Northern Fur Seal
About the Species
Northern fur seals are members of the "eared seal" family (Otariidae). They spend most of the year in the ocean. Weaned pups typically spend nearly 2 years away before returning to their breeding colonies. Northern fur seals primarily use open ocean for foraging and rocky beaches for resting and reproduction.
Historically, northern fur seals were hunted for their fur on land and at sea. In 1911, the Fur Seal Treaty created an international prohibition on hunting fur seals at sea. In 1984, the United States ended commercial harvest of northern fur seals on the Pribilof Islands.
Northern fur seals, like all marine mammals, are protected under the Marine Mammal Protection Act. The Pribilof Islands/eastern Pacific stock is listed as depleted under the MMPA.
NOAA Fisheries is committed to conserving and protecting northern fur seals. Our scientists and partners use a variety of innovative techniques to study, learn more about, and protect this species.
In 1988, the Pribilof Islands population was designated as a depleted stock under the MMPA because it had declined by more than 50 percent from its estimated population of 2.1 million seals in the 1950s. This stock was reclassified in 1994 as the eastern Pacific stock, which includes the Pribilof Islands population and a newly established breeding site on Bogoslof Island, and the California stock, which breeds on San Miguel and the Farralone Islands off the coast of California. The California Stock is significantly smaller than the eastern Pacific stock. Estimated at 14,050 northern fur seals in 2016, it is smaller than either of the populations on the Pribolof Island of St. George or Bogoslof Island. Trends in abundance since the designation of the eastern Pacific stock are different for individual islands and even breeding areas. From 1998 to 2016, pup production declined 4.12 percent per year on St. Paul Island and showed no significant trend (i.e., the population was stable) on St. George Island. From 1997 to 2015, pup production on Bogoslof Island increased 10.1 percent. Because the breeding population on St. Paul Island is so much larger than the other islands the decline there drives the overall stock decline. The 2017 abundance estimate for the eastern Pacific stock is 620,660 northern fur seals.
The first northern fur seals to populate San Miguel Island migrated from the Pribilof Islands, as seals tagged on the Pribilofs were observed on San Miguel among breeding California sea lions. The population grew 46 percent in the 1950s and early 1960s but afterward experienced declines due to major El Niño events. The population began to recover in 1999, but it has been affected by subsequent El Niño events, often resulting in the deaths of all newborn pups. A small population has been observed breeding on South Farallon Island (off the California coast).
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 also declined on all three islands between the late 1960s and the late 1980s. The Robben Island population now appears to be recovering.
- Throughout Its Range
- Pribilof Island/Eastern Pacific stock
Northern fur seals have a stocky body, small head, very short snout, and extremely dense fur (46,500 fibers/cm²) that ends at the wrist lines of their flippers. Their flippers are the longest in the Otariidae family. Their hind flippers can measure up to one-fourth of their total body length. Their fore flippers are incredibly strong allowing them to walk or run on all fours. They can outrun a human on slippery rocks and can climb nearly vertical cliffs. Northern fur seals exhibit sexual dimorphism, which means that adult males are much larger (up to 370 percent) than adult females. Males can grow to 7 feet and weigh up to 600 pounds, while females can grow to 5 feet and weigh more than 120 pounds. 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 adults also have white whiskers, known as vibrissae, while the juveniles and pups have black vibrissae.
Behavior and Diet
Northern fur seals are a highly pelagic (live in the open ocean), mostly solitary, nocturnal species. They are known to be aggressive on land, especially during breeding and mating season. Adult males forcefully defend their breeding territory site. Male to male aggression is most frequently used in defense of territories and consists of pushing and biting, sometimes to the death. Female to female aggression is frequent but mild (open mouth threat). Intense female to female aggression (biting and pushing) is rare.
Northern fur seals are described as generalist or opportunistic foragers, consuming a wide variety of midwater shelf fish and squid species. Walleye pollock is the predominant prey of northern fur seals that forage over the Bering Sea shelf. They consume greater amounts of oceanic fish and squid species when they forage over the slope and in off-shelf waters. Other primary prey include Pacific sand lance, Pacific herring, Northern smoothtongue, Atka mackerel, and Pacific salmon. The northern fur seal diet differs depending on geographic area and time of year. Northern fur seal diet and tracking (telemetry) studies indicate they forage in colony-specific areas, while they use their preferred land sites for resting and reproduction.
