Callorhinus ursinus (Linnaeus, 1758)
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publication ID |
https://doi.org/ 10.5281/zenodo.6604474 |
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DOI |
https://doi.org/10.5281/zenodo.6604423 |
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persistent identifier |
https://treatment.plazi.org/id/965C87FE-1E5E-564D-9C1A-93DA8B83F7F1 |
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treatment provided by |
Diego |
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scientific name |
Callorhinus ursinus |
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Northern Fur Seal
Callorhinus ursinus View in CoL
French: Otarie a fourrure / German: Nordlicher Seebar / Spanish: Lobo marino septentrional
Other common names: Alaskan Fur Seal, Pribilof Fur Seal
Taxonomy. Phoca ursina Linnaeus, 1758 View in CoL ,
“Habitat in Camschatcae maritimis inter Asiam & Americam proximam, primario in insula Beringii.” Restricted by O. Thomas in 1911 to “Bering Island.”
This species is monotypic.
Distribution. N Pacific, including the Bering Sea, Sea of Okhotsk, and Sea of Japan, S to Japan (Honshu), and N Mexico (Baja California). View Figure
Descriptive notes. Total length up to 210 cm (males) and 150 cm (females); weight 180-270 kg (males) and 40-60 kg (females). Newborns are 60-65 cm and 5.4-6 kg. Dental formula I 3/2, C 1/1, PC 6/5 (x 2) = 36. Northern Fur Seals are extremely sexually dimorphic. Mature males are 30-40% longer and 4-5-5 times heavier than mature females. Flipper characteristics are unique. Top of foreflipper has bare skin, demarcated by sharp line where furstarts on wrist. Hindflippers are relatively longer than on any other otariids’ due to long thin extensions of cartilage on each toe. In both sexes, muzzle is short and curved downward, and nose is small. Ear pinnae are long and prominent and may become bare as an individual reaches an advanced age. Vibrissae are long, often extending past ears. Mature adult Northern Fur Seals have pale vibrissae, subadults have vibrissae that are a mix of pale and black, and young have black vibrissae. Adult males are stocky and have mane of long guard hairs from head to neck, chest, and upper back. Their foreheads appearto rise steeply because crown is enlarged by skull’s sagittal crest. Adult females and subadults are moderately built, and it is hard to determine gender until males reach 4-5 years of age and exceed size of females. Furis very thick, with pale-colored underfur. Males are gray to black, or fur may be dark ruddy brown, and mane may show silvery or blonde tints. Adult females and subadults have more variation in fur color but are often dark gray to black above with buff on chest, sides, and neck (where fur may form a pale, contrasting V-shape). Muzzle may be buffy or ruddy colored. Young are born with blackish coat, with some creamy areas on sides and face, and they molt to subadult color by 3-4 months old.
Habitat. Highly pelagic, often far from shore or at edge of continental shelf or over continental slope. Terrestrial habitat usually consists of rocks and boulders, but it may also be a beach. Predators include Killer Whales (Orcinus orca), sharks, and Steller Sea Lions ( Eumetopias jubatus).
Food and Feeding. Dietary shifts of Northern Fur Seals occur depending on season and foraging area; diets often includes vertically migrating species. Off California and Washington, Northern Fur Seals eat anchovy ( Engraulidae ), hake, saury ( Scomberesocidae ), squid, rockfish ( Sebastidae ), and salmon ( Salmonidae ). Off Alaska, they eat walleye pollock (Theragra chalcogramma), capelin (Mallotus villosus), sand lance ( Ammodytidae ), herring ( Clupeidae ), Atka mackerel (Pleurogrammus monopterygius), and squid.
