Walleye Foraging Ecology in an Interconnected Chain of Lakes Influenced by Nonnative Species

Abstract

The Laurentian Great Lakes are a source of nonnative species for smaller inland lakes throughout the region; however, the foraging ecology of predators in smaller systems invaded by nonnative species has not been well studied. We used diet and stable isotope analyses to describe the contributions of native and nonnative forage species to the diets of Walleyes Sander vitreus within an inland lake chain invaded by multiple nonnative species. Our hypothesis was that the Walleyes' diet would be associated with the relative amount of prey available in littoral or offshore–pelagic habitats and would ultimately be linked to the dominant habitat type. We found that Walleyes in the study lakes exhibited flexibility in their dietary inclusion of nonnative prey species. Similar to predators in the Laurentian Great Lakes, Walleyes in smaller inland lakes integrated littoral nonnative species into their diets. However, Walleyes unexpectedly showed limited usage of accessible nonnative pelagic forage. We suggest that predator responses to species introductions are likely context dependent and warrant further investigation in multiple systems and with multiple predators to determine the full extent of nonnative species' integration into the food web and their influence on native populations.

Received June 27, 2015; accepted November 2, 2015

ACKNOWLEDGMENTS

We are grateful to the MDNR Fisheries Division staff, the Little Traverse Bay Band of Odawa Indians–Fisheries staff, Michigan State University students (Ryan MacWilliams, Joe Parzych, Mike Rucinski, Kevin Osantowski, and Elle Gulotty), and University of Vermont students for assistance with field and laboratory efforts. We also thank the numerous recreational anglers that participated in the voluntary collection of Walleye stomachs. Special thanks are extended to Gary Mittelbach and Mary Bremigan for providing insightful reviews on early drafts of this work. Funding for the project was provided by the Federal Aid in Sport Fish Restoration program, the Michigan Game and Fish Fund, and the Robert C. Ball and Betty A. Ball Michigan State University Fisheries and Wildlife Fellowship.