White and longnose sucker diet composition in Lake Michigan and Saginaw Bay, Lake Huron

Sucker species (Catostomidae) are a common benthic invertivore in North American waterbodies yet are understudied in the Laurentian Great Lakes. Despite large biomass and potential competition with more economically valuable fish species, the diets of Great Lakes suckers are poorly described. We explored the gut contents of adult white suckers ( Catostomus commersonii ) in Lake Michigan and Saginaw Bay, Lake Huron, and longnose suckers ( Catostomus catostomus ) in Lake Michigan. Chironomidae was a primary prey for white suckers in both lakes, along with Amphipoda in Saginaw Bay. For longnose suckers in Lake Michigan, gut contents were dominated by Amphipoda and Isopoda. Relative to other benthic invertebrate taxa, white suckers positively selected Chironomidae as preferred prey (indexed via Chesson’s alpha). Moreover, the average length of consumed Chironomidae and Amphipoda increased with white sucker length, suggesting preferential size selection of prey as suckers grow. Although dreissenid mussels are overwhelmingly abundant in the benthos of Lake Michigan and Lake Huron, relatively few dreissenid mussels were consumed by either sucker species. Thus, suckers are unlikely to contribute to the control of these invasive invertebrates.