Trophic impacts and distribution of invasive Blue Catfish Ictalurus furcatus in the Albemarle Sound Ecosystem, North Carolina

Abstract

Aquatic invasive species can severely disrupt ecosystems by outcompeting or consuming native species, reducing biodiversity, and causing economic losses to fisheries. The expanding presence of invasive blue catfish (Ictalurus furcatus) in the Albemarle Sound raises pressing concerns about their ecological impacts. Native to the Mississippi River Basin, blue catfish were introduced to Atlantic coast drainages to enhance recreational fishing and have since become invasive across many watersheds. This study examines their invasion extent and effects on native organisms in the Albemarle Sound, North Carolina. In chapter 1, long-term fisheries-independent survey data (North Carolina Division of Marine Fisheries Program-135 and Program-100) were analyzed to assess spatial and temporal patterns in blue catfish distribution. Generalized additive models of occurrence and abundance, and spatial distribution maps revealed that blue catfish have rapidly expanded in range and numbers since the early 2000s, with salinity as the primary environmental constraint on distribution. Blue catfish were predicted to use less optimal, higher salinity habitats when overall population densities were high and low salinity habitats might have been saturated. In chapter 2, dietary habits were investigated through stomach content analysis of blue catfish collected by gill net and electrofishing. Diet analysis revealed that filter-feeding bivalves, including clams (Corbicula fluminea and Rangia cuneata) and mussels (Mytilopsis leucophaeata), were primary prey with bivalves occurring in 64.2% of stomachs. Diet varied spatially, with C. fluminea dominating riverine samples and R. cuneata dominating in sound samples, reflecting the distribution of these bivalve species. Blue catfish exhibited an ontogenetic shift in diet, with larger individuals consuming larger prey including more fish and blue crabs. Other imperiled species including river herring (Alosa spp.) and southern flounder (Paralichthys lethostigma) were consumed in low numbers. These findings suggest that invasive blue catfish may be contributing to the shifting ecosystem state in the Albemarle Sound, with reduced productivity of traditional fisheries and declining water quality due to removal of filter-feeding bivalves. Proactive management of blue catfish populations in the Albemarle Sound is urgently needed to minimize further ecological degradation of this historically productive estuarine system.