Evaluation of Single-Pass Electrofishing and Rapid Habitat Assessment for Monitoring Redside Dace

Abstract

To date, monitoring of the status of the provincially threatened redside dace Clinostomus elongatus in Ontario has been ad hoc or incidental to other sampling programs. We evaluated the efficacy of single-pass backpack electrofishing without block nets to detect redside dace, provide an index of abundance, and characterize size-class distributions. We also examined whether a rapid stream habitat assessment method was suitable for monitoring habitat condition at redside dace sites. Based on 40 sites across 7 Lake Ontario tributaries, catch data and length frequency distributions from single-pass sampling were compared with those from multiple-pass depletion sampling. Single-pass electrofishing captured 47% of estimated redside dace abundance and 34% of biomass. Abundance and biomass data from the single-pass method were positively correlated (abundance r² = 0.83; biomass r² = 0.52) with estimates from the multiple-pass depletion method. Probability of detection and precision of single-pass estimates of abundance were similar to those reported in previous studies on stream salmonids. Single-pass and multiple-pass length frequency distributions were not significantly different. The habitat assessment method failed to detect expected habitat differences between sites that contained redside dace and those that did not. Habitat monitoring could be improved by including more detailed measurements of fine sediment, pool depth, and riparian vegetation.