Mammal Species of the World
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Northern fur seals have a wide geographic range throughout the northern Pacific Ocean, Bering Sea, Sea of Okhotsk, and Sea of Japan. The southern limit of their distribution is about 35˚ north, including Baja California in the eastern Pacific and Japan in the western Pacific. They have been found as far north as the eastern Beaufort Sea in the Arctic, however they are more typically found farther south. A majority of the population breeds on the Pribilof Islands in the Bering Sea. Other breeding sites include San Miguel Island, California, Robben Island, Russia, and Bogoslof Island, Bering Sea. Northern fur seals range 50 to 100 miles offshore except during the breeding season, when they remain on land.
Biogeographic Regions: arctic ocean (Native ); pacific ocean (Native )
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Transient
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: Breeding range is mostly the eastern and western Bering Sea and Sea of Okhotsk; also the vicinity of San Miguel Island, California. Primary breeding sites are the Pribilof Islands (St. Paul and St. George) in the eastern Bering Sea and the Commander Islands in the western Bering Sea; smaller breeding rookeries are on Robben Island in the Sea of Okhotsk, on the Kuril Islands north of Japan, on Bogoslof Island in the eastern Aleutians, and on San Miguel Island (Adams Cove, Castle Rock) in southern California (Reeves et al. 1992). A few haul out seasonally on Southeast Farallon Island and (rarely) on San Nicolas Island, California (Reeves et al. 1992). In winter, the species ranges south to the Honshu coast, Japan, to California, and occasionally the Mexican coast in the eastern Pacific. Adult females range farther south in winter than do males, about which little is known regarding nonbreeding distribution (perhaps remain near the Aleutians).
Northern fur seals are sexually dimorphic, with males (bulls) weighing from 180 to over 275 kg (maximum length of 213 cm), while females range from 40 to 50 kg (maximum length of 142 cm). This makes males up to 375% larger than females, which is unusually dimorphic. Adult males also develop short, bushy manes of contrasting, lighter-colored fur around their shoulders and neck, which are not often seen in the females. The color of the fur reflects its age, gender, and activities. At sea, females and young males typically have gray coats. While breeding on land, the fur typically becomes yellowish-brown from the mud and excrement on the rocks. Older males are usually brownish-black in color, but may also be dark gray or reddish-brown. Pups are born black with buff-colored markings along the sides, chin, axillary area, and muzzle; after 3 to 4 months, their pelage molts and they become gray.
Range mass: 40 (females); 180 (males) to 50 (females); 275 (males) kg.
Average length: 142 (females); 213 (males) cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently; sexes shaped differently; ornamentation
Weight: 270000 grams
Size in North America
Average: up to 2.1 m males; 1.2-1.5 m females
Range: 136-279 kg males; 30-50 kg females
Northern fur seals spend a great deal of time at sea and return to land almost exclusively during the breeding season in the summer. Thus, males spend only about 45 days per year on land, while females spend roughly 35 days per year ashore. Often they can be seen drifting on the surface of the ocean, but they dive occasionally to hunt. Typically they are a solitary species when ranging in the open ocean, although groups of up to 20 individuals have been reported.
Range depth: 207 to 0 m.
Average depth: 175 m.
Habitat Regions: polar ; saltwater or marine
Aquatic Biomes: pelagic ; coastal
Habitat and Ecology
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 2 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 oestrous 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 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 8-12 times over the lactation period and attended for a mean of 2.1 days during each visit, before being abruptly weaned at 4 months old.
Northern Fur Seals are one of the most pelagic pinnipeds. They spend most of the year at sea, 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, 2-3 years later. At sea, Northern Fur Seals are most likely to be encountered alone or in pairs, with groups of 3 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. They employ a wide variety of resting postures, including raising one or more flippers into the air, and draping one of their fore flippers over both of the rear flippers to form a posture known as the "jug handle" position.
Many animals, especially juveniles, migrate from the Bering Sea south to California or the waters off Japan, to spend the winter feeding.
The diet varies by location 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, several species of squid and rockfish, and salmon. In Alaskan waters, Walleye Pollock, Capelin, Sand Lance, Herring, Atka Mackerel, and several species of squid are important prey.
Predators include Killer Whales, sharks, and Steller Sea Lions.
