Steller's Sea Lion

Eumetopias jubatus

Description

The Steller's sea lion, sometimes known as the northern sea lion, is a large seal of the northern Pacific Ocean. It is a sexually dimorphic species, with bulls (males) being much larger than cows (females). Males typically have a body length of 9 ft (2.8 m) and weigh 1,250 lbs (566 kg), while females are 7.5 ft (2.3 m) long and weigh 585 lbs (265 kg). Steller's sea lions are colored light buffy to reddish brown.

Behavior

Their diet consists of various fish species, squid, octopus, and cuttlefish. The walleye pollock (Theraga chalcogramma ) is especially prominent in their diet.

Steller's sea lions have a polygamous breeding system, in which a single male breeds with numerous females. The bulls aggressively defend breeding territories on sloping beaches, where their harem of 10-20 breeding females is located. The bulls arrive to their traditional breeding islands in May to establish their territories. They do not feed during the breeding season. The females arrive about one month later, and give birth to a single pup. Soon after, they copulate with the territorial male. The longevity of males is up to 20 years and females 30 years. The lesser longevity of the males is due to their violent, stressful lifestyle while defending their territory and harem of breeding females.

Habitat

The Steller's sea lion occurs in north temperate and boreal waters. They tend to occur in relatively shallow waters of the continental shelf. They give birth on oceanic islands, which represent critical habitats for the species. The rest of the year is spent at sea, on continental-shelf waters.

Distribution

The Steller's sea lion occurs in the northern Pacific Ocean. Their range extends from the Kuril Islandsin the Sea of Japan in the northwestern Pacific, north across the Pacific Rim of the southern Aleutian Islands, and south to San Miguel Island off the coast of California. The U. S. Fish and Wildlife Service (FWS) has designated two populations: eastern and western. The eastern population occurs east of 144° longitude in Alaska, California, Oregon, Washington, and British Columbia, Canada. The western population occurs west of 144° longitude in Alaska and Russia.

Threats

Steller's sea lions were once subjected to a commercial hunt for their fur, hides, and oil, but this has not occurred since 1972. Nevertheless, this species has suffered a widespread population decline in recent decades, and is estimated to now have less than one third the abundance it had in the mid-1960s. The population of Steller's sea lions is now about 110,000 individuals, of which almost half breed in Alaska. Although the causes of the population decline are not yet known, they are thought to be related to reduced food supplies because of fish-stock depletions caused by commercial over fishing, deliberate killing by fishers as competitors, entanglement with fishing nets (this is sometimes known as by-catch mortality), and possibly contagious disease. In addition, about 600-700 animals are killed each year by aboriginal subsistence hunters in coastal Alaska and the Aleutian Islands.

Conservation and Recovery

In view of the recent decline of the Steller's sea lion, the species has been designated as endangered by both the International Union for the Conservation of Nature and Natural Resources (IUCN) and the FWS. Research is being undertaken to try to understand the causes of its recent population declines. It seems likely, however, that the damage is somehow related to conflicts between the Steller's sea lion (and other marine mammals) and commercial over-fishing within its range. This problem can be resolved if commercial fishing becomes more sensibly managed within sustainable catch limits, which would result in a viable fish resource for use by humans and other dependent species. Much of the by-catch mortality of Steller's sea lions can be avoided by the use of better designed netting systems, and by banning any use of pelagic drift-nets. To a great degree, this has already happened: between 1966 and 1988 about 20,000 Steller's sea lions were killed as by-catch in the Alaskan fisheries. Since 1990 only 30 per year have been killed in this way.

Contacts

National Oceanic and Atmospheric Administration
National Marine Fisheries Service
1315 East-West Highway SSMC3
Silver Spring, Maryland 20910

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

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1011 E. Tudor Rd., Room 135
Anchorage, Alaska 99503
Telephone: (907) 786-3909
Fax: (907) 786-3844
http://alaska.fws.gov/

Reference

Nowak, Ronald M. 1999. Walker's Mammals of the World. Sixth Edition. Johns Hopkins University Press, Baltimore.