Where They Live
Northern fur seals primarily inhabit two types of habitat: open ocean and rocky or sandy beaches on islands for resting, reproduction, and molting.
Northern fur seals seasonally breed on six islands in the eastern North Pacific Ocean and Bering Sea in the United States—St. Paul, Bogoslof, St. George, Sea Lion Rock, San Miguel, and South Farallon. They also breed on the Commander Islands, Kuril Island, and Robben Island.
The Pribilof Islands support the largest aggregation of northern fur seals, which breed on St. Paul, St. George, and Sea Lion Rock (about half of the world's northern fur seal population). Non-breeding northern fur seals haul-out on Walrus Island and Otter Island which are also part of the Pribilof Islands.
Adult northern fur seals spend more than 300 days per year (about 80 percent of their time) at sea. During the summer and autumn they intermittently fast while on land and feed at sea. During the winter and spring they are pelagic, occupying the North Pacific Ocean as well as the Bering and Okhotsk Seas. In the open ocean, concentrations of northern fur seals may occur around oceanographic features—such as eddies, convergence-divergence zones, and frontal boundaries—because of the availability of prey in those places. In the winter, the southern boundary of the northern fur seal range extends across the Pacific Ocean, between southern California and Honshu Island, Japan, but they are found as far north as the Bering Sea. In the spring, most northern fur seals migrate north to breeding colonies in the Bering Sea. Territorial adult male northern fur seals leave their breeding colonies in August and are thought to spend most of their time in the Bering Sea and North Pacific Ocean along the Aleutian Islands. Pregnant adult females begin their winter migration in November and generally travel to either the central North Pacific Ocean or to offshore areas along the west coast of North America to feed. Some northern fur seals may spend all year in the waters around San Miguel Island, California.
Lifespan & Reproduction
Male northern fur seals can live up to 18 years, while females can live up to 27 years. Beginning in May, male seals start returning to the breeding islands. Older males, or bulls, arrive first to vie for prime breeding territories before the females arrive. A male’s ability to mate depends on several factors, such as body size, fighting ability, size and location of the chosen breeding territory, and skill at interacting with females. Because males do not leave the breeding territory to feed, their ability to fast is critical. Males remain on their territory an average of 50 days, losing 20 percent to 25 percent of their body mass. Breeding males are typically 10 or more years old and maintain females within their territories. A small number of the total adult males in a territory accomplish most of the breeding. Adult males are counted annually during the peak of the breeding season as an index of the population size. They are categorized as territorial with females, territorial without females, or non-territorial. There is some turnover of territorial males in August, allowing non-territorial males to occupy sites abandoned by territorial males, but the vast majority of adult females have already mated at this point. Territorial males exclude juvenile males from the breeding areas. Juveniles instead congregate on land in areas called "haulouts" during the summer breeding season. The haulouts can be located inland, typically behind the breeding areas, or adjacent to the breeding areas. The typical structure of northern fur seal terrestrial habitat consists of the core group of breeding males with females, idle males without females on the fringe of the core area, and non-territorial males and juvenile males on haulouts outside the breeding areas.
Females generally have their first pup at 5 to 6 years of age and are in their reproductive prime between the ages of 8 and 13. They are not selective in their choice of mate, but they do show an affinity for a specific breeding site. Females typically start returning to the breeding islands in late June and give birth to a single pup a few days after arriving on land. Mating occurs within 5.3 days of giving birth. Female northern fur seals undergo embryonic diapause, meaning the embryo does not immediately implant in the uterus but is delayed until after lactation, or weaning. Females suckle their pups for 5 to 6 days and then go to sea to forage for 3.5 to 9.8 days. Pups are nursed until weaning (about 4 months) and leave the breeding site before their mothers.
