Antarctic fur seal (Arctocephalus gazella)

Description

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Antarctic fur seal fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
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Antarctic fur seal description

A large, hardy and charismatic inhabitant of the Antarctic region, the Antarctic fur seal (Arctocephalus gazella) is well adapted to the harsh climate of the Southern Ocean and the surrounding sub-Antarctic islands. Like other fur seals, the Antarctic fur seal has an insulating layer of fat, or blubber, to help it cope with the bitterly cold Antarctic temperatures, as well as a dense layer of underfur, which is much denser than that of terrestrial mammals ⁽⁵⁾.

Fur seals in the genus Arctocephalus have several distinguishing facial characteristics, with the generic name of the Antarctic fur seal being derived from the Greek words arktos and kephale, meaning ‘bear headed’ ⁽⁵⁾. The muzzle of the Antarctic fur seal is straight and fairly pointed and, unlike many seals, its nose is not bulbous, instead being of modest size, with forward-pointing nostrils ⁽²⁾. Compared with other species in the genus, the Antarctic fur seal has a relatively slender neck, a longer, less bulky body, and proportionately longer flippers ⁽⁶⁾. The prominent ears are long and pale in colour, with lighter tips ^{(2) (7)}. This species has small, almond-shaped eyes ^{(6) (7)}.

Generally, the Antarctic fur seal is greyish or brownish, usually with a somewhat grizzled appearance caused by the outer fur, or guard hairs, being whiter or paler than the underfur ^{(6) (8)}. The guard hairs often bunch up to reveal the fawn-coloured underfur. The adult male Antarctic fur seal is usually darker than the female, appearing dark greyish-brown to charcoal, with more extensive white guard hairs on the back, mane and sides ^{(2) (7)}.

The chest and underside of the Antarctic fur seal are paler than the upper parts of the body ^{(7) (8)}, usually appearing cream or light grey with shades of reddish-brown ⁽²⁾. The pale colour of the underside sometimes extends to the sides and the back of the neck ⁽²⁾, occasionally as high as the throat, eyes and muzzle ⁽⁷⁾. The face may also have lighter markings than elsewhere on the body ⁽²⁾. The flank is also typically slightly paler colour, and this may extend towards the hind flippers ^{(2) (7)}.

The stiff, creamy-white hairs, called vibrissae, on the nose and face of the Antarctic fur seal are particularly long and conspicuous, and, in adult male Antarctic fur seals, may sometimes reach lengths of up to 50 centimetres ^{(2) (7)}.

The flippers are generally darker than the rest of the body ^{(2) (7)}, and the back of the front flippers is covered with dark, sparse, short fur in a ‘V’ pattern which does not quite reach the tip, while the palm is covered with hairless leathery skin. The hind flippers are long and dark, with short, sparse hair covering the parts of the flipper nearest to the body, while the entire sole is covered in black, leathery skin ⁽⁷⁾.

The Antarctic fur seal exhibits one of the most extreme examples of sexual dimorphism of any mammal ⁽⁸⁾, with the male being much longer and weighing around five times more than the female ⁽⁷⁾.

The adult male Antarctic fur seal develops a mane on the chest, neck and top of the head, which is emphasised by extra layers of muscle and fat deposited under the skin. As well as providing extra insulation against the glacial temperatures of the Antarctic, the mane helps to protect the male Antarctic fur seal during aggressive interactions with other males ^{(2) (3) (7)}. 

Although the adult male is easily distinguished, the adult female, subadults and juveniles are fairly difficult to tell apart until the males grow larger at around four to six years old ⁽⁷⁾. The adult female and subadults often have additional lighter areas around the ears ⁽²⁾, while juveniles and subadults have darkish or a mix of light and dark vibrissae, which become more creamy-white as they age ⁽⁷⁾. At birth, Antarctic fur seal pups are blackish, though they may be pale on the face and muzzle ⁽²⁾. The dark brown or black coat of juveniles is generally shed for a more silvery pelage after several months ⁽⁷⁾. 

An unusual pale, yellowish off-white to honey coloured form of the Antarctic fur seal has been known to occur infrequently within the population on South Georgia ^{(2) (7) (8)}.

