Sea Otter — The sea otter (Enhydra lutris) is a marine mammal native to the coasts of the North Pacific, from northern Japan, the Kuril Islands and Kamchatka east across the Aleutian Islands and along the North American coast to Mexico.
Adult sea otters typically weigh between 14 and 45 kg, making them the heaviest members of the weasel family, but among the smallest marine mammals. Unlike most marine mammals, the sea otter’s primary form of insulation is an exceptionally thick coat of fur, the densest in the animal kingdom with up to 400,000 hairs per cm2 (2.5 million per in2). It preys mostly upon invertebrates such as sea urchins, diverse mollusks and crustaceans, and some species of fish, inhabiting nearshore environments where it can quickly dive to the sea floor to forage. Although sea otters can walk on land, they are capable of spending their entire lives in the ocean.
The sea otter is a keystone species, with a stabilizing effect on its local ecosystem that is disproportionate to its size and abundance. Specifically, sea otters control sea urchin populations, which would otherwise inflict extensive damage to the kelp forest ecosystems that provide crucial habitat and food for other marine organisms and help contain coastal erosion.
Sea otters were hunted extensively for their fur between 1741 and 1911, the world population falling to 1,000 – 2,000 individuals in a fraction of their historic range. A subsequent international ban on hunting, conservation efforts, and reintroduction programs into previously populated areas have all contributed to numbers rebounding in about two-thirds of the former range. The recovery of the sea otter is considered an important success in marine conservation, though populations in certain areas (the Aleutian Islands and California) have plateaued at depressed levels or are declining. For these reasons, as well as its particular vulnerability to oil spills, the sea otter remains classified as an endangered species.
The sea otter is one of the smallest marine mammal species. Male sea otters weigh 22 to 45 kg (nearly 100 lb) and are 1.2 to 1.5 m (nearly 5 ft) in length. Females are smaller, weighing 14 to 33 kg and measuring 1 to 1.4 m in length.
The species’ fur is the thickest of any animal, with densities of 100,000 to 400,000 hairs/cm2. The color is usually deep brown with sliver-gray speckles, however it varies between individuals, from yellowish or grayish brown to almost black. In adults, the head, throat, and chest are lighter in color than the rest of the body. The fur consists of long guard hairs and a layer of dense underfur. When clean, the guard hairs are fully waterproof, allowing the underfur to retain air and remain dry and keeping cold water completely away from the skin. As only the tips get wet, fur can take on a spiky appearance. Unlike other marine mamals, the sea otter has no blubber and it relies on its fur to keep warm. The fur is thick year-round, as it is shed and replaced gradually rather than in a distinct molting season. It can reach and groom the fur on any part of its body, as it has loose skin and an unusually supple skeleton.
The sea otter is diurnal. It has a period of foraging and eating in the morning, starting about an hour before sunrise, then rests or sleeps in mid-day. Foraging resumes for few hours in the afternoon and subsides before sunset. There may be a third foraging period around midnight; females with pups appear to be more inclined to feed at night. Observations of the amount of time a sea otter must spend each day foraging range from 24% to 60%, apparently depending on the availability of food in the area. To keep from drifting out to sea when resting and eating, sea otters may wrap themselves in kelp.