EDP Baixo Sabor: Reservoir Filling and Exploration Phase – Otter [2015-2020]

Sampling was designed to cover the whole valley of the lower Sabor river, its tributaries, and the rivers Maçãs and Angueira. A total of 50 transects was established in the study area. The transects had a minimum lenght of 200 m and, within this distance, the survey was stopped after the detection of the first confirmed sign of presence of the species (e.g., spraints, footprints). If there were no evidences of presence in the first 200 m, the transect was extended to a maximum of 600 m, after which, if the absence of signs persisted, the species was considered absent in the transect. Each transect was performed on foot, during daytime, by one or two observers, and the riverbed and its margins were carefully searched for signs of otter's presence (scats, footprints). All scats found were identified in the field and then taken to the laboratory for dietary analysis. The survey was based on indirect signs of otter presence, because individuals of the species are difficult to observe directly, and because the presence signs (spraints and footprints) can be unequivocally identified by experienced technicians. The database only includes the initial points of the transects along a particular water line, independently of the direction of the transect.