Effects of DC Electrofishing Pulse Frequency on Collection of Fish in the Wabash River

Large Midwestern river fisheries are both commercially and recreationally important; however, sampling these systems is difficult due to their large spatial scale and various habitats. Although several gears have been used to sample fish populations in large rivers these gears are often accompanied with issues of sampling selectivity and inefficiencies. Population demographic estimates rely on accurate information collected in the field using these gears. We sought to assess the differences in fish communities sampled with two pulse frequencies of DC electrofishing. We sampled ten 1.6-km sites using both low frequency (15 Hz) and high frequency (60 Hz) pulsed-DC electrofishing during fall and winter 2014, as well as spring and summer 2015. Sampling was conducted for 0.5 hrs for each pulse frequency at each site. As an estimate of relative density we calculated catch per unit of effort (CPUE) for each frequency. CPUE varied between sites and seasons for the various species collected. Non-metric multidimensional scaling (NMDS) ordinations using Bray-Curtis dissimilarity indicated assemblages varied by season. Our current findings suggest that 60 Hz selects for a more representative sample of species; whereas, low frequency seems to over select for flathead catfish and underestimate the relative densities of other commercially important species.