Interactions among hybrid striped bass, white bass, and walleye in Harlan County Reservoir

Walleye Sander vitreus, white bass Morone chrysops, and hybrid striped bass M. chrysops x M. saxatilis are common top-level predators in Midwestern reservoirs. However, the ecology and interactions among these species are not well understood. Therefore, I compared the food habits, diet breadth, diet overlap, isotopic composition, vertical distribution, and vertical overlap of these species in Harlan County Reservoir, Nebraska, during the months of June through September 2002 and 2003. In addition, prey selection of hybrid striped bass for walleye and golden shiner Notemigonus crysoleucas was evaluated using feeding experiments. All three species consumed similar prey (i.e., gizzard shad Dorosoma cepedianum), and diet overlap was high during all months in both years. No species was found to have consistently higher diet breadth. Vertical distribution was similar and spatial overlap was high for white bass and hybrid striped bass in 2002, and between white bass and walleye in 2003. Stable isotope analysis indicated that all three species occupied the same trophic level, and that each predator was deriving carbon from a similar prey source. Few hybrid striped bass consumed prey during feeding experiments, thus definitive selection by hybrid striped bass for walleye and golden shiner could not be determined. This study provides the first comprehensive evaluation of these three top-level predators in a reservoir system. Although resource overlap was high among these predators, competition is not suggested or expected because resources do not appear to be limited in Harlan County Reservoir.