As I told you last week, a sea otter burns calories at a rapid rate to help maintain its body temperature in its home in the cold North Pacific. It consumes between 23 and 33 percent of its body weight per day, so a fifty-pound otter eats 11 to 16 lbs. (5 to 7.3 kg) of food every day. Where does a sea otter find this much food, and what do they eat?

Sea otters are known to consume more than 150 different prey species, mostly slow-moving benthic invertebrates such as mollusks, crustaceans, and echinoderms, but if they are hungry enough, they also sometimes eat fish and even seabirds. Sea otters are the only marine animals capable of lifting and turning over rocks in search of prey and the only marine mammal that catches fish with its forepaws rather than with its teeth.

Studies done in southeast Alaska, Prince William Sound, and near Kodiak Island indicate that clams are the primary and preferred prey of sea otters in these regions. Clams constituted anywhere from 34% to 100% of the diet of sea otters near Kodiak. In areas where clams are less plentiful, and in areas where otters have depleted the clam populations, mussels and sea urchins comprise a larger percentage of otters’ diets. Crabs are also important prey species where they are available. On the west side of Kodiak Island, we see otters eating clams, scallops, crab, and octopus. Sea otters’ diets vary not only from one location to another and in response to available prey species, but also because individual otters have different food preferences, and a mother often passes on her fondness for certain foods to her pup.

A sea otter has a loose pouch of skin under each foreleg where it can store food collected on a dive. When the otter returns to the surface, it can rest on its back and leisurely retrieve one piece of food after another from its pouch. In addition to food, the sea otter also stores a rock in one of its pouches. The otter can use the rock underwater to pry loose mussels or other attached bivalves or to dislodge sea urchins wedged in crevices. When floating on the surface, the otter places the rock on its chest and pounds crabs, snails, clams, and other prey against the rock to break through the tough shells. Sea otters are one of the few animals other than humans known to use tools.

Sea otters are very efficient at finding and eating shellfish, and where large groups of sea otters reside, they reduce populations of abalones, clams, and sea urchins to the point where a commercial fishery for these species in the area is not viable. This competition between sea otters and fishermen creates a conflict which cannot be easily resolved by fish and wildlife managers.

Sea otters are considered a “Keystone” species, meaning they affect the ecosystem to a much greater degree than their numbers would suggest. Sea otters protect kelp forests off Northern California by eating herbivores such as sea urchins that graze on the kelp. In turn, the kelp forests provide food and cover for many other species of animals, and kelp forests play an important role in capturing carbon and reducing atmospheric carbon dioxide levels. Without sea otters, urchins over-graze the kelp, throwing the ecosystem out of balance.

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Robin Barefield is the author of three Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter. To download a free copy of one of her novels, watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. If you like audiobooks, check out her audiobook version of Murder Over Kodiak. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska.