Steller sea lion (Eumetopias jubatus) COSEWIC assessment and status report: chapter 6
Distribution
Steller sea lions inhabit the cool-temperate and subarctic coastal waters of the North Pacific Ocean from the Channel Islands off southern California, north to the Bering Strait, and south along the Asian coast to Hokkaido, Japan (Fig. 1, Kenyon and Rice 1961; Loughlin et al. 1984; Loughlin et al. 1992). They give birth on 55-60 rookeries and rest at >300 haulouts. Steller sea lions are non-migratory, but may disperse considerable distances from breeding sites (Rowley 1929; Fisher 1981; Calkins and Pitcher 1982; Loughlin 1997; Raum-Suryan et al. 2002). Animals haul out on a regular basis throughout the year.
Worldwide, two populations of Steller sea lions are recognized based on genetic differentiation of mitochondrial DNA (which reflects maternal lineage): an eastern population (California to southeast Alaska) and a western population (Gulf of Alaska, Bering Sea, Aleutian Islands, and Russia) (Bickham et al. 1996). More recent genetic analyses suggests the western population should be recognized as two distinct populations (Asia and Aleutians – Gulf of Alaska) (Bickham, unpubl. data). Separation of the two populations in North America is further supported by a phylogeographic analysis that considers such ancillary information as population trends, distribution, movements, and morphology (York et al. 1996; Loughlin 1997).
Arrows denote breeding rookeries and shaded areas the approximate range of non-breeding range. The dashed line shows the separation between the eastern and western stocks of Steller sea lions. (modified from Loughlin 1997 and Sease et al. 1999).
Within Canada, Steller sea lions make up part of the eastern population (Bickham 2000), and occuronly occur in British Columbia (Fig. 1). There are three main breeding areas: 1) the Scott Islands off the northwest tip of Vancouver Island, with rookeries situated on the Scot Islands (Triangle, Beresford and Maggot Islands); 2) at Cape St. James off the southern tip of the Queen Charlotte Islands, with rookeries situated on the Kerouard Islands; and 3) off Banks Island on the northern mainland coast, with rookeries situated on North Danger Rocks. A fourth breeding area was once located off the central mainland coast on the Sea Otter Group, with rookeries situated on Virgin, Pearl and possibly Watch Rocks, but this breeding aggregation was extirpated following intense predator control programs during the 1920s and 1930s (Bigg 1985). In addition to these breeding sites, there are about 21 haulout sites distributed mainly along the exposed outer coast that are used continuously on a year-round basis, as well as numerous winter sites used on a seasonal or irregular basis.
The offshore distribution of Steller sea lions is not well defined. In general most Steller sea lions appear to feed within about 60 km of shore during summer, and can range over 200 km from shore in winter (Kenyon and Rice 1961; Merrick and Loughlin 1997). They appear to feed over the continental shelf and along the shelf break (Kajimura and Loughlin 1988).
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