NORTHERN FUR SEAL

 

Male And Female With Pup

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.

Distinctive characteristics

Beginning at birth, males are much larger than females. Adult females and sub-adults are moderate in build. Sexes are difficult to distinguish until about age 5. The neck, chest, and shoulders of adult males are greatly enlarged over those of females and sub-adults, although at the end of the breeding season males may be thin to the point of emaciation. Male pups weigh 12 pounds and grow to 385-605 pounds and seven feet in length. In comparison, female pups only weigh 10 pounds and grow to 66-110 pounds and 4.5 feet in length.

Adult females and sub-adults are medium to dark silver-grey above. The flanks, chest, sides, and underside of the neck are cream to tan. There are variable cream to tan colored areas on the sides and top of the muzzle, chin, and as a "brush stroke" running backwards under the eye. The fur of the outer part of the ear near the naked tip and the insertion is often pale. Adult males are medium grey to black, or reddish to dark brown all over. Adult males also have gray hair on the backs of their necks. The mane can have variable amounts of silver-grey or yellowish tinting on the guard hairs. Pups are born with a black pelt, which becomes dark brown with lighter coloration on the chest and belly. After 3 to 4 months, pups molt to adult female or sub-adult male coloring.

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 fore flipper and there is an abrupt look of a "clean shaven line" across the wrist. The hind flippers are about one-fourth of the total body length, the longest in any eared seal; they have extremely long, cartilaginous terminal flaps on all of the toes, beyond the position of the nails on the 3 central digits.

Dental Formula    I 3/2, C 1/1, PC 6/5.

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. New-borns weigh 5.4-6 kg, and are 60-65 cm long.

Life Span    Male live up to 18 years old and female live up to 27 years old.

Gestation Period    250 days.

Can be confused with

Northern fur seals can be confused with three other otariid species in their range: the Guadalupe fur seal, and California and Steller sea lions. Coloration of Guadalupe and northern fur seals is similar. Guadalupe fur seals have fur on the dorsum of the fore flipper beyond the wrist, proportionately shorter rear flippers that only have moderate length cartilaginous extensions, and a long tapering muzzle with a bulbous nose that makes the muzzle seem slightly-upturned on the end. Distinguishing females and young can be difficult if not seen well.

At sea, both species of fur seal can be seen actively grooming while at the surface. Guadalupe fur seals will rest in a posture characteristic of fur seals of the genus Arctocephalus with the head down and both rear flippers held in the air and apart forming a ‘Y’ shape. Northern fur seals do not use this posture and routinely sleep in a ‘jug handle’ position with palm of one fore flipper draped over the soles of the hind flippers which are rotated forward to meet the fore flipper. Other fur seal species of the genus Arctocephalus use this posture, so it is possible that Guadalupe fur seals use it as well, although it has not been described for the species. The head is often held up at approximately a 45° angle while the seal is in this position.

Northern fur seals can be readily separated from both sea lions, based on differences in pelage density and coloration, overall size, length and lack of fur on the top of the fore flippers beyond the wrist, head and muzzle shape, and relative size and prominence of the ear pinnae. In California sea lions the muzzle tapers to a blunt end, and the first toe or hallux is larger and longer than all of the other toes. Adult female, sub adult, and juvenile California sea lions are tan to pale brown and much lighter in coloration than northern fur seals. Only adult and sub adult male California sea lions become dark brown and are similar in color to northern fur seal bulls. However, dark male sea lions have a sagittal crest in contrast to the head of northern fur seal bulls that is slightly domed and lacks a conspicuous sagittal crest. California sea lion bulls lack the light tipped hairs in their much shorter mane. The loud repetitive bark of male California sea lions is distinctive and different from all northern fur seal vocalizations. Steller sea lions are very large with a massive head, blunt thick muzzle, stocky body, pale color, and short fur, and should never present an identification problem with northern fur seals.

Distribution

Northern fur seals are a widely-distributed pelagic species in the waters of the North Pacific Ocean and the adjacent, Bering Sea, Sea of Okhotsk, and Sea of Japan. They range from Northern Baja California, Mexico north and offshore across the North Pacific to Northern Honshu, Japan. The southern limit of their distribution at sea across the North Pacific is approximately 35° N. Vagrants reach the Yellow Sea in the west and eastern Beaufort Sea in the Arctic. The vast majority of the population breeds on the Pribilof Islands, with substantial numbers on the Commander Islands as well. Still other sites are used, including San Miguel Island in California, Bogoslof Island in the Bering Sea, and Robben Island off Sakhalin Island in Russia. Numerous other sites were formerly occupied and may still be visited. Rookeries are inhabited in summer and fall. 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 from the Bering Sea south to southern California or the waters off Japan, to spend the winter feeding.

