Mundo Azul

Southern Fur seal, Punta San Juan (© Jean Pichon / Mundo Azul)

Family: Otariidae

Specie: Arctocephalus australis (Zimmermann 1783)

Common names:

Spanish: Lobo fino sudamericano, lobo marino, lobo fino austral, lobo de dos pelos, oso marino, lobo marino peletero sudamericano

English: Southern fur seal

French: Otarie d'Amérique du Sud

German: Südliche Pelzrobbe

The genus name Arctocephalus derives from the Greek words arktos ("bear") and kephale ("head"). Fur seals are characterized by a more pointed muzzle, longer foreflippers, and a thick, luxuriant coat. Their waterproof underfur is covered with longer "guard" hairs, often giving them a somewhat grizzled appearance. In addition, most Fur seals are smaller than Sea lions.

Pelaje del lobo fino

Adult males reach an average length of 1.9 meters and a mass of 150 - 200 kg. Their fur is blackish gray, with a mane of long guard hairs on the shoulder and neck area. The build of the male is proportionally broader in the shoulders than the female. Adult females average about 1.4 meters in length and a mass of 30 - 60 kg. Female and sub-adult fur is grayish black on the back and lighter on the ventral side. Newborn pups are all black. In general, these seals have a stocky build with a flat-topped, pointed muzzle and creamy white vibrissae. Ear pinnae are prominent. Dental formula 3/2, 1/1, 6/5.

Southern fur seals have an estimated lifespan of 25 - 30 years for females and 15 - 20 years for males.

Distribution

In the Atlantic Ocean, the state of Sao Paulo in Brazil (Recife dos Tôrres - 29°21'S) is the northern distribution limit of the species.

Reproduction colonies are located in:

Distribution area of the Southern Fur Seal

The islands of Uruguay
Coastal areas and islands of the provinces of Chubut, Santa Cruz and Tierra de Fuego in Argentina
On the Falkland Islands

Along the Southern Pacific there are also small concentrations of the species in Chile and Peru.

The abundance of Fur seals in Central and Southern Chile from Chiloe Island (42°00'S) to Los Estados Island (54°45'S) are relatively low. The main part of the Chilean population is located in northern Chile, between Punta Paquica and Rocas Abato (23°05'S). The distribution of the species continues from Chile to central Peru. Mazorca Island is the northern distribution limit of the reproductive area. Sometimes however, Fur seal specimens can be observed up north to the coast of Ecuador.

Population size

There is no exact information about the size of the population for the biggest part of the distribution area. The most recent estimates signal a total population of 350,000 to 450,000 specimens, including:

Peru(1999): 8,000
Chile (1997): 104,000
Falkland Islands: 17,000 - 19,000
Argentina: 20,000
Uruguay: 280,000 - 310,000

There are no reproduction colonies in Brazil.

There is also little knowledge about the tendencies in population growth of the species in Peru, however, the population was dramatically reduced by the last strong El Niño event in 1997/98 (from around 25,000 in 1997 to 6,000 in 1998 - IMARPE unpublished data).

Ecology

Fur seals spend the biggest part of their life in the water, while feeding and traveling between feeding areas and reproduction sites. It seems that the distribution and abundance of Fur seals is determined by the presence of their prey. Generally, they stay in shallow water areas (< 50 meters) and along the limit of the continental shelf where the highest fish concentrations can be found.

On land, their distribution is limited by the level of isolation or, in other words, by the level of disturbance that occurs. Generally, the Fur seals concentrate on inaccessible areas like islands or at the base of coastal cliffs. They are able to climb steep walls in order to rest high up in the cliff.

Along the pacific coast of South America, the animals tend to stay close to the reproduction colonies all year long. Generally, spoken females do not abandon the area while males are known to undertake long distance migrations outside the reproductive period. Nevertheless, during El Niño events, when the cold pacific water heats up and fish disappears, massive migrations of Fur seals occur southwards, frequently resulting in long term changes of the locations of breeding sites.

For Southern fur seals, sexual maturity is reached at 3 years for females and seven years for males. Females begin estrus usually 6 -8 days after they give birth and, though all will mate, only about 15% will give birth the next year if they are nursing a pup. After mating, implantation is delayed for 4 months. Total gestation time averages 11.75 months. Litter size is limited to one pup. Reproduction is synchronous in rookeries, with a peak birthing period at a time of peak food availability. If rearing takes longer than a year, a second pup will be born, resulting in competition for the mother's milk. After birth, the pup is nursed for 7 months to 3 years, depending on environmental conditions. Lactation period may vary and can overlap with pregnancy, resulting in energetic costs that are paid by a smaller young being born. It can also result in successful births only occuring every few years, rather than yearly. This phenomenon is unique for "Arctocephalus australis" among otariids. In addition, an Uruguayan study showed a significant difference in pregnancy rates in "Arctocephalus australis" from year to year, indicating that both environmental and demographic stochasticity play a role in population dynamics.

Pups are born throughout November and December along the Uruguayan coast and a bit earlier in Peru. Pups' average weight is 3-5 kg. Studies have shown that females that lactate during pregnancy give birth to smaller young. Growth rates of young are slow, varying between 0.05 - 0.09 kg/per day. The average pup length at birth is 60-65 cm for males, 57-60 cm for females. Females reach full size in ten years. Both male and female pups are born with a dark coat of fur but as they mature, females develop lighter coloration ventrally.

Mortality of pups can be caused by maternal aggression during times of movement to or from the water and is considered to be higher than in other species of otariids (10 - 48%). Death can also be caused by aggressive males or by males of South American Sea lions, Otaria byronia. However, South American fur seals have an overall high survival rate for young adults.

Bulls establish breeding territories, approximately 50 square meters in area. Although they try to herd females and create harems, females typically move about freely. Dominant males are more successful at mating with more females. Non-breeding males are pushed to a separate part of the rookery, closer to the ocean. There, the younger males will engage in mock territorial battles.

Pup rearing is done by the mother, with no help from the male. After birth, the mother will remain with the pup for 5 to 10 days before leaving to forage. Mothers will alternate between average foraging trips of 4 to 6 days and nursing their young for 1 to 3 days.

Southern fur seals are social mammals. These seals form rookeries on rocky coasts, where breeding takes place. Competitive interactions between this species and South American Sea lions, "Otaria byronia", are rare because their habitats don't overlap.