South American fur seal
South American fur seal. Wayne Dumbleton
The South American fur seal (scientific name: Arctocephalus australis) 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 American fur seal is considerably larger than the female.
Like other fur seals, the South American fur seal was long hunted for its skin and oil and is now largely protected.
There are two to four subspecies. Two are widely recognized and differentiated by size and distribution.
- Arctocephalus australis gracilis - larger - mainland South America
- Arctocephalus australis australis - smaller - Falkland Islands and South Georgia
Two others are more commonly seen as serate species, though some recently consider them as subspecies (Brunner, Society for Marine Mammalogy)
- Arctocephalus australis galapagoensis - Galapagos fur seal though considered by many to be its own distinct species (Arctocephalus galapagoensis)
- Arctocephalus australis forsteri - New Zealand fur seal though considered by many to be its own distinct species (Arctocephalusforsteri)
Here, the Galapagos fur seal and the New Zealand fur seal are treated as separate species though as noted, this is not universally accepted.
 South American fur seal. Source: Wikipedia |
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Conservation Status  |
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Scientific Classification Kingdom: Anamalia (Animals) |
Contents
Physical Description
Adult males reach an average length of 1.9 meters and 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 subadult 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.
Reproduction
In the austral spring (October – December) 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 territory battles.
For South American fur seals, sexual maturity is reached at 3 years for females and 7 years for males.
Females begin estrus usually 6 to 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 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, 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, a study in Uruguay showed South American fur seals to have an overall high survival rate for young adults.
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 4.6 days and nursing their young for 1.3 days.
Lifespan/Longevity
South American fur seals have an estimated lifespan of 25 to 30 years for females and 15 to 20 years for males.
Behavior
South American 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 lion, Otaria byronia, occur but are rare because their habitats don’t significantly overlap. Females remain in the rookery year-round, but not much is known about the movements of males and sub-adults. Groups of 15 – 20 seals have been observed travelling together offshore, where they compose rafts of animals. They frequently groom while floating on the surface. A satellite telemetry study of females showed that a shift in foraging behavior occurred throughout the year. When pups were still young, mothers stayed close, returning daily from foraging for food. As the pups grew, the forays were extended in distance and time. During the breeding season, males compete more for territorial areas than for individual females. In tropical parts of their range, the seals are forced to move between the rookery and the ocean to cool off. The frequent movement of females is a reason that many pups are displaced and become victimized by other aggressive females. In a 1988 study in Peru, it was found that play was an important part of growing for pups, but involved large costs. Though 6.1% of the daily time budget of pups was involved with play, 84.6% of those preyed upon by sea lions were killed while at play.
Distribution of the South American fur seal. Source: Mirko Thiessen/Wikipedia. Distribution
Neotropical ocean coasts; ranges from southern Peru (Paracas Peninsula) south to Cape Horn on the Pacific side, and northward to southern Brazil on the Atlantic side.
Also found in the Falkland Islands, Staten Island, Chile, and Escondida Island.
There are two subspecies considered here, based on size and range.
- Arctocephalus australi gracilis, the more widespread of the two, occurs throughout the entire range along the mainland.
- The smaller subspecies, Arctocephalus australis australis, inhabits the Falkland Islands. Recently, a population on South Georgia Island was determined to also be A. australis australis.
See separate articles on Galapagos fur seal and the New Zealand fur seal for the distribution of these seals which are considered by many to also be subspecies of the south American fur seal.
Habitat
South American fur seals apparently prefer rocky shores and islands, especially those with lots of vertical slope. This provides shady areas for them to escape the heat of the sun. During a given day there may be movement from drier rocks to areas close to the sea or in tide pools. They have been found in sea caves in Peru, where some climb up to 15 meters to find a spot to rest. Not much is known about their movements at sea, but a recent study with satellite telemetry has discovered that females will travel 15 to 200 km when foraging at sea.
Predators
South American fur seals are important members of the ecosystems in which they live. They are important predators on fish species and other marine organisms, and are preyed on by the largest predators in these oceans, such as great white sharks (Carcharodon carcharias), orcas (Orcinus orca), South American sea lions (Otaria byronia), and by humans. Their large size will protect them from many, smaller predators.
Food Habits
The diet consists of anchovies, sardines, and mackerel, along with cephalopods, crustaceans, bivalve mollusks, and gastropods. South American fur seals usually forage at night and will dive for 3 minutes to an average depth of 29 meters, but will reach a maximum time of 7 minutes and 170 meters in pursuit of food. Numbers of anchovy can fluctuate abruptly in the Pacific Ocean, where El Nino events occur every 2 – 7 years. This will affect reproductive success of females.
