Multipass Electrofishing Sampling Efficiency for Stream Crayfish Population Estimates

Abstract

We estimated the efficiency of electrofishing for collecting crayfishes in southern Appalachian Mountain streams (Alabama, USA). We conducted electrofishing depletion surveys at 20 sites in five large, species‐rich streams in two drainages. We collected five crayfish species during the depletion surveys. On average, catchability was 34%, with depletion surveys collecting 73% of the individuals that were estimated to reside within stream sections. Catchabilities were lower for pass 1 than for the subsequent passes in 21% of the depletion surveys. The number of species that was collected increased during the second electrofishing pass, indicating that conducting two electrofishing passes may be more effective than a single electrofishing pass is for estimating the richness of crayfish species. Crayfish catchability by electrofishing was higher in streams with higher conductivities, longer crayfish, higher water temperatures, and lower percentages of adult males. Our results show that multipass electrofishing can precisely assess population density for various crayfish species in species‐rich, large‐stream habitats and that multipass electrofishing provides more precise estimates of species richness for crayfish than single‐pass electrofishing does.

Monitoring and Managing Fishes that Are Invisible and Keep Moving Around: Influences of an Invasive Species and Environmental Factors on Capture Probability

“…The opposite trend for benthic‐associated and cryptic Bluehead Sucker suggests that electrofishing gear may dislodge individuals from preferred complex microhabitats with larger substrates and higher water velocities (Bottcher 2009; Laub and Budy 2015), enabling higher on subsequent passes. While uncommonly reported in fishes (Peoples and Frimpong 2011), a higher likelihood of capture on successive electrofishing passes has been reported for crayfishes, which was also attributed to individuals being dislodged from cover on the first pass (Barnett et al 2020).…”

Crayfish assemblages correlate with dam‐induced effects on abiotic factors and predatory fish assemblages in Alabama streams

“…Using Wolman pebble count procedures (Barnett et al, 2020b; Wolman, 1954), we analyzed streambed composition across the bankfull channel width. Ten zig‐zag transects were sampled at each site.…”

“…To estimate predator fish biomass, we conducted additional electrofishing surveys summer 2015–2017 (Barnett, Ochs, et al, 2020b) at 20 of the sampled sites. We recorded the species, total length, and weight of each predator fish.…”