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:
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
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.
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
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 )
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
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
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
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.
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 )
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)
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]
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.
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 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]
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]
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.
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]
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.
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.
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".
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.
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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