Using eDNA to Elucidate Silver and Bighead Carp Range Expansion in Two Missouri River Tributaries in Eastern South Dakota

ObjectiveThis study used environmental DNA (eDNA) sampling methods to determine the possibility of Bighead Carp Hypophthalmichthys nobilis, and Silver Carp H. molitrix, range expansion above barriers to fish movement in two tributaries of the Missouri River in eastern South Dakota. MethodsWe collected water samples above and below two perceived barriers to fish movement: a natural chain of waterfalls in the Big Sioux River and a spillway at the downstream end of a manmade reservoir in the Vermillion River. We used filtration methods to collect invasive carp eDNA from water samples and implemented qPCR techniques to quantify the amount of eDNA in each sample. A total of 213 samples and 38 field blanks were collected over two years (2021/2022). ResultWe detected carp eDNA below both barriers in both years, and above the barrier in the Vermillion River in 2022. The probability of detecting eDNA below the barrier in the Big Sioux River was 51% (95% Credible Interval (CrI): 2 to 97%) and 77% (95% CrI: 8 to 99%) in the Vermillion River. The probability of detecting eDNA above both barriers was significantly smaller: 1% (95% CrI: 0.02 to 24%) for both rivers. ConclusionThe detection of positive samples above the spillway barrier in the Vermillion River provides the first evidence that Bighead and Silver Carp may have expanded their range to habitats upstream of their documented range in eastern South Dakota. Impact StatementThis study demonstrates the utility of using eDNA sampling methods to detect Bighead and Silver Carp in areas of both known and unknown invasive carp presence in smaller tributary streams to the Missouri River.