"Temporal and River Discharge Effects on Silver Carp Abundance and Size Structure in the Wabash River"

The lower Wabash River is unimpounded and follows a more natural hydrological pattern than impounded Midwestern rivers. This temporally and spatially variable pattern has tremendous effects on biota within the system.  Invasive silver carp (Hypophthalmichthys molitrix) in the Wabash exhibit variable patterns of abundance between years, depending on environmental conditions. We sought to examine effects the hydrology of the Wabash has on silver carp populations through the Long Term Electrofishing Survey. During 2014, the Wabash River showed spring flooding that receded during summer and in 2015 flooding subsisted through much of the summer. Density of silver carp more than doubled between these years and preliminary results suggest that this difference is related to discharge. In 2014 silver carp were mostly large individuals (>500mm), and in 2015 a majority of small individuals (<200mm) appeared in June and persisted throughout the summer. This suggests that silver carp utilized the long flood period of 2015 for spawning, evident in the high number of young of year individuals. This supports previous findings that silver carp spawning is dependent on discharge, elucidates what factors affect the abundance of this invasive species, and could lead to the practice of improved control measures.