Evaluating the influence of climate change on Walleye and Largemouth Bass consumption rates in a northern Wisconsin lake

Abstract

In recent decades, some lakes in the Ceded Territory of Wisconsin have experienced increasing largemouth bass Micropterus salmoides abundance coupled with declining walleye Sander vitreus abundance. These shifts in abundance have become of management concern, as largemouth bass have been hypothesized to negatively influence walleye populations through potential competitive or predatory interactions. Yet, a mechanistic understanding of these ecological interactions remains relatively unknown. As climate change continues to alter thermal habitat in northern Wisconsin lakes, understanding how warming water temperatures may influence largemouth bass and walleye interactions, specifically their consumption rates of prey items, could assist in the future management of the two species. Thus, our objectives in this study were to 1) describe current diet proportions for largemouth bass and walleye in Little John Lake and 2) simulate consumption rates of largemouth bass and walleye in the current setting and in predicted climate change scenarios. Our study site, Little John Lake located in Vilas Co., Wisconsin, contains a naturally recruiting walleye population and fish assemblage similar to many other northern Wisconsin lakes. We intensively sampled diets of largemouth bass and walleye in Little John Lake from May-October in 2024. Based on several diet indices, yellow perch Perca flavescens were the most shared diet item between largemouth bass and walleye and contributed to moderately high diet overlap throughout the year. We took a bioenergetics approach to estimate and simulate consumption rates of yellow perch between largemouth bass and walleye with current climate conditions and in a moderate (+2.4℃) and major (+4℃) climate-change scenario. Decreased levels of yellow perch consumption were apparent for both species, but more so for walleye. In the climate change scenarios, consumption of yellow perch for walleye decreased by 4.6% (moderate scenario) and 11.3% (major scenario). The rate of yellow perch consumption for largemouth bass decreased by 1.5% (moderate scenario) and 2.2% (major scenario). Understanding how largemouth bass and walleye consumption rates differ under climate-change scenarios may give valuable insight into future interactions between these species in northern Wisconsin lakes.