Determining ecological niche overlap between reservoir Blue Catfish and other sport fishes using stable isotopes and stomach contents

Abstract Objective Stocking can produce new fisheries, but high niche overlap between stocked and resident species may cause competition that inhibits stocking goals and harms existing fisheries. Thus, stocking of Blue Catfish Ictalurus furcatus in reservoirs to create fisheries could intensify interspecific competition that results in failed fishery development and reduced growth of resident species. Given this potential, we characterized the trophic ecology of Blue Catfish and other sport fishes in two Ohio reservoirs—one with (Hoover Reservoir) and one without (Alum Creek Lake) an established Blue Catfish population. Methods We used stable isotopes (δ13C, δ15N, and δ34S) and diet data to quantify the trophic niches of Blue Catfish, Channel Catfish I. punctatus, Largemouth Bass Micropterus nigricans, crappies Pomoxis spp., and saugeye (Sauger Sander canadensis × Walleye S. vitreus) collected seasonally from summer 2022 through autumn 2024. We quantified the isotopic niches of all species, comparing their size and overlap within and between reservoirs. We used isotopic mixing models and diet analyses to understand the energy pathways underlying observed niche patterns. Results Niche size and overlap varied within and between reservoirs. In Hoover Reservoir, ictalurid niches overlapped and the Channel Catfish niche was larger than those of other sport fish; neither ictalurid niche overlapped with the niches of other sport fish. In Alum Creek Lake, the Channel Catfish niche was larger than the niches of all other sport fishes, with little overlap. Gizzard Shad Dorosoma cepedianum was the primary energy source in both reservoirs, although macroinvertebrates were consumed more in Hoover Reservoir (with established Blue Catfish) despite a higher prey fish density than in Alum Creek Lake. Conclusions Our findings show the potential for competition for prey between Blue Catfish and Channel Catfish, whereas the potential of either ictalurid to compete with other sport fishes for prey is unlikely. Thus, reservoirs that are best suited for creating a successful Blue Catfish fishery without harming existing sport fisheries may be those with abundant prey and small Channel Catfish populations.