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Arctocephalus tropicalisSubantarctic fur seal

By Hannah Walsh

Geographic Range

Subantarctic fur seals (Arctocephalus tropicalis) inhabit the Southern Hemisphere. They breed on islands north of Antarctica, including Amsterdam, the Crozets, Gough, Macquarie, Prince Edward, Saint Paul, and Tristan da Cunha islands. However, vagrant subantarctic fur seals have been recorded in South America, South Africa, and Australia, with the northernmost sighting off the Mayumba National Park in central Africa. (Hofmeyr and Kovacs, 2011; Zanre and Bester, 2011)

Habitat

Males spend the winter season out at sea, coming to shore in the spring to breed. Females with dependent young return to land from foraging trips at intervals throughout the year to feed their offspring. In the summer, females spend approximately 6 to 10 days at sea during a single foraging trip, and in winter foraging bouts increase to approximately 23 to 28 days. Between foraging trips, females spend about 4 days on land with pups. Subantarctic fur seals prefer rocky beaches with abundant boulders and shade. Adults can dive an average of 16 to 19 m deep in waters above 14 degrees Celcius for up to 4 minutes. (Georges, et al., 2000; Hofmeyr and Kovacs, 2011)

  • Range depth
    100 (high) m
    328.08 (high) ft
  • Average depth
    19 m
    62.34 ft

Physical Description

Males range from 70 to 165 kg and can grow up to 1.8 m in length. Females weigh between 25 and 67 kg and range from 1.19 to 1.52 m in length. Males have a chocolate brown to black back and a yellow chest and face. There is a crest of black fur on the head that is erected when the animal becomes excited. Females have dark gray or chocolate brown dorsal fur and pale yellow fur on their chest, neck, and face. At birth, pups are black with a chocolate brown underside. Both sexes have long, white vibrissae and external ear flaps. (Hofmeyr and Kovacs, 2011; Strahan, 1995)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • Range mass
    25 to 165 kg
    55.07 to 363.44 lb
  • Range length
    1.2 to 1.8 m
    3.94 to 5.91 ft

Reproduction

Subantarctic fur seals are polygynous with a harem mating system in which males defend territories containing from 6 to 20 females. Males come to shore in October and compete for territories; they will defend their territory and harem until all of the females have been mated. (Bester, 1990; Strahan, 1995)

Offspring are born in the southern spring and summer (October through January). Mating occurs once per year, approximately 8 to 12 days after parturition. Males are fertile only during this time, conserving energy during the winter by ceasing sperm production throughout the off season. A female gives birth to one offspring per season after a gestation period of 51 weeks. Although there are documented cases of a female successfully rearing twins, this is a rare occurrence.

Subantarctic Fur Seal pups are born weighing between 4 and 6 kg. Male pups grow faster, and have a higher weaning weight than females. Mothers nurse pups until 11 months of age, shortly before giving birth to their next pup. In males, puberty is reached at 3 to 4 years of age, but full adulthood is not achieved until 10 to 11 years of age, when males are first able to acquire a harem. Females are sexually mature at approximately 5 years of age. (Bester and Kerley, 1983; Bester, 1990; Hofmeyr and Kovacs, 2011; Strahan, 1995)

  • Breeding interval
    Subantarctic fur seals breed once per year.
  • Breeding season
    Mating occurs from October through January.
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    51 weeks
  • Average gestation period
    357 days
    AnAge
  • Average weaning age
    11 months
  • Average age at sexual or reproductive maturity (female)
    5 years
  • Range age at sexual or reproductive maturity (male)
    10 to 11 years

Female subantarctic fur seals nurse their offspring for 11 months, leaving to forage at regular intervals. Upon returning to shore, females must find their pup among the hundreds located at the rookery. Each pup has a unique vocal signature that the female uses to locate her offspring; once the pup is found, she uses sight and smell to verify its identity before allowing it to suckle. Recognition of offspring is essential to prevent her from feeding the wrong pup. Males leave the rookery after each female is mated and do not return to assist in parental care. (Bester, 1990; Charrier, et al., 2002; Hofmeyr and Kovacs, 2011)

