Reproduction

Breeding may take place year round. Males mate with multiple partners throughout the year. Males will find a receptive partner and then remain with her during estrus. When they mate he holds her in his jaw and scars are often present on females due to this.

Only a single pup is born at a time. Pups are initially carried on the mothers chest. She must leave the pup at the surface when she dives and she may tie it in a kelp frond during this time.

Due to the presence of delayed implantation these mammals have a highly varied gestation of 4 to 12 months.

After two months they will start to move off and feed on their own. Independence is reached by six months old.

Females reach sexual maturity at 4 years old with males not maturing until 6 years old. Most females breed once every 2 years.

As few as 25% of sea otter pups survive to reach adulthood.

Behavior

Another adaptation which helps to survive in their cold environment, apart from the fur, is a layer of air which is trapped against the fur when they dive.

The dense fur of a sea otter requires regular maintenance to ensure it is clean and remains waterproof.

Their entire life is spent at sea apart from females who may occasionally come to shore to give birth or during periods of stormy weather. They are well adapted for swimming. Their lungs are 2 and a half times the size of a similarly sized land animal. This allows them to dive to 30m (98ft) below the surface and remain submerged for 4 minutes.

Sea otters are active during the day. By night they will wrap kelp around them which stops them floating away while they sleep.

These social animals are often seen in groups known as rafts. In some areas these groups grow to include hundreds of individuals.

Males are slightly territorial and may work to exclude other males from their territory. This may involve small fights or aggression by the intruder. They will allow females to move freely through the territory.

Males work hard to defend their territory against other males. Most fights never turn violent instead being settled by splashing and vocal contests.

They are equipped with a strong sense of smell and good eyesight both in and out of water which helps them to find food.

When swimming they travel at speeds of between 4.8 and 8km/h (3-5mph).

Predators and Threats

Natural predators of the sea otter include killer whales, sharks, bald eagles, coyotes and brown bears.

As the availability of larger prey such as seals has declined predators such as killer whales have had to switch to the smaller sea otter.

In the 1700s it was estimated that there may be as many as 300,000 individual sea otters on Earth. By 1911 the animals had been hunted by near extinction but were afforded protection under the International Fur Seal Treaty. By this point as few as 2,000 sea otters were thought to remain.

A more recent estimate made from 2004 to 2012 placed the population at 89,000 in Alaska and 28,000 in Russia

In 1977 they were offered further protection under the Endangered Species Act.

Despite these larger numbers and the continued expansion of the population in areas where they have been reintroduced they are still considered to be decreasing.

Pollution in the water can prevent the air from trapping against their skin correctly. It can also be swallowed when they are grooming leading to health issues. This can cause them to die of hypothermia. Oil spills are now viewed as the largest threat to the species having overtaken hunting.

Fishing equipment presents a threat to this species as they can become trapped there.

The soft fur of the sea otter has long been sought by hunters and this saw them almost driven to extinction.

In parts of their range the sea otter is impacted by disease. Climate change is an emerging threat to this species.

Wear to the teeth is a major contributor to the death of adult animals.

Quick facts

Sea otters are the smallest species of marine mammal.

They have the densest fur of any mammal.