Sea otter

The sea otter, known scientifically as Enhydra lutris, is a unique marine mammal. It lives along the coasts of the northern and eastern North Pacific Ocean.

While it can walk on land, it can live its entire life in the ocean. Sea otters belong to the family Mustelidae. This group includes weasels, badgers, and minks. The sea otter is the heaviest member of this family. However, it is still one of the smallest marine mammals.

Because they play such a vital role in their environment, they are considered a keystone species.

Most marine mammals stay warm using a thick layer of fat called blubber. Sea otters do not have blubber. Instead, they rely on the densest fur in the animal kingdom.

Their coat consists of long, waterproof guard hairs and short underfur. The guard hairs keep the underfur dry. This creates a layer of trapped air between the fur and the skin. This air layer acts as insulation by trapping body heat. To keep this system working, the otter must keep its fur clean. They use their loose skin and supple skeletons to reach every part of their bodies for grooming.

Sea otters are highly skilled foragers. They dive to the sea floor to find marine invertebrates. This includes sea urchins, mollusks, and various crustaceans.

They are one of the few mammal species that use tools. An otter will often pick up a rock to smash open a shell. This allows them to reach the food inside. Their front paws have tough pads to grip slippery prey. For movement, they use long, webbed hind feet. They swim by moving their tail and hind feet up and down. This allows them to reach speeds of up to 5 miles per hour.

As a keystone species, sea otters maintain the health of kelp forest ecosystems. They do this by eating sea urchins. Without otters, urchin populations would grow very large. These urchins would then eat too much kelp and destroy the forest.

By controlling these populations, otters ensure the kelp forests remain thick and healthy. This habitat supports many other ocean creatures. However, their diet can also cause conflict with human fisheries. This happens because sea otters eat the same species that humans value as food.

The history of the sea otter includes a period of great danger. Between 1741 and 1911, sea otters were hunted extensively for their fur.

Their population dropped from an estimated 150,000–300,000 down to only 1,000–2,000 individuals. This event is called a population bottleneck. Such a sudden drop in numbers causes a loss of genetic diversity. This makes the species more vulnerable to disease and other changes. Thanks to international hunting bans and conservation programs, numbers are rebounding. They now occupy about two-thirds of their former range.

Despite this recovery, they are still classified as an endangered species. Some populations in Russia, California, and the Aleutian Islands have recently declined.

Scientists have used genetic analysis to study the evolution of the sea otter. They found that sea otters shared an ancestor with other otters about 5 million years ago.

The Enhydra lineage became isolated in the North Pacific about 2 million years ago. This led to the modern sea otter and the extinct Enhydra macrodonta. Some scientists once thought sea otters were related to earless seals. However, DNA evidence proved they are actually mustelids. The sea otter is a relative newcomer to the sea. Whales and seals entered the water millions of years before the sea otter did. This makes the sea otter a perfect example of how mammals adapt to the ocean.

There are three recognized subspecies of sea otters. The Asian sea otter, Enhydra lutris lutris, lives near Russia's Kuril Islands. It is the largest subspecies and has a wider skull. The northern sea otter, E. l. kenyoni, lives from the Aleutian Islands to Oregon. The southern sea otter, E. l. nereis, lives in central and southern California.

Each subspecies has small physical differences. For example, northern sea otters have longer lower jaws. Southern sea otters have longer rostrums and smaller teeth. These differences help them thrive in their specific parts of the Pacific Ocean.