Relaxation of territorial behavior in the Eurasian otter during low-water conditions in a Mediterranean river

Abstract

Abstract The Eurasian otter Lutra lutra is a territorial semi-aquatic carnivore usually found at low densities in rivers, coastal areas, and wetlands. Its diet is based on prey associated with aquatic environments. Mediterranean rivers are highly seasonal, and suffer reduced flow during the summer, resulting in isolated river sections (pools) that can sometimes dry out completely, leading to concentrations of food for otters. So far, this process has not been precisely described, nor have otter densities been estimated under these conditions. In this study, we describe the aggregation of otters in an isolated pool in the Guadiana River in the Tablas de Daimiel National Park (central Spain), which progressively dried out during the summer of 2022. Using non-invasive genetic sampling and spatial capture-recapture techniques, we estimated the otter density at 1.7 individuals/km of river under conditions of circulating flow in restricted pools, up to five times higher than previously described in a Mediterranean environment.