George Sanker / North American river otter (Lontra canadensis) swimming with head above water. Acadia National Park, Maine, USA. November.

George Sanker / North American river otter (Lontra canadensis) two in water with autumnal trees reflected in the water, Acadia National Park, Maine, USA, October.

George Sanker / North American River Otter (Lontra canadensis) two swimming near the surface with autumn leaves reflected in water, Acadia National Park, Maine, USA, October.

Bertie Gregory / Northern sea otter (Enhydra lutris kenyoni) floating amongst bull kelp, Vancouver Island, British Columbia, Canada, July.

Matthew Maran / Sea otter (Enhydra lutris) resting at the sea surface with paws in the air. Barkley Sound, Vancouver Island, Canada, August.

Mark Carwardine / Northern / North American river otter (Lontra canadensis) swimming, Captive, Slimbridge, Gloucestershire, UK, July

Shattil & Rozinski / Sea otter (Enhydra lutris) mother and pup off the coast, British Columbia, Canada, Pacific Ocean, September

Nick Garbutt / North American river otter (Lutra canadiensis), two standing at edge of frozen Upper Yellowstone River, Hayden Valley, Yellowstone, USA. February.

Danny Green / North American otter (Lontra canadensis) eating a fish, Yellowstone National Park, USA, February

John Cancalosi / Three River otters (Lutra canadensis) rolling, scratching and grooming itself on a log, Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) rolling, scratching and grooming itself on a log, Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) feeding on a Cutthroat trout (Oncorhynchus clarkii), Wyoming, USA, July.