Subantarctic fur seal (Arctocephalus tropicalis)

Also known as: Amsterdam Island fur seal, sub-Antarctic fur seal
Synonyms: Arctophoca tropicalis
  
French: Arctocéphale D'Australie
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderCarnivora
FamilyOtariidae
GenusArctocephalus (1)
SizeMale length: 150 – 180 cm (2)
Female length: 120 – 145 cm (2)
Male weight: 100 – 150 kg (2)
Female weight: c. 50 kg (2)

Classified as Least Concern on the IUCN Red List (1) and listed on Appendix II of CITES (3).

One of the best-known members of the family Otariidae (the eared seals), the Subantarctic fur seal has a distinctive colouration (4). The upperparts are a variable dark greyish-brown, fading to ginger on the belly and white to burnt orange on the chest, muzzle and face (2) (4) (5). This contrasting colouration is most pronounced on the male, which may also be identified by its conspicuous tuft of dark hair that stands prominently on the forehead (4). The dense, waterproof fur may have a slight grizzled appearance on older adults, due to the paler colour of outer layers, while the coat is a much softer, uniform black on the young pups (4) (5) (6). 

The scientific name, Arctocephalus, is derived from the Greek for “bear-headed” and refers to the bear-like skull shape of seals in this genus (4). The snout is short and flat, and leads to a pointed nose and elongated whiskers that often reach well beyond the ears and down to the neck. The flippers are comparatively shorter and broader on the Subantarctic fur seal than related species (2) (5). 

The Subantarctic fur seal is widely distributed throughout the southern hemisphere (1). It breeds on temperate islands in the south Atlantic and Indian Oceans, with the largest colonies at Gough, Amsterdam and the Prince Edward Islands, and smaller colonies at Tristan da Cunha, Saint Paul, Maquarie and the Crozets. Vagrants, most often juveniles, may also occasionally visit the coasts of Antarctica, southern South America, southern Africa, Australia, New Zealand and South Georgia and have even, in rare cases, been recorded as far afield as Madagascar, Mauritius, Comores and Zanzibar (1) (5) (7) (8) (9).

The Subantarctic fur seal breeds on isolated rocky islands north of the Antarctic Polar Front, where the cold currents to the south sink beneath warmer more northern waters (1) (2). While at sea, some seals will cross this barrier to visit colder waters, with some wandering individuals travelling many thousands of miles. On land, this seal prefers to haul out on the windward side of islands, where the cooling wind and spray are thought to prevent it from overheating (2).

Due to its limited mobility on land, the Subantarctic fur seal carefully selects islands with few or no predators upon which to breed (6). Although the first breeding males arrive on land in late October, with the females following a short while later, the bulk of breeding takes place in December (1) (10) (11). Only the territorial males and mature females congregate on established breeding grounds, with immature seals, and the smaller males without territories, gathering on peripheral grounds. Breeding beaches are often heavily crowded, with the females grouping around the more evenly spaced territorial males. The bulls defend their territories from rival males and although fighting rarely goes beyond display and threats, on the occasions that it does, fighting may ensue, often with life-threatening wounds inflicted upon the defeated bull (2) (6). Successful males gather a harem of usually 6 to 8 females and will breed with each female (2). 

Those females that mated the previous season will give birth to a single pup, after a gestation period of almost a year, within 6 days after coming ashore before mating 8 to 12 days later. Mothers stay with the newborn pup for around a week before returning to the sea to feed, returning 6 to 10 days later to feed their pup. Thereafter, the adult female undergoes a regular cycle of several days ashore with their pups followed by several weeks at sea foraging until the pup is weaned at an approximate age of 11 months. While the pups grows quickly on the energy-rich milk of its mother, and will start to swim in rock pools and shallows after six weeks, it will first go to sea after weaning (1) (2) (4) (7) (10) (11) (12) (13). 

Juvenile seals often venture far away from the breeding islands, with some individuals travelling many thousands of kilometres to feed as far away as off the coast of South America and South Georgia Island (2). Very little is known of the behaviour of the Subantarctic fur seal while at sea, but they feed largely on fish, to a lesser extent squid, occasionally krill and very occasionally penguins (2) (5). Using its modified eyes and vibration-sensitive whiskers, this seal is thought to actively seek out its prey, with most dives taking place at night-time when many fish species migrate towards the ocean’s surface (6) (8).