The Antarctic fur seal was formerly considered a subspecies of Arctocephalus tropicalis ⁽¹⁾.

Also known as

Kerguelen fur seal.

Synonyms

Arctocephalus tropicalis gazella, Arctophoca gazella.

French

Arctocéphale De Kerguelen.

Size

Adult male length: up to 2 m ^{(2) (3)}

Adult female length: up to 1.4 m ⁽²⁾

Newborn length: 63 - 67 cm ⁽²⁾

Adult male weight: 110 - 230 kg ⁽²⁾

Adult female weight: 22 - 51 kg ⁽²⁾

Newborn weight: 6 - 7 kg ⁽²⁾

Antarctic fur seal biology

The Antarctic fur seal is extremely territorial, and is known for its aggressive displays and fierce fighting between males. The male, known as a bull, arrives at the breeding colony in late October and immediately establishes a territory which is maintained throughout the breeding season ⁽¹⁾. Competition with other males over territory is resolved by ferocious, ritualised territorial displays, typically involving loud vocalisations, threat posturing, and slashing forcefully with an open mouth at its opponents ^{(1) (6)}.

Fighting between the males of this species leads to the creation of a dominance hierarchy, with stronger, undefeated males usually holding prominent territories on the beach, close to the water and above the high tide mark ⁽⁶⁾. Rocks, fracture lines and other natural features often delineate the territories of individual males, with the territories being most clearly defined at the peak of the breeding season ⁽⁵⁾. The male Antarctic fur seal tends to return to where it was born to establish its territory, and it will continue to return to the same place each breeding season once a territory has been established ⁽⁶⁾.

Female Antarctic fur seals arrive at breeding colonies from mid-November ^{(1) (6)}. The Antarctic fur seal is a polygynous species ⁽¹⁾, with several females forming groups which correspond to the bull territories. The number of females associated with the territory of an individual male is around 15, although this number can vary from 1 to 27 ⁽⁶⁾.

The female usually gives birth to a single pup, around one or two days after arriving at the breeding colony. The female cares for the pup for around six days before coming into oestrus and mating again. The Antarctic fur seal utilises a reproductive strategy known as ‘embryonic diapause’, in which the embryo does not immediately implant into the uterus. The delayed implantation period of the Antarctic fur seal is around 3 to 4 months, followed by a gestation period of around 12 months ^{(5) (6)}.

Around a week after mating the female will depart to forage, returning periodically to suckle the young pup ^{(1) (5) (6)}. The Antarctic fur seal has an exceptionally short lactation period compared to most other fur seal species ⁽⁵⁾, with the pup being fed on milk produced by the female’s mammary glands until it is weaned at around four months old ^{(1) (5) (6)}.

The young pups roam on the beach while the females forage at sea, often gathering with other young pups and engaging in play fighting and boundary displays at just a few weeks old ^{(5) (6)}. The female’s forging trips generally last for four or five days, followed by two or three days attending the pup on the shore ⁽¹⁾. On returning from a foraging trip, the female will identify her own pup by call and by detecting its individual scent. The pups may venture into the sea as early as January, although young Antarctic fur seals are not able to swim competently until early March. This species becomes sexually mature at 3 to 4 years old, although male fur seals are generally unable to hold a territory until they are at least 8 years old ⁽⁶⁾.

The Antarctic fur seal feeds primarily on krill (Euphausia superba) ^{(1) (2) (5) (6)}. It will also feed on a variety of other prey, including fish, cephalopods, crustaceans, and even penguins and other seabirds ^{(1) (5)}. It is known to exploit seasonally abundant prey, such as spawning squid or schools of migrating fish ⁽⁵⁾. The Antarctic fur seal forages mainly at night, usually making shallow dives to depths of around 60 metres ^{(1) (5)}. The male does not feed at all during the breeding season while it is defending a territory ⁽⁶⁾; however, during the winter males of this species will dive much deeper than the females to forage, sometimes reaching depths of around 200 metres ⁽⁵⁾. Like other fur seals, the Antarctic fur seal porpoises when it swims rapidly, and it has surprising agility on land, being able to travel quickly on land even over dense tussock ⁽⁶⁾.

