Fur seal families live separated by 3000 miles most of the year. The fathers enjoy themselves in Northern waters while the mothers, their pups and young males spend the winter in the balmy seas of California. In spring the females and bachelors begin their northern voyage, and take a straight course to a narrow passage between the Aleutian Islands; from there they head to the rocky Pribilof Islands in the Bering Sea, the only land they ever touch. Pribilof Islands, also called Fur Seal Islands, are a group of islands in the Bering Sea. All are hilly and of volcanic origin and are famous as mating places for most of the fur-bearing seals of the world. Otter, polar bear, blue and white fox, and many species of birds inhabit the islands during all or part of the year. The bulls await the females eagerly and herd as many females as they can collect into the world's largest mammal harems; the old "beachmasters" gather 40 to 60. A super-strong bull may acquire as many as 100 wives.
The harems are strictly defined pieces of land, and when an intruder crosses the line, it has a fight on its hand with blood streaming and pieces of flesh flying. The female then brings forth her single pup after which she is bred, and if she tries to escape or flirt with a neighbor, a heavy slap on the head will return her to the path of virtue. The master of the harem is in such a state of excitement that he hardly sleeps and never eats during the 3 months of family life. Early in August the fantastic show is over.
There are five stocks based at the following locations: Pribilof Islands, Commander Islands, Robben Island, Kuril Islands and San Miguel Island. A new colony has established itself on Bogoslof Island in the Aleutian Islands. As there is a southbound migration in winter, the overall range includes much of the north Pacific Ocean north of the convergence zone. Most of the population is concentrated along the edges of the continental shelf.
The fur seals were almost exterminated by whalers who killed them by the millions, but now they are protected by an international agreement and have recovered remarkably.
Adult males of this species are on average 210 cm long and weigh 180-270 kg. Adult females measure 100-140 cm and weigh 30-50 kg. At birth, male pups are 55-63 cm in length and weigh 5.4-5.9 kg. This species is characterized by long pinnae and long rear flippers. Males vary in color from gray to reddish-brown to black. Females have silvery-gray dorsal and reddish-brown ventral surfaces with a dull white to gray blaze on the chest. Pups are black with lighter coloring on the ventral surface.
Females reach maturity at the age of 2-5 in both asian and North American populations. Males reach the height of their reproductive status at about 9 years of age. Gestation lasts 51 weeks. Lactation lasts 4 months. Lifespan of this species is 25 years. Total first year pup mortality is 50%. Adult annual mortality for males is 38% and for females 11%. Northern fur seals usually take the most abundant fish and cephalopod species available. The diet includes squid, hake, anchovy, sandlance, capelin, mackerel, pollock and smelt. They consume about 10% of their body weight in fish per day. Adults fall prey to sharks and killer whales, while pups can be taken by Steller's sea lions.