Comparison of the electrified dozer trawl and boat electrofishing for fish community sampling in turbid and clear river systems

Objective Boat electrofishing has been a primary fish community sampling tool for decades, but it is well established that water clarity can significantly influence netters’ ability to capture stunned fish. Electrified trawls eliminate the need to see the fish prior to capture and may be a solution to the problem of decreased electrofishing efficiency in turbid systems. However, little research has been conducted to compare fish community sampling results using the electrified dozer trawl with results from boat electrofishing in both turbid and clear rivers. Methods We tested the hypothesis that electrified trawls improve sampling efforts in such systems by comparing the species richness, species composition via relative abundance and nonmetric multidimensional scaling, and CPUE (fish per hour of shock time) of select species sampled by boat electrofishing and an electrified dozer trawl in two case studies: one in the Detroit River, Michigan (low turbidity), and one in the Huron River, Ohio (high turbidity). Results Although boat electrofishing captured significantly more species than the dozer trawl in both the Detroit and Huron rivers, the shock time was considerably longer. Species composition analyses indicated that the two gears were likely sampling different fish communities in both rivers, with boat electrofishing targeting more benthic and epibenthic species and the electrified dozer trawl targeting pelagic species. This pattern was generally reflected in the CPUE results, with four epibenthic species and one pelagic species exhibiting significantly higher CPUE for boat electrofishing in the Detroit River, two epibenthic species exhibiting significantly higher CPUE for boat electrofishing in the Huron River, and three pelagic species and one epibenthic species exhibiting significantly higher CPUE for the dozer trawl in the Huron River. Conclusions These results indicate that the electrified dozer trawl may provide an added benefit for fisheries management programs by targeting a different fish community than boat electrofishing, depending on the habitat characteristics of the sample location and the objectives of the sample program.