Northern Fur Seal
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 cousins. Its head is smaller, snout shorter and the hind flippers are proportionately largest of any eared seal. The “fingers” on the hind flippers are conspicuous by their length. Males are substantially larger. They are 6.56 ft (2 m) long and weigh about 595.25 lb (270 kg). They are darker-colored (the pelage is dark brown or black) than the females. Females are about 4.92 ft (1.5 m) and weigh about 132.28 lb (60 kg). They are 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. It consists of longer lighter guard hairs and a dense waterproof under fur. 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. 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. Peak mating occurs somewhat later than peak birthing from late June to late July.
Fur seals are opportunistic feeders, primarily feeding on pelagic fish and squid depending on local availability. Identified fish prey includes hake, anchovy, herring, sand lance, capelin, pollack, mackerel and smelt.
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.