AUTHORS: Daniel Dembkowski, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Lauren Allex, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Spencer Baeckman, College of Natural Resources, University of Wisconsin-Stevens Point; Daniel Gillman, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Kayla Reed, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Russell Zwiers, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Maxwel Wilkinson, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Daniel Isermann, U.S. Geological Survey, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point
ABSTRACT: Over the past two decades, some northern Wisconsin lakes have experienced declines in walleye recruitment and abundance with concomitant increases in largemouth bass abundance, mirroring broader shifts in fish community structure and species dominance that are projected to occur in relation to changing climatic conditions. Differential trends in abundance of these two species could be mediated or exacerbated by trophic interactions. Previous research has indicated that few walleye have been observed in largemouth bass diets but demonstrated moderate-high diet overlap between the two species during some months, suggesting that potential competitive (rather than predatory) interactions may influence observed trends in recruitment, abundance, and community structure. However, whether the magnitude of diet overlap differs between lakes with and without sustained walleye recruitment is unknown. Furthermore, shifts in predatory species dominance from walleye to largemouth bass could have important implications for prey fish abundance and size structure because of differences in gape limitation and size-selective predation. To address these questions, our research objectives are to determine if: 1) diet compositions of walleye and largemouth bass vary in relation to fish size and season; 2) the magnitude of diet overlap between walleye and largemouth bass varies between lakes with declining and sustained natural walleye recruitment; and 3) sizes of predominant ingested prey fish vary between walleye and largemouth bass. Our approach includes an intensive assessment of diet composition for both species collected during May-October in 2012, 2013, and 2024 from northern Wisconsin lakes with and without sustained natural walleye recruitment. Results will provide insight into mechanisms underlying declines in walleye recruitment in some lakes and implications of shifts in predatory assemblages for size structure of prey fish.
