USING SIGHTINGS FOR ESTIMATING POPULATION DENSITY OF EURASIAN OTTER (Lutra lutra): A PRELIMINARY APPROACH WITH ROWCLIFFE et al's MODEL

Abstract: Because of the crucial importance for otter ecology and conservation, estimating population size (or standardizing it in density) is one of the major fields of research. However, the behaviour of the species makes estimates complicated. The vast majority of methods rely on the study of signs (mainly spraints, but also tracks), but this is insufficient for density measurements, or too costly. Other techniques with proven results use visual counts of otters, but they also have some faults and involve a disproportionate sampling effort. The encounter-based method of population estimation, proposed by Rowcliffe et al. (2008), has been applied to otter sightings in two sites of different habitat with known otter density, and under different survey designs. This provisional check appears to confirm that the method results in adequate population estimates, also when employing samples at random intervals of time and space. Moreover, it involves lower effort, and the census can be tackled by a reduced number of researchers. It is strongly suggested that this methodology be widely tested, to ascertain its performance under different sampling and environmental conditions