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By Jessica Holmes
Geographic Range
Northern fur seals migrate from the North Pacific Ocean in the winter to the Bering Sea in the summer. Northern fur seal populations occur along the coast of California (down to San Diego), Alaska, Russia, and Japan. (Gentry and Kooyman, 1986; Mori, Baba, and Kubodera, 2001; Nowak, 1999)
Biogeographic Regions:
nearctic 
(native ); palearctic (native ); arctic ocean (native ); pacific ocean (native ).
Habitat
(678.96 ft; avg. 574 ft)
Northern fur seals spend the majority of their lives in the cool water of the North Pacific Ocean. During the reproductive season northern fur seals arrive at island breeding grounds. Male northern fur seals remain on land. Females will remain on land during mating but will re-enter the ocean to hunt while nursing a pup. (Gentry, 1998; Nowak, 1999; Reidman, 1990)
These animals are found in the following types of habitat:
temperate ; saltwater or marine .
Physical Description
(94.6 to 598.4 lbs; avg. 324.5 lbs)
(69.88 in)
Northern fur seals are extremely sexually dimorphic. Male and female northern fur seals vary both in size and color. Adult females are smaller than males, measuring about 142 cm and weighing 43-50 kg, and are usually gray or brown. Adult males tend to be reddish in coloration or black, measure 213 cm, and weigh between 181 and 272 kg. Northern fur seal pups have black pelage. Additional characteristics include vibrissae, which are white on the adult and black on the pup. Pups usually have lighter markings on the nose and underside. Adults, especially males, have a mane, which is similar to the mantle of some squirrels. The adults have small noses, thick underfur,and long pinnae. The fur on the front flippers stops at the wrist. (Gentry, 1998; Nowak, 1999)
Some key physical features:
endothermic ; homoiothermic; bilateral symmetry .
Sexual dimorphism: male larger, sexes colored or patterned differently, ornamentation .
Reproduction
Northern fur seals breed annually.
Mating occur in summer, with the peak of mating falling in late June through mid-July.
Northern fur seals are polygynous. Males compete for territories and successful males can mate with many females.
Males arrive at the mating island prior to the females, at which time they begin to claim a mating territory. The mating islands in the Pribilofs, St. George and St. Paul,the southern California island San Miguel, and additional islands in the Bering Sea are the most common mating grounds.
Non-mating males will also travel to the island and usually end up on a territory on the outer edge. Non-mating males learn from their experiences until they reach mating age and are able to successfully compete with other males.
When females arrive it is believed that they choose a mate not based on the male's appearance, but the specific characteristics of the mating territory and possibly the presence of other females.
Males will participate in aggressive, but usually not lethal, behavior with other males. Females are more likely than males to be injured during the mating selection process. Occasionally, two males with fight over a female if she attempts to leave a mating territory, which could result in a tug of war. While males are sparing they will make attempts not to injure any pups in the area. (Gentry and Kooyman, 1986; Gentry, 1998; Nowak, 1999; Reidman, 1990)
Mating systems:
polygynous .
Northern fur seals are extremely polygamous. In some cases a single male may mate with up to 50 females during one breeding season. However, more typical is 15 to 20 females. The number of females a male mates with is dependent on the number of available females and the male’s ability to control a mating territory.
The female arrives at the mating island, gives birth to a pup which is a result of the prior year's mating, then mates. Mating occurs during summer. The fertilized egg undergoes delayed implantation. After the blastocyst stage occurs, development halts for approximately four months. Implantantion of the embryo occurs four months after fertilization.
Gestation lasts for approximately one year. Pups are born between June and July, and remain on land for 60-70 days. Peak pupping season is mid-June to mid-July, and peak mating occurs just after this, from late-June to late July.
Females typically become sexually mature between 3 and 6 years of age. Males reach sexually maturity between the same ages, but typically will not participate in mating until three years later.
The same group of males and females tends to return to the same mating island every year. However, male pups born on a particular island will go to a different island when they reach reproductive age. This can be considered dispersal of males. (Gentry and Kooyman, 1986; Gentry, 1998; Nowak, 1999; Reidman, 1990)
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous ; delayed implantation .