Entanglement in Marine Debris and Lost or Abandoned Fishing Gear
Northern fur seals can become entangled in lost or abandoned fishing gear such as trawl webbing, packing bands and monofilament nets, or other marine debris, either swimming off with the gear attached or becoming anchored. Northern fur seals encounter marine debris during their winter and spring migrations when they spend most of their time in the North Pacific foraging in the transition zone and eddies. They also encounter marine debris in the Bering Sea during their travels to and from their rookeries. Once entangled, seals may drag and swim with attached gear for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury, which may lead to reduced reproductive success and death.
Changes in Available Food Due to Commercial Fishing
The type of available prey, access to prey, and distribution of prey can change for a variety of reasons. For example, regional and local prey can change because of changes in climate, oceanography, and the overall complexity of the oceans ecosystem. In addition, cumulative and annual commercial fisheries may result in reduced availability of northern fur seal prey. Fishery interactions can include fisheries bycatch and indirect effects like competition for commercial fish species.
Contaminants can enter the ocean and subsequently affect the food chain of the northern fur seal. Contaminant studies on northern fur seals have shown exposure to various toxic substances and evidence of accumulation in various tissues. Contamination sources can include oil and gas development, industrial runoff, vessel discharge, microplastics, vessel grounding, and oil spills. These contaminants have the potential to affect the immune system of northern fur seals, leaving them more susceptible to disease.
Other threats include environmental changes, oil and gas exploration, habitat degradation, human presence, disturbance by marine vessels or aircraft, chronic pollution, and illegal harvests.
Northern fur seals were hunted and killed for their fur. Throughout history, there have been many treaties and management measures put into place to manage and protect this species.
Commercial Harvest History
Harvest management of northern fur seals on the Pribilof Islands has a long history, which began when Russians brought Aleuts to the islands as sealing crews in 1786. The Russians harvested about 3 million fur seals during their control of the Pribilof Islands. They also instituted the first fur seal research and harvest management measures in 1806, and in 1807, canceled the harvest. From 1822 to 1827, bulls and pups were not harvested, and by 1847 the Russians set up a "breeding reserve" to protect the females. The population increased due to these conservation measures.
After the sale of Alaska to the U.S. in 1867, commercial harvests continued, and generated large profits for fur merchants as well as tax revenues for the U.S. government. It has been estimated that by the early 1900's the tax and lease revenue, from the sale of Pribilof fur seal skins, paid for the 7.2 million dollar purchase of Alaska.
In 1869, the Pribilof Islands were set aside as a special reservation for the protection of fur seals and the U.S. Treasury was authorized to lease sealing privileges. The first 20-year lease of sealing privileges on the Pribilof Islands was issued to the Alaska Commercial Company and commenced in 1870 and the total harvest killed approximately 2,255,519 seals. A fierce dispute among countries began since sealing on land was now limited to a single company, and the remaining individuals and companies were only allowed to take seals at sea. A second 20-year lease of sealing privileges was issued to the North American Commercial Company.
Resolving years of international dispute about the United States’ jurisdiction over the nearshore marine waters, northern fur seals were given protection from all pelagic sealing with the signing of the North Pacific Fur Seal Treaty of 1911 (PDF, 10 pages) by Great Britain, Japan, Russia and the United States. The Treaty prohibited pelagic sealing by all countries, and established the U.S. to operate all land harvest activities and split the skins obtained among the signatory countries. The Treaty remained in force until 1941. A successive convention was signed in 1957 and amended by a protocol in 1963. The international convention was put into effect domestically by The Fur Seal Act of 1966.
