Diet and Trophic Ecology of Invasive Blue Catfish Ictalurus furcatus in an Eastern Shore Tributary of the Chesapeake Bay

Blue Catfish Ictalurus furcatus were first introduced to Virginia tributaries of the Chesapeake Bay in the 1970s and have greatly expanded in population size and distribution, prompting ecological and economic concerns. This study investigates the diet and trophic ecology of invasive Blue Catfish in tidal, low-salinity reaches of the Nanticoke River and Marshyhope Creek, on the Chesapeake Bay’s Eastern Shore (Maryland, USA), using complementary stomach content (SCA) and stable isotope (SIA) analyses. Stomach contents from Blue Catfish (n = 363 non-empty stomachs) were collected opportunistically from October 2021 through November 2022. For SIA, 136 individuals across 21 fish species, blue crab Callinectes sapidus, and arrow arum Peltandra virginica were sampled between October 2021 and October 2023. SCA revealed considerable seasonal and size-based diet variability, suggesting a shift from omnivory to piscivory at 563 mm total length. Primary prey included fish, arrow arum seeds, Asian clams Corbicula fluminea, and amphipods, along with seasonally available species of economic and ecological importance (river herring Alosa spp., blue crab, White Perch Morone americana, and Atlantic Menhaden Brevoortia tyrannus). Minimal isotopic niche overlap between large and small Blue Catfish size classes, alongside ontogenetic trends in δ13C and δ15N, substantiated SCA-detected diet shifts. Trophic level estimates derived from Blue Catfish δ15N (n = 54 individuals) were higher than those from SCA, particularly for individuals <563 mm. Blue Catfish occupied a relatively high trophic level, and carbon and sulfur SIA indicated marine resource utilization, substantiating SCA results. This research describes localized trophic interactions of invasive Blue Catfish to inform fishery management planning regarding Blue Catfish’s potential influence on other species of management interest.