Pups are born unable to swim or to move around much. Females care for their pups. They nurse the pups, providing milk to sustain them. During the nursing period, the mother makes feeding trips to the ocean. She may leave her pup for four to nine days! The mother returns to land to nurse the pup for about two days between feeding trips. Weaning occurs between three and four months of age, and is apparently begun by the pup. After the pup is weaned, there are no long-term social bonds in this species. (Nowak, 1999)
Parental investment:
altricial ; pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); pre-independence (protecting: female).
Lifespan/Longevity
Actual lifespans of up to 26 years have been measured, although it is thought that the actual maximum may be around 30 years of age. (Nowak, 1999)
Behavior
Northern fur seals are described as gregarious, but only during mating and feeding. At all other times males are solitary. Females are also solitary except while they are nursing young or mating.
Northern fur seals tend to be most active during the early morning and evening or night. The middle of the day is spent sleeping, usually floating on their sides. (Gentry, 1998; Nowak, 1999; Reidman, 1990)
Key behaviors:
crepuscular ; motile ; migratory ; solitary ; colonial ; dominance hierarchies .
Communication and Perception
Vocal communication is important twice during the lifetime of a northern fur seal. Vocalizations are crucial to the mother and pup relationship. While the mother and pup are on the mating island the mother frequently returns to the ocean to hunt. When the mother returns vocalizations are used to find the young. If the young becomes lost the mother is able to locate her young by distinctive individual vocalizations. This type of vocalization is described as being loud, repetitive, and low or deep. Once the mother and pup have located each other the mother uses scent to verify the pup is her young.
Verbal communication also becomes important when males are competing for territory. Males will bark at each other during competition.
These animals are also reported to use scent marks. (Insley, 2001; Reidman, 1990)
Communicates with:
acoustic .
Other communication keywords:
scent marks .
Food Habits
Northern fur seals are described as opportunistic feeders. The main components of the diet are fish and squid. Occasionally northern fur seals will feed on birds. The diet is mainly dependent on the availability of prey due to season and location.
Foods eaten include: pollack, herring, lantern fish, cod, rockfish, squid, loons and petrels. (Gentry and Kooyman, 1986; Nowak, 1999; Reidman, 1990)
Animal Foods:
birds; fish; mollusks.
Predation
- great white sharks (Carcharodon carcharias)
- killer whales (Orcinus orca)
- stellar sea lions (Eumetopias jubatus)
Since the main predators of northern fur seals are marine mammals, the main strategy of escape is to emerge onto land. (Reidman, 1990)
Ecosystem Roles
Because of their feeding habits, these seals play an important role in food webs, affecting the population of prey fishes. They also may have an effect on predator populations.
Economic Importance for Humans: Negative
This species has often been accused of having a negative impact on fisheries. However, analysis of stomach contents indicate that northern fur seals do not feed on the same species that humans take. Most of the diet of these seals appears to be lanternfish, which are not harvested by people. (Nowak, 1999)
Ways that these animals might be a problem for humans:
crop pest.
Economic Importance for Humans: Positive
Northern fur seals have been harvested mostly for their fur, but are also used as a food source. (Gay, 1987; Gentry, 1998)
Ways that people benefit from these animals:
food ; body parts are source of valuable material.
Conservation Status
IUCN Red List: [link]:
Vulnerable.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
Harvesting of the seal for its coat almost led to the species extinction in the mid 1700s. At the time of the Alaskan Treaty provisions where put into place in order to maintain population sizes. The treaty stated that only juvenile male seals, found on land, could be killed.
Current threats include loss of breeding habitat on islands. (Gay, 1987; Hilton-Taylor, 2001; Nowak, 1999)
For More Information
Find Callorhinus ursinus information at
Contributors
Nancy Shefferly (editor), Animal Diversity Web Staff.
Jessica Holmes (author), California State University Sacramento.
James Biardi (editor), California State University Sacramento.
