Fur seals are known and named for their thick fur, which has 300,000 hairs per square inch. Europeans first named them "sea bears" which is similar to their scientific name Callorhinus ursinus, meaning "bear-like." Pups are born with a black pelt, which becomes dark brown with lighter coloration on the chest and belly. Adult males also have gray hair on the backs of their necks. Males are much larger than females, even at birth. Male pups weigh 12 pounds (5.4 kg) and grow to 385-605 pounds (175-275 kg) and seven feet (2.1 m) in length. Female pups, however, only weigh 10 pounds (4.5 kg) and grow to 66-110 pounds (30-50 kg) and 4.5 feet (1.4 m) in length.
The full range of the northern fur seal extends throughout the Pacific rim from Japan to the Channel Islands of California, although the main breeding colonies are in the Pribilof and Commander Islands in the Bering Sea. Smaller rookeries (breeding grounds) exist on the Kuril Islands North of Japan, Robben Island in the Sea of Okhotsk, and on San Miguel Island off Southern California. After extensive hunting in the late 1800's on the Farallon Islands, west of San Francisco, the first pup in over 100 years was born there in 1996. By 2006, 80 pups were born and the Farallon Islands are again an established rookery. Northern fur seals are pelagic, living almost all of the time in the open ocean, and only use certain offshore islands for pupping and breeding. They rarely come ashore except during these times and are almost never seen on mainland beaches unless they are sick.
Adult males establish territories in late May to early June and aggressively guard and herd 40 or more females. Pregnant females arrive at the rookeries in June and give birth two days later. They nurse for about 10 days, then go to sea to feed for four or five days. After that, they feed for eight to ten days and nurse for one to two days. Pups are weaned after about four months on this cycle, which is seen in all otariids. Death rates are high -10-50% throughout a fur seal's life - but they can live to about 26 years.
Northern fur seals feed on small schooling fish, such as walleye pollock, herring, hake and anchovy, and squid. Although they feed on fish found in the open ocean, they are not deep divers. They usually dive to about 200 feet (68 meters), and their maximum dive depth is about 600 feet (about 200 m). These mammals are pelagic (open ocean), so they cannot always haul out to rest. They have developed a behavior called "jughandling," keeping their front and rear flippers out of the water while bobbing on the surface.
Once hunted in large numbers for their luxurious pelts (such as those made into coats worn at football games in the 1930s and 1940s), northern fur seals are now protected under the Marine Mammal Protection Act as a depleted species. This means that it is illegal to kill them except for research or native subsistence. The current world population is estimated at 1.1 million, but is declining. Commercial fishing operations may be contributing to the decline by decreasing availability of fish and entanglement in fishing gear. Also, fur seals are especially sensitive to changes in their environment, as seen in the record numbers of sick or starving fur seals rescued at The Marine Mammal Center during El Niño years.
At The Marine Mammal Center
In normal years, the Marine Mammal Center admits about five northern fur seals. During El Niño years, this number dramatically increases. This is because northern fur seals are very sensitive to the warming ocean waters of El Niño. In November of 2006, 33 fur seals were admitted to the Marine Mammal Center, with 22 being on-site at one time. Most scientists don't believe that the fur seal strandings were due to El Niño since other species weren't showing similar El Niño effects. There was no evidence of disease amongst the fur seals admitted, so at this point, there is no clear understanding of why the fur seals were unable to find food that year.