Comparison of two electrofishing gears (backpack and parallel wires) and abundances of fishes of the upper Greenbrier River drainage

The type of electrofishing gear influences capture efficiencies and abundance estimates of stream fishes. Few studies have examined the Holton and Sullivan (1954) parallel wires method of electrofishing. For this study, I modeled removal data with seven sampling occasions of three common species, western blacknose dace (Rhinichthys obtusus), fantail darter (Etheostoma flabellare), and mottled sculpin ( Cottus bairdi) from 10 paired sites in the upper Greenbrier River drainage, West Virginia, and estimated capture efficiencies of two electrofishing gear types (the Holton and Sullivan parallel wires method with alternating current and backpack units with pulsed-direct current). Ten candidate models represented alternative hypotheses of how capture efficiency differs among sites, among stream segments, among gear types, and by site covariates of stream width, water current velocity, water depth, and rock size. Additionally, depending on sample size, I modeled capture probabilities based on four sampling occassions for estimates of abundance or reported total numbers of fish species separated by site and gear type. For each sampling occasion and data for western blacknose dace and fantail darter, capture efficiencies of parallel wires exceeded that of the backpack electrofisher at all sites, and were obtained from the best approximating models of either gear or gear + stream width effects. For mottled sculpin, capture efficiencies of parallel wires was less than that of the backpack electrofisher at all sites, and were taken from the best approximating models with gear or gear + rock size effects. First pass estimates of capture probabilities of western blacknose dace and fantail darter were consistently higher for the parallel wires sampling. For mottled sculpin, first pass estimates of capture probabilities were consistently highest from backpack sampling. The parallel wires electrofisher with AC electrical current, through use of electrodes that span the width of the stream, effectively samples pelagic, near-benthic, and some benthic species, but is less effective than DC-pulsed backpack gears at sampling species that use under-rock habitats as refuge. Modification of parallel wires to include DC or pulsed-DC current should improve capture efficiencies of benthic fishes in cobble/boulder streams