Encyclopedia of Earth

South African fur seal

October 9, 2011, 9:46 pm
Content Cover Image

South African fur seals on Geyser Rock, Dyer Island, South Africa. Source: Klaus Jost

The South African fur seal (also Also known as the Cape fur seal, Australian Fur Seal; scientific name: Arctocephalus pusillus) 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 South African fur seal is considerably larger than the female.

Like other fur seals, the South African fur seal was long hunted for its skin and oil but is, today, largely protected.

Arctocephalus pusillus has two sub-species:

  • Arctocephalus pusillus pusillus (Cape fur seal - located on southern and southwestern coast of Africa
  • Arctocephalus pusillus doriferus (Australian fur seal) - located on southern and southeastern coasts of Australia, including Tasmania

 

caption South African fur seal. Source: Petr Baum/BioLib/Encyclopedia of Life

 

Conservation Status

 

Scientific Classification

Kingdom: Animalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Carnivora (Carnivores)
Family:-------- Otariidae (Eared Seals)
Genus:--------- Arctocephalus (Southern fur seals)
Species:-------- Arctocephalus pusillus (Schreber, 1775)

Common Names:
Australian fur seal
Cape fur seal
South African fur seal
Tasmanian fur seal
Brown fur seal
Giant fur seal

Physical Description

Males of the South African or cape fur seal subspecies, A. p. pusillus, are an average of 2.3 meters in length and weigh from 200 to 350 kg. Their coat is gray or black in color and is lighter on the underside. Female African fur seals are smaller, weighing an average of 120 kg and measuring an average of 1.8 meters long. Their coats are brown with lighter shading on the underside.

Males of the subspecies A. p. doriferus, the Australian fur seal, weigh anywhere from 218-360 kg and are 2-2.2 meters in length. Their coats are a gray-brown and they have a thick mane about their neck region which is slightly lighter. Female Australian fur seals vary greatly in size, weighing between 36 and 110 kg and measuring between 1.2 and 1.8m in length. Their coat is a silver-gray with a yellow colored throat and brown underside.

Skull characteristics of the two subspecies are similar enough to place them in one species. A notable difference between the two is the crest between the mastoid process and the jugular process of the exoccipital, which is proportionately larger in Arctocephalus pusillus.

Reproduction

The breeding season for both subspecies of the South African fur seal begins in the middle of October. At this time males haul out on shore at the breeding grounds, or rookeries, to establish territories by displays, sparring, or actual battle. They do not eat again until they mate in November or December.

Females come ashore slightly later and also fight amongst each other for smaller territories in which to give birth. Female territories are always within male territories and females who are located on a certain male's territory become part of his harem. While harem sizes of both subspecies can reach as many as 50 females, or cows, the average size of the South African fur seal harem is 28 cows, the Australian fur seal harem averages 10 cows. Breeding occurs between the male and each of his harem members. While copulation occurs about 6 days after cows give birth to a single pup there is a delay in implantation of the blastocyst. In South African fur seals this delay is approximately 4 months while in Australian fur seals it is about 3 months. Gestation in both subspecies averages 11.75 months.

South African fur seal pups are anywhere from 4.5 to 7 kg and 60-70 cm at birth, which occurs in late November or early December. The pups go through two different molts in their first year and a half. Their original coat is black and curly. This coat is replaced between 4 and 5 weeks with an olive-gray coat. The second molt takes place at about 13 months and replaces the olive-gray coat with a silver one which later fades in color.

Nursing in this subspecies begins immediately after birth and is continuous for the first six days. At this time the mother mates with her male harem leader and then begins going out to sea for food for a few days at a time. By the second month, however, she can be gone for up to two weeks before returning to feed the pup.

At four to five months old pups begin supplementing their diet with crustaceans and fish. Lactation does continue, however, until the next pup is born. Pups begin swimming early and continually increase the amount of time that they can spend in the water. At seven months they can swim for two or three days at a time (King, 1983). Females become sexually mature at about 3 years and males may also follow this trend but are unable to establish territory at this time so do not usually mate until several years later.

Australian fur seal pups weigh 4.5 to 12.5 kg and measure 62-80 cm in length at birth. They are a silver-gray in color and their entire ventral side is yellow. Pups in this subspecies are usually born in early to middle December. As in South African fur seals, nursing begins right after birth and is continuous for the first week or so, until the mother mates again and goes out to sea for food. At this time, however, the Australian fur seal returns once every week to feed her pup.

By the eighth month of life Australian fur seals are eating some solid supplements although lactation continues until the next pup is born. The pups start swimming for prolonged periods also at the eighth month.