Conservation Status
The population of South American fur seals in 1999 was estimated at 390,000, a drop from a 1987 estimation of 500,000. Although overall species numbers are healthy, the downward trend is causing some concern. Uruguay has the largest numbers of seals along its coast, numbering over 200,000. Peru’s number dropped to only 40 in the 1940’s, but subsequent protection has brought the numbers back up to about 20,000 by the 1980s. Because of the El Nino events and general overfishing along the Pacific coast of South America, the population in the Pacific is not recovering as quickly as it could. Presently, Peru has had a problem with fishermen illegally killing South American fur seals, claiming that the seals interfere with fishing operations and diminish the anchovy numbers. In the Falkland Islands, where commercial hunting greatly reduced their numbers, the population now contains about 15,000 seals. There are approximately 40,000 seals in Chile and 3,000 in Argentina. Arctocephalus australis is on appendix 2 of the CITIES.
Economic Importance for Humans
South American fur seals have been hunted for centuries, both by indigenous peoples and by whalers. Early peoples in the area of Tierra del Fuego, as well as in Uruguay and Peru, used the seal for meat and clothing. Commercial hunting of these seals began in Uruguay as early as the 1500s, mainly for their skins and oil. The oil was used for lighting and later as a medicinal for tuberculosis. Hunting pressure was unregulated until the 1940s, when a population decline in Uruguay was evident. Since then, take has had an annual limit, which now is about 7,000 – 12,000 seals, limited to young males. In Peru, commercial hunting of these fur seals continued until 1959, when it was prohibited. In Chile and Argentina, the seals were hunted and used for bait to catch king crab. Today, commercial hunting is only done in Uruguay.
Fishermen may complain that these fur seals compete with them for valuable fish, such as mackerel and sardines, though their true impact on fisheries is likely to be negligible.
Further Reading
- Arctocephalus australis (Zimmermann, 1783) Encyclopedia of Life (accessed April 3, 2009)
- Arctocephalus australis, Swolgaard, C. 2002, Animal Diversity Web (accessed April 3, 2009)
- South American Fur Seal, Catalogue of Life (accessed November 24, 2009)
- South American 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 American fur seal, MarineBio.org (accessed April 4, 2009)
- Brunner, S. 2004. Fur seals and sea lions (Otariidae): identification of species and taxonomic review. Systematics and Biodiversity 1:339—439.
- Committee on Taxonomy. 2009. List of marine mammal species and subspecies. Society for Marine Mammalogy, www.marinemammalscience.org, consulted on May 17, 2011.
- Couturier, L. 1996. Seal of approval. Wildlife Conservation, 99: 44-49,64.
- Daneri, G., C. Esponda, L. deSantis. 1997. A record of Arctocephalus australis (Zimmerman, 1783) (Carnivora, Otariidae) south of the Antarctic Convergence. Mammalia, 61: 451-454.
- Harcourt, R. 1991. Maternal aggression in the South American fur seal in Peru. Can. J. Zool., 70: 320-325.
- Harcourt, R. 1991. Survivorship costs of play in the South American fur seal. Animal Behaviour, 42: 509-511.
- Harcourt, R. 1992. Factors affecting early mortality in the South American fur seal (Arctocephalus australis) in Peru: density –related effects and predation. J. Zool., Lond., 226: 259-270.
- Harcourt, R. 1993. Individual variation in predation on fur seals by southern sea lions (Otaria byronia) in Peru. Can. J. Zool., 71: 1908-1911.
- Marine Mammals of the World: A Comprehensive Guide to Their Identification, Jefferson, M. Webber, and Pittman, R. Academic Press, 2007 ISBN: 0123838533
- Lima, M., E. Paez. 1995. Growth and reproductive patterns in the South American fur seal. J. Mammalogy, 76: 1249-1255.
- Lima, M., E. Paez. 1997. Demography and population dynamics of South American fur seals. J. Mammalogy, 78: 914-920.
- Majluf, P. 1992. Timing of births and juvenile mortality in the South American fur seals in Peru. J. Zool., Lond., 227: 367-383.
- Grzimek’s encyclopedia: mammals, vol. 4. Grzimek, B and Parker, S., McGraw-Hill, 1990 ISBN: 0801873436
- Phillips, A., I. Stirling. 2000. Vocal individuality in mother and pup South American fur seals, Arctocephalus australis. Marine Mammal Science, 16: 592-616.
- Trillmich, F. 1990. The behavioral ecology of maternal effort in fur seals and sea lions. Behaviour, 114: 3-20.
