What Do Sea Otters Eat? Diet, Tools and That Armpit Pouch

Sea otters eat mostly spiny and shelled seafloor animals: crabs, sea urchins, clams, mussels, snails and abalone, and northern sea otters add fish to the menu. They put away roughly a quarter of their body weight every day, find much of it by touch, and often crack it open with a rock on their bellies. Here is how the whole otter buffet works, from the dive to that famous armpit pouch.

What do sea otters eat?

Short version: the crunchy, spiny, shelled things that live on the seafloor near them. The U.S. Fish and Wildlife Service (USFWS), which manages sea otters in the U.S., describes southern sea otters as predators of bottom-dwelling invertebrates, naming clams, crabs, sea urchins and snails. Monterey Bay Aquarium adds abalone and mussels to that list.

Farther north, the menu widens a little. The Alaska SeaLife Center lists sea urchins, crabs, clams, mussels, octopus and fish for northern sea otters, and Monterey Bay Aquarium also notes that northern sea otters eat fish. Their teeth are built for crushing hard-shelled prey, which suits a diet that comes wrapped in armor.

A dash only means the sources we used didn't name that food for that population, not that an otter would never eat it. Sea otters are opportunists with a big appetite.

How much does a sea otter eat in a day?

A lot. Monterey Bay Aquarium says a sea otter eats about a quarter of its body weight each day. USFWS puts the daily range at 20 to 30% of body mass, and the Alaska SeaLife Center uses the same 25% figure for what an otter needs just to hold its weight steady.

The aquarium offers a fun way to picture it: for a 150-pound person, eating like an otter would mean roughly 35 to 40 pounds of food a day. That is a very large lunchbox.

So when you see an otter on a cam looking very busy, there is a good chance food is involved.

Why do sea otters eat so much?

Cold water pulls heat out of a body fast, and sea otters don't have the thick layer of blubber that keeps many other marine mammals warm. Instead they rely on what Monterey Bay Aquarium calls the world's densest fur, with more than a million hairs per square inch at its thickest, plus a body that burns through fuel quickly.

Food is the furnace fuel. Eating constantly keeps their metabolism high enough to stay warm in chilly Pacific water. The fur only does its job when it's clean and fluffed with air, which is why otters spend so much time grooming. Our guide on how sea otters stay warm digs into the fur side of the story.

It also explains why oil is so dangerous to them. USFWS notes that oily substances in an otter's fur can destroy its insulating power, leaving the animal exposed to the cold.

How do sea otters find food underwater?

Sea otters forage by diving to the bottom and feeling around. USFWS says they find prey mainly with sensitive whiskers and paws, which comes in handy when you are hunting along a dim seafloor.

Most trips are fairly shallow. According to USFWS, the vast majority of southern sea otter dives are less than 80 feet deep, with occasional dives to around 300 feet. Monterey Bay Aquarium notes that sea otters can reach depths of up to 600 feet and stay down for 6 to 7 minutes, but most dives are much shorter and shallower than that.

A typical foraging trip goes something like this:

1. Dive to the seafloor and search by touch.
2. Grab prey with the forepaws, tucking extras into the skin pocket under a forearm.
3. Surface and roll onto the back, turning the belly into a dinner table.
4. Open the meal with teeth, paws or a rock, then tidy up and head back down.

Do sea otters use rocks as tools?

Yes. Both Monterey Bay Aquarium and USFWS describe sea otters using rocks to break open hard-shelled prey such as crabs and clams. The classic move: float on the back, set a rock on the chest, and bang the shellfish against it until it cracks.

It is also one of the most fun things to spot on a live stream. Softer food doesn't need a hammer, so you won't see a rock every meal.

Where do sea otters keep their food (and rocks)?

In their armpits, more or less. Monterey Bay Aquarium explains that loose skin under each forearm forms a pocket, and otters use these pockets to stash prey during a dive. That way one trip to the bottom can bring up several snacks instead of just one.

Otter fans love to say a favorite rock rides along in there too. The aquarium page we relied on talks about storing food, so we'll file the rock part under popular otter lore and the snack part under confirmed. Either way, it's a built-in lunch bag, and it is adorable.

Do sea otters have favorite foods?

They really seem to. A long-term study of 10 adult female sea otters on the Monterey Peninsula, published in the Journal of Animal Ecology in 2003 by researchers including James Estes, found extreme differences in diet from one otter to the next, even though the otters lived in the same area at the same time.

Those habits held steady across the years of the study, which suggests they may last a lifetime. The researchers also found that preferences seem to run in the female line, most likely learned while young otters travel with their mothers. Different prey takes different skills, so an urchin specialist and a crab specialist are practicing different trades.

That learning starts early. See our guide to how sea otter moms raise their pups for the mom-as-teacher side of the story.

How to watch sea otters eat

Aquarium cams are a great way to see the whole routine up close: the floating, the busy paws, the belly turned dinner table. Feeding schedules vary by aquarium and change over time, so check each aquarium's own website instead of trusting a timetable you find elsewhere online.

Want a second view? Try the Seattle Aquarium cam, or switch to the Elkhorn Slough cam to see wild otters going about their own business in California.

seaotter.cam is an independent fan site and is not affiliated with any aquarium, zoo, agency or organization mentioned here. Facts are drawn from the sources above; check them for the latest information.