Description & Behavior

Northern fur seals, Callorhinus ursinus (Linnaeus, 1758), are a highly migratory species, and have been known to travel distances of up to 10,000 km! Females and juveniles from the Pribilof Islands migrate to offshore waters from Canada down to California, and to the west as far south as Japan. In spite of this long distance, the vast majority return to the Pribilof Islands off the coast of Alaska in the Bering Sea annually to breed.

The coat of adult males ranges in color from brownish-gray to reddish-brown or black. Adult females are silvery-gray on the dorsal (upper) side and reddish-brown in front with a light gray patch on their chest. Adult males grow to an average of 2.1 m in length and 175-275 kg in weight. Adult females are significantly smaller (making this species sexually dimorphic) averaging 1.4 m in length and 30-50 kg in weight. Northern fur seals can live up to about 25 years of age but have a life expectancy at birth of less than 4 years.

World Range & Habitat

Northern fur seals are found throughout the north Pacific Ocean from the Bering Sea to southern California in the east and to central Japan in the west. Their total population was estimated at 1 – 1.3 million fur seals, the majority of which breeds on the Pribilof Islands in the southern Bering Sea. The second largest northern fur seal breeding site is the Commander Islands where about 225,000 fur seals breed. Smaller breeding sites include the central Kuril Islands (estimated 50,000 – 55,000), Tyuleniy Island in the Okhotsk Sea (estimated 55,000 – 65,000 fur seals), Bogoslof Island in the Aleutian Islands (5,000), and San Miguel Island off of southern California (4,300).

Feeding Behavior (Ecology)

The primary prey of northern fur seals is walleye pollock and squid. They also feed on sand lances, salmon, capelin, herring, mackerel, hake, anchovy and other fish. The maximum recorded dive depth of a northern fur seal is 230 m.

Predators include sharks, foxes, orca (killer whales) and Steller sea lions.

Life History

Female northern fur seals reach sexual maturity at 2-5 years, males at 4-5 years, however males will not breed until they are about 8-9 years and the adult male reproductive peak is brief generally lasting about two seasons. This species shows strong fidelity to specific breeding sites, and males begin to arrive in May to establish territories. Females give birth about 2 days after they begin arriving in mid-June. Newborn pups measure 60 cm. Male pups weigh and average of 5.4 kg, females at 4.5 kg. Pup mortality in the first year is about 50%. Females mate 5-6 days after giving birth, then begin the feeding cycle feeding at sea for 4-10 days and returning to nurse her pup for 1-2 days. The nursing period lasts for about 4 months after which females migrate south. During the nursing period, call recognition is essential for mothers and pups to locate each other during the nursing period, however a research study in Alaska showed that mothers and their offspring were still able to recognize each other by their calls after four years of separation.

Adult males do not feed during breeding season, and tend to lose up to 20% of their weight. Some adult males begin migrating south in August while others remain on shore as late as November. Adult males from the Pribilof Islands generally only migrate as far south as the Gulf of Alaska, and some remain in the Bering Sea. Many pups remain at sea for up to 22 months before returning to the breeding islands and haulouts surrounding the rookery where they were born.

Conservation Status & Comments

Northern fur seals are another seal species hunted for their fur. Significant reductions in population due to unregulated hunting in the late 19th and early 20th centuries resulted in the 1911 North Pacific Fur Seal Convention signed by the US, Japan, Russia and the UK (for Canada). The Convention banned the hunting of northern fur seals at sea and restricted killing on land to immature males, however commercial hunting of immature males was discontinued on St. George Island in 1973 and on St. Paul Island in 1984. The population has remained fairly stable since the early 1980s but remains about half the size it was during the 1950s. Subsistence hunting of juvenile male fur seals by Aleut natives on St. George and St. Paul Islands still takes place. The fur seals killed by Aleut natives on the Commander Islands are used to produce fur products and meat for fur farms.

The commercial fishing of walleye pollock in the Bering Sea may impact northern fur seal populations because of reduced food availability, and this species is also at-risk of entanglement particularly in the Japanese squid driftnet fishery and in Alaskan gillnet and trawl fisheries. Additionally, studies in the Pribilof Islands have shown a significant number of fur seals, particularly juvenile males, entangled in floating marine debris from trawl nets, plastic packing, and synthetic or natural twine.

Callorhincus ursinus, Northern fur seals

Fortunately, mortality from entanglement has declined by about half since the 1980s. There is also concern that the breeding grounds on the Pribilof Islands are being negatively affected by pollution and other disturbances caused by the expansion of fishing industry services on St. Paul Island.

The waters off the Russian Sakhalin Island in the Okhotsk Sea may be opened to oil and gas development, which threatens northern fur seal populations with marine traffic and potential environmental contamination by oil spills.

The San Miguel population has suffered from decreases in prey caused by El Niño events. During the 1997 event, about 87% of the pups died before weaning.

Northern fur seals are listed as Vulnerable A2b on the IUCN Red List, and the Pribilof Islands/Bogoslof Island stock is designated as Depleted under the U.S. Marine Mammal Protection Act. The species is protected in Canada by the 1993 Marine Mammal Regulations, except for hunting by indigenous peoples.

References & Further Research

Seal Conservation Society (SCS): Northern Fur Seal, Callorhinus ursinus
Northern Fur Seal Research at the National Marine Mammal Laboratory (NMML)

Research Callorhinus ursinus @
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