Carbon sources for lake sturgeon in Lake Winnebago, Wisconsin

Because lake sturgeon Acipenser fulvescens, like other sturgeon species, are threatened or endangered in many aquatic ecosystems, it is imperative that we increase our understanding of their role in food webs. Our main objective was to determine the carbon sources for lake sturgeon in Lake Winnebago, Wisconsin, which contains one of the largest populations of lake sturgeon in North America. Gut content analysis revealed that gizzard shad Dorosoma cepedianum and Chironomas plumosus larvae (56% and 33% by gut content mass, respectively) were the primary prey items for lake sturgeon in the winter. Larger lake sturgeon were more piscivorous than smaller individuals. A mixing model using delta C-13 and delta N-15 suggests that Chironomus contributes 49% and gizzard shad 37% to the carbon assimilated by lake sturgeon. We estimated the carbon half-life in lake sturgeon to be about 0.6-3.0 years based on a model incorporating metabolism and growth. Thus, the stable isotope results integrate over a considerably longer time period than the gut content analysis. Our results provide critical baseline information about the carbon sources for lake sturgeon that can be used to assess how their role in food webs may change after perturbations such as the introduction of exotic species and changes in land use.