Steller sea lion (Eumetopias jubatus) COSEWIC assessment and status report: chapter 2

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Species Information

The Steller sea lion (Eumetopias jubatus Schreber 1776) is the largest member of the family otariidae (Order Carnivora, Suborder Caniformia). Steller sea lions exhibit significant sexual dimorphism. Adult females average 2.1-2.4 m in length and weigh 200-300 kg. Adult males are noticeably larger, attaining a length of 2.7-3.1 m and weighing 400-800 kg. Pups are born from late May to early July and weigh 16-23 kg at birth.

Distribution

Steller sea lions inhabit the cool-temperate and subarctic coastal waters of the North Pacific Ocean from southern California, north to the Bering Strait, and south along the Asian coast to Japan. Two stocks of Steller sea lions are recognized based on genetic different­ia­tion of mitochondrial DNA: an eastern population (California to southeast Alaska) and a western population (Gulf of Alaska, Bering Sea, Aleutian Islands, and Russia). Within Canada, Steller sea lions occur only in British Columbia and there are three main breeding areas: 1) off the northeastern tip of Vancouver Island (rookeries on Maggot, Sartine and Triangle Islands); 2) off the southern tip of the Queen Charlotte Islands (rookeries on the Kerouard Islands); and 3) off the northern mainland coast (rookeries on North Danger Rocks). Another breeding area off the central mainland coast (rookeries on Virgin, Pearl and Watch Rocks) was extirpated during the 1920s and 1930s by intense predator control programs. No new rookeries have been established in BC for over a century, but Steller sea lions have begun breeding at several new sites in Alaska.

At sea, animals are typically found within about 60 km of shore during summer, and can range over 200 km from shore in winter. Steller sea lions are non-migratory, but may disperse considerable distances from breeding sites.

Habitat

The terrestrial sites used by Steller sea lions include: 1) rookeries where animals congregate during May-August to give birth, mate, and nurse young pups; 2) year-round haulouts that are usually occupied continuously; and 3) winter haulout sites that are used less regularly and primarily during the non-breeding season. No new rookeries have been colonized in BC over the past century. Animals haul out on a regular basis throughout the year, and tend to be highly gregarious while on land with little or no physical separation between individuals.

Our understanding of how Steller sea lions use the aquatic environment is poor. In general, most Steller sea lions appear to feed over the continental shelf and along the shelf break. Animals are generally observed within 60 km of land and in water depths less than 400 m, but may venture several hundred kilometers offshore and occur off the continental shelf.

Biology

Steller sea lions are polygynous breeders. Females give birth to a single pup, which they typically nurse for just under a year, but may occasionally nurse up to 2-3 years. Longevity is about 14 years for males and 22 years for females, with a generation time of 10 years. Steller sea lions regularly haul out on established rookeries and haulouts between feeding trips. Preferred prey in BC includes herring, hake, sandlance, salmon, dogfish, eulachon, sardines, rockfish, flounder, skate, squid and octopus.

Population Sizes and Trends

Population increases have been observed in BC since Steller sea lions were protected in 1970. Abundance increased at an average of 3.2% annually, which has resulted in a doubling in the size of the breeding population. Most of this increase has occurred during the last two decades. A total of about 3400 pups were born in BC in 2002. The total BC population inhabiting coastal waters during the breeding season is estimated at 18 400–19 700 individuals (which includes non-breeding animals associated with rookeries in southeast Alaska). The number of sexually mature individuals is about 7600 (40% of the population).

Limiting Factors and Threats

Steller sea lions are threatened by shooting, incidental take in fishing gear, entanglement in debris, catastrophic accidents, environmental contaminants, and displacement or degradation of their habitat. They are also susceptible to fluctuating prey populations, predation by killer whales, and disease.

Special Significance of the Species

The Steller sea lion is the largest species of sea lion and the only otariid that resides year-round and breeds in Canadian waters. It is an important component of the coastal marine ecosystem, and contributes to a burgeoning eco-tourism industry.  BC rookeries now represent two of the largest breeding aggregations in the world. As a result of recent declines in the western part of its range, where the species is considered to be endangered, and the implications this listing may have for commercial fisheries, the Steller sea lion has recently been the focus of much research into factors influencing populations. There may be potential for using apex predators like the Steller sea lion as an indicator species of coastal ecosystem status given their widespread distribution, long life­span, and position near the top of the marine food chain.

Existing Protection or Other Status Designations

Since 1970, sea lions have been protected by various regulations enacted under the Fisheries Act and enforced by the Department of Fisheries and Oceans. The rookery at Cape St. James is protected under the National Parks Act, and the rookeries on the Scott Islands are part of a BC Ecological Reserve. The Steller sea lion was red-listed by the BC provincial government Conservation Data Centre. In the United States, the eastern stock, which occurs from California to southeast Alaska (including BC) is listed as threatened, and the western stock, which occurs in the Gulf of Alaska and Aleutian Islands is listed as endangered under the US Endangered Species Act.