Assessment of the Flathead Catfish Population in a Lightly Exploited Fishery in Lake Wilson, Alabama

Abstract

Population metrics and the fishery for flathead catfish Pylodictis olivaris were examined in Lake Wilson, an impoundment of the Tennessee River in Alabama. We described the recreational and commercial exploitation, angler size selectivity, and population demographics and used modeling to assess the impact of exploitation and minimum length limits on the abundance of memorable (860-mm) and trophy (1,020-mm) fish. A total of 1,113 flathead catfish were collected, and 646 of these fish (≥300 mm) were tagged and released to estimate exploitation. The length distribution indicated that there was a high proportion of larger fish in the population, the relative stock densities of preferred-, memorable-, and trophy-length fish being 21, 8, and 2%, respectively. Ages were estimated from otoliths (N = 198), and it was found that fish were slow growing (von Bertalanffy growth coefficient, 0.066) and long-lived (maximum age, 34 years) and expressed a high annual survival rate (83%) and low instantaneous natural mortality (range, 0.099–0.159). From a liberal tag loss rate (2.617%/month) and range of angler nonreporting (20–70%), estimates of exploitation ranged from 5% to 13%. Commercial angling accounted for 26% of the harvest. However, comparison of the observed and simulated length distributions and the difference between catch-curve survival and natural mortality strongly suggested that exploitation was about 5%. Anglers preferred to harvest larger fish, the highest selection being for fish 600–800 mm long. A reduction in harvest rates would have a larger impact on the maintenance of memorable- and trophy-length fish in the population than 356-, 508-, or 610-mm minimum length limits. At exploitation rates greater than 12%, very few trophy-size flathead catfish would remain in the population even if a high minimum length limit (610 mm) were imposed. Currently, flathead catfish are lightly exploited in this section of the Tennessee River and regulations to maintain the quality size of the population are not necessary at this time. However, this population is slow growing and long-lived with low natural mortality and would be sensitive to overfishing. If exploitation should increase and exceed natural mortality, the abundance of memorable- and trophy-size fish would be greatly reduced.