Using mark-recapture techniques to assess factors affecting survival of fall stocked walleye Sander vitreus in two Iowa lakes

Abstract

Stocking walleye Sander virteus is a common management technique to supplement populations where natural reproduction is limited. However, numerous factors can influence the survival of fall stocked walleye including environmental conditions, predation, and stocked walleye total length (TL), condition, and foraging ability. The relative effects of these factors on survival of stocked walleye are challenging to evaluate and rarely assessed simultaneously. Our objective was to determine factors that influence survival rates of stocked fingerling walleye (98−287 mm TL) from stocking until ice cover in two Iowa systems (East Okoboji and West Okoboji) during fall 2015, 2016, and 2017 using mark-recapture techniques. Each fall, roughly 4000 stocked walleye were implanted with passive integrated transponder tags, stocked across both systems, and recaptured via boat electrofishing. Cormack-Jolly-Seber recapture models estimated walleye weekly apparent survival was negatively related to the weekly average proportion of walleye recovered from predator diets (β = −0.89; 95 % credibility interval = −1.74 to −0.03) and positively related to weekly average water temperatures (β = 2.62; 95 % credibility interval = 1.04–4.21). At an average fall water temperature (13.2 ℃), mean walleye apparent survival was 0.83 (95 % credibility interval = 0.75–0.91) when no walleye were recovered from predator diets and declined to 0.54 (95 % credibility interval = 0.28–0.84) when walleye comprised 60 % of predator diets. Between 41–97 % of stocked walleye were lost to apparent mortality from stocking through ice-up and survival was influenced by post-stocking predation rather than walleye body size or condition. Thus, strategies that minimize predation following stocking may result in the greatest improvements in walleye stocking success.