Age, Growth, and Mortality of Introduced Flathead Catfish in Atlantic Rivers and a Review of Other Populations

—Knowledge of individual growth and mortality rates of an introduced fish population is required to determine the success and degree of establishment as well as to predict the fish’s impact on native fauna. The age and growth of flathead catfish Pylodictis olivaris have been studied extensively in the species’ native and introduced ranges, and estimates have varied widely. We quantified individual growth rates and age structure of three introduced flathead catfish populations in North Carolina’s Atlantic slope rivers using sagittal otoliths, determined trends in growth rates over time, compared these estimates among rivers in native and introduced ranges, and determined total mortality rates for each population. Growth was significantly faster in the Northeast Cape Fear River (NECFR) than in the Lumber and Neuse rivers. Fish in the NECFR grew to a total length of 700 mm by age 7, whereas fish in the Neuse and Lumber river populations reached this length by 8 and 10 years, respectively. The growth rates of fish in all three rivers were consistently higher than those of native riverine populations, similar to those of native reservoir populations, and slower than those of other introduced riverine populations. In general, recent cohorts (1998–2001 year-classes) in these three rivers exhibited slower growth among all ages than did cohorts previous to the 1998 year-class. The annual total mortality rate was similar among the three rivers, ranging from 0.16 to 0.20. These mortality estimates are considerably lower than those from the Missouri and Mississippi rivers, suggesting relatively low fishing mortality for these introduced populations. Overall, flathead catfish populations in reservoirs grow faster than those in rivers, the growth rates of introduced populations exceed those of native populations, and eastern United States populations grow faster than those in western states. Such trends constitute critical information for understanding and managing local populations. Quantification of age and growth is a vital component for understanding the ecology and life history of any fish species. This is especially important for an introduced species like flathead catfish Pylodictis olivaris in the Atlantic slope and elsewhere in the United States. Knowledge of the individual growth rates and age structure of an introduced population is required to determine the success and degree of establishment as well as to predict the fish’s impact on native fauna. Growth rate information can also be used to compare dynamics among water bodies, years, and fish sizes; describe trends over time; examine total mortality rates; and determine the general status of a population. Flathead catfish age and growth have been studied sufficiently to allow elucidation of trends among geographic regions, aquatic habitats (rivers and reservoirs), and native and introduced populations (Tables 1–3). In native riverine populations of flathead catfish, the maximum reported age ranged from 5 years in the Neosho River, Kansas (Minckley and Deacon 1959), to 28 years in the Tallapoosa River, Alabama (Nash 1999). Growth to quality size (510 mm; Quinn 1991) may be obtained between 3 years (Francis 1993) and 9 years (Nash 1999). Memorable-size flathead catfish (860 mm; Quinn 1991) range in age from 8 years (Cross and Hastings 1956; Francis 1993) to 22 years (Nash 1999); however, most populations yield fish of that size by age 12. Fish over age 13 or 1,000 mm are rare to nonexistent in most populations; the maximum reported length was 1,118 mm from a fish captured in the Kansas River, Kansas (Cross and Hastings 1956). The Tallapoosa River population studied by Nash (1999) was perceived to grow considerably slower and live longer than any other native population. Most investigators have used pectoral spines to age flathead catfish, and the results may be variably biased, especially for older fish. Nash and Irwin (1999) compared otoliths and pectoral spines for use in aging flathead catfish and determined that otoliths yielded more accurate age estimates due to annuli being more * Corresponding author: [email protected] 1 Present address: Department of Fisheries and Aquatic Sciences, University of Florida, 7922 Northwest 71st Street, Gainesville, Florida 32653, USA. 2 Present address: Kansas Department of Wildlife and Parks, Glen Elder Area Office, 2131 180 Road, Glen Elder, Kansas 67446, USA. 3 The Unit is jointly supported by North Carolina State University, North Carolina Wildlife Resources Commission, U.S. Geological Survey, and Wildlife Management Institute. Received August 19, 2004; accepted September 27, 2005 Published online January 5, 2006 73 North American Journal of Fisheries Management 26:73–87, 2006 American Fisheries Society 2006 DOI: 10.1577/M04-144.1 [Article]