Northern fur seals are members of the “eared seal” family (Otariidae). They have a stocky body, small head, and a very short snout. Their flippers are the longest in the Orariidae family–their hind flippers can measure up to one-fourth of their total body length.
Adult males are much heavier and longer, with much larger necks, shoulders, and chests, than females. Males can grow to 7 feet (2 m) and weigh up to 600 pounds (270 kg) while females can grow to 5 feet (1.5 m) and weigh up to 130 lb (60 kg). Northern fur seals have very dense coats that end at the wrist line of their flippers. Pups are uniformly black until they molt when they are around 3 months old. Adult males are dark brown to black, and adult females are dark gray or brown on their backs and light gray, silver, or cream on their throat, chest, and stomach.
The lifespan of fur seals is approximately 10 years for males and 27 years for females.
Males establish territories early in the breeding season in May. Females arrive around mid-June to early July and give birth to one pup. The peak of pupping is usually in early July. During the breeding season, females alternate between feeding at sea, where they forage for fish and squid, and nursing on shore. While females are foraging, pups play and sleep in groups with other pups (often called “puppy pods”). Adult males present on breeding beaches do not forage while maintaining territories. Upon returning, mothers identify their pups from vocalizations and, when closer, scent. Pups are weaned at 4-5 months (late October-early November). When the breeding season ends, animals travel south and remain “pelagic” for the winter migration period (from October-November to May-June). Females travel farthest south, and pups scatter in all directions on their first migration, but eventually make
their way south.
MMPA Depleted – Pribilof Island/ Eastern Pacific stock
(All other stocks are also protected under the MMPA, but not considered depleted.)
|up to 130-600 pounds (60-270 kg), with males being much heavier than females|
|up to 5-7 feet (1.5-2 m), with males being larger than females|
|stocky body, small head, and a very short snout that is brown, gray, or black|
|10-27 years, with females living longer than males|
|fish and squid|
|Males establish territories early in the breeding season (in May)|
Northern fur seals primarily use two types of habitat:
- open ocean for foraging
- rocky beaches for reproduction
Adult fur seals spend more than 300 days per year (about 80% of their time) foraging at sea. In the open ocean, concentrations of fur seals may occur around major oceanographic features such as seamounts, canyons, valleys, and along the continental shelf break because of the availability of prey in those places. The North Pacific Transition Zone is an important productive region. Breeding seals tend to haul-out on rocky beaches, but colonies can use broad sandy beaches as well.
Northern fur seals breed at six locations in the North Pacific and Bering Sea. Three of these locations–Pribilof Islands, Bogoslof Island and San Miguel Island–are in the United States. The other three–Commander Islands, Kuril Island, and Robben Islands–are in Russia.
The Pribilof Islands support the largest breeding rookery of northern fur seas (about half of the world’s fur seal population).
In the winter, the southern boundary of the northern fur seal range extends across the Pacific Ocean, between southern California and the Okhotsk Sea and Honshu Island, Japan. In the spring, most fur seals migrate north to breeding colonies in the Bering Sea. Male northern fur seals leave the breeding colony in September, and spend most of their time in the Bering Sea and North Pacific Ocean along the Aleutian Islands. Females return to sea by late October, and generally travel to either the central North Pacific or south along the California coast to feed. Some fur seals may spend all year around San Miguel Island.
The Pribilof Island population was designated as “depleted” under the Marine Mammal Protection Act (MMPA) in 1988 because it had declined by more than 50% since the 1950s. Trends from 2009 show that the Pribilof Islands population has continued to decline.
The Eastern Pacific stock is estimated to have a historical high of 2.1 million in the early 1950s. We currently allow a subsistence harvest by Alaskan natives based on need. This is not thought to be a cause of continued population decline.
The first fur seals to populate San Miguel Island likely migrated from the Pribilof Islands. The population grew steadily in the 1950s and early 1960s (46%), but experienced declines from major El Niño events. The population began to recover in 1999, and recent estimates of San Miguel Island are over 9,000. A small population has developed on South Farallon Island (off the California coast), presumably immigrants from San Miguel Island.
The Commander Islands, Kuril Islands, and Robben Islands in Asia experienced a severe decline of northern fur seals in the early 1900s from commercial sealing. The number of seals declined on all three islands between the late 1960s and the late 1980s. The Robben Island population now appears to be recovering.
Historical declines were caused by
- commercial harvest
- After unregulated “pelagic” harvests were stopped in 1911, the fur seal population recovered, and by the 1950s was thought to be at pre-harvest levels. The most recent decline began soon after an experimental female harvest was implemented in 1956 to increase the productivity of the herd. Although the consequences of this program were recognized within a few years and the female harvest ended in 1968, the northern fur seal population on the Pribilof Islands continued to decline.
- Regulated commercial harvests ended on St. George Island in 1976 and on St. Paul Island in 1984.
Today, northern fur seals face a variety of threats including:
- changes in the availability of prey
- bycatch in fishing gear
- habitat change
- entanglement in marine debris
- disturbance from vessels and humans
- climate change
- environmental pollutants
The factors affecting northern fur seal survival are poorly understood, particularly while the animals range outside the Bering Sea. Studies of Steller sea lions, which have experienced similar population declines, suggest that factors limiting recovery include changes in quantity and quality of prey and possible increased predation by killer whales. Reduced survival rates of northern fur seal adult females and juveniles may also limit recovery.
International agreements to conserve declining fur seals were made with Great Britain (for Canada), Japan, Russia, and the United States in 1911 and again in 1957. In 1984, the U.S. ended commercial harvest of northern fur seals within U.S. waters.
Under the MMPA, extensive monitoring and research has focused on the Pribilof Island and San Miguel Island populations. Our conservation plan [pdf] is focused on identifying and lessening impacts from human related threats such as marine debris and incidental take in commercial fishing gear.
Co-management agreements of northern fur seals with the tribal governments of St. Paul and St. George (Pribilof Islands), especially regarding subsistence harvest, are another aspect of our conservation plan. Through this arrangement, the U.S. and tribal governments are implementing programs that promote full utilization of edible and inedible parts of northern fur seals, promote community outreach and education efforts, monitor shorelines and rookeries through the Island Sentinel Program, and monitor and remove marine debris. The tribal governments of St. Paul and St. George also maintain and repair research infrastructure on fur seal rookeries.
Northern fur seals were afforded protection in U.S. waters under The Fur Seal Treaty of 1911 [pdf].
The Pribilof Island/ Eastern Pacific population of the northern fur seal was designated as “depleted” under the Marine Mammal Protection Act in 1986.
We issued a Conservation Plan for the Eastern Pacific Stock of Northern Fur Seals in 2007.
- Subsistence harvest regulations modified for Eastern Pacific stock.
- Northern fur seals have very dense fur (approximately 46,500 hairs/cm2) that covers all but their flippers.
- They can spend extremely long periods in the open ocean–nearly 2 years–before returning to their breeding colonies.
- Male fur seals can grow to be over three times larger than females.