Lentic Stock Assessment Program 2008-2009 (2009)
Project Leader: Bill Patterson
Primary Staff: Shane Wood, Nathan Carruthers, Troy Furukawa, Brendan Ganton, Ryan Hermanutz, Clayton James, Tyler Johns, Chad Lyttle, Oksana Izio, Bill Patterson, Roy Schmelzeisen, Jennifer Straub, and Stefanie Van Huystee
Partnerships: Alberta Tourism, Parks, Recreation and Culture, Alberta Sustainable Resources Development
Introduction
Walleye (Sander vitreus) populations in Alberta experience considerable fishing pressure, resulting from an imbalance of high angler population and limited fishing opportunities (Sullivan 2003). In 1995, Alberta Sustainable Resource Development (ASRD) implemented the Alberta Walleye Management and Recovery Plan (AWMRP) to facilitate the protection and recovery of exploited walleye fisheries (Berry 1995). Based on AWMRP criteria, Elinor and Ironwood lakes were classified as vulnerable and managed under a 3-walleye catch limit; Haig and Wadlin lakes were classified as collapsed and a managed under a catch-and-release regulation (Berry 1995). To evaluate the effectiveness of these management strategies, we conducted gill net surveys in the four lakes from 13 to 26 September 2008 to examine population structure and growth of walleye. The information collected in these surveys will help ASRD determine the current status of these walleye populations and revise sport fishing regulations accordingly.
Findings
- All four lakes (Elinor, Ironwood, Haig, and Wadlin) exhibited moderate densities of walleye, with estimated mean catch rates ranging from 10.5 - 21.8 fish/100m2/24h.
- Overall, size of walleye in the four lakes ranged from 80 to 675 mm FL but there were very few fish >500 mm FL in Elinor and Ironwood lakes.
- Populations in all four lakes displayed slow growth rates and early maturing fish.
- Walleye from Elinor, Ironwood, and Haig lakes showed wide and stable age-class distributions, while Wadlin Lake displayed a wide but unstable age-class distribution.
Methods
We captured walleye using gill nets following the Fall Walleye Index Netting (FWIN) protocol by Morgan (2000). Each net consisted of eight 7.6 x 1.8 m panels of different mesh sizes (ranging 25 - 152 mm stretched mesh) and was set for 21 to 27 h. We used a stratified-random sampling design based on surface area and depth (shallow: 2 - 5 m and deep: 5 - 15 m) to determine the number and location of sampling sites. We set 11 nets (5 shallow, 6 deep) at Elinor Lake, 8 (6 shallow, 2 deep) at Haig Lake, 11 (3 shallow, 8 deep) at Ironwood Lake, and 18 (5 shallow, 13 deep) at Wadlin. We recorded species, fork length (FL, mm), total length (TL, mm), total weight (g), sex, and state of maturity from each captured fish. We also collected otoliths for aging walleye.
We used a "bootstrap" technique to estimate mean catch rate (fish/100 m2/24 h) and associated 95% confidence intervals (CI) following Haddon (2001). We examined growth rate with the von Bertalanffy growth model. We interpreted population descriptors (age-class distribution, age-class stability, and length-at-age) using the AWMRP criteria developed using the 500 mm FL fish as standard size. Age at maturity was described as when 50% of the walleye are mature.
Results
We captured 227 walleye from Elinor Lake, 197 from Wadling Lake, 192 from Haig Lake, and 127 from Ironwood Lake. Corresponding estimated mean catch rates were 18.7 fish/100 m2/24 h (95% CI = 16.3 - 21.1) for Elinor, 10.5 fish/100 m2/24 h (95% CI = 7.6 - 13.5) for Wadlin Lake, 21.8 fish/100 m2/24 h (95% CI = 17.7 - 27.5) for Haig Lake, and 10.4 fish/100 m2/24 h (95% CI = 7.2 - 14.3) for Ironwood Lake.