Breeding. All fur seals, including Northern Fur Seals, have a polygynous breeding system with the same general features. Males hold territories onshore and fight, vocalize, or make postural displays to maintain them. Mature males arrive first at a breeding rookery to establish a territory, followed by pregnant females. Almost always, more than one female will select a male’s territory and give birth to a single neonate soon after arriving. Non-breeding subadult males, referred to as bachelors, congregate outside territories at the edge of the rookery. Breeding males remain ashore continuously. A few days after parturition, a female leaves her neonate to go to sea on a foraging trip. Young are left alone or in a group of other unattended young, and males have no role in parenting. Territorial males may pose a threat to young, sometimes trampling or attacking them, but their presence can benefit young by keeping bachelors at bay and reducing crowding in the territory. After a female’s milk stores are replenished, she returns to the territory, attracting her offspring with a special high-pitched call. This pattern of nursing bouts and foraging trips repeatsitself until the offspring is weaned. Foraging trips tend to be short when offspring are young and become longer as they get older. Soon after a female gives birth, she enters estrus and usually copulates with the male in whose territory she resides. Thus, females are likely to be pregnant and lactating throughout most of their entire adult lives. After conception, development of the fertilized egg is suspended at the blastocyst stage and then resumes a few months later after the blastocyst becomes implanted in the uterus. Breeding of Northern Fur Seals on Pribilof Islands occurs from mid-June through August and c.2 weeks earlier on San Miguel Island. Northern Fur Seals reach sexual maturity at 3-5 years old, but males are not large enough to compete for a territory until they are 8-9 years old. Gestation lasts 51 weeks, including the delayed implantation phase of 3-5-4 months. Pregnant females usually give birth a day after arriving at the breeding territory and enter estrus an average of 5-3 days later. They remain with their neonates for an average of 8:3 days before leaving on the first foraging trip. Subsequent nursing bouts ashore usually last less than two days. The female will provide 8-12 nursing bouts, each lasting c.2 days, before the offspring is weaned at c.4 months. Life span is ¢.25 years.
Activity patterns. Northern Fur Seals are among the most pelagic of all pinnipeds (seals), with adults remaining at sea for most of the year, except for the breeding season, which lasts 4-5 months for females, including rearing of offspring, and c.45 days for males. They generally avoid hauling-out between breeding seasons, and weaned offspring go to sea and do not touch land until they return to their natal rookery 2-3 years later. At sea, Northern Fur Seals are most likely to be sighted alone or in pairs. When not foraging or traveling at sea, they groom or rest on the water’s surface during the day and usually feed at night or twilight. Typical resting postures at the water’s surface include lying on back or side with one or more flippers extended in the air or held pressed together. They commonly elevate hindflippers, rotate them forward, and drape one or both foreflippers over the top, and hold them above the surface—a posture known as the “jug-handle.” Fur seals groom their pelage by rubbing foreflippers over their bodies and scratching with their three exposed claws on hindflippers. Dives of lactating female Northern Fur Seals lasted 2-2 minutes to an average depth of 68 m; maximum dive lasted 7-6 minutes to a depth of 207 m.
Movements, Home range and Social organization. Most Northern Fur Seals breed on the Pribilof Islands in the Bering Sea. Significant numbers also breed on Commander and Kuril islands, Russia; small rookeries occur, on Bogoslof Island in the Bering Sea; Robben Island, Russia; and San Miguel and south-east Farallon Islands off California. Annual migrations of Northern Fur Seals are the longest of any species of otariid, with many individuals traveling from the Bering Sea to winter-feeding areas off California or Japan. Even during the breeding season, lactating females at the Pribilof Islands make longer foraging trips than most other female otariids, lasting 6-9 days on average, to reach the edge of continental shelf. Vagrants have been recorded as far west as the Yellow Sea, near China, south to Taiwan, and north to the Arctic’s Beaufort Sea.
Status and Conservation. Classified as Vulnerable on The IUCN Red List. Total population of Northern Fur Seals is 900,000-1-1 million individuals and declining. Breeding population on the Pribilof Islands is ¢.650,000 individuals. Luxurious pelt of Northern Fur Seal was the target of intensive hunting soon after breeding rookeries were discovered in the 18" century. By 1984, when controlled commercial hunting ended, the population had suffered several cycles of declines and recoveries. In the 1950s, it was estimated to be 2-5 million individuals, and that number may be considerably lower than during the pre-exploitation era. Currently, international treaties and agreements are in place to manage the population. Small numbers of Northern Fur Seals on the Pribilof Islands are still killed in a subsistence harvest by Alaskan Natives; 478 subadults were taken in 2007. Fishing-gear entanglement is known to be a lethal threat to Northern Fur Seals. A high level of mortality occurred during the 1980s when the driftnet fishery in the North Pacific Ocean was at its height. Continuing entanglement, commercial catches of walleye pollock (Theragra chalcogramma)—one of the seal’s main prey species—and possible increased predation by Killer Whales may be contributing to the current population decline of Northern Fur Seals.
Bibliography. Call & Ream (2012), Dickerson et al. (2010), Fowler (1987), Gelatt & Lowry (2008a), Gentry (1998, 2009b), Jefferson et al. (2008), Kajimura (1985), Kuhn (2011), Kurle & Worthy (2001), Merrick et al. (1994), NMFS (1993, 2007), Reijnders et al. (1993), Rice (1998), Thomas (1911), Towell et al. (2006), Wickens & York (1997), York (1987).
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