Otter Lutra lutra population expansion: assessing habitat suitability and connectivity in southern Italy

The Eurasian otter is one of the most endangered mammals in Italy and its distribution is now restricted in two isolated portions in southern Italy. However, in recent times, this species has shown a tendency to expand its range. especially northwards. It is therefore important to identify suitable areas oil the border of its expansion range where the species call establish and disperse, so that these areas call be targeted for conservation actions. To this aim. the distribution. quality and connectivity of habitats of seven river catchments located in the northern portion of the current otter range in Italy were assessed. Catchments included both rivers where the otter currently occurs and where it is likely to expand in the short-medium term. An expert-based Habitat Suitability (HS) model was developed and validated using otter presence-absence data based oil standard field surveys. Fine scale riverbank land cover. extra-riparian coarse scale land cover, attitude, bank slope, and human disturbance were considered as the main factors in the HS model. These variables were available or newly created in the form of digital maps (layers) and the HS model was built by sequentially filtering these layers. Connectivity was assessed within and between river basins through landscape algorithms by taking into account variables that could influence otter dispersal. The results indicated that the seven rivers considered are heterogeneous both in terms of habitat suitability and in terms of connectivity. Among these, one river in particular (the river Volturno). where otters are currently present, showed one of the largest extensions Of Suitable habitats and the best connectivity both within the river and between the river and the neighbouring catchments, suggesting that this river could play a strategic role in the survival and expansion of otters in the surrounding areas.