By Cortney Hiller
Geographic Range
Arctocephalus tropicalus, the Subantarctic Fur Seal, can be found on islands near the South Pole just north of the Antarctic Convergence. These include the islands of Amsterdam, Crozet, Grough, Marion, Prince Edward, St. Paul, and Tristan (King, 1983). (King, 1983)
Biogeographic Regions:
ethiopian 
(native ); neotropical (native ); australian (native ); oceanic islands (native ); atlantic ocean (native ); pacific ocean (native ).
Habitat
The males of the species spend most of the year out at sea, hauling out on the rookeries only during the mating season. Females spend much of their time close to the rookeries, hauling out at regular intervals for nursing and again during the breeding season. Breeding occurs on land and rocky coastal areas are preferred for the rookeries (King, 1983; Riedman, 1990).
Aquatic Biomes:
coastal .
Physical Description
(110 to 308 lbs; avg. 209 lbs)
Subantarctic fur seal males measure between 1.5 and 1.8 meters in length and weigh from 95 to 140 kilograms (King, 1983: 46). The coat on the male is a dark gray or brown in color dorsally while the underside and face area are paler and a little more orange. The males also have a crest of slightly longer and rougher white tipped hairs on top of their head. The females of the species are slightly smaller, measuring between 1.2 and 1.3 meters in length and weighing approximately 50 kilograms (King, 1983: 46). The female's coat is very similar to the male's, the notable difference being their lack of the white tipped crest. Both males and females have long white whiskers (King, 1983: 46). Subantarctic fur seal pups are colored differently from their parents. Pups are black with pale orange fur on the underside. Their whiskers are also black. This coat is replaced by an adult coat during the pups' first molt between 8 and 12 weeks of age (King, 1987: 47).
Some key physical features:
endothermic ; bilateral symmetry .
Reproduction
The breeding season for A. tropicalus begins in September when the males haul out on shore at the breeding grounds, or rookeries, to establish territories by displays, sparring, or actual battle. The females come ashore in October and November and choose male territories within which to bear their young. They later mate with the male possessing that territory. It is also at this time that immature animals begin avoiding the rookeries.
Pups are born beginning in late November through January. Most pups are born in early December. Cows give birth to a single pup and begin lactation almost immediately. Lactation is almost continuous for the next 8-12 days, after which the cow mates and begins returning to the sea. She will spend increasing amounts of time at sea over the next year, returning only to nurse her pup. Lactation continues throughout the pup's first year or until the cow's next pup is born. Copulation occurs between 8 and 12 days after the cow gives birth, but there is a delay of about 4.3 months in the implantation of the blastocyst (Riedman, 1990: 250). The pups are approximately 4.5 kilograms and 60 centimeters at birth, the males being slightly larger than the females. Females reach sexual maturity between 4 and 6 years of age while males reach sexual maturity earlier, between 3 and 4 years of age (Riedman, 1990: 237).
Key reproductive features:
gonochoric/gonochoristic/dioecious (sexes separate); sexual .
Behavior
While the Subantarctic fur seal is basically nonmigratory it does exhibit seasonal movements. Males spend most of their year at sea, hauling out at the rookeries only during the mating season. Females, while they will go to sea in order to find food, remain close to the rookery in order to continue nursing their pups throughout the year. The rookery is never fully evacuated because the mothers and pups return to it continually.
Males at sea often travel in small feeding groups. Interestingly, some individuals have been found in colonies of other species of seals, including A. pusillus, A. forsteri, A. gazella and A. australis. Most of these individuals are male. While A. tropicalus is distinguishable by its coloring and the male's crest, some variation in these traits have been noted in areas where mixed species groups of seals have been reported. For this reason it is postulated that interbreeding does occur (Riedman, 1990; King, 1983).
Arctocephalus tropicalus is facultatively polygynous, meaning that they are solitary most of the year but come together during the mating season. At this time they form harems where one male mates with several females.
Arctocephalus tropicalus exhibits what is called a "pup call." When the mother returns from sea to feed her pup, she emits a loud call. Upon hearing this all of the pups on land come to her, but she responds only her own pup. This same call is used by cows in other species, such as the northern fur seal, South American fur seal, New Zealand fur seal and others. It is suggested that the mother uses smell, not sight, to distinguish her pup from the others (Riedman, 1990).
Key behaviors:
motile .
Food Habits
The Subantarctic fur seal's diet consists mainly of squid and is supplemented by krill, fish and, at times, penguins or other birds (Riedman, 1990; King, 1987). Like most marine mammals, A. tropicalus finds at least some of its food in the ocean.
Economic Importance for Humans: Positive
In the past, these seals were hunted for their fur.
Conservation Status
Much of the subantarctic fur seal populations had been taken by sealers by the 1830s, but enough of the animals survived in order to make a comeback. A majority of the population, which was estimated at 214,000 individuals in 1983, is located on Gough Island (King, 1983: 46). In 1990 the population was estimated at 300,000 individuals (Riedman, 1990: 60). More recently the population was estimated at 310,000 individuals and rising. Currently there are no recognized threats to the subantarctic fur seal population.
For More Information
Find Arctocephalus tropicalis information at
Contributors
Cortney Hiller (author), University of Michigan.
Phil Myers (editor), Museum of Zoology, University of Michigan.