After the early years of indiscriminate fur seal harvesting, U.S. management of land-based commercial sealing restricted killing to non-breeding males on the haulouts during the summer. As a result, the population thrived and was estimated to number about 2.1 million seals on the Pribilof Islands in the 1950s. The Japanese threatened to abrogate the convention if the U.S. did not take action to reduce the herd over concern that their fisheries resources were being reduced by fur seals. As a result the U.S. began a herd reduction program which authorized killing female fur seals from 1956 through 1968. The commercial harvest continued on the Pribilof Islands reaching a peak of almost 96,000 juvenile male fur seals in 1956 in addition to almost 27,000 female fur seals. The highest quality and most valuable skins came from 2- to 4-year old male fur seals, this subgroup of juvenile or non-breeding males are referred to as sub-adult males and they became the focus of the commercial harvest by using size limits. The population declined as expected from the female killing, but continued to decline unexpectedly through the 1970s. In order to investigate the population effects of harvesting NOAA Fisheries discontinued harvests on St. George Island in 1973. NOAA set aside St. George Island as a research control site (i.e., no harvests) for scientific study under the convention, and St. Paul Island was the experimental site (i.e., continued harvests). The U.S. did not sign the Interim Convention on the Conservation of North Pacific Fur Seals in 1984, which led to the cessation of commercial harvesting on St. Paul Island. A subsistence harvest of subadult male fur seals has continued on both islands under the authority of the Fur Seal Act since 1985. The subsistence harvest is limited to fewer than 2,500 subadult male seals a year.
Northern fur seals are protected under the Marine Mammal Protection Act and the Fur Seal Act. About 50 percent northern fur seals breed on the Pribilof Islands. The Pribilof Islands’ northern fur seal population was listed as depleted in June 1988 under the MMPA, meaning that this stock is below its optimum sustainable population level.
Scientists with NOAA Fisheries Marine Mammal Laboratory have been collecting population data on St. Paul and St. George Island (Pribilof Islands) to evaluate the trends and status of the northern fur seals since the early 1900s. This includes monitoring subsistence harvests, assessing possible adverse effects of human-related activities on or near the Pribilof Islands, and conducting research and analyzing data to determine the cause of population changes in the Pribilof Islands’ northern fur seal population. NOAA Fisheries managers have also created a conservation plan to increase the population of northern fur seals to a level where it is no longer considered depleted under the MMPA.
In 1994, the MMPA was amended to include section 119, which reads, "The Secretary may enter into cooperative agreements with Alaska Native Organizations to conserve marine mammals and provide co-management of subsistence use by Alaska Natives." NOAA managers pursued a more active harvest management and monitoring role for local tribal members from 1994 to 2001. As a result, NOAA Fisheries and the tribal governments on both St. Paul Island and St. George Island had already been co-managing subsistence use of northern fur seals before signing their co-management agreements in 2000 and 2001, respectively.
Managing Subsistence Harvest
NOAA Fisheries issued an emergency interim rule in 1985, followed by a final rule in 1986, to initiate a subsistence harvest of northern fur seals by Alaska Natives on the Pribilof Islands. The subsistence harvest is regulated under the authority of section 105(a) of the Fur Seal Act. Under a co-management agreement with NOAA Fisheries, the tribal governments of St. Paul and St. George have a formal role in managing the harvest of northern fur seals to meet their subsistence needs; the commercial harvest for fur had always exceeded the subsistence need for meat on the Pribilof Islands. Fewer than 1,000 juvenile male northern fur seals have been harvested annually since 2000. To address population concerns about the accidental harvest of young females, NOAA Fisheries revised the northern fur seal harvest regulations and removed the option to extend the harvest season beyond August 8. We also set a 3-year rather than an annual harvest to relieve the information collection burden on the tribal community. In 2014, NOAA Fisheries revised the subsistence harvest regulations to allow residents of St. George to harvest pups to meet their subsistence needs.
The tribal governments of St. George and St. Paul manage, monitor and report their subsistence marine mammal harvests with their co-management partners at NOAA Fisheries.
Reducing Entanglement in Marine Debris
The NOAA Fisheries Marine Mammal Laboratory and tribal governments have conducted disentanglement studies on the Pribilof Islands. These studies provide entanglement estimates and remove debris from captured animals.
The tribal governments of St. Paul and St. George have coordinated annual beach cleanup and derelict fishing debris removal select locations.
