Comparison of resource use by invasive Black Carp and native fishes using isotopic niche analysis reveals spatial variation in potential competition

Invasive Black Carp (Mylopharyngodon piceus) pose a dual threat to North American freshwater ecosystems through consumption of threatened and endangered mussels and competition with native molluscivores. Despite the potential for Black Carp to compete with native riverine fishes for mussels and other invertebrate prey, only one published study has compared Black Carp trophic position with that of native fishes and only encompassed a single river. The objectives of this study were to assess trophic overlap between Black Carp and two native fish species in the Mississippi River Basin using isotopic niche analysis. Dorsal muscle tissue samples were collected from Black Carp, Freshwater Drum (Aplodinotus grunniens), and Blue Catfish (Ictalurus furcatus) and analyzed for δ¹³C and δ¹⁵N. Although overlap in isotopic niches between Black Carp and native species was low to moderate (10–48%) across most comparisons, native species isotopic niches were entirely or almost entirely inside Black Carp isotopic niche in the Upper/Middle Mississippi River and Lower Mississippi River, indicating that potential for competition for food resources may vary spatially. Intraspecific isotopic niche overlap among locations within the Mississippi River Basin was highly variable (0–69%) for all three species. This variation appeared to be driven by differences among locations, highlighting the importance of assessing interspecific isotopic niche overlap spatially. Broad isotopic niches exhibited by Black Carp in the Mississippi River Basin are indicative of substantial trophic diversity among individuals and use of multiple basal energy sources. The large breadth of their trophic niche has likely contributed to Black Carp invasion success.