Reproductive Ecology of Silver Carp Along the Upper Mississippi River Invasion Front

Silver Carp (Hypophthalmichthys molitrix) are an 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 Silver 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 Silver Carp reproduction in four southeastern Iowa tributaries and the Mississippi River using adult gonad development and ichthyoplankton densities. Adults were collected monthly and ichthyoplankton samples were collected every ten days from April to October, 2014. Declines in gonadosomatic index during May and June in the Mississippi and Des Moines rivers coincided with the progression of gonads from full to spent. Ichthyoplankton samples are being processed for eggs and larvae to verify reproduction and identify potential limitations to early life stages.  If Silver Carp are able to successfully reproduce in upper Mississippi River tributaries, population abundance may increase rapidly despite inadequate reproductive habitat in impounded sections of the Mississippi River. Additional adult, egg, and larval sampling will occur in 2015 to evaluate annual variation in reproductive patterns.