Habitat Type: Marine
Comments: Open ocean and coastal waters. Rocky shores during breeding season.
Water temperature and chemistry ranges based on 1685 samples.
Depth range (m): 0 - 0
Temperature range (°C): 3.487 - 16.999
Nitrate (umol/L): 0.116 - 11.410
Salinity (PPS): 30.381 - 33.496
Oxygen (ml/l): 5.554 - 7.600
Phosphate (umol/l): 0.330 - 1.408
Silicate (umol/l): 1.436 - 30.351
Temperature range (°C): 3.487 - 16.999
Nitrate (umol/L): 0.116 - 11.410
Salinity (PPS): 30.381 - 33.496
Oxygen (ml/l): 5.554 - 7.600
Phosphate (umol/l): 0.330 - 1.408
Silicate (umol/l): 1.436 - 30.351
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Males arrive in breeding areas in late May and early June, migrate south to winter range from early August to early October. Females and young migrate south beginning in October (e.g., see Ragen et al. 1995 for information on migration from St. Paul Island south through the Aleutian Islands), gone from Bering Sea by late November; begin returning north to rookeries in March (Reeves et al. 1992). San Miguel Island population probably stays in California waters all year.
Northern fur seals are carnivorous, feeding mainly on fish species and cephalopods. They primarily feed on small, schooling fish such as anchovy, herring, and capelin. Squid are also common prey. However, northern fur seals are not particular and will take prey opportunistically, including hake, saury, rockfish, and salmon. Based on stomach contents, 53 species of fish and 10 species of squid have been identified as northern fur seal food sources, although only approximately 14 species of fish and 6 species of squid are considered to be primary prey. They tend to feed at night, as many species of prey rise to the upper water layers during this time, but they will feed during the day if prey is available.
Animal Foods: fish; mollusks; other marine invertebrates
Primary Diet: carnivore (Piscivore , Molluscivore )
Comments: Feeds mostly on small schooling fishes and squids, including a wide variety of species in both groups. Occasionally eats birds. Feeds mostly at night. Adult males fast 1-2 months during breeding season. In the Pribilof Islands, lactating females forage usually within 160 km of rookery, occasionally up to 430 km away; feeding dives average about 68 m, sometimes exceed 200 m (Reeves et al. 1992).
Aside from their roles as predators of squid and schooled fish and as prey of some larger marine species, northern fur seals do not have a particularly influential role in their ecosystem.
Large sharks and orcas are known predators of adult and juvenile northern fur seals. In addition, Steller's sea lions have been observed to feed on seal pups. To escape marine predation, northern fur seals may seek land if it is available. Mothers protect their pups for the first few days of life, after which they are often absent. Even when present, mothers will flee from predators, allowing their pups to fend for themselves.
- great white sharks (Carcharodon carcharias)
- killer whales (Orcinus orca)
- Steller's sea lions (Eumetopias jubatus)
This list may not be complete but is based on published studies.
Known prey organisms
This list may not be complete but is based on published studies.
10,000 to >1,000,000 individuals
Comments: Total population was estimated at 1.75 million in 1976, with nearly 900,000 in the Pribilofs and 256,000 in the Commander Islands. The Pribilof herd totaled about 2.5 million in the late 1950s; total population in 1983 was estimated at about 1.2 million (NMFS, Federal Register, 15 March 1996); in 2002, population estimate was 888,120 (NMFS 2003). San Miguel Island, California, population was about 10,500 in the mid-1990s (Barlow et al., cited by NMFS, Federal Register, 15 March 1996). Nearly 1,400 pups were born at the two San Miguel Island rookeries in 1988 (Reeves et al. 1992) and 2,634 in 1994 (Barlow et al.).
Solitary or slightly gregarious at sea.
Large sharks, killer whales, and northern sea lions are the primary predators. Mortality rate is nearly 50% in first year; natural mortality averages 10-20% per year for 2-3-year-olds, 10-11% for mature females, and 32-38% for adult males (Reeves et al. 1992).
Some movement occurs among rookeries; immigrants from the Pribilof, Commander, and Robben islands contributed to growth of the San Miguel Island colony, and recent repopulation of the Kuril Islands evidently resulted from immigration of seals from western and eastern Bering Sea rookeries (Reeves et al. 1992).
Life History and Behavior
Although male and female northern fur seals congregate in high densities on land during the breeding season, their social behavior is simple and individuals participate in no group behavior or hierarchies. However, communication between individuals does occur in these social settings. Males engage in territorial defense in order to protect breeding territories. This rarely escalates to physical fighting and is usually contained to threat displays which include both visual and vocal signals. Females do not actively seek mates, but use a variety of indications to signal to males that they are in estrus. These include unusual gaits and facial expressions, special vocalizations, and olfactory cues. Pups have highly specific vocalizations that bind them to their mothers and allow females to find and recognize their pups when they return from foraging. A female will call to her pup, beginning immediately after birth, and will continue to call when separated from her pup in order to find it.
Communication Channels: visual ; acoustic ; chemical
Other Communication Modes: pheromones ; scent marks
Perception Channels: visual ; tactile ; acoustic ; chemical
Comments: Feeds mostly at night. Active day and night in breeding aggregations.
Although it has been estimated that northern fur seals can live up to 26 years or older (estimated from dental records), the average lifespan of males is only about 2 years and for females it is approximately 4.6 years, taking into consideration the high mortality rates of young. There are no records of lifespans of northern fur seals kept in captivity.
Status: wild: 26 (high) years.
Status: wild: 2 (males); 4.6 (females) years.
Status: wild: 25.0 years.
Status: wild: 30.0 years.
Lifespan, longevity, and ageing
Northern fur seals are polygynous, with bulls controlling territories occupied by 1 to 100 females, average harem size is 40 females. Males arrive on land (annual breeding islands) prior to females joining them. They usually return to their natal rookeries, although this may vary. Males establish and aggressively defend a specific territory, although such defense rarely escalates to physical fights. Typically, territories closer to the shore are more highly prized by females, but it is currently unknown what other features of the territory attract females. Some territories that look nearly identical by human observation may have large disparities in female density, with some containing no females and others crowded with females. It is the territory, not the particular male, for which the female shows preference. Males are unable to control members of their harem that choose to move to a different male’s territory. However, female preference does not seem to affect male’s choice of territory. Males will continue to occupy and defend a territory to which few to no females visit for years, without establishing a new location. Although northern fur seals are traditionally viewed as polygynous mating systems in which the males control the females through the use of harems, this is a misconception. Females control the mating system. Females predictably come ashore each year to give birth to their pups and are drawn to communal breeding grounds. This allows the males access to a large number of females at once and males are able to compete for territories that the females may happen to occupy, a system known as resource defense polygyny.
Mating System: polygynous
Northern fur seal females arrive on shore from late June to late July, joining the males who have staked out territories prior to their arrival. The majority of arriving females are pregnant and have come ashore to give birth to their young, which are typically born one day after the mother’s arrival on land. Females typically give birth to only one precocial offspring per season, following a 51 week gestation period which commences at the end of the previous year’s breeding season. Five to six days after parturition, females come into estrus and copulate on average only 1.2 times with a male of any size or age who attempts to mate with her. While fertilization occurs at this time, implantation does not occur for another four months, following the end of lactation. Within a few days after the birth of her young, the female departs to sea in order to feed for days at a time. These feeding excursions can take 8 to 14 days, after which the mother must return to nurse her pup. The pup must ingest enough milk to survive during these absences. Pups are nursed for 3 to 4 months, during which the female continuously returns to the rookery to nurse her young. Pups are weaned abruptly at about 4 months old when the mothers leave the islands to migrate south for the winter. Females reach sexual maturity between 4 and 6 years old, with their peak reproductive capacity occurring between the ages of 8 and 13, although they remain able to reproduce into their early twenties. Males become capable of mating between the ages of 8 and 10, when they are large enough to defend a territory and command a harem. However, this reign is short-lived; most males are usually deposed after only a few breeding seasons.
Breeding interval: Northern fur seals breed once annually.
Breeding season: Northern fur seals breed from June to July.
Range number of offspring: 1 to 1.
Average gestation period: 51 days.
Range weaning age: 3 to 4 months.
Range time to independence: 3 to 4 months.
Range age at sexual or reproductive maturity (female): 4 to 13 years.
Average age at sexual or reproductive maturity (female): 8 years.
Range age at sexual or reproductive maturity (male): 8 to 10 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; broadcast (group) spawning; viviparous ; delayed implantation ; post-partum estrous
Average birth mass: 5281 g.
Average gestation period: 240 days.
Average number of offspring: 1.3.
Northern fur seal pups are precocial when born and require little parental care. Males provide no parental care and females provide only lactation and minimal protection. For the first 5 days of the pup’s life, the females remain with their young to nurse and guard them. Following this period, females leave the pup unattended for days at a time in order to forage for food. When they return they spend very little time with their pups, only enough to nurse them sufficiently before leaving again. The pups are weaned at 4 months, when they then transition to solid food that they find themselves. There is no evidence that mothers teach their young any life skills, including hunting or foraging skills.
Parental Investment: precocial ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
Females arrive at rookery mainly in June, with some arriving as late as early August. Pups are born 2-3 days after pregnant females arrive. Pupping peaks about July 15, usually ends about August 1. Mating occurs 4-7 days after single pup is born. In the Pribilofs, pups are weaned in October and November, about 125 days after birth; young go to sea soon afterward. Females sexually mature usually at 4-5 years, few males breed before they are 8-9 years old. In a given year, about 57% of adult females give birth. Few males breed in more than 2 seasons. Maximum longevity about 26 years. Male territory may contain from less than 10 to about 100 females.
Molecular Biology and Genetics
Barcode data: Callorhinus ursinus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Callorhinus ursinus
Public Records: 6
Specimens with Barcodes: 6
Species With Barcodes: 1
Historically northern fur seals have faced population decimation from the human fur trade but they are not currently considered threatened. However, it continues to be a vulnerable species that requires careful observation and management. Threats to the species include entanglement in fishing nets, oil spills, and habitat encroachment. Careful sealing management programs have ensured that only juvenile males and certain females are killed for their furs to keep the population from declining. Despite this, fur trading remains a threat to these seals, although sealing has declined rapidly over the last few decades.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: vulnerable
IUCN Red List Assessment
Red List Category
Red List Criteria
IUCN Evaluation of the Northern Fur Seal, Callorhinus ursinus
Prepared by the Pinniped Specialist Group
A. Population reduction Declines measured over the longer of 10 years or 3 generations
A1 CR > 90%; EN > 70%; VU > 50%
Al. Population reduction observed, estimated, inferred, or suspected in the past where the causes of the reduction are clearly reversible AND understood AND have ceased, based on and specifying any of the following:
(a) direct observation
(b) an index of abundance appropriate to the taxon
(c) a decline in area of occupancy (AOO), extent of occurrence (EOO) and/or habitat quality
(d) actual or potential levels of exploitation
(e) effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
Male Northern Fur Seals begin competing for a territory at approximately 7-9 years of age and females begin breeding after the age of four. Generation time is unknown but since females can breed successfully into their early twenties, it is likely in excess of 12-15 years. Northern Fur Seals have shown a significant decline in recent years but the reasons for the reductions are not fully understood, have not ceased despite a ban in commercial hunting and therefore are not clearly reversible.
A2, A3 & A4 CR > 80%; EN > 50%; VU > 30%
A2. Population reduction observed, estimated, inferred, or suspected in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.
Although other areas within the range of the species have shown slight increases and the proportion of the population on the Pribilofs has decreased, St. Paul Island remains the largest Northern Fur Seal rookery in the world with over 122,000 pups born in 2004. Accordingly, some rookeries are decreasing in size. The Eastern Pacific stock of Northern Fur Seals (Pribilof Islands and Bogoslof Island) experienced a decline of >50% between the early 1950’s and 2005. However, this decline was at least in part due to a steady harvest of fur seals that ended on St. Paul Island in 1984. However, despite the cessation of the commercial harvest, the population in the Pribilofs has continued to decline and pup production on the largest rookery at St. Paul Island declined by over 22% between 2000 and 2004 and experienced an average annual rate of decline of 6% (SE = 0.7%) between 1998-2004. Although the overall world population has not declined as dramatically as that of the Pribilofs, because the Pribilofs represent almost half of the species population, the species should still be considered to be Vulnerable.
A3. Population reduction projected or suspected to be met in the future (up to a maximum of 100 years) based on (b) to (e) under A1.
A population reduction of northern fur seals is suspected in the future based on current trends at the largest rookeries. The likely amount of population reduction has not been projected, but if the current trend continues on the Pribilof Islands for the next 30 years, the population will move from being Vulnerable to being Endangered.
A4. An observed, estimated, inferred, projected or suspected population reduction (up to a maximum of 100 years) where the time period must include both the past and the future, and where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.
B. Geographic range in the form of either B1 (extent of occurrence) AND/OR B2 (area of occupancy)
B1. Extent of occurrence (EOO): CR < 100 km²; EN < 5,000 km²; VU < 20,000 km²
The EOO of Northern Fur Seals is > 20,000 km².
B2. Area of occupancy (AOO): CR < 10 km²; EN < 500 km²; VU < 2,000 km²
The AOO of Northern Fur Seals is > 2,000 km².
AND at least 2 of the following:
(a) Severely fragmented, OR number of locations: CR = 1; EN < 5; VU < 10
(b) Continuing decline in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) area, extent and/or quality of habitat; (iv) number of locations or subpopulations; (v) number of mature individuals.
(c) Extreme fluctuations in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) number of locations or subpopulations; (iv) number of mature individuals.
C. Small population size and decline
Number of mature individuals: CR < 250; EN < 2,500; VU < 10,000
The current global abundance of Northern Fur Seals (all age classes) is approximately one million.
AND either C1 or C2:
C1. An estimated continuing decline of at least: CR = 25% in 3 years or 1 generation; EN = 20% in 5 years or 2 generations; VU = 10% in 10 years or 3 generations (up to a max. of 100 years in future)
C2. A continuing decline AND (a) and/or (b):
(a i) Number of mature individuals in each subpopulation: CR < 50; EN < 250; VU < 1,000
(a ii) % individuals in one subpopulation: CR = 90–100%; EN = 95–100%; VU = 100%
(b) Extreme fluctuations in the number of mature individuals.
D. Very small or restricted population
Number of mature individuals: CR < 50; EN < 250; V number of mature individuals < 1,000 AND/OR restricted area of occupancy typically: AOO < 20 km² or number of locations < 5
The current abundance of Northern Fur Seals is approximately one million. AOO is > 20 km² and the number of locations is > 5.
E. Quantitative analysis
Indicating the probability of extinction in the wild to be: CR > 50% in 10 years or 3 generations (100 years max.); EN > 20% in 20 years or 5 generations (100 years max.); VU > 10% in 100 years
There has been no quantitative analysis of the probability of extinction for Northern Fur Seals.
Listing recommendation— The Eastern stock of Northern Fur Seals is predominantly located in the Pribilof Island; this stock has experienced a significant, steep decline since the 1950’s that stabilized and then began dropping again recently. The reasons for the current downward trend remain a mystery. The most troubling aspect of this decline is that the Pribilof population currently has a pup production level similar to that in 1918, a time of strong growth, yet the numbers continue to drop. Because the Pribilof population represents approximately one half of the world-wide population the species should be considered in the threatened category of Vulnerable, based on 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.
National NatureServe Conservation Status
Rounded National Status Rank: N2M - Imperiled
Rounded National Status Rank: N3 - Vulnerable
NatureServe Conservation Status
Rounded Global Status Rank: G3 - Vulnerable
Reasons: Occurs in the North Pacific Ocean; declines have occurred in recent decades in the north, but California breeding population has increased; population decline in the Pribilof Islands in the 1980s apparently was due to harvests of females during the 1960s, increased mortality at sea (e.g., due to entanglement in debris such as discarded fishing nets), and perhaps reduced prey availability caused by increased commercial fishing; substantial numbers are killed in the high-seas squid driftnet fishery.
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 this species is uncertain. However, any further negative disruption of the ecosystem of the northern fur seal should be considered a threat.
Small numbers of Northern Fur Seals are taken annually by Alaska Natives in a subsistence harvest on the Pribilof Islands. For the period 1999-2003, the average annual harvest was 869 animals; all animals taken were juvenile and sub-adult males. Subsistence harvest has declined in recent years to the level of 478 taken in 2007 on both Pribilof Islands (Lestenkoff and Zavadil 2007, Malavansky 2007).
Comments: Population decline in the Pribilof Islands in the 1980s apparently was due to harvests of females during the 1960s, increased mortality at sea (e.g., due to entanglement in debris such as discarded fishing nets), and perhaps reduced prey availability caused by increased commercial fishing in the North Pacific and Bering Sea. Substantial numbers are killed in the high-seas squid driftnet fishery between 40 and 50 degrees N latitude (Reeves et al. 1992). Until a new international fur seal treaty is established, this species remains vulnerable to renewed killing at sea.
Relevance to Humans and Ecosystems
There are no known adverse affects of northern fur seals on humans.
Historically, northern fur seals have been hunted by humans for their pelts, which continue to be harvested through a managed system. The carcasses are then used for meat, oil, or animal foods.
Positive Impacts: food ; body parts are source of valuable material
Comments: Long history of commercial exploitation for pelts, both at sea and at breeding rookeries (see Reeves et al. 1992 for details). Commercial harvest on Pribilof Islands ended in the mid-1980s, but a relatively small subsistence harvest by Aleuts is allowed. Subsistence harvest by Aleut residents on Pribilof Islands in 1993 was 1518 seals on St. Paul Island and 319 seals on St. George Island (Federal Register, 1 November 1993).
Northern Fur Seal
The Northern fur seal (Callorhinus ursinus) is an eared seal found along the north Pacific Ocean, the Bering Sea and the Sea of Okhotsk. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only species in the genus Callorhinus.
Northern fur seals have extreme sexual dimorphism, with males being 30–40% longer and more than 4.5 times heavier than adult females. The head is foreshortened in both sexes because of the very short down-curved muzzle, and small nose, which extends slightly beyond the mouth in females and moderately in males. The pelage is thick and luxuriant, with a dense underfur that is a creamy color. The underfur is obscured by the longer guard hairs, although it is partially-visible when the animals are wet. Features of both fore and hind flippers are unique and diagnostic of the species. Fur is absent on the top of the fored flippers and there is an abrupt "clean shaven line" across the wrist where the fur ends. The hind flippers are proportionately the longest in any otariid because of extremely long, cartilaginous extensions on all of the toes. There are small claws on digits 2–4, well back from the flap-like end of each digit. The ear pinnae are long and conspicuous, and naked of dark fur at the tips in older animals. The mystacial vibrissae can be very long, and regularly extend beyond the ears. Adults have all white vibrissae, juveniles and subadults have a mixture of white and black vibrissae, including some that have dark bases and white ends, and pups and yearlings have all-black vibrissae. The eyes are proportionately large and conspicuous, especially on females, subadults, and juveniles.
Adult males are stocky in build, and have an enlarged neck that is thick and wide. A mane of coarse longer guard hairs extends from the top of the head to the shoulders and covers the nape, neck, chest, and upper back. While the skull of adult males is large and robust for their overall size, the head appears short because of the combination of a short muzzle, and the back of the head behind the ear pinnae being obscured by the enlarged neck. Adult males have an abrupt forehead formed by the elevation of the crown from development of the sagittal crest, and thicker fur of the mane on the top of the head.
Canine teeth are much longer and have a greater diameter in adult males than those found on adult females, and this relationship holds to a lesser extent at all ages.
Adult females, subadults and juveniles, are moderate in build. It is difficult to distinguish the sexes until about age 5. The body is modest in size and the neck, chest, and shoulders are sized in proportion with the torso. Adult females and subadults have more complex and variable coloration than adult males. They are dark-silver-gray to charcoal above. The flanks, chest, sides, and underside of the neck, often forming a chevron pattern in this area, are cream to tan with rusty tones. There are variable cream to rust-colored areas on the sides and top of the muzzle, chin, and as a "brush stroke" running backwards under the eye. In contrast, adult males are medium gray to black, or reddish to dark brown all over. The mane can have variable amounts of silver-gray or yellowish tinting on the guard hairs. Pups are blackish at birth, with variable oval areas of buff on the sides, in the axillary area, and on the chin and sides of the muzzle. After 3–4 months, pups molt to the color of adult females and subadults.
Males can be as large as 2.1 m and 270 kg. Females can be up to 1.5 m and 50 kg or more. Newborns weigh 5.4–6 kg, and are 60–65 cm long.
The teeth are haplodont, i.e. sharp, conical and mostly single-rooted, as is common with carnivorous marine mammals adapted to tearing fish flesh. As with most Caniforms, the upper canines are prominent. The dental formula of the adult is:
The northern fur seal is found in the north Pacific – its southernmost reach is a line that runs roughly from the southern tip of Japan to the southern tip of the Baja California peninsula, the Sea of Okhotsk and the Bering Sea. There are estimated to be around 1.1 million Northern Fur Seals across the range, of which roughly one half breeds on the Pribilof Islands in the east Bering Sea. Another 200–250,000 breed on the Commander Islands in the west Bering Sea and some 100,000 breed on Tyuleni Island off the coast of Sakhalin in the southwest Sea of Okhotsk and another 60–70,000 in the central Kuril Islands in Russia. Smaller rookeries (around 5,000 animals) are found on Bogoslof Island in the Aleutian Chain and San Miguel Island in the Channel Island group off the coast of California. Recent evidence from stable isotope analysis of Holocene fur seal bone collagen (δ13C and δ15N) indicate that prior to the maritime fur trade, it was more common for these animals to breed at local rookeries in British Columbia, California and likely along much of the northwest coast of North America.
During the winter months, northern fur seals display a net movement southward, with animals from Russian rookeries regularly entering Japanese and Korean waters in the Sea of Japan and Alaskan animals moving along the central and eastern Pacific as far as Baja California.
The northern fur seal's range overlaps almost exactly with that of Steller sea lions, with which they occasionally cohabit reproductive rookeries, notably in the Kurils, the Commander Islands and Tyuleni Island. The only other fur seal found in the northern hemisphere is the Guadalupe Fur Seal which overlaps slightly with the northern fur seal's range in California.
Fur seals are opportunistic feeders, primarily feeding on pelagic fish and squid depending on local availability. Identified fish prey include hake, anchovy, herring, sand lance, capelin, pollock, mackerel and smelt. Their feeding behavior is primarily solitary.
Northern fur seals are preyed upon primarily by sharks and orcas. Occasionally, very young animals will be eaten by Steller sea lions. Occasional predation on live pups by arctic foxes has also been observed.
Due to very high densities of pups on reproductive rookeries and the early age at which mothers begin their foraging trips, mortality can be relatively high. Consequently, pup carcasses are important in enriching the diet of many scavengers, in particular gulls and arctic foxes.
Seals aggregate on traditional breeding grounds (rookeries) in May. Generally older males (10 years and older) return first and compete for prime breeding spots on the rookeries. They will remain on the rookery fasting throughout the duration of the breeding season. The females come somewhat later and give birth shortly thereafter. Like all other otariids, northern fur seals are polygynous, with some males breeding with up to 50 females in a single breeding season. Unlike Steller sea lions, with whom they share habitat and some breeding sites, Northern fur seals are possessive of individual females in their harem, often aggressively competing with neighboring males for females. Deaths of females as a consequence of 'tug-of-war's have been recorded, though the males themselves are rarely seriously injured. Young males unable to acquire and maintain a territory of a harem typically aggregate in neighboring "haulouts" occasionally making incursions into the reproductive sections of the rookery in an attempt to displace an older male.
After remaining with their pups for the first eight to ten days of their life, females begin foraging trips lasting up to a week. These trips last for about four months before weaning, which happens abruptly, typically in October. Most of the animals on a rookery enter the water and disperse towards the end of November, typically migrating southward. Breeding site fidelity is generally high for fur seals females, though young males might disperse to other existing rookeries, or occasionally found new haulouts.
Peak mating occurs somewhat later than peak birthing from late June to late July. As with many other otariids, the fertilized egg undergoes delayed implantation: after the blastocyst stage occurs, development halts and implantantion occurs four months after fertilization. In total, gestation lasts for approximately one year, such that the pups born in a given summer are the product of the previous year's breeding cycle.
Recently there has been increased concern about the status of fur seal populations, particularly in the Pribilof Islands, where there has been a roughly 50% decrease in pup-production since the 1970s and a continuing drop in pup production of about 6–7% per year. This has caused them to be listed as "vulnerable" under the U.S. Endangered Species Act and has led to an intensified research program into their behavioral and foraging ecology. Possible causes are increased predation by orcas, competition with fisheries and climate change effects, but there is, to date, no scientific consensus. The IUCN (2008) lists the species as globally threatened under the category "vulnerable".
Northern fur seals have been a staple food of native northeast Asian and Alaskan Inuit peoples for thousands of years. The arrival of Europeans to Kamchatka and Alaska in the 17th and 18th centuries, first from Russia and later from North America, was followed by a highly extractive commercial fur trade. The commercial fur trade was accelerated in 1786, when Gavriil Pribylov discovered St. George Island, a key rookery of the seals. An estimated 2.5 million seals were killed from 1786 to 1867. This trade led to a decline in fur seal numbers. Restrictions were first placed on fur seal harvest on the Pribilof Islands by the Russians in 1834. Shortly after the United States purchased Alaska from Russia in 1867, the U.S. Treasury was authorized to lease sealing privileges on the Pribilofs, which were granted somewhat liberally to the Alaska Commercial Company. From 1870 to 1909, pelagic sealing proceeded to take a significant toll on the fur seal population, such that the Pribilof population, historically numbering on the order of millions of individuals, reached a low of 216,000 animals in 1912.
Significant harvest was more or less arrested with the signing of the North Pacific Fur Seal Convention of 1911 by Great Britain (on behalf of Canada), Japan, Russia and the United States. The Convention of 1911 remained in force until the onset of hostilities among the signatories during World War II, and is also notable as the first international treaty to address the conservation of wildlife. 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 (Public Law 89-702)," said an Interior Department review of the history. Currently, there is a subsistence hunt by the residents of St. Paul Island and an insignificant harvest in Russia.
- ^ Gelatt, T. & Lowry, L. (2008). Callorhinus ursinus. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 30 January 2009. Listed as Vulnerable (VU A2b)
- ^ Chiasson, B. (August 1957). "The Dentition of the Alaskan Fur Seal". Journal of Mammalogy (Journal of Mammalogy, Vol. 38, No. 3) 38 (3): pp. 310–319. doi:10.2307/1376230. http://jstor.org/stable/1376230
- ^ Ream, R.; Burkanov, V. (2005). "PICES XIV Annual Meeting" (PDF). http://www.pices.int/publications/presentations/PICES_14/S3/Ream.pdf
- ^ Szpak, Paul; "Orchard, Trevor J., Grocke, Darren R." (2009). "A Late Holocene vertebrate food web from southern Haida Gwaii (Queen Charlotte Islands, British Columbia)". Journal of Archaeological Science 36 (12): 2734–2741. doi:10.1016/j.jas.2009.08.013. http://uwo.academia.edu/PaulSzpak/Papers/156301/A-Late-Holocene-vertebrate-food-web-from-southern-Haida-Gwaii--Queen-Charlotte-Islands--British-Columbia-.
- ^ "North Pacific Fur Seal Treaty of 1911". National Oceanic and Atmospheric Administration. http://celebrating200years.noaa.gov/events/fursealtreaty/welcome.html#treaty.
- ^ Baker, R.C., F. Wilke, C.H. Baltzo, 1970. The northern fur seal, U.S. Dep. Int., Fish Wildlf Serv., Circ. 336, overall quote pp. 2-4, 14-17. Quoted on 4th p. of PDF, in "Fisheries Management: An Historical Overview" by Clinton E. Atkinson; p. 114 of Marine Fisheries Review 50(4) 1988.
|This includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (January 2011)|
- R. Gentry: Behavior and Ecology of the Northern Fur Seal. Princeton University Press, 1998 ISBN 0-691-03345-5
- R. Nowak: Walker's Marine Mammals of The World. Johns Hopkins University Press, 1999 ISBN 0-8018-7343-6
- J. E. King: Seals of the world. Cornell University Press, 1983 ISBN 0-8014-1568-3
- Randall R. Reeves, Brent S. Stewart, Phillip J. Clapham and James A. Powell (2002). National Audubon Society Guide to Marine Mammals of the World. Alfred A. Knopf, Inc. ISBN 0375411410.
Names and Taxonomy
Comments: Gardner and Robbins (1998) pointed out that Otoes and Halarctus are the earliest available generic names for northern and southern fur seals, respectively; they have petitioned the ICZN to preserve the generic names Callorhinus and Arctocephalus for these seals.
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