Effect of Sample Duration on Catch Rate and Size Structure Data for Blue Catfish Collected by Low-Frequency Electrofishing

Although low-frequency, pulsed-DC electrofishing is considered the most effective method for sampling Blue CatfishIctalurus furcatusin reservoirs, efforts to improve sampling efficiency have not been fully explored. Optimizing sampling duration can reduce cost and effort if shorter sample times still produce precision similar to that of longer samples. We compared several catch rate and size structure metrics from the first and second 5-min intervals of 10-min low-frequency electrofishing samples for Blue Catfish in three Oklahoma reservoirs (N = 40 sites total). The total Blue Catfish CPUE (CPUETotal), CPUE of preferred-length fish (>760 mm; CPUE760), mean TL, proportional size distribution (PSD), and PSD of preferred-length fish did not significantly differ between sampling intervals. One reservoir had a higher proportion of 200-299-mm fish in the second 5-min interval; however, no other differences in length frequency or other size metrics were detected between the first and second 5-min intervals in any reservoir. Sampling precision met the target level (relative standard error = 20) for CPUE(Total)but not CPUE(760)during both the first 5 min and the full 10-min sample at all reservoirs. Monte Carlo simulation indicated that 10 samples would be needed to achieve the target precision (relative standard error <= 20) for CPUE(Total)and 38-65 samples would be needed for precise CPUE(760)metrics regardless of sample duration. In fisheries with moderate catch rates like those we observed (150-500 fish/h), we recommend short-duration (i.e., 5-min) sampling because data of the same quality can be collected with reduced cost and effort. For situations in which sampling precision is low (e.g., CPUE760), we recommend increasing the number of replicate 5-min samples. Using shorter sample durations provides a method for managers to obtain quality population data more efficiently, allowing time for other worthwhile management activities that would otherwise not be possible.

Automated summary

Low-frequency pulsed-DC electrofishing is considered effective for sampling Blue Catfish, but efforts to improve sampling efficiency are needed. Research shows that there were no significant differences between 5-minute and 10-minute samples in reservoirs, indicating that shorter sampling durations can reduce costs.