Antarctic fur seal range

The Antarctic fur seal is found primarily on islands south, and in some areas slightly north, of the Antarctic Convergence, where the colder, northward-flowing Antarctic waters meet the relatively warmer waters of the sub-Antarctic ^{(1) (2) (6)}.

Almost 95 percent of the Antarctic fur seal population breeds on South Georgia ^{(1) (6)}. Smaller colonies are found on the South Shetland, South Orkney and South Sandwich Islands, as well Heard, McDonald and Macquarie Islands, the Prince Edward Islands, Îles Crozet and Îles Kerguelen, and Bouvetøya ⁽¹⁾.

Vagrant Antarctic fur seals have also been recorded at Gough Island, on the coasts of Antarctica and southern South America, and even as far as Australia ⁽¹⁾. The southernmost limits of this species are not well known, although it has been recorded on pack ice of the Antarctic Peninsula ⁽⁶⁾.

The distribution of the Antarctic fur seal outside of the breeding season is not well documented, but this seal is known to disperse widely at sea in the winter, between May and November ^{(1) (2) (6)}. Some adult male and juvenile Antarctic fur seals are found on breeding islands throughout the year ⁽⁶⁾.

Antarctic fur seal habitat

Breeding colonies of the Antarctic fur seal are usually located on rocky stretches of beach where there is some protection from the sea. On South Georgia, the inland habitat of the island is comprised mainly of dense tussock grass, and this seal will readily move into these more vegetated areas during the breeding season ^{(2) (6)}.

During the winter months the Antarctic fur seal is found mostly at sea, although males and subadults frequently occur along the edge of the pack ice and are known to haul out on sea ice ⁽²⁾, as well as sandy beaches ⁽²⁾.

Antarctic fur seal status

The Antarctic fur seal is classified as Least Concern (LC) on the IUCN Red List ⁽¹⁾ and is listed on Appendix II of CITES ⁽⁴⁾.

Antarctic fur seal threats

Nearly all species of southern fur seal were massively overexploited during the 18th and 19th centuries because of large scale commercial sealing ⁽⁵⁾, which drove the Antarctic fur seal to the brink of extinction ^{(1) (2) (6)}. Populations of many other seal species became so depleted they were considered commercially extinct ⁽⁵⁾.

Although the Antarctic fur seal has now made a remarkable recovery, it was reduced to just a few, very small, isolated populations in the late 19th century. This caused a severe population ‘bottleneck’, and inbreeding has greatly reduced the genetic diversity of the Antarctic fur seal, making it more vulnerable to environmental change and placing it at increased risk from outbreaks of disease ⁽¹⁾.

The Antarctic fur seal population is now relatively stable, and it is currently no longer at risk of extinction. However, a number of threats to this species still exist and although it is no longer targeted by most fisheries, it is vulnerable to entanglement in fishing debris, such as discarded fishing line, nets, packing bands and other objects ^{(1) (2)}.

Global climate change is perhaps the biggest future threat to the Antarctic fur seal ^{(1) (5)}. Although the current and future effects of climate change on this species are not known, it is likely that changes in ocean temperatures and ocean currents will affect several aspects of its life cycle and may result in population declines. For example, alteration to ocean currents may affect the distribution of the Antarctic fur seal’s main prey species, while changing temperatures may directly alter the timing of breeding and other important behaviours. Climate change may also facilitate the spread of disease ⁽¹⁾.

Tourism occurs on several islands within this species’ range and may cause some disturbance to breeding colonies; however, due to the isolated nature of the majority of haul out sites and breeding locations, it is unlikely to have a severe impact on the population ⁽¹⁾.

Antarctic fur seal conservation

The Antarctic fur seal is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) ⁽⁴⁾, meaning that all international trade in this species should be carefully monitored. It is also legally protected by all the nations that govern the islands on which it breeds, as well as receiving protection under the Antarctic Treaty ⁽⁹⁾ and the Convention for the Conservation of Antarctic Seals (CCAS) ^{(1) (6) (10)}.

The Convention for the Conservation of the Antarctic Marine Living Resources (CCAMLR) also means that any proposals for the exploitation of living resources in the Antarctic must consider the effects that such exploitation is likely to have on marine mammals, whether or not the mammals are the target species ^{(5) (10) (11)}.

