Grass Carp Reproduction in Small, Hydrologically Erratic Reservoir Tributaries: Implications for Range Expansions and Establishment of Asian Carps in Novel Habitats

Adult Grass Carp are regularly captured in Truman Reservoir, Missouri, but it is unclear if their presence is from natural reproduction or escapees from nearby ponds. We used ichthyoplankton tows and environmental DNA between May and June, 2014 to investigate Grass Carp spawning in five Truman Reservoir tributaries (basin area: 1,504 – 5,302 km²). Grass Carp eggs were collected in four of the tributaries during four days in June. Egg presence and elevated eDNA coincided with rapid increases in discharge and were verified by quantitative PCR and further confirmed by DNA sequencing.  This is the second documentation of Grass Carp reproduction in a North American reservoir system.  These free-flowing tributaries may be the smallest rivers worldwide, in terms of base flows, annual and flashy discharge and basin area, in which spawning of grass carp has been detected. The Wabash River (Illinois), considered a “small” river for Asian carp spawning, is 69 times larger in basin area and mean annual discharge is 294 times greater than that of the smallest river where spawning was detected in this study. These results have broad implications concerning the risk of Asian carp establishment in other novel habitats including other reservoirs and the Great Lakes.