Assessment of Electrofishing Bias, Angler Exploitation, and a Creel Survey, and Flathead Catfish Population Assessment in Lake Wilson, Alabama
Type of DegreeThesis
Fisheries and Allied Aquacultures
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A popular recreational and commercial catfish fishery for blue catfish Ictalurus furcatus, channel catfish I. punctatus, and to a lesser extent, flathead catfish Pylodictus olivaris exists on Lake Wilson, Alabama. Catfish were collected using low-frequency (15 pulses/s), and temporal and size bias associated with electrofishing recapture was determined for blue catfish and flathead catfish. A roving creel survey was conducted from April to October 2006 to evaluate catfish angling effort, catch, and harvest. Fish greater than 300 mm total length (TL) were tagged with Carlin dangler tags to estimate electrofishing recapture rates and exploitation from angler tag returns. For flathead catfish, simulation modeling was conducted to explore the impacts of three minimum length limits and exploitation on yield, number of fish harvested by anglers, and memorable-size and trophy-size fish abundance. Immediate (24 h) recapture rates were low for blue catfish (2%) and flathead catfish (1%) from an enclosed cove, and longer recovery periods may be required before these fish again become susceptible to electrofishing gear. Similarly, overall recapture rates of tagged blue catfish and flathead catfish were low (0 to 4%) during routine electrofishing surveys despite an increase in the number of tagged catfish at large and indicated low capture probabilities and/or high abundance of catfish. The recapture of tagged channel catfish was not observed possibly due to inefficiency of low-frequency electrofishing for this species. A roving creel survey was conducted from April to October 2006 and about 73,000 h of angler effort were directed at catfish and anglers harvested 49,015 kg (8 kg/ha). Angler catch was predominantly blue catfish and channel catfish and the catch of flathead catfish was not observed.. Despite high angler effort and harvest, catch and harvest rates were high and averaged 1.5 and 1.2 catfish/hour, respectively. Harvest was 72% higher in 1990 than 2006, and this decrease was possibly attributed the a decline in commercial anglers and differences in creel survey design. Catfish anglers supported a regulation beneficial to trophy-size blue catfish, but were concerned about bag limits as most anglers describe larger blue catfish (= 9 kg) as poor quality for consumption. The majority of blue catfish and channel catfish harvested were between 300 and 550 mm and fish greater than 700 mm were rarely harvested. For all catfish species, the probability of harvest was highest at 600-700 mm and declined for larger catfish (= 800 mm) indicating preference for angler-quality and angler-preferred sized catfish. Most angler tag returns occurred from April to October and were located in the vicinity of the Wheeler Dam tailrace. Estimates of exploitation from tag returns ranged from 6 to 19% for blue catfish, 4 to 13% for channel catfish, and 4 to 15% for flathead catfish at varying levels of angler non-reporting. Based on results of my simulation modeling, flathead catfish predicted exploitation rates (˜ 6%) were similar to estimates computed from angler tag returns (5.4%). Thus, exploitation did not exceed natural mortality estimates (17%) and growth overfishing was very unlikely even if exploitation rates increased about three fold in the current fishery. A minimum length limit of 610 mm would be beneficial for maintaining the flathead catfish population, but the number of fish available for anglers to harvest would be reduced by about 50% compared a 356 and 508 mm minimum length limit. Although the flathead catfish fishery is lightly exploited, growth is slow and fish are extremely long lived, and a potential increase in exploitation caused by the popularity of the Lake Wilson catfish fishery may become a concern for future management of the fishery.