Northern Fur Seals (Callorhinus ursinus) are the largest of the sub-family Arctocephalinae. They are also the only species in the genus Callorhinus and are one of the most sexually dimorphic of all seals, with adult males being 40% longer and weighing 4 and a half times more than females.
They are found in the Northern Pacific, from the Southern tip of Japan, through the Southern tip of the Baja Californian Peninsula, the Sea of Okhotsk and the Bering Sea. During winter months, Northern Fur Seals will move slightly southward, with animals from Russian rookeries entering the Sea of Japan and Alaskan animals moving along the central and Eastern Pacific as far as Baja California. The only other fur seal in the Northern Hemisphere is the Guadalupe Seal, which overlaps its range with the Northern Fur seals in California. Steller Sea Lions have an almost identical range and rookeries are often shared.
Northern Fur Seals begin their breeding season in May, with older males arriving some time before the females at traditional rookeries to compete for territory and breeding space. Here they will remain, fasting throughout the breeding season as they compete (rather aggressively) with neighbouring males. They are very possessive and tug of wars over a particular female in the harem may even result in her death.
As with all other otariids, Northern Fur Seals are polygamous and males can mate with up to 50 females in a season. Younger males who are unable to raise their own harem will usually haul out in adjacent sites, making frequent incursions into the established breeding grounds in the hope of getting lucky.
Gestation period is around a year. Peak mating period occurs just before peak birthing. Females will stay with pups for the first 8-10 days before going off on foraging trips. Northern Fur Seal pups take around four months to wean and are mostly off the teat by October.
Northern Fur Seals spend up to 50% of their time out at sea. They sleep on their backs with their fins sticking out of the water as they float along on the surface.
The females cover the longest migration of all seals when traveling to their breeding grounds and back. This distance can be as far as 6 000 miles. (9600kms)
This species has a varied diet and they will even consume small alligators. Though they are known to eat 63 species of fish, they usually feed off just 8.
These are solitary animals and will only gather in numbers during the breeding season. The males are so much larger than the females that at one stage they were thought to be two completely different species.
One of their largest breeding sites are the Pribilof Islands off Alaska. The main reason why the United States purchased Alaska from the Soviet Union in the 1800’s was to gain control of the fur trade. Revenues from this trade covered the purchase cost within three years.
By 1835, commercial sealing operations had nearly wiped out the entire species. In 1911, the United Kingdom, Japan, the US and the Soviet Union imposed prohibitions on killing these seals at sea.
These animals are under threat due to global warming, pollution, reduced food sources, entanglement in fisheries nets and loss of habitat. Their numbers have recently seen a marked decline and they are listed on the IUCN Red list of threatened species as vulnerable.