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

Find out more about the Antarctic fur seal:

• Jefferson, T.A., Leatherwood, S. and Webber, M.A. (1993) FAO species Identification Guide. Marine Mammals of the World. FAO, Rome. Available at:
  ftp://ftp.fao.org/docrep/fao/009/t0725e/t0725e00.pdf

Find out more about conservation in the Antarctic:

• British Antarctic Survey:
  http://www.antarctica.ac.uk/
• Secretariat of the Antarctic Treaty:
  http://www.ats.aq/
• Discovering Antarctica:
  http://www.discoveringantarctica.org.uk/
• Antarctic and Southern Ocean Coalition (ASOC):
  http://www.asoc.org/
• International Polar Foundation:
  http://www.polarfoundation.org/
• Antarctica New Zealand:
  http://www.antarcticanz.govt.nz/
• Australian Antarctic Division:
  http://www.antarctica.gov.au/
• Institut polaire français Paul Émile Victor (IPEV):
  http://www.institut-polaire.fr/

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Glossary

Cephalopods

A group of marine molluscs with grasping tentacles and either an internal or external shell. Includes squids, octopuses, cuttlefish and nautiloids.

Crustaceans

Diverse group of animals with jointed limbs and a hard external skeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Delayed implantation

The process of a fertilised egg remaining unattached in the uterus for a period of time, therefore delaying the start of development.

Embryonic diapause

Also known as delayed implantation. A reproductive strategy found in some mammals, such as some marsupial, rodent, bear and mustelid species, in which the embryo does not immediately implant in the uterus, but remains dormant, only implanting and continuing development when conditions are favourable.

Genetic diversity

The variety of genes within a particular species, population or breed causing differences in morphology, physiology and behaviour.

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Gestation

The state of being pregnant; the period from conception to birth.

Guard hairs

In some mammals, long, coarse hairs that protect the softer layer of fur below.

Mammae

The organs of females that produce milk. Also known as mammary glands.

Oestrus

The time of ovulation (release of an egg from the ovary) in female mammals, when the female becomes receptive to males. Also known as ‘heat’.

Pack ice

Sea ice that floats on the surface of the water. Often formed from large pieces of ice that consolidate into a single ice mass, pack ice typically moves with currents, tides and wind.

Polygynous

A mating system in which males have more than one female partner.

Sexual dimorphism

When males and females of the same species differ in appearance.

Spawning

The production or depositing of eggs in water.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Territory

An area occupied and defended by an animal, a pair of animals or a group.

Vagrant

An individual found outside the normal range of the species.

References

1. IUCN Red List (October, 2011)
   http://www.iucnredlist.org/
2. Jefferson, T.A., Leatherwood, S. and Webber, M.A. (1993) FAO species Identification Guide. Marine Mammals of the World. FAO, Rome. Available at:
   ftp://ftp.fao.org/docrep/fao/009/t0725e/t0725e00.pdf
3. Burnie, D. (2001) Animal. Dorling Kindersley, London.
4. CITES (October, 2011)
   http://www.cites.org/
5. Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds.) Encyclopedia of Marine Mammals. Academic Press, San Diego, California.
6. Nowak, R.M. (1991) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore and London.
7. Jefferson, T.A., Webber, M.A. and Pitman, R.L. (2008) Marine Mammals of the World: A Comprehensive Guide to their Identification. Academic Press, London.
8. Reijnders, P., Brasseur, S., van der Toorn, J., van der Wolf, P., Boyd, I., Harwood, J., Lavigne, D. and Lowry, L. (1993) Seals, Fur Seals, Sea Lions, and Walrus. IUCN/SSC Seal Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
   http://data.iucn.org/dbtw-wpd/edocs/1993-034.pdf
9. Secretariat of the Antarctic Treaty (October, 2011)
   http://www.ats.aq/e/ats.htm
10. British Antarctic Survey (October, 2011)
    http://www.antarctica.ac.uk/index.php
11. The Convention for the Conservation of the Antarctic Marine Living Resources (October, 2011)
    http://www.ccamlr.org/pu/e/gen-intro.htm