Assessing sampling effort for lentic Blue Catfish populations using low-frequency electrofishing

ABSTRACT Objective We sought to estimate the amount of low-frequency electrofishing sampling effort that is required to precisely characterize the relative abundance and length distribution of seven lentic Blue Catfish Ictalurus furcatus populations. Methods We used low-frequency electrofishing (15 Hz, 30% duty cycle) to sample Blue Catfish from seven Kansas impoundments using standardized methods and randomized site selection between 2018 and 2023. A resampling approach was used to determine the precision of estimates of relative abundance (catch per effort [CPE]) and CPE of preferred-length (≥760 mm) fish as a function of increasing sampling effort (e.g., number of 300-s sampling sites). We considered the number of sample sites to be acceptable if 80% of the resampled iterations exhibited a relative standard error of the CPE estimate ≤25%. We used a similar resampling approach to compare the length distribution of subsampled populations with those of reference populations. In these tests, we considered the estimated number of sample sites to be acceptable when 80% of the resampled iterations showed no difference from the respective population’s reference length distribution using Kolmogorov–Smirnov tests. Results The sampling effort that was needed to collect precise and representative estimates varied widely by impoundment and metric. Acceptable precision of CPE values was predicted to occur with 40 to 105 sites except in one low-density population where suitable precision was not attained at 200 sites. Suitable precision of preferred-length CPE was attained in one population at 190 sites, but it could not be attained with 200 sampling sites for the other populations. We were able to collect representative length distributions by sampling between 10 and 110 sites. Conclusions Greater sampling effort (40 to 100 sites) than has been reported previously in other studies was needed to accurately estimate the Blue Catfish population metrics in Kansas impoundments. However, alternate methods are likely needed to determine the portion of the population ≥760 mm. These benchmarks and recommendations provide additional guidance for managers in tailoring effective, efficient sampling strategies to inform future Blue Catfish management plans.