Blue Zoo: Sea Otter

Sarah Bedolfe
Sea otters are a keystone species for kelp forests. They keep the kelp beds healthy by preying on sea urchins.

Featuring one amazing marine animal per week.

Sea otters (Enhydra lutis) are the world’s smallest marine mammal, although they are larger than otter species that live in freshwater. Males can reach 45kg (100 lbs) and 1.5m (5ft) while females are slightly smaller. They spend almost all of their time doing one of three things: grooming, sleeping, or eating.

Unlike many other marine mammals, sea otters don’t have blubber. Instead, they use their thick fur to stay warm in the cold water. No other mammal in the world has fur as dense as a sea otter, which has about 100,000 hairs per square centimeter of skin! They have to spend much of their day grooming their fur and blowing air into it. The trapped air acts as insulation and special oil keeps the fur waterproof.

Sea otter fur is the densest of any mammal. Photo courtesy of Mike Baird at flickr.bairdphotos.com via Flickr, Creative Commons License.

Sea otters spend almost no time on land. They have a strong tail that acts like a rudder that helps to steer when they swim. Their hind feet are like flippers. Because of the air in their fur, they look silver underwater. When sea otters sleep, they float on their backs. In order to stay in place and keep from floating out to sea while sleeping, they may wrap themselves up in kelp or hold hands with one another.

A mother otter holds her pup on her belly. Photo courtesy of Mike Baird via Flickr, Creative Commons License.

Sea otters also float on their backs when eating. Otters have to eat a lot – about 25% of their body weight per day. They are predators and eat many types of shellfish. They bring their prey to the surface and lay on their backs to open the shells. Sometimes, they use tools like rocks to help open them.

There are several subspecies of sea otters, all of which live in the North Pacific, along the coasts of North America and Asia. However, they were heavily hunted for their fur prior to the 1900s and reached a devastating low of about 2,000 individuals in 1911, forcing the end of the fur trade. They have been very slow to recover and their range now is much smaller than it once was.

The IUCN Red List now classifies sea otters as Endangered and they are now protected, but they still face many threats.

The healthiest otter population can be found in Alaska, but new problems have arisen there. Orcas have been preying on otters because of a decline in their usual prey, sea lions and seals.

Oil spills are a particular threat for sea otters anywhere because of the sensitivity of their fur. Oil can destroy the insulating properties of otter fur, causing them to freeze; the otter may also accidentally eat the oil if it is grooming when coated in oil.

Sleeping otters wrap themselves in kelp or hold hands to keep from floating apart. Photo courtesy of K Chen via Flickr, Creative Commons License.

Sea otter conservation is important because they are a keystone species for kelp forests because they prey on sea urchins. Sea urchins can devour kelp, and when there are no otters, a kelp forest can turn into an “urchin barren.” When the otter population is healthy, the urchin population stays in check, and the kelp forest can thrive.

Recent research has given another reason why otters matter: sea otters may be helping to alleviate climate change. A new theory suggests that since kelp consumes carbon dioxide and creates oxygen, like plants through photosynthesis, we need healthy kelp forests to slow climate change. Because otters are so important to protecting kelp from urchin predation, they are indirectly contributing to the reduction of greenhouse gases.