Developing Oil Spill Contingency Plans
NOAA cooperated with numerous agencies to develop an area oil spill contingency plan that has been in effect for over 20 years. The Alaska Regional Response Team plan is reviewed and updated as needed to ensure its applicability to ever-changing oil spill risks and to integrate experience gained from oil response in other regions. As part of the plan, state, federal, and local agencies identified sensitive habitats in the Pribilof wildlife protection guidelines and created a sensitive habitat map.
Monitoring Domestic Fisheries
NOAA monitors domestic fisheries through an observer program that identifies sources of mortality for marine mammals, including northern fur seals. Fisheries observer program biologists placed on fishing vessels record fishing efforts (e.g.,number of sets, size of nets, time and location of sets) and bycatch of non-target species. They also document the number, sex, and age of all marine mammals observed and caught. NOAA Fisheries then summarizes the observers’ incidental take data in its annual stock assessment reports.
Reviewing Proposed State and Federal Permits, Environmental Analysis, and Identifying Mitigation Measures
Under the National Environmental Policy Act, NOAA regularly reviews proposed state and federal permits and actions that may affect northern fur seals. NOAA Fisheries works with agencies and applicants to determine whether such actions could harm northern fur seals or damage habitats essential to their survival and to identify measures to avoid or minimize possible adverse effects. We also review marine mammal research permits.
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings. When stranded animals are found alive, NOAA Fisheries and its partners assess the animal’s health and try to return it to the water. When stranded animals are found dead, our scientists work to understand and investigate the cause of death. Although the cause often remains unknown, scientists can sometimes attribute strandings to disease, vessel strikes, fishing gear entanglements, pollution exposure, or underwater noise. Some strandings can serve as indicators of ocean health, giving insight into larger environmental issues that may also have implications for human health and welfare. NOAA Fisheries also responds to marine mammals entangled in fishing gear or other lines or debris and, when feasible, attempts disentanglement.
Preventing Rats on the Pribilof Islands
The U.S. Fish and Wildlife Service, NOAA, and a variety of local community organizations and other federal agencies work collectively to prevent the introduction of rats onto the Pribilof Islands. Rats would rapidly devastate the abundant seabird populations and potentially introduce disease to marine mammals. Rat prevention training occurs periodically. Activities include setting up and regularly maintaining trapping stations, providing visitor education programs, identifying rat introduction risks, and establishing emergency response protocols.
All marine mammals, including northern fur seals, are protected in the United States under the MMPA. One stock of northern fur seals—the Pribilof Island/eastern Pacific stock—is listed as depleted under the MMPA.
Regulatory Actions & Documents
Proposed Modification to Subsistence Use Regulations for the Eastern Pacific Stock of Northern Fur Seals
Extension of the Opening Date of the Subsistence Use Season of the Eastern Pacific Stock of Northern Fur Seals
Subsistence Taking of Northern Fur Seals on the Pribilof Islands - Annual Subsistence Harvest Levels
Notice of Availability of a Draft Supplemental Environmental Impact Statement - Management of the Subsistence Harvest of Northern Fur Seals on St.
NOAA Fisheries conducts various research activities on the biology, behavior, and ecology of northern fur seals. The results of this research are used to inform management decisions for this species. Our work includes:
- Stock assessments.
- Satellite tagging.
- Studying diet and foraging ecology.
- Monitoring population abundance and distribution.
- Checking vital rates.
Northern Fur Seals in Alaska and California
Our research on the population dynamics, biology, health, distribution, and movement patterns of northern fur seals provides information crucial for understanding and protecting fur seal populations in Alaska and California.
Review Draft - Regulatory Impact Review - Revision to Regulatory Requirements for the Subsistence Taking of Northern Fur Seals on St. Paul and St. George Island, Alaska
Evaluation of the costs and benefits of a revision to the northern fur seal subsistence use…
Subsistence Harvest Report for the 2017 Season: September 15 to November 30, 2017
Draft Environmental Impact Statement - Management of the Subsistence Harvest of Northern Fur Seals on St. Paul Island, Alaska (2017)
Subsistence use of northern fur seals on St. Paul Island, Alaska.
Data & Maps
This online bibliography is based on a 2006 publication which lists northern fur seal (Callorhinus…
Northern fur seal pup and adult male counts.