Ecology and behavior

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. 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). Northern fur seals become sexually mature at 3-5 years old, at which time females usually produce one pup a year for most of the rest of their lives. Males do not become physically mature, and large enough to compete for a territory that will be used by females, until they are 8-9.

Northern fur seals usually give birth a day after arrival at the rookery. Mean time from birth to estrous is 5.3 days, and 8.3 days for departure on the first feeding trip. Females breed at the Pribilof Islands relatively far from the foraging areas at the edge of the continental shelf and 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 duration is 2.2 minutes with maximum depth recorded of 207 m, and duration of 7.6 minutes. Pups are visited 8-12 times and attended for a mean of 2.1 days before being abruptly weaned at 4 months old.

Northern fur seals are one of the most pelagic pinnipeds. Adults are at sea most of the year, only coming ashore for the breeding season for 35 and 45 days (on average) for adult females and males respectively. They do not haul-out between breeding seasons, and 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 very active at 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. Predators include killer whales, sharks, and Steller sea lions.

Predation

Large sharks and orcas are known predators of adult and juvenile Northern fur seals. In addition steller’s sea lions have been observed to be feed on seal pups. To escape Marine predation northern fur seals may seek land if it is available. Mothers protect their pup for the first few days of life, after which they are often absent. Even when present mother will flee from predators, allowing their pups to fend for themselves.

Feeding and prey

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.

Exploitation

Climate Change Global climate change is expected to have profound impacts on arctic and sub-arctic marine ecosystems. This may affect the composition, spatial and temporal distribution, and abundance of prey available to fur seals. Sea Level Rise caused by climate change may directly alter access to or the utility of terrestrial rookery and haul out sites currently used by fur seals. Traditional sites on some islands with low relief may be submerged, but other habitat may become accessible. Temperature Changes Decadal scale regime shifts, and shorter-term oceanographic anomalies such as  El Niño Southern Oscillation (ENSO) events and marine heat waves, also can have large effects on distribution and abundance of fur seal prey. Marine heat waves have already shown to reduce fur seal survival. Ocean Acidification effects on fur seals are uncertain but are likely to include serious impacts on ecosystems and may have adverse effects on specific species prey through food web effects.

Harmful Algal Blooms (HAB) toxins cause sickness and death in humans and fur seals. Warming water temperatures increases toxic algae growth, prevents water from mixing, allowing algae to grow thicker and faster, and algal blooms absorb sunlight, making water even warmer and promoting more blooms.

Environmental Contaminants can enter the ocean and subsequently affect the food chain of the northern fur seal. Contaminant studies on northern fur seals have shown exposure to various toxic substances and evidence of accumulation in various tissues. Contamination sources can include oil and gas development, industrial runoff, vessel discharge, micro plastics, vessel grounding, and oil spills. These contaminants have the potential to affect the immune, digestive, or endocrine systems of northern fur seals, leaving them more susceptible to disease and reducing their survival and reproduction.

Threats and status

Northern fur seals have one of the longest and most complex histories of commercial harvesting, which began when the main breeding colonies were discovered in the late 18th century, and lasted until 1984. Numerous international treaties and agreements were put in force in efforts to manage this species. There were many periods of decline and recovery over this long period. It is estimated that the population numbered up to 2.5 million animals in the 1950s. They may have been considerably more numerous than this recent high level, when there were many more active rookeries before the onset of exploitation by Europeans and Americans. The current population is estimated at 1.3-1.5 million and is declining.

Entanglements in commercial fisheries, and in derelict and discarded fishing gear and marine debris, have caused significant annual mortality in the past. This mortality was highest during the period of active high seas drift net fishing in the North Pacific in the 1980s. Entanglement in debris is ongoing and affects juveniles and sub adults more than adults. Northern fur seals compete for walleye Pollock with one of the largest commercial fisheries world. Mortality from interactions with numerous fisheries and entanglement in debris, large annual harvests of prey species in commercial fisheries, long-term ecosystem regime change in the North Pacific, and possible changes in the foraging patterns of a key predator (the killer whale), may all be working synergistically to cause the current population decline.

Factors hypothesized include

The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.

 IUCN status    Vulnerable

Picture From Exploring nature