Diet Selectivity of Introduced Flathead Catfish in Coastal Rivers

—In two coastal North Carolina rivers (Contentnea Creek and the Northeast Cape Fear River), we found the food habits of introduced flathead catfish Pylodictis olivaris to be primarily piscivorous, which could restructure or suppress native fish communities through direct predation. Fish or crayfish contributed more than 50% of the stomach contents by percent occurrence, percent by number, and percent by weight in both rivers during each of 2 years. Significant differences in diet composition (percent by number) were found between rivers and between years in the Northeast Cape Fear River but not between years within Contentnea Creek. Chesson’s selectivity index values and trends in relative abundances of fish availability relative to those occurring in the diet suggest that flathead catfish feeding is generally random, indicating that these introduced flathead catfish do not selectively feed on prey species with which they did not coevolve. Our research represents the first assessment of prey selectivity by an introduced ictalurid population and provides evidence of the potential impact on native fish communities through their piscivorous food habits. The flathead catfish Pylodictis olivaris is a large piscivorous catfish native to drainages of the Rio Grande, Mississippi, and Mobile rivers (SmithVaniz 1968; Jenkins and Burkhead 1994) that has been introduced by legal and illegal means into at least 13 states and one Canadian province (Jackson 1999). Fuller et al. (1999) considered the introduction of flathead catfish as probably the most * Corresponding author: [email protected] 1 Present address: Department of Fisheries and Aquatic Sciences, University of Florida, 7922 NW 71st Street, Gainesville, Florida 32653, USA. 2 The Unit is jointly supported by North Carolina State University, North Carolina Wildlife Resources Commission, U.S. Geological Survey, and Wildlife Management Institute. 3 Present address: Kansas Department of Wildlife and Parks, Glen Elder Area Office, Rural Route 1, Post Office Box 162A, Glen Elder, Kansas 67446, USA. Received September 30, 2004; accepted March 17, 2005 Published online June 22, 2005 biologically harmful of all fish introductions in North America. The first known flathead catfish introduction into North Carolina waters occurred in 1966 when 11 adults (total weight, 107 kg) were released into the Cape Fear River near Fayetteville, North Carolina (Guier et al. 1984). Within 15 years, the flathead catfish distribution had expanded to cover a 200-km section of the river, and it had emerged as the dominant predator fish within the Cape Fear River system (Guier et al. 1984). Here we examine diet patterns in introduced populations of flathead catfish from two coastal river systems in North Carolina and compare these results with published foraging information for both native and other introduced flathead catfish populations. Invasive species are widely thought to, at least initially, exploit an abundance of prey types that did not coevolve with the invading predator and their mode of predation (Moyle and Light 1996; White and Harvey 2001). Unlike most other catfishes, flathead catfish are obligate carnivores