Introduction In the 1960s, northern fur seals (Callorhinus ursinus) successfully recolonized San Miguel Island after the local population was extirpated by hunting. San Miguel Island is now one of three American northern fur seal colonies and the southernmost breeding colony in the world. The first seals to arrive had flipper tags identifying them as being from the Pribilof or Commander Islands in the Bering Sea. Today the San Miguel colony numbers around 10,000 animals. 4 The northern fur seal's scientific nameCallorhinus ursinusmeans "bear-like," which reflects "sea bear," the name originally given them by Europeans. Their common name alludes to the thick coat that is needed by the species for protection from the cold weather and frigid waters found in both their feeding grounds and the majority of their breeding grounds.2
Quick and Cool Facts
A Northern fur seal bull will defend territory against any intruders including other bulls and even humans.5
Northern fur seal bulls can be more than 4.5 times heavier than adult females. 3
Northern fur seals can spend extremely long periods in the open ocean. Before returning to the breeding colonies, many pups will remain at sea for up to 22 months. 1
The northern fur seal has 300,000 hairs per square inch. 2
A northern fur seal mother finds her pup by listening for its distinctive voice. 5
Northern fur seals feed mainly at night, when prey species are closer to the ocean surface. 5
Appearance Beginning at birth, males are much larger than females. Adult females and sub-adults are moderate in build. Sexes are difficult to distinguish until about age 5. The neck, chest, and shoulders of adult males are greatly enlarged over those of females and sub-adults, although at the end of the breeding season males may be thin to the point of emaciation. Male pups weigh 12 pounds and grow to 385-605 pounds and seven feet in length. In comparison, female pups only weigh 10 pounds and grow to 66-110 pounds and 4.5 feet in length.
Adult females and sub-adults are medium to dark silver-grey above. The flanks, chest, sides, and underside of the neck are cream to tan. There are variable cream to tan colored areas on the sides and top of the muzzle, chin, and as a "brush stroke" running backwards under the eye. The fur of the outer part of the ear near the naked tip and the insertion is often pale. Adult males are medium grey to black, or reddish to dark brown all over. Adult males also have gray hair on the backs of their necks. The mane can have variable amounts of silver-grey or yellowish tinting on the guard hairs. Pups are born with a black pelt, which becomes dark brown with lighter coloration on the chest and belly. After 3 to 4 months, pups molt to adult female or sub-adult male coloring.6
The head of northern fur seals looks deceptively small because of the very short down-curved muzzle and small nose. The nose extends slightly beyond the mouth in females and moderately in males. Fur is absent on the top of the fore flipper and there is an abrupt look of a "clean shaven line" across the wrist. The hind flippers are about one-fourth of the total body length, the longest in any eared seal; they have extremely long, cartilaginous terminal flaps on all of the toes, beyond the position of the nails on the 3 central digits. 6,7
Range 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 breeding grounds exist on the Kuril Islands North of Japan, Robben Island in the Sea of Okhotsk, and on San Miguel Island. 2
Habitat Northern fur seals are pelagic, spending most of their lives in the open ocean and only using certain offshore islands for pupping and breeding. They rarely come ashore except to breed or pup and are almost never seen on mainland beaches unless they are sick.2
Feeding Northern fur seal diet is well known from their range in the Bering Sea and North Pacific Ocean. They are carnivores that feed primarily at night without chewing their food;they swallow it whole or in large chunks. Northern fur seals eat a wide variety of small schooling fishes and squids. Diet composition varies between the six major breeding islands and changes during their annual migration. Sixty-three species of fishes and squids have been identified as part of the northern fur seal diet throughout their range. In the Bering Sea, northern fur seals primarily consume walleye pollock, squid, salmon, Pacific sandlance, northern smooth tongue, and Pacific herring. Between Alaska and California the primary prey species are northern anchovy, Pacific herring, squid, capelin, Pacific sandlance, Pacific whiting, salmon, Pacific saury, and various species of rockfish. 2
Reproduction Northern fur seals often return to the rookery of their birth. 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 one or two days later to a single pup. . The initial bonding of the female and pup is crucial;the female and pup must learn to recognize each other's smell and "voice" in order to find each other in the rookery after long periods of separation. Once the female and pup have bonded and nursed for 5-10 days, the female comes into estrus and is ready to mate once more, usually with the male in whose territory she gave birth.
Once they have mated, females returns to the ocean for their first feeding trip after fasting for up to 10 days. During the next four months, nursing females make repeated trips to sea to feed, spending 7 to 10 days at sea and returning to land to spend time nursing their pups. Females deliver fat-rich milk to their pups, which depend on their mother for food until they are approximately 4 months old. Females, juveniles of both sexes, and pups begin to leave the islands in October to migrate south for the winter. 2
Conservation Status The northern fur seal is listed by the International Union for Conservation of Nature (IUCN) Red List of Threatened Species as Vulnerable. Referring to the population of animals in the Pribilof Islands, the IUCN states that "[they have] experienced a significant, steep decline in recent years and [have] failed to recover despite the cessation of commercial harvesting. Although the global population is still over a million animals, the current downward trend in abundance remains a mystery." 3
