Wild Relatives: The tool-using sea otter

Editor’s note: Our Wild Relatives story series will explore the connections between our local wildlife species and related animals from around the globe. By learning about these exotic species, we hope to foster appreciation for the remarkable creatures that live in our backyards and neighborhoods.

The world is home to 13 otter species, but only two live in North America: the river otter and the sea otter. River otters prefer freshwater habitats like rivers, lakes and marshes. They can be found in Illinois and elsewhere across the United States. Meanwhile, sea otters live in salt water. They are only found along the Pacific Coast.

A sea otter. (Photo via Adobe Stock)

Otters are related to weasels. They are the only member of the weasel family that are strong swimmers. Other animals in the weasel family include badgers and wolverines.

Sea otters are much larger than river otters, generally weighing between 45 pounds and 90 pounds. River otters weigh no more than 30 pounds.

Water lovers

Unlike river otters, which spend more of their time on land than in the water, sea otters spend almost all their time in water. They even give birth in the water. They are the only otter species to do so.

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Words to know

Brink: The point at which something is about to happen.

Enact: To make law.

Follicle: A small cavity, sac or gland.

Intertwine: To connect or link closely.

Submerge: To cause to be underwater.

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Sea otters usually only come ashore to sleep and rest. In the water, they can typically be seen floating on their backs. And while they sometimes go on land to sleep, they can even sleep while floating.

Sea otters often gather together and will rest and float in groups called rafts. These rafts can be big — with hundreds or even more than 1,000 otters floating around together. Sometimes they will intertwine themselves in floating masses of seaweed and kelp to anchor themselves while floating.

To help them stay warm in the often cold waters where they live, sea otters have the thickest fur of any animal. They have between 600,000 and 1 million hair follicles per square inch. Curious how that compares to humans? We have between 800 and 1,300 follicles per square inch.

Sea otters spend a lot of time grooming and conditioning their fur so it is able to trap heat and air next to their skin to insulate them. Another key adaptation for their aquatic lifestyle is their ability to go without oxygen for long stretches — as long as five minutes at a time.

They will submerge themselves to hunt for food and also to escape danger. And while five minutes underwater may seem like a long time, it's not as long as some other semiaquatic mammals. River otters can stay underwater for as long as eight minutes, and beavers have them both beat, able to hold their breath for as long as 15 minutes.

Big eaters

While many marine mammals have a layer of blubber to insulate themselves, sea otters have just their thick fur to provide warmth against the cold water. That means they have to eat a lot each day to maintain their metabolism.

A sea otter eating a crab. (Photo via Adobe Stock)

Their diet mainly consists of crabs, mussels, sea urchins and clams. They eat frequently throughout the day, consuming about 25% of their body weight daily.

Sea otters will dive down into the water to hunt for food, but they only eat while at the surface. After catching a meal, they will typically flip on their backs to eat. They are one of the only mammals that is known to use tools and will use rocks to crack open clams and other food items.

The rock they use as a tool can be carried around with them in "pockets" formed from loose skin under their forearms. That's not all they use their pockets for, though. They will also store away food they find when underwater so their paws are free to continue hunting for more before returning to the surface to eat.

Back from the brink

Like beavers, sea otters were once hunted to the brink of extinction because their thick fur was so valuable in the fur trade. At one point in the 19th century, their population was estimated at just 2,000 otters living in scattered colonies along the Pacific Coast.

In 1911, the International Fur Seal Treaty was enacted to help protect otters and other animals. Further protections came in the 1970s when both the Marine Mammal Protection Act and Endangered Species Act were enacted. Today, their population has recovered, but they remain endangered.

About 90% of the world's sea otter population lives off the coast of Alaska, including around some of the state's national parks. Additional populations of sea otters live off the coast of California.