Single-Pass Electrofishing Predicts Trout Abundance in Mountain Streams with Sparse Habitat

Abstract

Fish abundances in mountain streams are typically estimated over a reach with multiple-pass-removal electrofishing techniques, but such estimates are time consuming and they potentially harm fish. Recent research has indicated that a single electrofishing pass can provide an index of trout abundance in some streams, but applicable circumstances were not clarified. We sampled 30 stream reaches in northwestern Wyoming to determine if the number of trout captured with a single electrofishing pass could be used to predict trout abundance as estimated by a multiple-pass-removal maximum-likelihood model. Stream width, depth, channel slope, instream cover, and substrate were also assessed to determine their possible influences on the relationship between the number of fish captured with a single pass and multiple-pass estimates. We found that trout samples from a single electrofishing pass accurately indexed the abundance of trout in small mountain streams with little instream cover and low fish densities. The relationship between the number of trout captured with a single pass and a multiple-pass estimate was highly significant (r ² = 0.94) and inclusion of stream width in a multivariate model accounted for additional variance (R ² = 0.96). Single pass samples in small mountain streams with little cover and low trout densities can provide accurate estimates of abundance while circumventing problems of differential capture probabilities on subsequent passes, potential harm to trout, and time in the field. Similar relationships may exist within other geographic areas with homogenous habitat, but preliminary testing is required to determine the relationship between abundance and a single-pass estimate.