Trophic Ecology and Potential Effects of Invading Asian Carp in Missouri River Tributaries

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 and its prairie stream tributaries in the Great Plains.  Long-term effects of Asian carps in prairie streams are difficult to predict, but we expect altered food web structure and potentially detrimental levels of competition with native filter feeders.  Standardized sampling was conducted in 2009 during the fall season and in 2010 during spring, summer, and fall seasons at ten sites stratified by stream reach in each of the three tributaries to the Missouri River in eastern South Dakota (Big Sioux, James, and Vermillion Rivers).  We collected 52 species (n = 14,200 fish) using a variety of methods (e.g. boat electrofishing, mini-fyke nets, hoop nets) including adults of eight silver carp, four grass carp, and four bighead carp. How many and where: Juvenile Asian carps were collected in fall 2010.  We observed 6 different assemblages with confluence sites being the most similar and decreasing in similarity as distance increases.   Previous studies in the Illinois River identified diet overlap between Asian carps and native filter feeders such as bigmouth buffalo and gizzard shad.  Gizzard shad ranked 6^th in abundance across sample reaches, and their isotopic signature overlapped with that of Asian carps in our study area. Although Asian carps are currently rare in Missouri River tributaries, our results suggest that their populations are increasing.