For most otters, fish is the staple of their diet. This is often supplemented by frogs, crayfish and crabs.
Some otters are expert at opening shellfish, and others will feed on available small mammals or birds.
Prey-dependence leaves otters very vulnerable to prey depletion. Sea otters are hunters of clams, sea urchins and other shelled creatures. They are notable for their ability to use stones to break open shellfish on their stomachs. This skill must be learned by the young.