Invasive carps versus native fish: A first-pass trait-based index for assessing competition threats

Leandro E. (Steve) Miranda^1*Mirtha A Angulo-Valencia²

• ¹US Geological Survey and Mississippi State University, Mississippi State, MS, United States
• ²Mississippi State University, Mississippi State University, United States

Bigheaded carp (Hypophthalmichthys spp.) are invasive fish in the Mississippi River basin. Their swift proliferation in recent decades has generated concerns regarding possible exploitative competition with native species, resulting in consequences that are not fully understood. Our aim was to identify the species most susceptible to competition based on their overlap with bigheaded carp in terms of dietary and habitat traits. Towards this goal, we applied an established traits database to assess dietary and habitat overlaps between bigheaded carp and 100 native fish species. We then integrated the two overlaps into a competition index. Overall, dietary similarities with the native assemblage exceeded habitat similarities, raising the possibility that although competition with certain native species may occur, it may generally be limited due to spatial separation. No correlation was observed between dietary and habitat similarity coefficients, suggesting that when bigheaded carp exhibited substantial dietary overlap with native species, they did not necessarily share similar habitats, and the reverse was also true. About 20% of the species were classified as high competition risk. The highest competition threats included bigmouth buffalo (Ictiobus cyprinellus), threadfin shad (Dorosoma petenense), black redhorse (Moxostoma duquesnii), bluntnose minnow (Pimephales notatus), highfin carpsucker (Carpiodes velifer), and gizzard shad (Dorosoma cepedianum). We recognize the limitations of our approach grounded on traits; yet its predictions are consistent with empirically documented interactions. Dietary overlaps, habitat overlaps, and the derived competition indices, although first pass, may offer direct and valuable decision-support implications for managing competition between bigheaded carp and native species. We offer 10 concrete, practical ways to turn our predictions into conservation and management action.