Effect of Electrofishing Sampling Design on Bias of Size-Related Metrics for Blue Catfish in Reservoirs
Kristopher A. Bodine, David L. Buckmeier, J. Warren Schlechte, and Daniel E. Shoup
Abstract.—We used electrofishing data from Oklahoma and Texas reservoirs to evaluate potential temporal (spring, summer, and fall) and spatial (reservoir section and habitat) biases associated with different sampling strategies for estimating size-related metrics (mean total length, proportional size distribution [PSD], and proportion of stock length fish [PSL]) of blue catfish Ictalurus furcatus. Regardless of how many individual fish were sampled, site-specific estimates of mean total length often deviated from the population mean, suggesting that fish within a site were of similar size. Bias across seasons was not consistent for any of the length metrics tested. Only one population had length-related differences between reservoir sections. Blue catfish collected from channel habitats were consistently larger than those collected from point or ﬂat habitats. To identify the number of sites required to reduce deviations in estimates of size-related metrics, we used a Monte Carlo simulation technique to evaluate 3, 5, 10, 20, or 50 randomly selected sites. Regardless of how many individual fish were sampled, when too few sites were sampled, size-related metrics deviated farthest from the population mean. Notably, the population with a truncated length distribution had the least deviation. Simulations indicated that randomly sampling 10–20 sites resulted in estimates with consistent deviations ≤50 mm from the population mean. More effort may be required to routinely estimate PSD and PSL within 10 units. In some situations, biologists may consider stratifying the sample by habitat; however, gains in accuracy and precision may not compensate for increased effort needed to precisely quantify the habitat.