How can one distinguish between
- Harp Seal (Phoca groenlandica) [mainly from Canada and Greenland]
- Grey Seal (Halichoerus grypus) [mainly, I think, Scottish]
(both not allowed to cross into United States territorial space)
and some more common otters such
- European Otter

All of them, I think, have quite directional hairs, are dense and greasy. Hair length? I don't know.. Any ideas?