The Northern Fur Seal, Callorhinus ursinus, is an eared seal. It is the only species in the genus Callorhinus. It is found in the north Pacific Ocean.

Physical description and behavior

The Northern Fur Seal, has substantial physical differences compared to its otariid cousins: its head is smaller, snout shorter and the hindflippers are proportionately largest of any eared seal. The "fingers" on the hindflippers are conspicous by their length. Males are substantially larger (2m, 270kg) and darker-coloured (the pelage is dark brown or black) than the females (1.5m, 60kg, light brown to grey). In fact, northern fur seals probably exhibit the greatest sexual dimorphism among any mammal. Northern fur seal pups have black pelage. Pups usually have lighter markings on the nose and underside. Males live for up to 20 years, and females 25.

The most conspicuous physical feature of the fur seal is the fur itself; indeed, its genus name comes from the Greek for "beautiful hide". It consists of longer lighter guard hairs and a dense waterproof underfur of about 46,500 hairs per square centimeter.

Northern Fur seal breeding grounds are fairly densely packed, though activities at sea are generally solitary. Individuals return to the breeding grounds in May and the peak of pupping occurs between mid-June and mid-July. Northern fur seals are polygynous, with some males breeding with up to 50 females in a single breeding season. Unlike Steller sea lions, with whom they share habitat and some breeding sites, Northern fur seals are possessive of individual females in their harem, often aggressively competing with neighboring males for females. Deaths of females as a consequence of 'tug-of-war's have been recorded, though the males themselves are rarely seriously injured.

After remaining with their pups for the first eight to ten days of their life, females begin foraging trips lasting up to a week. These trips last for about four months before weaning, which happens abruptly, typically in October. Most of the animals on a rookery enter the water and disperse towards the end of November, typically migrating southward. Breeding site fidelity is generally high for fur seals females, though young males might disperse to other existing rookeries, or occasionally found new haulouts.

Peak mating occurs somewhat later than peak birthing from late June to late July. As with many other otariids, the fertilized egg undergoes delayed implantation: after the blastocyst stage occurs, development halts and implantantion occurs four months after fertilization. In total, gestation lasts for approximately one year, such that the pups born in a given summer are the product of the previous year's breeding cycle.

Fur seals are opportunistic feeders, primarily feeding on pelagic fish and squid depending on local availability. Identified fish prey include hake, anchovy, herring, sand lance, capelin, pollack, mackerel and smelt.

[Range

The Northern Fur Seal is found in the north Pacific – its southernmost reach is a line that runs roughly from the southern tip of Japan to the southern tip of the Baja California peninsula, the Sea of Okhotsk and the Bering Sea. The largest breeding colonies are the Pribilof Islands and Commander Islands in the Bering Sea. Breeding also occurs on Tyuleni Island off the coast of Sakhalin Island in Russia, islands around the north of Japan and San Miguel Island off California.

There are estimated to be around 1.7m Northern Fur Seals across the range. The other fur seals found in the northern hemisphere is the Guadalupe Fur Seal – the two species' ranges overlap in the north-east Pacific.

Fur trade

Northern Fur Seals have been a staple food of native northeast Asian and Alaskan Inuit peoples for thousands of years. The arrival of Europeans to Kamchatka and Alaska in the 17th and 18th centuries, first from Russia and later from North America, was followed by a highly extractive commercial fur trade. An estimated 2.5 million seals were killed from 1786 to 1867. This trade led to a decline in fur seal numbers. Restrictions were first placed on fur seal harvest on the Pribilof Islands by the Russians in 1834. Shortly after the United States purchased Alaska from Russia in 1867, the U.S. Treasury was authorized to lease sealing privileges on the Pribilofs, which were granted somewhat liberally to the Alaska Commercial Company. From 1870 to 1909, pelagic sealing proceeded to take a significant toll on the fur seal population, such that the Pribilof population, historically numbering on the order of millions of individuals, reached a low of 216,000 animals in 1912.

Significant harvest was more or less arrested with the signing of the North Pacific Fur Seal Convention of 1911 by Canada, Japan, Russia and the United States. The Convention of 1911 remained in force until 1941. A successive convention was signed in 1957 and amended by a protocol in 1963. The international convention was put into effect domestically by The Fur Seal Act of 1966 (Baker et al., 1970). Currently, there is a subsistence hunt by the residents of Pribilof island and an insignificant harvest in Russia.

[edit] References

• R. Gentry: Behavior and Ecology of the Northern Fur Seal. Princeton University Press, 1998 ISBN 0-691-03345-5
• R. Nowak: Walker's Marine Mammals of The World. Johns Hopkins University Press, 1999 ISBN 0-8018-7343-6
• J. E. King: Seals of the world. Cornell University Press, 1983 ISBN 0-8014-1568-3
• Seal Specialist Group (1996). Callorhinus ursinus. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Listed as Vulnerable (VU A1b v2.3)
• Randall R. Reeves, Brent S. Stewart, Phillip J. Clapham and James A. Powell (2002). National Audubon Society Guide to Marine Mammals of the World. Alfred A. Knopf, Inc. ISBN 0375411410. 

Wikipedia

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