The Subantarctic fur seal was once the victim of intensive hunting for its dense, waterproof coat. This was most severe during the late 18thand early 19thcenturies, and by the 1830s the species was close to extinction, with many breeding colonies completely eradicated. However, due to the reduced demand for seal fur, the species gradually started to recover, although small-scale hunting continued at Gough Island up until the 1950s. Today, after a remarkable recovery, the Subantarctic fur seal numbers well over 300,000 individuals, and the population is continuing to increase, although a legacy of previous declines is the species’ low genetic diversity (1) (14) (15). The species’ stronghold is on Gough Island, which supports over 200,000 seals, and large numbers are also found on Amsterdam Island and the Prince Edward Islands (1) (2) (12). However, climate change has the potential to threaten the Subantarctic fur seal by changing prey availability through changes in water temperatures and rising sea levels (1) (16).

A widespread and numerous species, the Subantarctic fur seal is not currently threatened with extinction (1). All of its breeding colonies are protected by their respective governments, including those on Tristan da Cunha, which are protected by the Tristan da Cunha Conservation Ordinance (1) (14) (17). However, with the potential for climate change to have serious negative effects on this species, monitoring of its status may be required (16).

To find out more about the Subantarctic fur seal and its conservation, see:

For more information on the wildlife and conservation of Tristan da Cunha, see:

Authenticated (23/08/2010) by Greg Hofmeyr, Marine Mammal Biologist and Curator, Bayworld (Port Elizabeth Museum, Oceanarium and Snakepark), Port Elizabeth, South Africa.
http://www.bayworld.co.za

  1. IUCN Red List (May, 2010)
    http://www.iucnredlist.org/
  2. Nowak, R.M. (1999) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore.
  3. CITES (May, 2010)
    http://www.cites.org/
  4. Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (1999) Encyclopedia of Marine Mammals. Academic Press, London.
  5. Jefferson, T.A., Leatherwood, S. and Webber, M.A. (1993) FAO Species Identification Guide. Marine Mammals of the World. FAO, Rome. Available at:
    http://nlbif.eti.uva.nl/bis/marine_mammals.php?selected=beschrijving&menuentry=soorten&id=42
  6. Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
  7. MarineBio (May, 2010)
    http://marinebio.org/species.asp?id=315
  8. The Seal Conservation Society (May, 2010)
    http://www.pinnipeds.org/species/subfursl.htm
  9. Hofmeyr, G.J.G. and Amir, O. (2010) Vagrant Subantarctic fur seal on the coast of Tanzania. African Zoology, 45:144-146
  10. Bester, M.N. (1981) Seasonal changes in the population composition of the fur seal Arctocephalus tropicalis at Gough Island. South African Journal of Wildlife Research, 11: 49-55.
  11. Kerley, G.I.H. (1983) Comparison of seasonal haulout patterns of fur seals Arctocephalus tropicalis and A. gazella on Subantarctic Marion Island. South African Journal of Wildlife Research, 13: 71-77.
  12. Georges, J-Y. and Guinet, C. (2000) Maternal care in Subantarctic fur seals on Amsterdam Island. Ecology, 81(2): 295-308.
  13. Kirkman, S.P., Bester, M.N., Hofmeyr, G.J.G., Pistorius, P.A. and Makhado, A.B. (2002) Pup growth and maternal attendance patterns in Subantarctic fur seals. African Zoology, 37: 13-19.
  14. 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. Status Survey and Conservation Action Plan. IUCN, Gland, Switzerland.
  15. Wynen, L.P., Goldsworthy, S.D., Guinet, C., Bester, M.N., Boyd, I.L., Gjertz, I., Hofmeyr, G.J.G., White, R.W.G. and Slade, R.W. (2000) Post sealing genetic variation and population structure of two species of fur seals (Arctocephalus gazella and A. tropicalis). Molecular Ecology, 9: 299-314.
  16. Learmonth, J.A., Macleod, C.D., Santos, M.B., Pierce, G.J., Crick, H.Q.P. and Robinson, R.A. (2006) Potential effects of climate change on marine mammals. Oceanography and Marine Biology: An Annual Review, 44: 431-464.
  17. Tristan da Cunha Conservation Ordinance (May, 2010)
    http://www.tristandc.com/wildordinance.php