Efficiency of electrofishing as a sampling method for freshwater crayfish populations in small creeks

Abstract

A total of 56 successive depletion electrofishing surveys were carried out on Austropotamobius pullipes (Lereb.) populations from June 1997 to June 1998, in three small Spanish creeks. Some adaptations of the technique to crayfish sampling were using a low voltage (30-SO V) output, fitting a net on a square shaped-anode, a very slow upstream progression of the fishing team and hand-catching narcotized crayfish. Mean overall catchability was p=0.603, with catches amounting to an average 93.90% of the estimated population number. Crayfish smaller than 40 mm TL comprised a significant proportion (3 1.25%) of the catch. Catchability was found to increase with crayfish size. No significant differences in catchability were found between sexes. Cheliped loss was observed in 26.75% of the individuals captured. This proportion decreased significantly with total length, as did the proportion of individuals suffering loss of both chelipeds. High cheliped loss remains as a major disadvantage of this technique. Nonetheless, our data suggest that electrofishing can be regarded as an effective tool for sampling crayfish populations in this kind of habitats, although its use is scarcely reported.