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(Linnaeus, 1758) - Northern fur seal

Distinctive Characteristics

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 and Steller sea lions. See the section on the Guadalupe fur seal for distinguishing these 2 fur seals. 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.

Size

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.

Geographical Distribution

Northern fur seals are widely distributed in the waters of the North Pacific Ocean and Bering and Okhotsk Seas. The vast majority of the population breeds on the Pribilof Islands, with smaller numbers on the Commander Islands as well. Rookeries are inhabited in summer and autumn. These oceanic pinnipeds spend most of the year at sea, rarely (if ever) returning to land until the beginning of the next breeding season. Many animals, especially juveniles, migrate south to southern California or the waters off Japan.

Biology and Behaviour

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.

Exploitation

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 Status

Insufficiently known.

Northern fur seal (Callorhinus ursinus)