Callorhinus ursinus 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Carnivora Otariidae

Scientific Name: Callorhinus ursinus (Linnaeus, 1758)
Common Name(s):
English Northern Fur Seal
Arctocephalus ursinus (Linnaeus, 1758)
Phoca ursina Linnaeus, 1758
Taxonomic Notes: The Northern Fur Seal, Callorhinus ursinus, (Linneaeus, 1758) is in the family Otariidae and  is the only extant species within the genus Callorhinus. Although earlier work had suggested that more than a single species or subspecies might exist, the current belief is that there is only the one species (Rice 1998) and genetic studies suggest that they are panmictic (Dickerson et al. 2010). Despite the genetic history that indicates mixing, there are currently two recognized stocks of Northern Fur Seals in North America. The Eastern Pacific stock includes those Fur Seals breeding on the three primary rookeries in Alaska, the Pribilof Islands and Bogoslof Island in the Aleutian chain. The San Miguel stock includes those seals breeding on the Channel Islands and the Farallon Islands of California.

Assessment Information [top]

Red List Category & Criteria: Vulnerable A2b ver 3.1
Year Published: 2015
Date Assessed: 2015-03-26
Assessor(s): Gelatt, T., Ream, R. & Johnson, D.
Reviewer(s): Lowry, L.
Facilitator/Compiler(s): Lowry, L., Ahonen, H., Pollock, C.M., Chiozza, F. & Battistoni, A.
The global population of Northern Fur Seals includes breeding areas extending from the Kuril Islands of Russia, across the Bering Sea, south to the west coast of the United States with the southernmost rookery in the Channel Islands of California. The population has shown inconsistent trends at particular areas with the most dramatic change occurring at the largest breeding rookery, St. Paul Island, Pribilof Islands, Alaska. The Pribilof population has experienced a significant, steep decline in recent years and has failed to recover despite the cessation of commercial harvesting. Although the global population is still in excess of a million animals, the current downward trends in abundance at St. Paul and nearby St. George Island remain unexplained. The Pribilof Islands population represents just under one half of the world-wide population and has declined by approximately 66% over the last three generations (1972–2014). The global change in abundance during that same period was 30.1% (95% CI -47.1% to 14.5%). Therefore, Northern Fur Seals should remain in the IUCN Red List category of Vulnerable under criterion A2b (due to the fact that the causes of the reduction do not appear to have ceased, are not understood, and may not be reversible based on the unknown cause, and that an index of abundance appropriate to the taxon (direct counting and mark-recapture) was used to assess population size).
Previously published Red List assessments:

Geographic Range [top]

Range Description:Northern Fur Seals are a widely-distributed pelagic species in the waters of the North Pacific Ocean and the adjacent Bering Sea, Sea of Okhotsk and Sea of Japan. They range from northern Baja California, Mexico, north and offshore across the North Pacific to northern Honshu, Japan. The southern limit of their distribution at sea is approximately 35°N (Rice 1998). Vagrants reach the Yellow Sea in the west and eastern Beaufort Sea to the north. They breed on rookeries in Russia (Kuril Islands, Commander Islands and Tuleny Island (Kuzin 1999), Alaska (Pribilof Islands and Bogoslof Island) and California (San Miguel Island) (Loughlin et al. 1994). In the past, the vast majority of the population bred at rookeries on the Pribilof Islands, with substantial numbers on the Commander Islands. However, a significant population decline on the Pribilofs concurrent with the establishment of a new breeding site in the eastern Aleutian Islands and population increases in the Kuril Islands of Russia has resulted in the Pribilof Islands now representing approximately 45% of the global population.
Countries occurrence:
Canada; Japan; Korea, Democratic People's Republic of; Korea, Republic of; Mexico; Russian Federation; United States
China; Taiwan, Province of China
FAO Marine Fishing Areas:
Pacific – northeast; Pacific – eastern central; Pacific – northwest
Additional data:
Estimated area of occupancy (AOO) - km2:16996944Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:20302016
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:No
Upper elevation limit (metres):10Lower depth limit (metres):207
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The population history for Northern Fur Seals throughout the North Pacific and Bering Seas has been tied to the harvest of seals for their pelts (Kuzin 1999, NMFS 2007). Between the mid 1700s and early 1800s, Russian sealers used Aleut labour to harvest an average of 100,000 Fur Seals, mostly pups, annually in Alaskan waters (Roppel 1984). The commercial harvest of Fur Seals on the Pribilof Islands continued with periodic modifications to the sex/age classes of focus until and after the United States purchase of Alaska in 1867. In the late 1800s and early 1900s commercial harvests on land and pelagic sealing continued unregulated until the Fur Seal act of 1911 was signed by Japan, Russia, Great Britain (for Canada) and the United States. This treaty prohibited pelagic sealing and reduced the take on land which at its peak in 1868 had harvested 240,000 seals in a single year (Roppel and Davey 1965, NMFS 2007).

