Alberta. Data report produced by Alberta Conservation Association, Edmonton, Alberta. 34 pp Slipke, J.W., and M.J. Maceina Fisheries analyses and simulation tools (FAST2.0). Department of Fisheries and Allied Aquacultures, Auburn University, Alabama, USA. Sullivan, M.G Active management of walleye fisheries in Alberta: dilemmas of managing recovering fisheries. North American Journal of Fisheries Management 23: Sullivan, M.G Personal Communication. ACA and ASRD joint meeting regarding total allowable catch risk analysis, Calgary, Alberta. Sullivan, M.G., and D. Park Alberta walleye index netting protocols: summary of joint ACA/ASRD index netting subcommittee. Alberta Fish and Wildlife Division and Alberta Conservation Association, Edmonton, Alberta. 13p. von Bertalanffy, L A quantitative theory of organic growth. Human Biology 10: Watters, D Long Lake fall walleye index netting survey, Alberta Fish and Wildlife Division, Edmonton, Alberta. Unpublished report. 28pp. 24

37 6.0 APPENDICES Appendix 1. Catch distribution of walleye by gill net and depth stratum at Crawling Valley Reservoir, Codes: walleye = WALL; northern pike = NRPK; lake whitefish = LKWH; cisco = CISC; longnose sucker = LNSC; white sucker = WHSC; spottail shiner = SPSH. Set Grid # location & depth stratum Easting Northing Temp ( C) Time fished (h) WALL NRPK LKWH CISC LNSC WHSC SPSH Total 1 7B, shallow D, shallow C, deep B, deep C, deep D, shallow C, deep A, deep Total/Mean

38 Appendix 2. Description of population classification criteria from the Alberta Walleye Management and Recovery Plan (Berry 1995; Sullivan and Park 2004) Criterion Stable Vulnerable Collapsed Age class Distribution Wide > 8 y classes Mean age 6 9 y Narrow 1 3 y classes Mean age 4 6 y Wide or Narrow Mean age 6 10 y Age class Stability Stable Unstable Stable or unstable Length at age Slow 50 cm in 9 12 y Moderate 50 cm in 7 9 y Fast 50 cm in 4 7 y Age at maturity (mean age) Females 8 10 y Males 7 9 y Females 7 8 y Males 5 7 y Females 4 7 y Males 3 6 y Mean CUE (density) High Moderate Low Walleye/100 m 2 /24 h > 24/100 m 2 /24 h /100 m 2 /24 h < 4.5/100 m 2 /24 h Table from ASRD Walleye Management and Recovery Plan, modified from Berry 1995 and Patterson 2004 (Sullivan and Park 2004) 26

39 Appendix 2. Continued. Alberta Walleye Management and Recovery Plan Description of Status Categories Stable Status Age class distribution relatively broad Minimal variation in individual year class strengths Abundant adult fish, many 3 to 5 y fish Moderate rate of fish growth 9 to 12 y to reach 50 cm in length Mean age at maturity 8 12 y for females 7 9 y for males. High catch rates: CUE >24 fish/100 m 2 /24 h Vulnerable Status Low numbers of fish Narrow, unstable age class distributions Year classes fluctuate between successful and unsuccessful spawning years Adult densities are low Fast fish growth and young age at maturity 7 to 9 y to reach 50 cm Mean age at maturity 7 8 y for females, 5 7 y for males Lower catch rates: CUE = /100 m 2 /24 h Collapsed Status Very low fish densities Unstable age class distribution very narrow to very broad, absence of year classes Few fish reach maturity Very fast growth and young maturity 4 to 7 y to reach 50 cm Mean age at maturity 4 7 y for females, 3 6 y for males Catch rates poor: CUE < 4.5/100 m 2 /24 h Divided into two sub categories: 1. Native (natural) populations severely over harvested 2. Stocked populations that have not become self sustaining 27

40 Appendix 3. Catch by mesh size for various fish species from FWIN survey, Crawling Valley Reservoir, Walleye Capture by Net Mesh Size (mm) Set # Depth (m) Easting Northing Total Total CUE Northern Pike Capture by Net Mesh Size (mm) Set # Depth (m) Easting Northing Total Total CUE

41 Appendix 3. Continued. Cisco Capture by Net Mesh Size (mm) Set # Depth (m) Easting Northing Total Total CUE White Sucker Capture by Net Mesh Size (mm) Set # Depth (m) Easting Northing Total Total CUE

42 Appendix 3. Continued. Lake Whitefish Capture by Net Mesh Size (mm) Set # Depth (m) Easting Northing Total Total CUE

43 Appendix 4. von Bertalanffy growth curves and residual plots for walleye from Crawling Valley Reservoir in 1998 and in All graphs were created by FAST software ver Growth Curve 2004 Residuals Plot 2003 Growth Curve 2003 Residuals Plot 2002 Growth Curve 2002 Residuals Plot 1998 Growth Curve 1998 Walleye Residuals Plot 31

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45 CONSERVATION REPORT SERIES

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