Lutra lutra (European Otter)  

Scotland is the principal stronghold for the European otter (Lutra lutra) within the UK and the islands of the Outer Hebrides support a thriving population.
Otters are largely solitary, semi-aquatic mammals that obtain most of their food from lochs, rivers or the sea. The Scottish population unusually comprises a particularly high proportion (perhaps 50% or more) of coastal-dwelling individuals that feed almost exclusively in the sea. The coast and islands of western Scotland are particularly important for this species and coastal otters are occasionally referred to as 'sea otters' despite the fact that they are exactly the same species as the animals which inhabit freshwaters further inland.

Additional Information
Mammal Society Fact Sheet