Population Characteristics and Invasion Status of Asian Carps in Missouri River Tributaries, South Dakota

Bighead and silver carps recently invaded the middle Missouri River and associated tributaries in eastern South Dakota (Big Sioux, James, and Vermillion rivers).  Standardized sampling was conducted in fall, 2009 and in spring, summer, fall, 2010 and 2011 at ten sites within the three tributaries. Relative abundance of both carps consistently increased in all tributaries and their distribution expanded upstream each year. Numerous standardized sampling methods were deployed, but boat electrofishing was the only successful method.  The increase in abundance of Asian carps coincided with record flooding during 2010 and 2011.  The higher water levels during this period likely facilitated passage over the numerous lowhead dams present in these systems.  Ninety-seven silver carp and twelve bighead carp were collected at seven sites. Size structure ranged from 179 - 905 mm - although the majority of carps in our samples (79%) were juveniles (<470 mm TL).  Age-0 silver carp (n=2) were collected for the first time in 2011.  Although Asian carps are currently rare in Missouri River tributaries, the young age structure and consistently increasing abundance suggest that they are early in the invasion process and these populations may continue to expand.