Meet the sea otter

Photo by Marshal Hedin. Retrieved from Wikipedia on 08-17-2023. Shared under CC BY-SA 2.0.

BREAKING NEWS: At the time of writing, Otter 841 is still at large!

Otter 841 is a sea otter stealing surfboards off the coast of Santa Cruz, California. The government has been trying to catch Otter 841 for weeks, but they just can’t get her! Like other members of her species, she seems to be a crafty, clever otter.

But what is an otter? Well, otters are members of the previously-discussed mustelid family (just like badgerswolverinesmink, and fishers). There are 13 species of otters; of these, sea otters (Enhydra lutris) are the largest. Male sea otters can reach 40 – 65 inches (100 – 160 cm) long and weigh 35 – 90 pounds (16 – 40 kg); at their largest, a male sea otter is roughly the size of a fourth grader. But even though they have the distinction of being the largest mustelid, sea otters are the smallest marine mammals found in North America.

Sea otters are found off North America’s west coast and Russia’s east coast. Northern sea otters are found in the waters around Alaska, while southern sea otters live in the more temperate waters around California. The southern population of sea otters is generally smaller than their northern cousins. This could be because northern sea otters need more body mass to stay warm in colder Alaskan waters.

That ocean life

Sea otters are the only fully aquatic otter species. While they may go to land to warm up or escape a shark, sea otters can spend their entire life in the ocean.

Much of that ocean time is spent in a kelp forest. These kelp forests provide both food in the form of sea urchins and a lovely anchor for sleeping. Sea otters often wrap themselves in kelp to ensure they don’t float away in the ocean current as they sleep.

Kelp forest. Photo by Daderot. Retrieved from Wikipedia on 08-17-2023. Shared under CC0 1.0 Universal.

Although sea otters don’t mix sexes except during mating, they will gather in large same-sex groups called rafts while resting. These rafts can get up to 1,000 individuals. To keep themselves together, sea otters will hold each other’s paws!

No blubber here!

Unlike other sea animals, sea otters don’t have any blubber to keep them warm in chilly water. Instead, they rely on an extremely thick fur coat.

In fact, sea otters have the thickest fur of any animal, with about 100,000 hairs per square centimeter of skin. This is about the same amount of hair humans have on their entire head!

This thick fur coat has two layers: a dark undercoat and a longer, lighter coat of guard hairs. This traps a layer of air next to their skin, keeping them warm and dry, like a wetsuit. In addition, this air layer helps keep otters buoyant in the water and lets them float.

Because sea otters rely on their fur to keep them warm, they spend a lot of time grooming. Grooming helps keep their coat clean and reapplies natural skin oils to help keep it waterproof. It also fluffs up their fur, adding more air bubbles near their skin to keep them warm. This is why sea otters are so impacted by oil spills – if their fur gets dirty, it has trouble absorbing these air bubbles.

Here’s a fun fact: a sea otter pup’s coat traps so much air that it can’t dive in the water. It just pops back up! To keep their pups from floating away, mother sea otters will wrap them in kelp before foraging for food.

So fluffy! Photo by Mimi. Retrieved from Flickr on 08-17-2023. Shared under CC BY-NC 2.0.

Sea hunter

In addition to their thick fur, sea otters have a high metabolism to help keep them warm. The flip side is that sea otters need to eat a lot – they will eat 20 to 25% of their body weight daily!

The good news is that sea otters are pretty good at hunting. They can dive 45 feet below the surface and hold their breath for around 5 minutes. After searching the ocean floor and kelp beds for food with their sensitive whiskers, their dextrous paws can flip over boulders to attack. Sea otters are the only marine mammal that catches food with its hands, not its mouth!

But what an adult sea otter eats depends greatly on what its mother ate. Sea otters have different tastes and preferences; these are passed from mother to pup and have a lot to do with how deep each animal likes to forage. Some might dive deeper to go after fish, while others might forage near the surface and eat black snails.

Use tools

Sea otters are also some of the only mammals to use tools. While sea urchins can be chomped pretty quickly since sea otters have teeth twice as strong as human teeth, shellfish are considerably harder to get into. So, sea otters have learned to break apart shells using a rock. After bringing their food to the surface, sea otters float on their backs and smash their rock into their prey until the shell breaks open.

But how do sea otters keep hold of their rock while diving? Never fear! Sea otters have patches of loose skin in their armpits that form a pouch. This is a handy place to store your favorite rock as you dive for food. These armpit pouches also serve as a grocery basket – sea otters sometimes store food in them as they return to the water’s surface.

A raft of sea otters floating in the ocean
Sea otter raft. Photo by USFWS. Retrieved from Flickr on 08-17-2023. Shared under CC BY 2.0.

Keystone species

Sea otters are a keystone species. Keystone species are any plant or animal that plays a critical role in their ecosystem. If the keystone species disappears, there are cascading effects on the local ecosystem and the species that reside within it.

More specifically, sea otters keep the sea urchin population under control. Left unchecked, sea urchins will overgraze and decimate a kelp forest so that nothing can live there. So, having a healthy population of sea otters means that the kelp forest and the animals that depend on it are also healthy.

That’s otter-ly amazing! (Yes, yes, I know that’s a bad pun. But I had to).



Animal Diversity Web

National Marine Sanctuary Foundation

The Washington Post

National Geographic


Monterey Bay Aquarium

World Wildlife Fund

U.S. Department of the Interior

San Diego Zoo

Smithsonian Magazine

How Stuff Works

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