Callorhinus ursinus

Geographic Range

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 arctic ocean
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

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.

• Habitat Regions
• polar polar
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

Physical Description

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.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• sexes shaped differently
• ornamentation ornamentation

Reproduction

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 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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• broadcast (group) spawning
• viviparous viviparous
• delayed implantation delayed implantation
• post-partum estrous

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 precocial
• female parental care 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

Lifespan/Longevity

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.

Behavior

Northern fur seals are relatively asocial species. They tend to be solitary during the winter feeding months, although they have been known to swim in larger groups. During the summer breeding months they congregate in rookeries. Males engage in some territorial aggressive displays against other males, but only when their particular territory is encroached upon. Females do not form any sort of social bond with either their male partners or with other females. Although females vocally bond with their pups, they leave them for days at a time to feed and do not engage in any form of parental care other than feeding. Philopatry (repeated returns to the natal site) is a defining characteristic of northern fur seals. Males often return to natal islands to stake out their territories and females return to their own natal sites to give birth to their pups and engage in breeding for the following season. Northern fur seals are incredibly particular about these sites, continuing to return to the same islands despite years of hunting by humans and population decimation.

• Key Behaviors
• natatorial natatorial
• motile motile
• nomadic nomadic
• migratory migratory
• solitary solitary
• territorial territorial
• colonial colonial

Home Range

There is no recorded information on home range size in northern fur seals.

Communication and Perception

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 visual
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• pheromones pheromones
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

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.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • molluscivore molluscivore

• Animal Foods
• fish
• mollusks
• other marine invertebrates

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 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.

Ecosystem Roles

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.

Economic Importance for Humans: Positive

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 food
• body parts are source of valuable material

Economic Importance for Humans: Negative

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

Conservation Status

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.

Additional Links

Encyclopedia of Life

Contributors

Rebecca Sackler (author), Yale University, Rachel Racicot (editor), Yale University, Eric Sargis (editor), Yale University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Baker, R., F. Wilke, C. Baltzo. 1970. The Northern Fur Seal . Washington, D.C.: U.S. Bureau of Commercial Fisheries.

Gelatt, T., L. Lowry. 2011. "Callorhinus Ursinus" (On-line). IUCN Red List of Threatened Species. Accessed February 08, 2012 at http://www.iucnredlist.org/apps/redlist/details/3590/0 .

Gentry, R. 1998. Behavior and Ecology of the Northern Fur Seal . Princeton, NJ: Princeton University Press.

2011. "National Marine Mammal Laboratory" (On-line). Alaska Fisheries Science Center. Accessed February 08, 2012 at http://www.afsc.noaa.gov/nmml/species/species_nfs.php .

Smithsonian. 2011. "North American Mammals: Callorhinus Ursinus" (On-line). Smithsonian Institution National Museum of Natural History. Accessed February 08, 2012 at http://www.mnh.si.edu/mna/image_info.cfm?species_id=28 .

National Advisory Committee on Oceans and Atmosphere. North Pacific Fur Seals: Current Problems and Opportunities Concerning Conservation and Management. Washington, D.C.: National Advisory Committee on Oceans and Atmosphere. 1985.