Stocking Practices and Lake Characteristics Influence Probability of Stocked Walleye Survival in Wisconsin’s Ceded Territory Lakes

Abstract

AbstractAs culturally important fisheries for Walleye Sander vitreus exhibit declining densities and reductions in natural recruitment, stocking has increased in popularity as a management tool in Wisconsin’s Ceded Territory. Walleyes were stocked in an average of 160 lakes per year in the 1980s compared with 223 lakes per year in the 2010s. However, many Walleye fingerling stocking events are unsuccessful, with zero or few fish being detected as yearlings in electrofishing surveys the following year. We integrated 31 years of stocking and electrofishing data with lake habitat characteristics to identify factors that influence stocked fingerling survival, measured by the number of individuals stocked compared with those sampled in stocking evaluation surveys. Notably, 21% of stocking events exhibited zero returns in the following year. To handle the prominence of zeros, we used a zero‐inflated mixed‐effects model to test for effects of stocking practices and lake attributes along with lake‐level random effects. Our results suggest that the average length and stocking density are important stocking‐practice‐level characteristics, while water clarity, water temperature, and lake surface area are important lake‐level characteristics for predicting survival. Concerningly, we found a significant reduction in stocked fingerling survival through time. Managers should weigh these factors when determining whether stocking is worthwhile for the system in question and, if so, when selecting a stocking product. Although overall survival of stocked fingerlings is relatively low, better understanding stocking efficacy can help managers maximize utility of limited resources. Future work should assess stocking success in the context of recruitment to the fishery or return to creel. In light of recent work on Walleye fishery collapses and shifting environmental conditions, managers need to temper presumptions of Walleye stocking success and shepherd realistic expectations of stocking utility in regional Walleye rehabilitation efforts.