In the early 1900s the Pribilof stock continued to grow in abundance despite commercial harvest. Between 40,000 and 126,000 seals were harvested each year during 1943-1968 (NMFS 2007). A new harvest regime was followed in the early 1960s which allowed for annual harvests of approximately 300,000 adult females and 30,000-96,000 subadult males (York and Hartley 1981). The population did not increase as anticipated after this new regime and ultimately commercial harvest of Fur Seals was terminated on St. George Island in 1973 and on St. Paul Island in 1983. Subsistence harvest of subadult males has continued on both islands since that time (NMFS 2007). In 2014, subsistence harvest rules were changed to allow the annual take of up to 150 male pups on St. George Island during a new autumn harvest season. This harvest occurred for the first time in the autumn of 2014.

Contrasting to the Northern Fur Seal abundance trend on the Pribilof Islands is Bogoslof Island, a small volcanic island in the eastern Aleutian Islands of Alaska. Northern Fur Seals were first reported on Bogoslof in 1976 with the first breeding seals noted in 1980 (Lloyd et al. 1981, Loughlin and Miller 1989). Subsequent surveys revealed an exponential growth rate during the 1990s and early 2000s with the estimated number of pups increasing at a rate of 48.5% annually between the time pups were first observed in 1980 and 2005. This rate then dropped to approximately 10% annually between 2005-2011, the last time the island was surveyed. Such a dramatic growth rate can only be explained by a combination of recruitment and immigration from other sites (Ream et al. 1999). Recent studies suggest that the recent slowing in growth rate coupled with increases in foraging trip duration and distance may represent a typical density dependent response to a limited resource (Kuhn et al. 2014). The Northern Fur Seal population on Bogoslof has increased to the point that it is the second largest Northern Fur Seal rookery in the United States, surpassing St. George Island. This growth has served to ameliorate the overall decline of the population.

Northern Fur Seal rookeries in Russia have not been counted since 2006-2009 depending on the site. However, basic trends until that time are documented. Overharvesting in the 19th century eradicated the population on the Kuril Islands where Northern Fur Seals were considered extinct until the mid 1950s. Pup production grew rapidly on the Kurils during 1962-1977 (19.9% annual increase). The population stabilized around 1978 and trend became slightly negative (-0.8%) during 1978-1988. Pup production in the Kuril Islands has increased 82.4% since 1988 (+3.8% annually) and is now comparable to the Tuleny (Robben) Island population. During the last count in 2006, approximately 27,090 pups were counted. Total abundance of Fur Seals in the Kuril Islands currently exceeds 100,000 individuals (Kuzin 1999).

In 1999, A. Kuzin published a detailed description of the biology and history of Northern Fur Seals in Russia with special emphasis on Tuleny Island. He reported that the population at Tuleny at the time of its discovery in 1852 was approximately 120,000. Subsequent unregulated harvest reduced the population to as low as a few thousand animals in the late 1890s. Tuleny Island then underwent a series of population highs and low during various periods of harvest. The maximum population was approximately 180,000 individuals in the late 1960s (Kuzin 1999). The most recent estimate was 140,000 individuals including 42,200 pups in 2009 (Kuzin 2010).

The San Miguel stock of Northern Fur Seals breeds primarily on San Miguel Island, California, at the southern extent of the breeding range. This population has increased or been stable since its discovery in 1968 (Caretta et al. 2013). The trend in pup births includes a steady increase followed by a sharp decline that has been shown to be directly tied to El Niño events; pup production in 1997-1998 declined 81% due to the redistribution of prey caused by the event. Overwinter satellite telemetry studies have shown that Northern Fur Seals from all of the US breeding sites use similar foraging grounds along the west coast of Southeast Alaska, British Columbia, Washington and Oregon (Lea et al. 2009, Ream et al. 2005, Sterling and Ream 2004). The overlap is not limited to foraging habitat as genetic studies indicate that there is very little differentiation between animals throughout the range (Dickerson et al. 2010).

Population estimates for Northern Fur Seals are generally derived by multiplying pup counts by a correction factor of 4.4747 to include all non-pups. A global abundance estimate was generated from the most recently available count and estimate data for all subpopulations in the range using the agTrend model (Johnson and Fritz 2014). The 2014 estimate for localities other than the Pribilofs is a projected number based on the trends at each site. The modelled population estimate used all of the data available since 1966 to project the estimates reported above. The most recent actual count and estimated numbers used in the model are shown below.

