Antarctic fur seal
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Also Kerguelen fur seal. The Antarctic fur seal (scientific name: Arctocephalus gazella) is one of 16 species of marine mammals in the family of Eared seals which include sea lions and fur seals. Together with the families of True seals and Walruses, Eared seals form the group of marine mammals known as Pinnipeds.
Eared seals differ from the true seals in having small external earflaps and hind flippers that can be turned to face forwards. Together with strong front flippers, this gives them extra mobility on land and an adult fur seal can move extremely fast across the beach if it has to. They also use their front flippers for swimming, whereas true seals use their hind flippers.
Like other Eared seals, the male Antarctic fur seal is considerably larger than the female.
Like other fur seals, the Antarctic fur seal was long hunted for its skin and oil and was nearly exterminated. A small colony survived on Bird island, South Georgia where, today, most Antarctic fur seals breed.
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Conservation Status  |
Scientific Classification Kingdom: Anamalia (Animals) |
Physical Description
Extreme sexual dimorphism is evident in Antarctic fur seal, with the males weighing between 60 and 120 kg and the females weighing between 30 and 51 kg. Adult males are 1-2 m long, whereas the females vary between .5 and 1 m. The adults are covered in a dense velvety underpelt, which is both waterproof and windproof, and an outer layer of coarse grey-brown hair. The males can be distinguished from the females by their long mane of shoulder fur. At birth, pups weigh between 4.5 and 6.5 kg and measure a length of between 60 and 73 cm. The pups have black wooly fur, which is retained for 2-3 months. The pups then display a silver-grey coat which lasts until adulthood.
Reproduction
In this polygynous mating system, a dominance hierarchy of males is established through the displays and fights that occur while defending territories. Some subordinate males are forced inland while others assume a completely aquatic lifestyle.
The breeding season of this species is from November to January. The males arrive earlier than the females to compete for territories, which will eventually hold a harem of 4-5 females. The competition is fierce and males don't feed while defending their territories on shore. Breeding incurs significant costs to the males of the species, which lose an average of 1.5 kg a day throughout the season. Females give birth to a single young approximately two days after arrival on shore. The females become sexually receptive 6-8 days after giving birth and then begin mating.
During lactation, females spend 3-5 days feeding at sea to maintain their supply of milk. This period is followed by 1-2 days of nursing on shore. This cycle is repeated for 4 months. The lactation period is one of the shortest of all fur seals and is probably due to the harsh weather conditions and strong seasonality of the breeding area. While the female is away, the pup hides in a sheltered area. Both the mothers and the pups use vocalization as a means to relocate each other when the mothers return from the sea.
Lifespan
Males live up to 15 years and females up to 23 years.
Behavior
Antarctic fur seal is surprising agile on land, reaching speeds of 20 km/hr on smooth surfaces. It is quite probable that they reach even higher speeds in the water. Using time-depth recorders, the dives of several lactating females have been measured. The deepest dives average about 181 m and last almost 5 minutes.
Distribution
The breeding range of Antarctic fur seal is primarily restricted to seasonally ice free islands south of the Antarctic Convergence, but individuals have been found as far north as Brazil. South Georgia is the site of the greatest concentration of Antarctic fur seals, particularly on Bird Island. It is estimated that 95% of the species breed near the coast of South Georgia. Other breeding locations include Bouvet Island, Crozet Islands, Heard Island, Kerguelen Islands, Macquarie Island, Marion Island, McDonald Islands, Prince Edward Islands, South Orkney Islands, South Sandwich Islands, and South Shetland Islands. The total population may be over 4 million.
Some adult males and juveniles stay ashore year round, but the direction of the female migrations in the Southern ocean are unknown.
Habitat
Though the species appears to be capable of traveling long distances over ice, it doesn't seem well adapted to such an environment. Breeding occurs on rocky beaches sheltered from the sea. The islands they inhabit commonly support lush grass growth inland. During the months of May and November, there is a general movement out to sea, but specific migration paths are unknown. Some adult males are found ashore or in the general area of the breeding islands year-round.
Food Habits
The main food of the Antarctic fur seal is krill, but individuals also consume squids and even birds. Nursing mothers are almost completely dependent on krill and the reproductive success of this species is, therefore, closely linked with the availability of this food resource. Antarctic fur seal mainly feed at night in the shallower waters of the ocean.
Conservation Status
This species almost became extinct in the 18th and 19th centuries due to intense commercial sealing for their fur. The population growth has now reached about 10% per annum due to increasing concern about their well-being. They are protected under the Convention for Conservation of Antarctic Seals (CCAS) and the Antarctic Treaty System. On a more local level they are protected by the legislation of each of the islands they inhabit. They have also been placed under Appendix II of CITES.
Economic Importance for Humans
Although the Antarctic fur seal is no longer of economic importance to humans, the species was heavily hunted throughout the 18th and 19th centuries for its fur. Commercial krill harvesting is now being developed in small countries and this move threatens to begin a battle between human interests and those of the Antarctic fur seal.
Further Reading
- <em>Arctocephalus gazella</em> (Peters, 1875) Encyclopedia of Life (accessed April 3, 2009)
- Arctocephalus gazella, Edwards, H., 2000, Animal Diversity Web (accessed April 3, 2009)
- Antarctic fur seal, Seal Conservation Society (accessed April 3, 2009)
- The Pinnipeds: Seals, Sea Lions, and Walruses, Marianne Riedman, University of California Press, 1991 ISBN: 0520064984
- Encyclopedia of Marine Mammals, Bernd Wursig, Academic Press, 2002 ISBN: 0125513402
- Marine Mammal Research: Conservation beyond Crisis, edited by John E. Reynolds III, William F. Perrin, Randall R. Reeves, Suzanne Montgomery and Timothy J. Ragen, Johns Hopkins University Press, 2005 ISBN: 0801882559
- Walker's Mammals of the World, Ronald M. Nowak, Johns Hopkins University Press, 1999 ISBN: 0801857899
- <span> </span>Antarctic fur seal, MarineBio.org (accessed April 4, 2009)