Evidence of Asian carp spawning above a key choke point in the Mississippi River: Data

Bighead Carp, Silver Carp and Grass Carp (collectively Asian carp) were introduced to North America in the 1960s and 70s and have established in the lower Mississippi River basin. Previously published evidence for spawning of these species has been limited in the upper Mississippi River to just downstream of Dam 22 (near Saverton, MO). In 2013 and 2014, we sampled ichthyoplankton at 18 locations in the main stem of the upper Mississippi River from Dam 9 through Dam 19 and in four tributary rivers that empty into the Mississippi River (Des Moines, Skunk, Iowa and Wisconsin Rivers). We identified eggs and larvae using morphological techniques and then used genetic tools to confirm species identity. The spawning events we observed often included more than one species of Asian carp and in a few cases included eggs that must have been derived from more than one upstream spawning event. The upstream extent of genetically confirmed Grass Carp ichthyoplankton was in the Wisconsin River, while Bighead Carp and Silver Carp ichthyoplankton were observed in Pool 16 of the Mississippi River. In all these cases, ichthyoplankton likely drifted downstream for several kilometers prior to collection. Higher water velocities (and to a lesser extent higher temperatures) were associated with increased likelihood of observing eggs or larvae, although the temperature range we encountered was mostly above 17°C. Several major spawning events were observed in 2013, but not in 2014. The area between dams 15 and 19 appears to be the upstream edge of spawning activity for both Silver Carp and Bighead Carp, suggesting this area could be a focal point for management designed to limit further movement of these species upstream.