Hydrological Conditions Associated with Bigheaded Carp Spawning in Two Iowa Tributaries to the Upper Mississippi River

Silver and Bighead (i.e., Bigheaded) Carp are invasive species that have been expanding their range throughout the Mississippi River basin. A lock and dam system has transformed the Upper Mississippi River into a series of lentic habitats that may not support successful Bigheaded Carp reproduction. However, free flowing tributaries to the Upper Mississippi River may provide necessary habitat for reproduction, but reproduction in these systems has not been evaluated. Our objective was to evaluate Bigheaded Carp movements and reproduction in two southeastern Iowa tributaries using acoustic telemetry and ichthyoplankton densities to determine hydrological conditions associated with reproduction. Acoustically tagged Bigheaded Carp were monitored with an array of receivers and manual tracking. Ichthyoplankton samples were collected every ten days from April to October 2014 and 2015. Bigheaded Carp moved into tributaries in May with the majority of fish leaving in June. Larval Bigheaded Carp were captured in late May through June during increasing and decreasing hydrographs when water temperatures were between 19 and 24^°C. If Bigheaded Carp are able to successfully reproduce in Upper Mississippi River tributaries, population abundance and continued invasion may increase rapidly despite inadequate reproductive habitat in impounded sections of the Mississippi River.