Overall, size range of walleye in the four lakes ranged from 80 mm (in Ironwood) to 675 mm (in Haig). However, there were few walleye >500 mm FL in Elinor and Ironwood lakes (Figure 1). The population in Elinor Lake exhibited a unimodal distribution with a dominant peak in the 304-370 mm range. In contrast, populations of the other three lakes exhibited multi-modal distributions. For Ironwood, strong peaks include the 250 and 400-500 mm size ranges. For Haig Lake, strong peaks occurred within the 400-500 mm size ranges. The population in Wadlin Lake exhibited three distinct size ranges with peaks around the 180, 280, and 520 mm size ranges (Figure 1).
Figure 1. Length-frequency distributions of walleye from Elinor, Ironwood, Haig, and Wadlin lakes, Alberta during the 2008 gill netting survey.
Based on AWMRP criteria, walleye populations in all lakes exhibited wide age-class (> 8 year-classes) distributions (Figure 2). Age ranges were 0 - 15 y for Elinor Lake, 0 - 20 y for Ironwood, and 0 - 18 y each for Haig and Wadlin lakes (Figure 2). Corresponding mean (±SE) ages were 6.5 ± 0.2 y (n=217) for Elinor, 6.7 ± 0.4 y (n=126) for Ironwood, 8.1 ± 0.3 (n=188) for Haig and 9.5 ± 0.5 (n=194) for Wadlin. However, older fish (>11 y) were poorly represented in Elinor Lake. Also, the Wadlin Lake population consisted primarily of six year-classes only; ages 3-7, 9-11, and 13-16 were poorly represented. Thus, under the AWMRP age-class distribution is considered stable (6-9 age-classes present) for Elinor, Ironwood, and Haig lake populations but unstable for Wadlin Lake.
Walleye from Haig and Wadlin lakes showed slow growth rates with fish reaching 500 mm FL by age-10. In contrast, although a few individuals >500 mm FL were captured in both lakes, estimated average maximum sizes were 456 mm for the Elinor and 477 for Ironwood lake suggesting that fish in these two lakes are unlikely to attain the 500 mm FL standard size.
Walleye from Elinor, Ironwood, and Haig lakes appear to mature at a young age, with both males and females maturing before age 8. Males matured at age 4 from Elinor, Ironwood, and Haig lakes, while females matured at age 7, age 5, and age 6, respectfully. We could not accurately determine the age-at-maturity of walleye from Wadlin Lake because no ages 4 - 7 fish were caught; however both sexes had reached sexual maturity by age 8.
Figure 2. Age-class distributions of walleye from Elinor, Ironwood, Haig, and Wadlin lakes, Alberta during the 2008 gill netting survey.
Conclusion
Elinor, Haig, Ironwood, and Wadlin lakes displayed a range of moderate densities of walleye with estimated mean catch rates between 10.4 - 21.8 fish/100m2/24h. Overall, size range of walleye in the four lakes ranged 80 - 675 mm. However, there were few walleye >500 mm FL in Elinor and Ironwood lakes. Walleye populations in Elinor, Haig and Ironwood lakes displayed wide and stable age-class distributions, while that of Wadlin Lake showed a wide but unstable age-class distribution. Populations in all four lakes displayed slow growth rates and early maturing fish.
Communications
- ACA data reports prepared to summarize results.
Literature
Berry, D. 1995. Alberta's walleye management and recovery plan. Alberta Fish and Wildlife Division, Edmonton, Alberta, Canada. 32 pp.
Haddon, M. 2001. Modeling and quantitative methods in fisheries. Chapman and Hall/CRC, Boca Raton, Florida, USA. 406 pp.
Morgan, G.E. 2000. Manual of instructions, fall walleye index netting (FWIN). Ontario Ministry of Natural Resources, Fish and Wildlife Branch, Peterborough, Ontario, Canada. 37 pp.
Sullivan, M.G. 2003. Active management of walleye fisheries in Alberta: dilemmas of managing recovering fisheries. North America Journal of Fisheries Management 23: 1343-1358.
Photo 1. Staff removing a northern pike from gill net at Elinor Lake. Left: Roy Schmelzeisen, right: Stefanie Van Huystee. (Photo: Troy Furukawa)
Photo 2. Staff inspecting a gill net at Ironwood Lake. (Photo: Bill Patterson)
Photo 3. Calm day at Elinor Lake. (Photo: Troy Furukawa).
Photo 4. Morning mist at Ironwood Lake. (Photo: Bill Patterson).