Recruitment Bottlenecks for Age‐0 Walleye in Northern Wisconsin Lakes

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Since the mid-2000s, recruitment of Walleye Sander vitreus in some northern Wisconsin lakes has declined, potentially because of climate-induced changes in lake environments. Yellow Perch Perca flavescens is also an ecologically and culturally important fish species in this region, but mechanisms driving Yellow Perch recruitment are unclear because of a lack of targeted sampling. Previous studies have suggested that recruitment of these two species may be regulated by similar factors, and observed declines in Walleye recruitment may be cause for concern about Yellow Perch recruitment. Our objectives were to determine if abiotic factors related to recruitment success were similar between Walleye and Yellow Perch populations in northern Wisconsin lakes and if the probability of successful Walleye recruitment was related to estimates of juvenile Yellow Perch abundance before Walleye recruitment declines were observed. We addressed these objectives using historical data from Wisconsin lakes. Random forest analysis incorporating lake-specific averages of predictor variables indicated that winter conditions (duration or severity), growing degree days, variation in spring temperatures, peak summer temperature, and Secchi depth were important predictors of recruitment success for both species. Logistic regression indicated that before Walleye recruitment declines were observed on some lakes (2000)(2001)(2002)(2003)(2004)(2005)(2006), Walleye recruitment success was related to relative abundance of juvenile Yellow Perch in mini-fyke-net sampling. Our results indicate that landscape-level patterns in recruitment success for the two species are likely similar and additional research to understand Yellow Perch recruitment trends is warranted. Better information on Yellow Perch recruitment could contribute to a better understanding of Walleye recruitment trends as declines in Yellow Perch could influence prey availability and survival of age-0 Walleye. Furthermore,

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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Similar Environmental Conditions are Associated with Walleye and Yellow Perch Recruitment Success in Wisconsin Lakes

Brandt

Feiner

Latzka

et al. 2022

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“…More specifically, significant Walleye recruitment declines have occurred among formerly strong, naturally recruiting populations (Rypel et al 2018; Hansen et al 2019). Studies have identified juvenile recruitment as a major contributing mechanism for declines in adult stocks (Hansen et al 2015; Boehm 2016; Gostioux 2018). That said, there is a growing body of literature pointing to a myriad of factors inhibiting Walleye persistence in north temperate lakes, including aquatic invasive species (Hansen et al 2020), fish community interactions (Hansen et al 2015, 2017, 2018), water clarity (Hansen et al 2019), temperature (Hansen et al 2015, 2019), habitat loss (Carpenter et al 2017; Hansen et al 2020), and overharvest (Embke et al 2019) among others (see Raabe et al 2020 for review).…”

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confidence: 99%

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

Lawson

Latzka

Eslinger

2022

As 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.Fisheries for Walleye Sander vitreus are important recreationally, socially, and economically throughout the upper Midwest (Schmalz et al. 2011; Embke et al. 2020). Unfortunately, this area is also within the epicenter of recently described Walleye stock reductions (Bethke and Staples 2015;Rypel et al. 2018). More specifically, significant Walleye recruitment declines have occurred among formerly strong, naturally recruiting populations (Rypel et al. 2018;Hansen et al. 2019). Studies have identified juvenile recruitment as a major contributing mechanism for declines in adult

“…Stocking to rehabilitate and support Wisconsin Walleye fisheries has yielded mixed success (Lawson et al 2022). Additionally, the importance of Yellow Perch as prey for larval Walleye in northern Wisconsin lakes (Gostiaux et al 2022) and indications of declining Yellow Perch populations in Minnesota (Bethke and Staples 2015) have led to increased efforts to sample and characterize Yellow Perch populations in both states (Brandt et al 2022;Holbrook et al 2022) and consideration of expanding standard sampling techniques (Holbrook et al 2022). While this research has helped to reduce the number of viable hypotheses for Walleye recruitment declines, the direct mechanisms have yet to be determined.…”

Section: Variable Observations and Knowledge Gapsmentioning

confidence: 99%

Special Section Overview: Effects of Ecosystem Change on North American Percid Populations

Boehm

Isermann

Ermer³

et al. 2022

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Walleye Sander vitreus, Sauger S. canadensis, and Yellow Perch Perca flavescens (referred to as percids herein) are collectively among the most culturally and ecologically important fish species in North America. As ecosystems change in response to environmental drivers, such as climate change, nutrient loading, and invasive species, there is a need to understand how percid populations respond to these changes. To address this need, a symposium was held during the 81st Annual Midwest Fish and Wildlife Conference to bring fishery scientists and managers together to describe and discuss percid population responses to ecosystem change. Prevailing symposium themes included the challenge of identifying mechanisms responsible for population‐level changes, developing strategies to adaptively manage for resilient fisheries, and consideration of scale, context, and methods when interpreting variable results. Given the uncertainty of how ecosystem changes affect percid populations, participants emphasized the importance of communicating uncertainties to stakeholders, implementing data‐driven management strategies, setting realistic goals, and revising management actions in an adaptive framework. There was universal agreement on both the challenge and necessity of facilitating constructive engagement among stakeholders in cooperative decision making. Symposium participants identified knowledge gaps and discussed future efforts to build on our current understanding of percid populations, including continuation of long‐term monitoring, improved standardization of evaluation metrics, implementing adaptive management experiments to identify causal relationships, development of more robust analytical methods, use of historical data sources, and refining techniques to realistically convey management options to stakeholders.