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Summary

Trout-perch are abundant in many North American aquatic systems, but the ecological roles of trout-perch as predators, competitors and prey remain relatively understudied. To elucidate the ecological role of trout-perch in Saginaw Bay (Lake Huron, North America), the spatial and temporal diet composition was quantified and the frequency of occurrence of trout-perch in diets of piscivorous walleye and yellow perch was evaluated. From May through November 2009–2010, trout-perch and their potential predators and prey were collected monthly from five sites in Saginaw Bay using bottom-trawls. Trout-perch were abundant components of the Saginaw Bay fish community, and in 2009, represented 13.5% of fish collected in trawls, with only yellow perch (38%) and rainbow smelt (19.1%) being more common. Trout-perch primarily consumed Chironomidae (84.0% of diet biomass) and exhibited strong, positive selection for Chironomidae and Amphipoda, suggesting that their diet preferences overlap with the economically important yellow perch and juvenile walleye. Energy content of trout-perch averaged 4795 J g−1 wet and was similar to yellow perch (4662 J g−1 wet) and round goby (3740 J g−1 wet). Thus, they may provide a comparable food source for larger piscivorous fish. However, despite their high energy density, abundance, and spatial overlap with other fish prey species, trout-perch were very rare in diets of piscivorous walleye and yellow perch in Saginaw Bay, indicating that trout-perch are a weak conduit of energy transfer to higher trophic levels.