Northern fur seal  (Callorhinus ursinus)

Northern fur seals belong to the family known as eared seals, more commonly called sea lions. They differ from the true seals in having small external earflaps and hind flippers that can be turned to face forwards. Together with strong front flippers, this gives them extra mobility on land and an adult fur seal can move extremely fast across the beach if it has to. They also use their front flippers for swimming, whereas true seals use their hind flippers (3).

Sea lions show a considerable size difference between the sexes. A bull northern fur seal is a big heavy animal, over two metres in length and weighing as much as 270 kg. Their fur varies in colour, ranging from reddish to black, and they have thick necks and a mane (2). The females (cows) are much smaller, less than a metre and a half in length and weighing a fifth as much as the bulls (2). Their colouring differs, too, having a silvery-grey back, with reddish-brown at the front and a whitish-grey patch on the chest (4). Young seal pups are black with paler markings around the nose and mouth (2).

Northern fur seals range over most of the northern Pacific Ocean, as far south as southern California in the east and to central Japan in the west. Northwards, their range extends to the Bering Sea, north of the Aleutian Islands, and the Sea of Okhotsk, west of the Kamchatka peninsular (4). Their main breeding grounds are on the Pribilof Islands of St. George and St. Paul in the southern Bering Sea. They also breed on a number of other islands scattered throughout their range, principally the central Kuril Islands and Tyuleniy Island in the Sea of Okhotsk, the Commander Islands off the coast of Alaska, Bogoslof Island in the Aleutians and San Miguel Island off the coast of California (4).

Although northern fur seals spend most of the year at sea in the cold northern waters of the Pacific Ocean (2), their breeding grounds are on rocky coastlines close to the edge of the continental slope (4).

At the start of the breeding season, males begin arriving at their traditional sites about a month ahead of the females and start competing for breeding territories (4). These fights can be extremely violent, with each mature bull aiming to slash an opponent's neck with his sharp canine teeth. Only the largest and heaviest bulls can hope to claim the title of ‘beachmaster'; the smaller younger males, who have no chance of competing with the fully-grown animals, occupy the fringes of the breeding territories (3).

The females arrive in mid-June and give birth to the pups, conceived the year before, some two days after their arrival. Within a week of the birth, the females will mate again (4). Males compete to secure as many females as he can within his harem, although it is thought that females are influenced by the presence of other females and the characteristics of the territory rather than the mere size and power of the male (2). The beachmasters will continue to squabble and fight over females right through the breeding season, usually because these colonies are crowded, and wandering females sometimes stray into another male's territory (3). Occasionally, younger males will attempt to steal a mating with a female and, if spotted by one of the beachmasters, he will be chased off (2). In order to ensure that his females are not claimed by another male, bull northern fur seals do not feed throughout the breeding period and may eventually loose 20% of their body weight (4).

Mothers suckle their pups for up to 10 days before returning to feed at sea, usually during the night. She will stay at sea from between four and ten days feeding, returning to feed her pup for one or two days. She will do this for four months before leaving her youngster and migrating south, usually in late October (4). Fur seals feed on a variety of prey, including squid and pollack (4) and have also been recorded taking seabirds (2).

The fertilised egg within the female fur seal undergoes a four month period of delayed implantation. This ensures that that the developing pup will be born at the right time the following year when the animals return to their breeding grounds. The pups will spend as long as 22 months at sea before returning to the beach where they were born (4). Fur seals mature between the ages of three and six, but males will probably not begin to breed for an additional three years (2).

The principal natural predators of fur seals are orca (killer whales), great white sharks and the much larger Steller sea lion Eumetopias jubatus. On land, pups can fall prey to foxes (4).

The fur that protects the northern fur seal from the cold has led to the animals being hunted for centuries. Although early native peoples made little impact on their numbers, the ‘discovery' of the species in the 18th century was followed by commercial hunting that nearly led to the seals' extinction by the end of the 19th century. In 1911 a treaty, the North Pacific Fur Seal Convention was signed by the USA, Japan, Russia and the UK (acting for the Dominion of Canada), limiting hunting to immature males on land and banning all sea hunts (4).

Although serious commercial hunting of the northern fur seal has ended, the animals no longer enjoy the protection of the international treaty which lapsed in 1984. Neither is the animal currently protected under CITES (Convention on International Trade in Endangered Species) (5).

There is still some hunting permitted under licence in Canadian waters by native peoples only (5), and a similar agreement exists for natives of the Aleutian Islands (4). But the main threats globally are now believed to be caused by entanglement in the nets of the Japanese squid fishing fleets and in the Bering Sea. Seals are also threatened by marine pollution such as plastic twine and waste packaging, as well as discarded trawl nets. The animals are very vulnerable to oil pollution and, with an increase in oil and gas exploration around several of their breeding grounds, there are fears that accidental oil spills and the inevitable industrial disturbance will affect seal populations (4).

The North Pacific Fur Seal Convention lapsed in 1984 after an extension was vetoed by the USA (5), but all commercial hunting has ceased at sea and only limited numbers are now taken under licence. It is believed the world population currently stands at about 1,350,000 animals, but with no current international agreement, some experts fear that commercial hunting could start again at some time in the future. There is also evidence that the El Niño event of 1997-8 affected the pup survival rate of the San Miguel Island breeding colony. A drop in the availability of fish led to 87% of young fur seals dying before they were weaned (4).

Seal Conservation Society:
http://www.pinnipeds.org/species/norfursl.htm

The Smithsonian Institution's North American Mammals website:
http://www.mnh2.si.edu/education/mna/image_info.cfm?species_id=28

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk