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Lifespan, longevity, and ageing

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Observations: After fertilization, implantation is delayed for 3.5 to 4 months, making the total gestation period to be approximately 11.75 months (Ronald Nowak 2003). In the wild, females have been estimated to live more than 30 years (http://www.demogr.mpg.de/longevityrecords), which is possible but unverified. Their longevity in captivity has not been studied in detail but one wild born specimen was about 25.1 years old when it died in captivity (Richard Weigl 2005).
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Associations

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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.

Known Predators:

  • great white sharks (Carcharodon carcharias)
  • killer whales (Orcinus orca)
  • Steller's sea lions (Eumetopias jubatus)
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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Tanya Dewey, University of Michigan-Ann Arbor
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Morphology

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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

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Life Expectancy

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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.

Range lifespan
Status: wild:
26 (high) years.

Average lifespan
Status: wild:
2 (males); 4.6 (females) years.

Average lifespan
Status: wild:
25.0 years.

Average lifespan
Status: wild:
30.0 years.

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Habitat

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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

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Tanya Dewey, University of Michigan-Ann Arbor
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Distribution

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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 )

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Behavior

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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

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Rachel Racicot, Yale University
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Tanya Dewey, University of Michigan-Ann Arbor
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Conservation Status

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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

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Benefits

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There are no known adverse affects of northern fur seals on humans.

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Benefits

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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

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Associations

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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.

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Rachel Racicot, Yale University
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Tanya Dewey, University of Michigan-Ann Arbor
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Trophic Strategy

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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 )

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Rachel Racicot, Yale University
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Tanya Dewey, University of Michigan-Ann Arbor
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Reproduction

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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)

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Sackler, R. 2012. "Callorhinus ursinus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Callorhinus_ursinus.html
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Rebecca Sackler, Yale University
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Rachel Racicot, Yale University
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Eric Sargis, Yale University
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Tanya Dewey, University of Michigan-Ann Arbor
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Biology

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At the start of the breeding season, males begin arriving at their traditional sites about a month ahead of the females and start competing for breeding territories (4). These fights can be extremely violent, with each mature bull aiming to slash an opponent's neck with his sharp canine teeth. Only the largest and heaviest bulls can hope to claim the title of 'beachmaster'; the smaller younger males, who have no chance of competing with the fully-grown animals, occupy the fringes of the breeding territories (3). The females arrive in mid-June and give birth to the pups, conceived the year before, some two days after their arrival. Within a week of the birth, the females will mate again (4). Males compete to secure as many females as he can within his harem, although it is thought that females are influenced by the presence of other females and the characteristics of the territory rather than the mere size and power of the male (2). The beachmasters will continue to squabble and fight over females right through the breeding season, usually because these colonies are crowded, and wandering females sometimes stray into another male's territory (3). Occasionally, younger males will attempt to steal a mating with a female and, if spotted by one of the beachmasters, he will be chased off (2). In order to ensure that his females are not claimed by another male, bull northern fur seals do not feed throughout the breeding period and may eventually loose 20% of their body weight (4). Mothers suckle their pups for up to 10 days before returning to feed at sea, usually during the night. She will stay at sea from between four and ten days feeding, returning to feed her pup for one or two days. She will do this for four months before leaving her youngster and migrating south, usually in late October (4). Fur seals feed on a variety of prey, including squid and pollack (4) and have also been recorded taking seabirds (2). The fertilised egg within the female fur seal undergoes a four month period of delayed implantation. This ensures that that the developing pup will be born at the right time the following year when the animals return to their breeding grounds. The pups will spend as long as 22 months at sea before returning to the beach where they were born (4). Fur seals mature between the ages of three and six, but males will probably not begin to breed for an additional three years (2). The principal natural predators of fur seals are orca (killer whales), great white sharks and the much larger Steller sea lion Eumetopias jubatus. On land, pups can fall prey to foxes (4).
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Conservation

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The North Pacific Fur Seal Convention lapsed in 1984 after an extension was vetoed by the USA (5), but all commercial hunting has ceased at sea and only limited numbers are now taken under licence. It is believed the world population currently stands at about 1,350,000 animals, but with no current international agreement, some experts fear that commercial hunting could start again at some time in the future. There is also evidence that the El Niño event of 1997-8 affected the pup survival rate of the San Miguel Island breeding colony. A drop in the availability of fish led to 87% of young fur seals dying before they were weaned (4).
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Description

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Northern fur seals belong to the family known as eared seals, more commonly called sea lions. They differ from the true seals in having small external earflaps and hind flippers that can be turned to face forwards. Together with strong front flippers, this gives them extra mobility on land and an adult fur seal can move extremely fast across the beach if it has to. They also use their front flippers for swimming, whereas true seals use their hind flippers (3). Sea lions show a considerable size difference between the sexes. A bull northern fur seal is a big heavy animal, over two metres in length and weighing as much as 270 kg. Their fur varies in colour, ranging from reddish to black, and they have thick necks and a mane (2). The females (cows) are much smaller, less than a metre and a half in length and weighing a fifth as much as the bulls (2). Their colouring differs, too, having a silvery-grey back, with reddish-brown at the front and a whitish-grey patch on the chest (4). Young seal pups are black with paler markings around the nose and mouth (2).
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Habitat

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Although northern fur seals spend most of the year at sea in the cold northern waters of the Pacific Ocean (2), their breeding grounds are on rocky coastlines close to the edge of the continental slope (4).
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Range

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Northern fur seals range over most of the northern Pacific Ocean, as far south as southern California in the east and to central Japan in the west. Northwards, their range extends to the Bering Sea, north of the Aleutian Islands, and the Sea of Okhotsk, west of the Kamchatka peninsular (4). Their main breeding grounds are on the Pribilof Islands of St. George and St. Paul in the southern Bering Sea. They also breed on a number of other islands scattered throughout their range, principally the central Kuril Islands and Tyuleniy Island in the Sea of Okhotsk, the Commander Islands off the coast of Alaska, Bogoslof Island in the Aleutians and San Miguel Island off the coast of California (4).
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Status

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Classified as Vulnerable (VU A1b) on the IUCN Red List 2003 (1).
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Threats

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The fur that protects the northern fur seal from the cold has led to the animals being hunted for centuries. Although early native peoples made little impact on their numbers, the 'discovery' of the species in the 18th century was followed by commercial hunting that nearly led to the seals' extinction by the end of the 19th century. In 1911 a treaty, the North Pacific Fur Seal Convention was signed by the USA, Japan, Russia and the UK (acting for the Dominion of Canada), limiting hunting to immature males on land and banning all sea hunts (4). Although serious commercial hunting of the northern fur seal has ended, the animals no longer enjoy the protection of the international treaty which lapsed in 1984. Neither is the animal currently protected under CITES (Convention on International Trade in Endangered Species) (5). There is still some hunting permitted under licence in Canadian waters by native peoples only (5), and a similar agreement exists for natives of the Aleutian Islands (4). But the main threats globally are now believed to be caused by entanglement in the nets of the Japanese squid fishing fleets and in the Bering Sea. Seals are also threatened by marine pollution such as plastic twine and waste packaging, as well as discarded trawl nets. The animals are very vulnerable to oil pollution and, with an increase in oil and gas exploration around several of their breeding grounds, there are fears that accidental oil spills and the inevitable industrial disturbance will affect seal populations (4).
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Diagnostic Description

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Adult male northern fur seals have long coarse guard hairs, particularly on the neck, chest, and upper back; females and subadults have shorter, finer guard hairs. Adult females and subadults are moderate in build. It is difficult to distinguish the sexes until about age 5. The neck, chest, and shoulders of adult males are greatly enlarged over those of females and subadults (although those at the end of the breeding season may be thin to the point of emaciation). The head of northern fur seals looks deceptively small because of the very short down-curved muzzle and small nose. The nose extends slightly beyond the mouth in females and moderately in males. Fur is absent on the top of the foreflipper and there is an abrupt look of a "clean shaven line" across the wrist. The hindflippers are about one-fourth of the total body length, the longest in any otariid; they have extremely long, cartilaginous terminal flaps on all of the toes, beyond the position of the nails on the 3 central digits. The ear pinnae are long and conspicuous; in older animals they are naked at the tips. The vibrissae are long, and regularly extend to beyond the ears; they are white in adults. Newborns have black vibrissae that become white by way of "salt and pepper" stages in subadults. Adult females and subadults are medium to dark silver-grey above. The flanks, chest, sides, and underside of the neck (often forming a "V" pattern in this area) are cream to tan. There are variable cream to tan coloured areas on the sides and top of the muzzle, chin, and as a "brush stroke" running backwards under the eye. The fur of the ear pinnae near the naked tip and the insertion is often pale. Adult males are medium grey to black, or reddish to dark brown all over. The mane can have variable amounts of silver-grey or yellowish tinting on the guard hairs. Pups are blackish at birth, with variable oval areas of buff on the sides in the axillae, and on the chin and sides of the muzzle. After 3 to 4 months, pups moult to the colour of adult females and subadults. The dental formula is I 3/2, C 1/1, PC 6/5. Can be confused with: Northern fur seals can be confused with 3 other otariid species in their range: the Guadalupe fur seal, and California sea lion and Steller sea lion. Northern fur seals can be separated from both sea lions, based on differences in size, pelage, flippers, head and muzzle shape, and relative size and prominence of the ear pinnae.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Size

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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 average 5.4 to 6 kg and 60 to 65 cm.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Brief Summary

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This is a highly polygynous species. In general, males arrive at the rookeries before females; they fight and display to establish and maintain territories. 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). At sea, northern fur seals are most likely to be encountered alone or in pairs, but at times in groups of 3 or more. Dive depth has been studied in lactating females and was found to average about 68 m and 2.6 minutes. 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 1 or more flippers into the air, and draping their flippers in a "jug handle" position.The diet is varied and includes many varieties of epipelagic and vertically migrating mesopelagic schooling and non-schooling fish and squid. They seem to feed mainly at night.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Food and Agriculture Organization of the UN
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Conservation Status : Northern fur seals have been exploited by humans in both historic and prehistoric times. Their remains can be found in the middens of many peoples that have lived around the Pacific rim. First discovered by Europeans in 1786, sealing commenced and proceeded with highs and lows, but few periods of no commercial harvesting. All time population lows in the early 20th Century prompted a convention on conservation and led to international cooperation and management and an end to wasteful and destructive pelagic sealing. Commercial sealing ended on Saint Paul Island in the Pribilofs in 1984. A limited subsistence harvest by and for Native Americans continues to this day. The population of northern fur seals has also suffered from the depletion of commercial fish species that are important food resources for seals. They are also thought to be declining at least in part due to mortality from frequent entanglement in nets and debris of all types. All fur seals are susceptible to oil in the water so production and transport of petroleum products offshore creates an ongoing risk from accidents. IUCN: Insufficiently known.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Northern fur seal

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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 living species in the genus Callorhinus.[3] A single fossil species, Callorhinus gilmorei, is known from the Pliocene of Japan and western North America.[4]

Description

Northern fur seals have extreme sexual dimorphism, with males being 30–40% longer and more than 4.5 times heavier than adult females.[1] 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 in 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 fore flippers and an abrupt "clean line" is seen across the wrist where the fur ends.[5] The hind flippers are proportionately the longest in any otariid because of extremely long, cartilaginous extensions on all of the toes.[5] Small claws are 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.[6]

Adult males are stocky in build, and have enlarged (thick and wide) necks. A mane of coarse, longer guard hairs extends from the lower neck to the shoulders.[5] and covers the nape, neck, chest, and upper back. While the skulls of adult males are large and robust for their overall size, their heads appear short because of the combination of a short muzzle, and the backs of the head behind the ear pinnae being obscured by the enlarged necks. Adult males have abrupt foreheads formed by the elevation of the crown from development of the sagittal crests, and thicker fur of the mane on the top of their heads.[7]

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.

Fur seal pups, including one rare albino

Adult females, subadults, and juveniles are moderate in build. Distinguishing the sexes is difficult until about age five. 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. Variable cream to rust-colored areas are 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. Their manes 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 three to four months, pups molt to the color of adult females and subadults.

Males can be as large as 2.1 m (6 ft 11 in) and 270 kg (600 lb). Females can be up to 1.5 m (4 ft 11 in) and weigh 50 kg (110 lb) or more. Newborns weigh 5.4–6 kg (12–13 lb), and are 60–65 cm (24–26 in) long.

The skull

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 3.1.4.22.1.4.1[8]

Close up of face and ears

Like other otariids, northern fur seals are built for efficient terrestrial locomotion. Their hind limbs are in a plantigrade stance and are able to rotate under the body for quadrupedal locomotion and support.[9] When swimming, there are two different types of movement: locomotion and diving. These seals swim primarily with forelimb propulsion due to their physiology. They have flexible joints between vertebrae for better maneuverability in the water as well as "greater muscular leverage" for pectoral strokes.[10] Stroke patterns are different for different dive types and locomotion, and stroke rates vary for individuals since there's a relationship between maximum stroke rate and body size.[11]

Distribution and habitat

Overview of rookery

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.[12] An estimated 1.1 million northern fur seals occur across the range, of which roughly half breed on the Pribilof Islands in the east Bering Sea. Another 200–250 thousand breed on the Commander Islands in the west Bering Sea, some 100,000 breed on Tyuleniy Island off the coast of Sakhalin in the southwest Sea of Okhotsk, and another 60–70 thousand in the central Kuril Islands in Russia. Smaller rookeries (around 5,000 animals) are found on Bogoslof Island in the Aleutian Chain, San Miguel Island in the Channel Island group and South Farallon Island off the coast of California.[13][14] Recent evidence from stable isotope analysis of Holocene fur seal bone collagen (δ13C and δ15N) indicates that before 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.[15]

During the winter, 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 to British Columbia, Canada and as far south as Baja California.

The northern fur seal's range overlaps almost exactly with that of Steller sea lions; occasional cohabitation occurs at reproductive rookeries, notably in the Kurils, the Commander Islands, and Tyulen'i Islands. 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.

Ecology

Fur seals are opportunistic feeders, primarily feeding on pelagic fish and squid depending on local availability. Identified fish prey include hake, herring, lantern fish, capelin, pollock, and mackerel.[12] Their feeding behavior is primarily solitary.

Northern fur seals are preyed upon primarily by sharks and killer whales.[12] Occasionally, very young animals are eaten by Steller sea lions.[12] 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.

In 2017, 14 samples of spiny lice were collected off of the nasal passage of fur seal puppies. In 2021, these spiny lice were identified as having unique bristle arrangements, and were given the scientific name Antarctophthirus nevelskoyi. They were named after the famous Russian explorer, Admiral Gennady Ivanovich Nevelsky.[16]

Reproductive behavior

Male and harem

Seals enter breeding rookeries in May. Generally, older males (10 years and older) return first and compete for prime breeding spots on the rookeries. They remain on the rookery, fasting throughout the duration of the breeding season.[12] 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 which 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.[17] Deaths of females as a consequence of these conflicts have been recorded, though the males themselves are rarely seriously injured.[17] 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.

Northern fur seal pups

After remaining with their pups for the first eight to ten days of their lives, 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 seal females, though young males might disperse to other existing rookeries, or occasionally find new haulouts.[17]

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 implantation occurs four months after fertilization. In total, gestation lasts around a year, such that the pups born in a given summer are the product of the previous year's breeding cycle.

Status

An orca feeding on a Northern fur seal

Recently, concern about the status of fur seal populations has increased, particularly in the Pribilof Islands, where pup production has decreased about 50% since the 1970s, with a continuing drop 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 killer whales, competition with fisheries, and climate change effects, but to date, no scientific consensus has been reached. The IUCN (2008) lists the species as globally threatened under the category "vulnerable".

Fur trade

Men killing fur seals on Saint Paul Island, Alaska, 1890s

Northern fur seals have been a staple food of native northeast Asian and Alaska Native 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.[18] 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.[19] Currently, a subsistence hunt by the residents of St. Paul Island and an insignificant harvest in Russia are allowed.

See also

References

  1. ^ a b Gelatt, T.; Ream, R.; Johnson, D. (2015). "Callorhinus ursinus". IUCN Red List of Threatened Species. 2015: e.T3590A45224953. doi:10.2305/IUCN.UK.2015-4.RLTS.T3590A45224953.en. Retrieved 19 November 2021.
  2. ^ Linnæus, Carl (1758). Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I (in Latin) (10th ed.). Holmiæ: Laurentius Salvius. p. 37. Retrieved 23 November 2012.
  3. ^ Wozencraft, W. C. (2005). "Order Carnivora". In Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. p. 592. ISBN 978-0-8018-8221-0. OCLC 62265494.
  4. ^ Berta, A. & Churchill, M. (2012). "Pinniped Taxonomy: evidence for species and subspecies". Mammal Review. 42 (3): 207–234. doi:10.1111/j.1365-2907.2011.00193.x.
  5. ^ a b c Randall R. Reeves; Brent S. Stewart; Phillip J. Clapham; James A. Powell (2002). National Audubon Society Guide to Marine Mammals of the World. Alfred A. Knopf, Inc. ISBN 0-375-41141-0.
  6. ^ "Learn More About Northern Fur Seals". The Marine Mammal Center. Retrieved 7 May 2021.
  7. ^ "Northern Fur Seal (Callorhinus ursinus) Species Profile". State of Alaska · Department of Fish and Game. Retrieved 7 May 2021.
  8. ^ Chiasson, B. (August 1957). "The Dentition of the Alaskan Fur Seal". Journal of Mammalogy. 38 (3): 310–319. doi:10.2307/1376230. JSTOR 1376230.
  9. ^ Deméré, Thomas A.; Yonas, Joshua H. (2009). "Locomotion, Terrestrial". Encyclopedia of Marine Mammals. pp. 672–673. doi:10.1016/B978-0-12-373553-9.00154-1. ISBN 9780123735539.
  10. ^ Pierce, S.E. (June 2011). "Comparative axial morphology in pinnipeds and its correlation with aquatic locomotory behaviour". Journal of Anatomy. 219 (4): 502–514. doi:10.1111/j.1469-7580.2011.01406.x. PMC 3196755. PMID 21668895.
  11. ^ Insley, S.J. (January 2008). "Acoustic determination of activity and flipper stroke rate in foraging northern fur seal females" (PDF). Endangered Species Research. 4: 147–155. doi:10.3354/esr00050.
  12. ^ a b c d e Waerebeek, K. V., Wursi, B. "Northern Fur Sea Callorhinus ursinus" pp. 788–91 of Encyclopedia of Marine Mammals (edited by Perrin, W. F., Wursig, B and J. G.M. Thewissen), Academic Press; 2nd edition, (2008)
  13. ^ Ream, R.; Burkanov, V. (2005). "Trends in abundance of Steller sea lions and northern fur seals across the North Pacific Ocean" (PDF). Vladivostok, Russia: PICES XIV Annual Meeting.
  14. ^ Lee, Derek E.; Berger, Ryan W.; Tietz, James R.; Warzybok, Pete; Bradley, Russell W.; Orr, Anthony J.; Towell, Rodney G.; Jahncke, Jaime (2018). "Initial growth of northern fur seal (Callorhinus ursinus) colonies at the South Farallon, San Miguel, and Bogoslof Islands". Journal of Mammalogy. doi:10.1093/jmammal/gyy131. S2CID 109546688.
  15. ^ 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.
  16. ^ Shchelkanov, M. Y.; Shchelkanov, E. M.; Moskvina, T.V. (2021). "Antarctophthirus nevelskoyi n.sp. (Anoplura: Echinophthiriidae) - a new species-parasite of the northern fur seal (Callorhinus ursinus L., 1758) on the island of Seals (Sea of Okhotsk, Russia)". South of Russia: Ecology, Development. 16 (2). doi:10.18470/1992-1098-2021-2.
  17. ^ a b c R. Gentry: Behavior and Ecology of the Northern Fur Seal. Princeton University Press, 1998 ISBN 0-691-03345-5
  18. ^ "North Pacific Fur Seal Treaty of 1911". National Oceanic and Atmospheric Administration.
  19. ^ Baker, R.C., F. Wilke, C.H. Baltzo, 1970. The northern fur seal, U.S. Dep. Int., Fish and Wildlife Service, 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.
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Northern fur seal: Brief Summary

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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 living species in the genus Callorhinus. A single fossil species, Callorhinus gilmorei, is known from the Pliocene of Japan and western North America.

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