|dc.description.abstract||On Lake Wilson, Alabama, a popular recreational and commercial catfish fishery exists and this study was initiated to assess population metrics and estimate exploitation. Currently, creel or length limits are not used to manage this fishery. Blue catfish Ictalurus furcatus, channel catfish I. punctatus, and flathead catfish Pylodictis olivaris were collected using low-pulse (15 mHz) DC electrofishing, and a sub sample of fish were aged with otoliths to describe longevity, growth and survival. Growth increments from back-calculated length at age and catch-curve residuals were used to compare annual growth variation and year-class strength to discharge from Wheeler Dam into Lake Wilson. Average discharge was computed for each year and month from 1985 to 2004 and various temporal time periods were used to assess the influence of discharge on growth and year-class strength. Fish greater than 300 mm total length (TL) were tagged with Carlin dangler tags and exploitation estimates were made based on angler returns that provided a reward. In addition, exploitation for blue catfish was estimated by examining differences in natural mortality and total annual mortality estimates. For blue catfish, simulation modeling was conducted to explore the impacts of variable minimum length limits and exploitation on yield, and number of fish that could potentially be harvested with implications for supporting a trophy fishery.
Male blue catfish and channel catfish grew faster than females, and no difference was observed between growth of male and female flathead catfish. The time to reach harvestable size (30 cm) was 2.3, 3.0, and 3.7 years for channel catfish, blue catfish, and flathead catfish, respectively. Maximum ages for channel catfish, blue catfish and flathead catfish were 12, 25, and 34 years and average annual survival rates based on linear catch-curve regressions were 73, 67, and 85%, respectively.
Age accounted for the majority of the variation in growth of all species of catfish, and less than 1% of the variation in growth was explained by various temporal windows of discharge from Wheeler Dam. Year-class strength was positively related to average discharge from Wheeler Dam prior to spawning period for channel catfish (January-April) and flathead catfish (March-May), and greater blue catfish year-class strength was weakly associated to higher average discharge into Lake Wilson in July.
For blue catfish, I observed length-dependent differences in mortality using a piecewise non-linear model, as total annual mortality was 41% for fish less than 760 mm TL (10.3 years old) and only 16% for fish greater than this length. However, exploitation estimates from tag returns ranged from 5% to 15% for blue catfish when adjusted for non-reporting, and were similar to estimates obtained from linear catch-curve analysis (13-18%), but lower than the maximum exploitation rate of 28% computed for small blue catfish from the non-linear catch-curve regression. From linear catch curve analysis, estimates of natural mortality, and angler tag returns, exploitation ranged from 5 to 20% for channel catfish and flathead catfish. Growth overfishing for blue catfish would likely occur if exploitation was greater than 20%, but fishing mortality likely did not exceed natural mortality. The production of angler-memorable size (813 mm TL) blue catfish at an exploitation rate of 15% would increase 29% with a 457 mm minimum length limit compared to a 305 mm minimum length limit, but yield would only increase 17%. However, the number of fish available for harvest would decline 32% with the more restrictive minimum length limit (457 mm TL), compared with ba||en_US