Assessing the Influence of Tilapia on Sport Fishes in North Carolina Reservoirs

Nonnative Redbelly Tilapia Tilapia zilli and Blue Tilapia Oreochromus aureaus now occur throughout much of the southern United States.  Foraging flexibility and wide salinity, oxygen and temperature tolerances are thought to account for the general invasion success of these and other tilapia species.  A paucity of empirical data about their winter thermal tolerance and influence on native fishes, however, leaves managers with limited information regarding the likelihood or consequences of further introductions.  This investigation focuses on two NC reservoirs with extant tilapia populations: Lake Hyco, a large reservoir in northcentral NC and Lake Julian, a small impoundment in western NC.  These reservoirs receive heated effluent that is assumed to provide winter refuge for tilapia at a time when temperatures would ordinarily be lethal.  We quantified growth and maturity patterns of tilapia and native sport species (e.g., bluegill, black bass and crappie) in these systems and examined trophic interactions among these species via diet and stable isotope analyses.  We also measured seasonal spatial-distribution patterns and use of thermal refugia for tilapia and sport fishes throughout the year.  Preliminary analyses indicate that the spatiotemporal distributions of sport fishes and tilapia are largely independent of seasonal thermal patterns in these reservoirs.