Southern Sea Otter

Enhydra lutris nereis

Description

Also known as the California sea otter, the southern sea otter, Enhydra lutris nereis, is a marine mammal of the family Mustelidae, which includes land mammals such as skunks, badgers, and ferrets. The sea otter weighs up to 80 lb (36 kg) and at maturity is more than 4 ft (1.2 m) long from its nose to the tip of its tail. Its thick glossy fur varies in color from black to dark brown and is grizzled by white-tipped hairs. Its head, throat, and chest are creamy white. It has small forefeet and large, flipperlike, webbed hind feet. Its heavy molars are adapted for crushing shellfish. The tail is horizontally flattened for enhanced propulsion, and its forepaws are used primarily for grooming and foraging, rather than for propulsion. It also has a loose pouch of skin at the axilla of each foreleg, used for the temporary storage and transport of food.

Behavior

The sea otter spends most of its time in the ocean. If it does venture ashore, it stays within a few yards of the sea. It dives to depths of 250 ft (76 m) and can remain underwater for as long as five minutes. The southern sea otter eats while floating on its back, breaking shells against a stone placed on its chest. A mature male can eat about 15 lb (7 kg) of shell-fish a day. Sea otters breed year round and, after a gestation period of eight or nine months, the female bears a single pup in their kelp-bed habitat. The pup is highly developed at birth. Its eyes are open, its fur and milk teeth fully formed, and it is a strong swimmer. The mother nurses her young while swimming on her back with the pup resting on her chest. Because it has no layer of blubber, as seals do, the otter must rely on its thick fur for warmth. The otter's high-quality pelt almost brought about its extinction during the nineteenth century. At one time its fur was prized more than Russian sable; pelts brought as much as US$1,000 each.

Habitat

The southern sea otter lives in shallower waters off the rocky Pacific coasts, staying inside and very close to large kelp beds, which provide protection and support large numbers of shellfish.

Distribution

During the nineteenth century, the southern sea otter was known along the entire Pacific coast of North America, from Alaska to central Baja California. Its range extended across the Aleutians to the Siberian coast. Fur hunters systematically exterminated all California coastal populations but one, which they overlooked. During the seventeenth century, sea otters were an abundant mammal; but starting in the eighteenth century, fur trappers began hunting the plush pelted animal in such great numbers that, by 1911, the California population, previously estimated at around 20,000, had plunged to a mere 50 animals, living in a colony near Big Sur. In 1938, a healthy population was discovered off the coast at Big Sur by workers building the Pacific Coast Highway. A 1987 census showed the population had slowly expanded to about 1,650 animals dispersed along 220 mi (354 km) of coast from Monterey Bay south. The population continued to grow slowly; by 1996, the U. S. Fish and Wildlife Service (FWS) estimated the existence of about 2,400 individuals, ranging between Point Ano Nuevo south to Purisima Point. Approximately 17 sea otters, including pups, are at San Nicolas Island as a result of translocation efforts to establish an experimental population.

Alaskan populations have fared even better because of their relative isolation, although events such as the Exxon Valdez oil spill damaged certain populations. Still, the sea otter is considered fairly abundant in Alaskan waters.

Threats

In 1910 a law was passed prohibiting the taking of sea otters in American waters. Although many believed that the law came too late to save the otter, an isolated population survived and continues to expand its range. Because the sea otter competes directly with commercial fishermen for shellfish, recovery efforts have sparked opposition from fishermen, who claim otters can quickly deplete shell-fisheries worth millions of U. S. dollars. Many sea otters have been ensnared and drowned in the nets of halibut fishermen. When this was discovered, a law was passed requiring halibut fishermen to move to deeper waters away from sea otter habitat. Nevertheless, since the best halibut fishing grounds are in the shallows, fishermen have been reluctant to move too far off the coast, and the conflict continues. To confront this issue, the FWS has defined a "no otter" management zone south of Point Conception, including all of the Channel Islands except San Nicolas. Theoretically, otters will be kept out of these waters, which can then be fished commercially. Major oil tanker traffic flows steadily along the Pacific coast. Because the otter population is spread narrowly along the coast, a single major oil spill could decimate it. Oil mats the otters' fur, causing it to lose its insulating properties, and the otters soon die of hypothermia or pneumonia.

Conservation and Recovery

To ensure against extinction in the event of a major oil spill, the FWS is attempting to establish a second experimental population at San Nicolas Island, 80 mi (129 km) southwest of Los Angeles. The colony's size and range will be restricted to protect commercial shellfish beds. In early 1988, 68 otters were netted along the central California coast and transported to the Monterey Bay Aquarium for examination and tagging. Most of these animals were then released at San Nicolas Island. The results were mixed. Many died of various causes, some returned to the parent population, and others were classified as "missing." The aquarium runs the unique Sea Otter Research and Conservation program, which rescues and rehabilitates sea otter pups, and returns them to the wild when possible. Since 1984 the program has received more than 125 animals (adults as well as pups), many of them seriously ill or wounded, and has managed to save around 50 of them. The program also provides information and research support used in the recovery of animals during large-scale environmental disasters such as oil spills. The process of transplantation is also being refined as FWS biologists learn to be more selective in choosing otters for transport. Younger animals seem to take better to new surroundings, while many older animals try to return to their home kelp beds. In 1969 and 1970, sea otters were captured in Alaska and released off the coast of Washington state. Survey counts have shown the population steadily increasing, suggesting that the transplantation has succeeded.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

Calkins, D. G. 1978. "Feeding Behavior and Major Prey Species of the Sea Otter in Prince William Sound, Alaska." National Marine Fisheries Service, Fisheries Bulletin 76: 125-31.

Carey, J. 1987. "The Sea Otter's Uncertain Future." National Wildlife.

Ladd, W. N., Jr., and M. L. Riedman. 1987. "The Southern Sea Otter." Audubon Wildlife Report 1987. Academic Press, San Diego.

Morris, R., et al. 1981. "The British Columbia Transplant of Sea Otters." Biological Conservation 20: 291-295.

U. S. Fish and Wildlife Service. 1981. "The Southern Sea Otter Recovery Plan." U. S. Fish and Wildlife Service, Portland.