Antarctic Fur Seal
(Arctocephalus gazella) 

Arctocephalus gazella - Image 1

Photo: Michael Bryden,
University of Sydney

IUCN STATUS (2010) - LEAST CONCERN

 

Distribution and Numbers
The breeding range of the Antarctic fur seal, also formerly known as the Kerguelen fur seal, is restricted mainly to seasonally ice-free islands south of, or close to, the Antarctic Polar Front with over 95% of the species breeding on South Georgia. Other breeding sites, many fuelled by migrants from South Georgia, are established at South Orkney, South Shetland, South Sandwich, Bouvetiya, Heard, Marion, Macquarie, McDonald, Crozet, Prince Edward and Kerguelen Islands. The total population size was estimated as 1.5 million in 1990 but it is thought that the population may have since increased to over 4 million. Wandering seals have been found as far north as Brazil and the Juan Fernandez Islands.

Status
Antarctic fur seals were almost made extinct by commercial sealing for their fur in the 18th and 19th centuries, perhaps only a few hundred of the seals remaining, and small scale hunting continued until 1907. The species is now protected by the Convention for the Conservation of Antarctic Seals (CCAS), the Antarctic Treaty and the legislation of various countries within its range. In addition, the Antarctic fur seal is listed as an Appendix II species under CITES. Since protection, the population has been growing steadily, particularly at South Georgia since the 1950s, and population growth is now about 10% per annum.


 
A plan by Norwegian scientists to kill 20 Antarctic fur seals, as well as 60 other seals, in the summer of 2000-2001 for research into environmental contaminants was cancelled after the Norwegian government rejected the plan. Several environmental organisations had vigorously opposed the plan, questioning its necessity and also its appropriateness given the option of alternative non-lethal sampling techniques.
The importance of krill in the diet of Antarctic fur seals at South Georgia could result in the species being affected by an increased krill fishery in the Southern Ocean as well as by increased competition for krill with other marine mammal species that are now recovering from previous exploitation. The entanglement of Antarctic fur seals in man-made debris, particularly around the neck, is a problem as it can cause death by drowning or starvation. A 1988-1989 study at Bird Island, South Georgia, found 208 sightings of entanglement, the main culprits being polypropylene straps, nylon string and fishing net, indicating a figure of 5,000-10,000 fur seals entangled for the entire South Georgia population. The debris is most likely to come from marine traffic in the Southern Ocean.
In January 2000 it was reported that Chilean scientists had found Brucella antibodies in Antarctic fur seal samples and a Weddell seal sample obtained in the South Shetland Islands, the first discovery of antibodies to the serious reproductive disease Brucellosis in Antarctic seals. Unusually high levels of toxic heavy metals have also been found in Antarctic fur seals but the effects and sources of these are uncertain. Some scientists, claiming that the growing population of Antarctic fur seals is now causing environmental problems by polluting lakes and destroying plants in Antarctica, have been pushing for the downgrading of the fur seals' conservation status.
Antarctic fur seals on World Heritage listed Macquarie Island were afforded additional protection in 2000 by the creation of a new federal 16 million hectare Marine Park on the eastern side of the island. The Tasmanian government also announced in 2000 an extension to the Macquarie Island Nature Reserve to cover all Tasmanian waters out to three nautical miles surrounding the island.
Lifestyle
The breeding season takes place from November to January, the males arriving early to compete, with frequent fighting, for breeding territory that will eventually contain about 10 females. Females give birth about 2 days after arriving at the rookery and the pups are normally born in November and December with a black fur coat.
This fur moults 2-3 months later and the pups acquire a silvery-grey coat that eventually turns grey-brown to a dark gingery colour by adulthood. Adult females and juveniles often have a creamy coloured front and the occasional seal has a creamy white colour all over. The mother mates 6-8 days after giving birth and then leaves to feed at sea, usually for 3-5 days and probably at a maximum range of 150km-240km from the breeding site, before returning to shore


Photo: Rodrigo Hucke-Gaete,
Universidad Austral de Chile		  
to nurse her pup for 1-2 days. This cycle of feeding and nursing lasts about 4 months, shorter than most other eared seals. Males do not feed during their time on shore in the breeding season and lose about 1.5kg in weight per day over the 30 or so days that they are on land. There has been some cross-breeding of Antarctic and Subantarctic fur seals (Arctocephalus tropicalis) at Macquarie and Marion Islands.
   
The main food of Antarctic fur seals at South Georgia is krill but fish, squid and even some birds are also eaten, especially outside the breeding season. The BBC (Planet Earth) has filmed fur seals preying on penguins. The almost total dependence of nursing mothers on krill during the breeding season at South Georgia means that the reproductive success of these colonies is very closely linked to its local availability. Occasionally there are years in which krill abundance is poor and colonies are affected both for that season and, to a lesser extent, for the next season. The colonies at Macquarie Island and the Kerguelen Islands rely more on a diet of fish and squid. Antarctic fur seals usually dive to a depth of 30-40m for an average of about 2 minutes, diving to a shallower depth at night, when they do most of their feeding, than during the day. Leopard seals prey on some juveniles and pups, while killer whales may also be a predator.

Statistics
Adult males measure 1.6-2m in length and weigh 90-210kg (average of 188kg) while adult females are smaller at 1.2-1.4m and 25-55kg (average 37kg). Pups are born measuring 60-73cm in length and weighing 4.5-6.5kg, male pups slightly heavier than female pups. Pup mortality over the first year of life has been calculated at 24% and is greater on the denser breeding beaches. Antarctic fur seals have been known to dive for up to 10 minutes and as deep as 250m. Both sexes reach sexual maturity at 3-4 years but males do not attain territorial status until about 6-10 years. Males can live up to 15 years of age, females up to 23 years.

 

References

BBC (Planet Earth). Seals hunting penguins.

Arctocephalus gazella - Image 3

Photo: Rodrigo Hucke-Gaete,
Universidad Austral de Chile