Evaluation of different kinds of disturbance on the efficiency of sampling methods employed for an endangered freshwater crayfish, Austropotamobius pallipes Lereboullet, 1858 (Decapoda: Astacidea: Astacidae), in the northern Iberian Peninsula

We discuss the suitability of several sampling methods in terms of effort, efficiency, accuracy, obtained data, and the degree of disturbance in the endangered crayfish Austropotamobius pallipes (Lereboullet, 1858) and its habitat. Not all sampling strategies can be undertaken in headwater streams, and it is difficult to reach and work in remote areas. We compared three different sampling methods for five years at five sites in two small headwater streams in the Basque Country (Euskadi), northern Iberian Peninsula. We used night viewing from the river bank, hand searching during one removal pass, and the removal method by hand searching (abundance estimates) to determine their accuracy, efficiency, effort, and the disruption of crayfish and their habitat. Comparison of data between both relative abundance estimates, evaluated as captures per unit effort, were not significantly different between the estimates but they both differed significantly from the abundance estimates. Night hand searching or night viewing from the river bank required a longer surveying time and even some risk due to night work. Daylight manual searching could be consequently suitable if management of the species is supported by presence/absence data. The removal method is otherwise recommended when population estimates are required, even if it implies greater disturbance and effort from surveyors.