Pribilof Islands, 2014

St. Paul Island: 91,737 pups x 4.4747 = 410,496 (Towell et al. 2014)

St. George Island: 18,937 pups x 4.474 = 84,737 (Towell et al. 2014)

Sea Lion Rock: 5,250 pups x 4.4747 = 23,492 (Towell et al. 2014)

Commander Islands, 2006: 59,805 x 4.4747 = 267,609 (Burkanov and Calkins 2007)

Tuleny Island, 2009: 42,200 x 4.4747 = 188,832 (Kuzin 2010)

Kuril Islands, 2006: 25,164 pups x 4.4747 = 112,601(Burkanov et al. 2007)

Bogoslof Island, 2011: 22,905 pups x 4.4747 = 102,493 (Towell et al. 2012)

San Miguel Island, 2014 (not including Castle Rock): 2,327 x 4.4747 = 10,412 (A. Orr, NMFS pers. comm.)

Farallon Islands, 2014: 656 pups x 4.4747 = 2,935 (R. Berger, Point Blue Conservation Science pers. comm.)

The global population of Northern Fur Seals is estimated to be approximately 1.29 million in 2014, a decline of approximately 658,000 since 1976. Note that this number is different than the sum of abundances given above because most were projected forward to 2014 in the model. Using the agTrend model to project the population reduction at all sites over the past three generations (1972-2014) gives an estimated reduction of 30.1% (95% CI -47.1% to 14.5%). Annual abundance estimates for the entire range do not exist as there are no consistent monitoring strategies in place. Although abundance is declining, the overall decline is not proportional across all sites. The greatest decreases are occurring in the Pribilof Islands, while populations in the Kuril Islands and Tuleny Island in Russia, and on Bogoslof Island in Alaska have increased.

The decline described above understates the total reduction of the Northern Fur Seal population in historic times. It is estimated that the population numbered up to 2.5 million animals in the 1950s, and it may have been considerably larger than that when there were many more active rookeries before the onset of human exploitation.

To date the only population viability analysis conducted for Northern Fur Seals was described in a report from the Canadian Science Advisory Secretariat, Department of Fisheries and Oceans, Canada (Olesiuk 2012). This analysis concluded that all subpopulations are presently secure with little risk (0.00%-0.42%) of extirpation within the next century.
Current Population Trend:Decreasing
Additional data:
Number of mature individuals:650000Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:Northern Fur Seals exhibit extreme sexual dimorphism, with adult males measuring 30-40% longer and more than 4.5 times heavier than adult females. Males can be as large as 2.1 m and 270 kg. Adult females can measure 1.5 m and 50 kg or more. Newborns weigh 5.4-6 kg, and are 60-65 cm long. Pups are blackish at birth, with variable oval areas of buff color on the sides, in the axillary area, and on the chin and sides of the muzzle. After three to four months, pups moult to the colour of adult females and subadults. Northern Fur Seals become sexually mature at three to five years old, at which time females can produce one pup each year for most of the rest of their lives (Scheffer and Wilke 1953, Scheffer 1962). Kuzin (1999) noted that at times of rapid population growth on Tuleny Island, some females were fertilized as early as age two with five year old females achieving a pregnancy rate of 80%. Gestation lasts 51 weeks, which includes a delay of implantation of 3.5-4.0 months (York and Scheffer 1997). Females may produce pups up to age 23 (Lander 1981). Males do not become physically mature, and large enough to compete for a territory that will be used by females, until they are eight to nine years old. The generation time for females is approximately 12-15 years depending on the determination methods used. Pacifici et al. (2013) estimated the generation time at 14.1 years.

Breeding on the Pribilof Islands occurs from mid-June through August, with a peak in early July (the median date in southern California is approximately two weeks earlier than at the Pribilofs). This is a highly polygynous species. Males arrive at the rookeries up to one month before females and vocalize, display, and fight to establish and maintain territories.

Northern Fur Seals usually give birth a day after arrival at the rookery. Mean time from birth to estrous is 5.3 days, followed by a departure for a mean of 8.3 days for the first feeding trip. Females breeding at the Pribilof Islands of Alaska are located relatively far from the foraging areas, which are concentrated at the edge of the continental shelf and hence females in this population consistently make longer foraging trips than most other female otariids, with a mean trip length of 6.9 days. Once foraging begins the mean depth of dives is 68 m and average duration is 2.2 minutes with maximum depth recorded of 207 m and maximum duration of 7.6 minutes. Pups are visited eight to 12 times over the lactation period and attended for a mean of 2.1 days during each visit, before being abruptly weaned at four months old.

