The relative influence of riparian habitat structure and fish availability on otter Lutra lutra L. sprainting activity in a small Mediterranean catchment Original Research Article

The influence of riparian habitat structure and fish availability on otter Lutra lutra marking activity was studied at the head of the Guadalete river (southern Spain). Otter habitat in the study area could be ordered along two gradients in structural properties (altitude, stream order, channel form, water current, bank vegetation), water quality and bankside plant species composition. Generally, higher altitude sites had more dense bankside vegetation cover and better water quality. The dominant upstream bankside plant assemblage consisted of species such as Rubus sp., Salix spp., and Arundo donax, which provided secure shelter for otters. In contrast, at downstream sites the typical plant assemblage was Tamarix africana, Nerium oleander and helophytes, overall bankside cover was lower but wider and the water was more eutrophic. Otter sprainting activity was correlated with this gradient, being higher in downstream sites, especially in areas dominated by short vegetation and scarce human presence. Similarly, fish biomass was greater downstream. A strong positive correlation was observed between otter sprainting activity and larger fish size. Thus, the variability in otter marking intensity along the upper Guadalete seemed to be more dependent on fish availability, and secondly on human disturbance, than on particular riparian habitat features, including the species composition of vegetation growing on the river banks. Implications for conservation management of otters in Mediterranean areas are discussed.