Sea Otter

views updated May 08 2018

Sea otter

The sea otter (Enhydra lutris ) is found in coastal marine waters of the northeastern Pacific Ocean, ranging from California to as far north as the Aleutian Islands. Sea otters spend their entire lives in the ocean and even give birth while floating among the kelp beds. Their ability to use tools, often "favorite" rocks, to open clam shells and sea urchins is well-known and fascinating since few other animals are known to exhibit this behavior. Their playful, curious nature makes them the subjects of many wildlife photographers but also has aided in their demise. Many are injured or killed by ship propellers or in fishing nets.

Some sea otters are killed for their highly valued fur. Their thick hair traps air, insulating the otter from the cold water in which it lives. Before they were placed under international protection in 1924, 800,000 to one million sea otters were slaughtered for their pelts, eliminating them from large portions of their original range. Despite poaching , which remains a problem, they are slowly returning through relocation efforts and natural migration . Their proximity to human settlement, however, still poses a problem for their continued survival.

Pollution , especially from oil spills , is deadly to the sea otter. The insulating and water-repellant properties of their fur are inhibited when oil causes the fine hairs to stick together, and otters die from hypothermia. Ingestion of oil during grooming does extensive, often fatal, internal damage. In 1965, an oil spill near Great Sitkin Island, Alaska, reduced the island's otter population from 600 to six. In 1989, the oil tanker Exxon Valdez spilled over 11 million gal (40 million l) of crude oil into Prince William Sound , Alaska, leading to the nearly complete elimination of the Sound's once thriving sea otter population. In California, fears that a similar incident could destroy the sea otter population there have led to relocation efforts.

Sea otters have few natural enemies, but they were extensively hunted by Aleuts and later by Europeans. Sea otters were hunted to extinction around several islands in Alaska, an event that led to studies on the importance of sea otters in maintaining marine communities. Attu Island, one of the islands that has lost its otter population, has high sea urchin populations that have, through their grazing, transformed a kelp forest into a "bare" hard ground of coralline and green algae. Few fish or abalone are present in these waters anymore. On nearby Amchitka Island, otters are present in densities of 7.711.6 per mi2 (2030 per km2) and forage at depths up to 22 yd (20 m). In this area, few sea urchins persist and dense kelp forests harbor healthy fish and abalone populations. These in turn support higher-order predators such as seals and bald eagles.

Effects of sea otter foraging have also been documented in soft-bottom communities, where they reduce densities of sea urchins and clams. In addition, disturbance of the bottom sediment leads to increased predation of small bivalves by sea stars. Otters' voracious appetite for invertebrates also brings them into conflict with people. Fishermen in northern California blame sea otters for the decline of the abalone industry. Farther south, residents of Pismo Beach, an area noted for its clam industry, are exerting pressure to remove otters. Sea urchin and crab fishermen have also come into conflict with these competitors. It remains a challenge for fishermen, environmentalists, and regulators to arrive at a mutually agreeable management policy that will allow successful coexistence with sea otters. The sea otter census of 2001 counted only 2,161 otters in California, less than 6,000 in Alaska, 2,500 in Canada, 555 in Washington, and about 15,000 in Russia. They are considered endangered by the IUCN.

[William G. Ambrose Jr. and Paul E. Renaud ]



Sumick, J. L. An Introduction to the Biology of Marine Life. 5th ed. Dubuque, IA: W. C. Brown, 1992.


Brazil, Eric. "Annual Census Begins in State for Nearly Extinct Sea Mammal. San Francisco Chronicle (May 18, 2001): A3.

Kvitek, R. G., et al. "Changes in the Alaskan Soft-Bottom Prey Communities Along a Gradient of Sea Otter Predation." Ecology 73 (1992): 41328.

"Northern Sea Otters may be Declared Endangered." The Grand Rapids Press (November 12, 2000): A3.

Raloff, J. "An Otter Tragedy." Science News 143 (1993): 200202.


Help Save the Sea Otters. [cited May 2002]. <>.

Friends of the Sea Otter. [cited May 2002]. <>.

sea otter

views updated May 29 2018

sea ot·ter • n. an entirely aquatic marine otter (Enhydra lutris) of North Pacific coasts, formerly hunted for its dense fur. It is noted for its habit of floating on its back with a stone balanced on the abdomen, in order to crack open bivalve mollusks.