Omnivory or Piscivory in Non-Native Blue Catfish in Tidal Rivers

Native to the Midwest, blue catfish Ictalurus furcatus have been widely introduced into many Atlantic slope rivers, and are now found in several drainages of the Chesapeake Bay. As a large, long-lived species, fisheries managers are concerned that these catfish are preying upon native species including American shad, river herring, blue crab, and menhaden, all of which once supported or continue to support commercial fisheries. A stratified random design was used to collect diet contents from over 15,000 blue catfish in tidal freshwater, oligohaline, and mesohaline portions of the James, Pamunkey, Mattaponi, and Rapphannock Rivers, which are all major tributaries of the Chesapeake Bay. Blue catfish ranged from 200 mm TL to 1300 mm TL, and included hundreds of catfish > 1000 mm TL. Most sampling occurred from May – September, though some supplemental sampling occurred during the winter on the James River. Blue catfish exhibited broad, omnivorous diets with significant ontogenetic shifts to piscivory at larger sizes. More focused analyses were conducted to describe spatiotemporal variation in prey consumption, which varied seasonally and along the salinity gradient.