In the south east of the Massif Central, the National Cevennes Park covers about 3000 km² of medium sized mountains, criss-crossed by contrasted and flow-variable hydrographical network dividing between the Atlantic and Mediterranean catchment areas. The Eurasian otter appears to have disappeared from that region around the 1960’s. Since 1990, evidence of otters presence has again been found in some rivers and the evolution of the population has been monitored by systematic research of their sign in the principal watercourses. Today, with a GIS (Geographical Information System), spatio-temporal analysis of 13 years survey brings out a progressive recolonization of some catchments by otters tracks and spraints (faeces). But the spatial structure of the population, the dispersal corridors and the seasonal use of the landscape by otters are still badly known. Spraints genotyping by PCR, as non-invasive sampling, and GIS tools will then be used to model the recolonization of this still endangered species and protect it against increasing anthropogenic pressures.