Benthic Fish Sampler for Use in Riffle Habitats

The quantitative accuracy and effectiveness of a 1-m2 benthic fish sampler was determined in riffles of three central Kentucky streams. The portable sampler is screened on three sides and has a collection bag on the downstream side; the top and bottom are open and, when in use, the sampler is placed directly on the substrate. Electrofishing and substrate disturbance within the sampler were used to dislodge fish into the collection bag. Electrofishing efficiency and sampler accuracy were estimated by subsequent application of a toxicant within the sampler and in blocknetted stream areas around it, respectively. In Kentucky streams, the mean efficiency of electrofishing within the sampler was 59% for fish collected in riffles, but efficiency was higher in spring and autumn than in other seasons. Kick-sampling was more effective than electrofishing in autumn and winter. Riffle fish population densities were estimated at an accuracy of approximately 63% when the sampler was used. For fish densities less than 6 fish/m2, over 200 samples may be needed to gain 95% confidence that the sample mean is within 10% of the population mean, but the minimum number of samples decreases rapidly as fish density or allowable statistical error increases. This sampler appears to be a useful and reliable device for obtaining quantitative samples of small benthic fishes in riffle habitats.