Points vs. passes: A comparison between electric fishing techniques for sampling fish populations in upland headwater...

Point-abundance sampling by electric fishing (PASE) was compared with single-pass (DF1) and triple-pass depletion sampling (DF3) electric fishing on the same reaches of four headwater streams sampled over multiple years in the Ribble catchment, UK. Juvenile salmonids, mostly brown trout Salmo trutta with some Atlantic salmon S. salar, or the sculpin, common bullhead Cottus perifretum, dominated the species-poor fish assemblage in all streams. Generalised linear mixed models and linear mixed models comparing differences in numerical (ind. m^-2) and biomass density (g m^-2) found that PASE generally returned statistically significant higher estimates for both measures compared to DF1, with the exception of C. perifretum. In comparison to DF3, PASE tended to underestimate the numerical density of the different species and groups, but the difference was not significant for S. trutta, the dominant salmonid. Moreover, biomass density estimates for all fish combined, combined salmonids and S. trutta were not significantly different. Any differences between PASE and DF3, including for Simpson's Diversity Index and fish median length, were mostly linked to C. perifretum, a small, benthic and cryptic species with low capture probability. Overall, for free-swimming, commercially important salmonids, PASE performed comparably with DF3 and outperformed DF1. This study suggests that PASE is generally preferable to DF1 and may be a useful alternative to DF3 with the advantages of rapid deployment through reduced sampling effort alongside minimal disturbance and lessened concern over fish welfare. Further comparison of PASE with DF and more research to better verify the effective sampling area of PASE is warranted.