COS 240-2 - Risk Assessment Meets Damage Report: A Look into the Impact of Invasive Carp on the Kansas River Using Stable Isotopes

Abstract: Since the 1970’s invasive carp have expanded throughout much of the Mississippi River basin plaguing fish communities, water recreationists, and wildlife managers alike. Bighead (Hypophthalmichthys nobilis) and Silver (H. molitrix) carps’ diets heavily overlap with many native fishes and impact resident fish communities in habitats they overtake. As generalist fish with massive reproductive capacity, invasive carp alter food webs by drastically reducing plankton when their populations get too dense. The lower Kansas River has a highly stratified invasion gradient between impoundments in the understudied Missouri River sub-basin. The lowest reach of the Kansas River has a high density of invasive carp from its confluence with the Missouri River to WaterOne Dam (river kilometer [rkm] 24), above this lowest dam there is a moderate population up to the Bowersock Dam (rkm 84), while the upper reach of river (above the Bowersock Dam) remains carp-free. The goal of this study was to articulate the effect of these carps at low and high density on resident fishes of the Kansas River relative to an uninvaded reach using stable isotopes. Stable isotopes of carbon (C) and nitrogen (N) are routinely used in ecological studies to describe food webs as the relative abundance of C and N isotopes demonstrate trophic relationships between producers and consumers (primary, secondary and tertiary+). We collected muscle tissue from ten individuals of each target species, from multiple niches, at each of our three study sites to accomplish this. The data produced show species-specific shifts in nutrient uptake as well as constriction in overall niche space across the invasion gradient. These shifts demonstrate the trophic cascade these carp created, more clearly elucidating the toll taken on resident fish communities. We provide a forecast for managers contending with future invasions in the sub-basin by demonstrating carp density-dependent effects on the food webs of native fishes.