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

Introduction: 

Bigheaded carp (Hypophthalmichthys spp.) are invasive fish in the Mississippi River basin. Their rapid proliferation has raised concerns about exploitative competition with native fishes, with consequences that remain incompletely understood. We aimed to identify native species most susceptible to competition based on overlap with bigheaded carp in dietary and habitat traits.

Methods: 

We used an established fish traits database to quantify dietary and habitat overlap between bigheaded carp and 100 native fish species. We then integrated dietary and habitat overlap into a composite competition index.

Results: 

Dietary similarity with the native assemblage exceeded habitat similarity, suggesting that while competition with some native species may occur, it may often be limited by spatial separation. Dietary and habitat similarity coefficients were not correlated, indicating that strong dietary overlap did not necessarily coincide with similar habitat use (and vice versa). Approximately 20% of species were classified as high competition risk. The highest-risk species 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).

Discussion: 

Although trait-based predictions have limitations, our results are consistent with empirically documented interactions and provide a rapid, first-pass assessment of potential competitive vulnerability. Dietary overlap, habitat overlap, and the derived competition index offer actionable decision-support for managing potential competition between bigheaded carp and native species. We included ten practical recommendations to translate predictions into conservation and management actions.