Food Preferences and Resources
Food habits vary significantly according to species, location, and season.
River otters' diets consist largely of crayfishes, crabs, and other aquatic invertebrates; fishes; and frogs. Despite concern that otters compete with game fishers, the fishes that otters consume are mainly non-game species. Otters may also occasionally prey on birds, rabbits, and rodents.
Giant otters eat mainly fishes and crabs.
Cape clawless and Asian small-clawed otters feed mainly on crabs and other crustaceans, molluscs, and frogs. Fish are relatively insignificant in their diets. Congo clawless otters probably feed on fairly soft prey items such as small land vertebrates, frogs, and eggs.
A sea otter's diet consists mainly of slow-moving fishes and marine invertebrates including crabs, sea urchins, abalones, clams, mussels, and snails. Food preferences vary among individuals.
Two or more otter species occupying the same geographical area usually have different food habits.
In Thailand, the ranges of at least three otter species overlap. Of these, scientists have determined that the Asian small-clawed otter eats mainly crabs, the smooth otter relies primarily on large fishes, and the Eurasian otter feeds mainly on smaller fishes and amphibians.
In South America, the neotropical otter preys on small fishes, while the giant otter preys on larger species.
In some areas where two or more species overlap, one may be a marine species and the other a freshwater species, such as the marine and southern otters of southern South America.
In Monterey Bay, California, researchers found that each sea otter tends to specialize in only a few types of the more than 50 available invertebrates. This behavior may reduce competition in the California population.
An otter's high metabolic rate - important for generating body heat - requires a substantial amount food.
River otters eat 15% to 20% of their total body weight each day.
Sea otters eat about 25% to 30% of their weight. A large male may consume as much as 11 kg (25 lb.) of food daily.
Methods of Collecting Food
River otters and giant otters hunt by using their vibrissae to detect movements of prey in the water. They catch prey with their teeth.
Giant otters often hold their prey in their paws while eating it. They normally eat small fishes in the water, and bring larger prey to shore.
Shellfish-eating clawless otters catch prey with their paws. Cape clawless otters have been observed using rocks and other hard objects to break open mussel shells.
Sea otters dive to the ocean floor to retrieve food. They catch prey in their forepaws then bring it to the surface.
A sea otter eats in the water, lying on its back, with its food on its chest. Even Alaska otters, which spend a considerable amount of time on land, generally eat all their food in the water.
A sea otter may remove an abalone by repeatedly hitting it with a rock. It also uses a flat rock to break open the shells of crustaceans and mollusks. Holding the rock on its chest, the otter pounds the animal on the rock until it breaks or opens.
Researchers have observed a feeding hierarchy among sea otters. Larger, dominant animals take food from smaller ones. Smaller animals often eat less desirable food than larger animals, including discarded bits of food.