Fish assemblage structure, trophic ecology, and potential effects of invading Asian carp in Missouri River tributaries, South Dakota

Biological invasions initiate the fastest rates of global change, including biodiversity loss and associated loss of ecosystem function.  One pair of invaders, bighead and silver carp (Asian carps), continue to expand their range northward in the Missouri River basin.  Long-term effects of Asian carps are difficult to predict, but we expect altered food web structure and potentially detrimental levels of competition with native filter feeders.  We conducted standardized sampling in three tributaries to the Missouri River in eastern South Dakota (Big Sioux, James, and Vermillion Rivers) using a variety of gears.  Forty-five species (n = 6,250 fishes) were collected including five silver carp, two grass carp, and one bighead carp. All carp were adults and were collected only at confluence sites.  We evaluated patterns in fish assemblage structure and related these patterns to abiotic (e.g. land-use, river size) features at different spatial scales (e.g. local and watershed).  Filter feeding fishes (e.g., bigmouth buffalo and gizzard shad) were abundant, suggesting that suitable food resources exist for Asian carps in these systems.  We combined assemblage structure data with stable isotope analysis to evaluate the potential extent of food web alteration caused by Asian carps.