Northern Fur Seals are one of the most pelagic pinnipeds. They spend most of the year at sea, and rarely (if ever) returning to land between one breeding season and the next. Thus, males spend an average of only 45 days ashore a year and females only 35 days a year. Once weaned, juveniles go to sea and do not haul out until they return, usually to the island of their birth, two to three years later. At sea, Northern Fur Seals are most likely to be encountered alone or in pairs, with groups of three or more being uncommon. They forage relatively far from shore, over the edge of the continental shelf and slope. Diving is concentrated around dawn and dusk. Northern Fur Seals spend quite a bit of time rafting at the surface, either asleep or grooming. Many animals, especially juveniles, migrate from the Bering Sea south to California or the waters off Japan, to spend the winter feeding. (Sterling et al. 2014).

The Northern Fur Seal diet varies by site, oceanic domain and season and includes many varieties of epipelagic and vertically-migrating mesopelagic schooling and non-schooling fish and squid. Prey species of importance in the waters off California and Washington include Anchovy, Hake, Saury, Salmon, and several species of Squid and Rockfish. On the Pribilof Islands, prey species reflect foraging patterns on and off the continental shelf. Satellite telemetry and stable isotope analysis indicate that those seals foraging on the shelf use typical on-shelf species like Walleye Pollock, Pacific Herring and gadid species while off shelf foragers included species such as myctophids. Bogoslof Island in the Aleutian Islands of Alaska is a volcanic island surrounded by deep water and the most common prey species there included Northern Smoothtongue and gonatid squid species (Zeppelin and Orr 2010).

Predators include Killer Whales, Sharks and Steller Sea Lions (Gentry 1998).
Systems:Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat:No
Generation Length (years):14.1
Movement patterns:Not a Migrant
Congregatory:Congregatory (and dispersive)

Use and Trade [top]

Use and Trade: Northern Fur Seals have a long and complex history of commercial harvesting, which began when the main breeding colonies were discovered in the late 18th century. Commercial exploitation continued through 1984, and there were many periods of decline and recovery over this long period. Numerous international treaties and agreements were put in force in efforts to manage harvests. There is currently no commercial harvesting.

Small numbers of Northern Fur Seals are taken annually by Alaska Natives in a subsistence harvest on the Pribilof Islands. For the period 1999-2014, the average annual harvest on St. Paul Island was 463 subadult males/year. Subsistence harvest has declined in recent years such that the harvest has not exceeded 400 since 2005 on St. Paul. On St. George Island an average of 218 males were taken annually between 1985 and 2012 (Angliss and Allen 2009, Allen and Angliss 2014).

Threats [top]

Major Threat(s): Northern Fur Seals have one of the longest and most complex histories of commercial harvesting, which began when the main breeding colonies were discovered in the late 18th century; exploitation continued through until 1984. Numerous international treaties and agreements were put in force over time in efforts to manage this species, and they are no longer harvested commercially. Small numbers are taken annually by Alaska Natives in a subsistence harvest on the Pribilof Islands. Harvest levels are declining and are unlikely to be affecting the status of the Fur Seal population.

Northern Fur Seals compete for Walleye Pollock with one of the largest commercial fisheries world. Measurable annual mortality, especially for juveniles and subadults, is caused by entanglements in derelict and discarded fishing gear, marine debris and direct interactions with commercial fisheries. This mortality was highest during the period of active high seas drift net fishing in the North Pacific in the 1980s, but entanglement in debris is an ongoing problem. Long-term ecosystem regime change in the North Pacific and possible changes in the foraging patterns of a key predator (the Killer Whale), may be working synergistically with the fisheries related issues to cause the current population decline.

Like all fur seals, Northern Fur Seals are vulnerable to oil spills because of their dependence on their thick pelage for thermoregulation. The small colonies at San Miguel Island in the California Channel Islands and on the Farallon Island may be at greatest risk due to proximity to major harbours, shipping lanes and offshore oil extraction facilities.

The effect of global climate change on Northern Fur Seals is uncertain. However, any further negative disruption of their ecosystem should be considered a threat.

Conservation Actions [top]

Conservation Actions: Following the termination of the Interim Convention on the Conservation of the North Pacific Fur Seal in 1984, the Northern Fur Seal is now managed on land independently by the Russian Commonwealth of Independent States and the United States. The eastern north Pacific stock of the Northern Fur Seal was listed as depleted under the U.S. Marine Mammal Protection Act in 1988, and a final conservation plan was completed in December 2007.

Citation: Gelatt, T., Ream, R. & Johnson, D. 2015. Callorhinus ursinus. The IUCN Red List of Threatened Species 2015: e.T3590A45224953. . Downloaded on 20 September 2018.
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