Steller's Sea Lion

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{{Taxobox | color = pink | name = Steller's Sea Lion | status = Conservation status: Endangered | image = steller sea lion bull.jpg | image_width = 240px | image_caption = Steller Sea Lion bull | regnum = Animalia | phylum = Chordata | classis = Mammalia | ordo = Carnivora | familia = Otariidae | subfamilia = Otariinae | genus = Eumetopias | genus_authority = Gill, 1866 | species = E. jubatus | binomial = Eumetopias jubatus | binomial_authority = (Schreber, 1776) }}

The Steller's Sea Lion (Eumetopias jubatus), also known as the Northern Sea Lion, is a sea lion of the temperate eastern Pacific, named by Georg Steller. It is the largest of the eared seals, measuring up to 3.3 m in length, with males weighing up to 1,100 kg while females weigh around 350 kg. Their coloration is lighter than in most sea lions, ranging from a pale yellow to a tawny and occasionally reddish, though they often appear darker in the water. The pups are born almost black and remain dark for several months.

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Range and Status

The range of the Steller sea lion extends from the Kuril Islands and the Sea of Okhotsk in Russia to the Gulf of Alaska in the north, and down to the Farallon Islands off central California. They formerly bred as far south as the Channel Islands but have not been observed there since the 1980s. Based on genetic anаlyses and local migration patterns, the global Steller sea lion population has traditionally been divided into an Eastern and Western stock at 144° W longitude, roughly through the middle of the Gulf of Alaska. Recent evidence suggests that the sea lions in Russia in the Sea of Okhotsk and the Kuril islands comprise a third Asian stock, while the sea lions on the eastern seaboard of Kamchatka and the Commander Islands belong to the Western stock.

While the populations of the Eastern and Asian stocks appear stable, the population in the Western stock, particularly along the Aleutian Islands, was estimated to have fallen by 70-80% since the 1960's. As a consequence, in 1990 the Western stock of Steller sea lions was listed as endangered under the Endangered Species Act while the remaining populations have been listed as threatened. They have since been the object of intense study and the focus of much political and scientific debate in Alaska.

One suspected cause of their precipitous decline is overfishing of walleye pollock, herring, and other fish stocks in the Gulf of Alaska. Other hypotheses include increased predation by orcas, indirect effects of prey species composition shifts due to changes in climate, effects of disease or contaminants, shooting by fishermen, and others. The decline is certainly due to a complex of interrelated factors which have yet to be definitively teased apart by the research effort.

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Reproduction

Reproductively mature male sea lions aggregate in May, usually on beaches on isolated islands, to form reproductive rookeries. The larger, males establish and defend distinct territories on the rookery. A week or so later, adult females arrive, accompanied occsionally by sexually immature offspring, and form fluid aggregations throughout the rookery. Like all other otariids, Steller sea lions are polygynous. However, unlike most other species, they do not coerse individual females into harems, but control spatial territories among which females freely move about. Pregnant females give birth soon after arriving, and copulation generally occurs one to two weeks after giving birth. The fertilized egg does not become implanted in the uterus until the fall. Pups may remain with their mothers for several years. In fact, incidents of mothers feeding daughters who are simultaneously feeding their own newborn pups have been documented. Reproductive males fast until August, when the structure of the reproductive rookeries begins to fall apart as many animals leave in for the open seas to forage or to non-reproductive haulouts.

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