Sexual maturity is widely varied within the subspecies. Females reach maturity any time between 3 and 6 years of age. Males probably reach maturity between four and five years of age but cannot hold a harem until they are closer to seven or eight years old.

Behavior

Groups of seals that share a rookery every year are called colonies. South African fur seal colonies range in size from 500-3000 bulls, although some have been spotted with over 3000. Australian fur seals colonies tend to range in size from 500-1500.

Neither subspecies of the South African fur seal migrates and they never fully evacuate the rookeries since the mothers and pups return to them throughout the year. For most of the year, however, they are at sea. During this time they often travel in small feeding groups. While there is no record of established dispersal some seals have been found in other colonies. There are no true boundaries between colonies, as they all travel separately throughout the year until the breeding season.

During the breeding season both subspecies are polygynous but males do not herd the females, who are free to choose their own mates and do so by the value of their territory. In Australian fur seals 82% of the copulations in one breeding season were by males whose harems were located directly on the water.

Both subspecies have 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. It is suggested that she uses smell, not sight, to distinguish her pup from the others. Pups, when alone, stay in groups and play during the evenings.

 

caption Distribution of the South African fur seal. Dark blues indicates breeding locations, light blue indicates non-breeding locations. African and Australian distributions are also distinct subspecies. Source: Mirko Thiessen/Wikipedia.

 

Distribution

The subspecies Arctocephalus pusillus pusillus can be found along the southern and southwestern coast of Africa. They are commonly spotted throughout Namibia and as far east as Port Elizabeth.

The subspecies Arctocephalus pusillus doriferus can be found along the southern and southeastern coasts of Australia. They are commonly spotted in places like Victoria, New South Wales, Tasmania and scattered islands.

Habitat

Both subspecies of the South African fur seal spend most of their year at sea but not too far from land. A maximum of 160 km from land is recorded but is not a common (King, 1983). Breeding occurs on the mainland or small islands in the sand or rocks (King, 1983). Both subspecies prefer small rocky islands for mating and pupping.

Food Habits

Stomach contents of South African fur seals indicate that fish make up about 70% of their diet, squid 20%, crab 2%. The remaining portion is composed of other crustaceans, cephalopods and sometimes birds. Australian fur seals commonly eat squid, octopus, fish and lobsters, along with other crustaceans and cephalopods.

Like most air-breathing marine mammals, the South African fur seal finds its food in the ocean. In order to do so it must store oxygen and swim below the surface to the depth at which its particular prey is located. Both subspecies of the South African fur seal dive for their food but they each occupy different depth niches in their respective locations. South African fur seals are surface divers with an average dive of about 45 meters and 2.1 minutes although they can dive as deep as 204 meters and for as long as 7.5 minutes when necessary. While there is extensive overlap, Australian fur seals generally feed at a much lower depths. Their average dive is about 120 meters and they commonly go as deep as 200 meters.

Conservation Status

South African fur seals are more abundant than are Australian fur seals. Both are at the mercy of poachers, even though there are legal hunting seasons for South African fur seals. Much of the poaching danger is in the form of fishermen and large fishing corporations who believe the seals to be jeopardizing their livelihood by stealing from their nets. While this does occur it is believed to be exaggerated by those in the fishing industry.

Humans are also inadvertently threatening these seals through pollution. Plastic, pieces of netting, and pieces of fishing line kill or injure thousands of these seals a year.

Non-human threats include killer whales and white sharks. Stingrays can cause some dangerous injuries. Pups left on the mainland are also sometimes taken by terrestrial predators, such as the black-backed jackal in South Africa.

Economic Importance for Humans

Sealing has been common for centuries. Seals are taken for their pelts, their blubber, or their meat. Currently there are seasons for hunting different classes of the South African fur seal, but this is controversial. Seal pups are valued for their softer fur and male genitalia is taken and sold as an aphrodisiac. The Australian fur seal is protected and is not legally hunted by humans today, although it was hunted for meat in the past.

Further Reading

  • Arctocephalus pusillus Encyclopedia of Life (accessed April 5, 2009)
  • Arctocephalus pusillus,Hiller, C., 2002, Animal Diversity Web (accessed April 3, 2009)
  • South African Fur Seal,Catalogue of Life (accessed November 24, 2009)
  • South African 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
  • South African fur seal, MarineBio.org (accessed April 4, 2009)
Glossary

Citation

Life, E. (2011). South African fur seal. Retrieved from http://www.eoearth.org/view/article/51cbeee87896bb431f69b1a6

0 Comments

To add a comment, please Log In.