Lifespan/Longevity

There is little information available about the lifespan of subantarctic fur seals either in captivity or in the wild. However, studies have recorded reproductive females living up to 16 years, and non-reproductive females up to 19 years. Even less is known about male longevity. In a related species, the New Zealand fur seal, males can live to 15 years of age. (Dabin, et al., 2004; McKenzie, et al., 2007)

  • Range lifespan
    Status: wild
    16 to 19 years

Behavior

Adult female subantarctic fur seals spend much of their time providing for their offspring. After giving birth to a pup, females alternate foraging at sea with coming ashore to nurse their offspring. Prior to weaning, pups remain at the rookery. They spend time both on land and in the water; however as they age, pups spend less time diving. This is because as females spend more time foraging, pups have to wait longer between feedings, and therefore have less energy as the year progresses. As they grow, pups are able to dive progressively deeper into the water. (Bester and Rossouw, 1994; Guinet, et al., 2005; Hofmeyr and Kovacs, 2011)

Males spend much of the year at sea or at idle colonies with other males, hauling out onto breeding territories in early summer to mate. While on land, males display little activity outside of breeding season. The activity pattern of non-breeding males is largely dependent on environmental temperature. Subantarctic fur seals are poor thermoregulators, because of their thick blubber. As such, when ambient temperatures become high, seals have to adjust their behavior in order to cope. When the surrounding temperatures are under 18.5 degrees Celsius, males are nocturnal; during which time they leave the land to forage in the evening, and return in the late-morning. However, when the ambient temperatures are higher, their activity pattern becomes diurnal; they leave the land at midday when temperatures are high, cooling themselves in the water, and haul out in the evening to rest. During the breeding season, males come to shore and compete for territories using vocalizations, threat displays, and physical fights. (Bester and Rossouw, 1994; Guinet, et al., 2005; Hofmeyr and Kovacs, 2011)

Home Range

The distances traveled by foraging female subantarctic fur seals vary by season. Foraging distances of up to 600 km from the rookery occur during the summer; these increase to up to 1800 km from the shore during the winter. This increase in foraging distance from summer to winter coincides with an increase in the amount of time females spend at sea. (Beauplet, et al., 2004)

Communication and Perception

A female uses auditory communication to find and identify her pup when she hauls out to nurse. She emits a "contact call" to which hundreds of pups respond; she must then distinguish her offspring from the rest. Each pup has a unique call that is recognized by the mother. The mother uses sight and smell to a lesser extent to verify the pup’s identity before nursing. Males utilize auditory, visual, and tactile communication while competing for breeding territories. They use vocalizations, postural dominance and threat displays, as well as participating in physical fights. (Charrier, et al., 2002; Hofmeyr and Kovacs, 2011)

Food Habits

Subantarctic fur seals feed on a variety of marine animals including myctophid and notothenid fish, cephalopods, crustaceans, and sometimes even rockhopper penguins. (Hofmeyr and Kovacs, 2011)

  • Animal Foods
  • birds
  • fish
  • mollusks
  • aquatic crustaceans

Predation

Subantarctic fur seals are known to be preyed upon by killer whales and sharks. Because of relatively large population sizes, predation does not present a major threat to subantarctic fur seal populations. (Reisinger, et al., 2011; Souto, et al., 2009)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Subantarctic fur seals are an important food source for sharks and orcas, and a key predator of myctophid, notothenid fish, cephalopods, crustaceans, and rockhopper penguins. (Hofmeyr and Kovacs, 2011; Reisinger, et al., 2011; Souto, et al., 2009)

Economic Importance for Humans: Positive

In the 18th and 19th centuries, subantarctic fur seals were hunted to the brink of extinction for their pelts. Today, due to measures taken by local governments, the seals are protected on preserved land. Subantarctic fur seals are of potential interest to tourists, however tourism is relatively rare in the remote locations that seals inhabit. (Hofmeyr and Kovacs, 2011)

  • Positive Impacts
  • body parts are source of valuable material
  • ecotourism

Economic Importance for Humans: Negative

There are no known adverse effects of subantarctic fur seals on humans.

Conservation Status

Although the population of subantarctic fur seals are currently stable or growing, with a total of over 310,000 individuals, there are several factors that could put this species at risk. After a large population decline during the 18th and 19th centuries, the current population is the product of a severe bottleneck that reduced genetic diversity. A loss of genetic diversity of this magnitude can make a population especially vulnerable to disease and other environmental perturbations, such as climate change. (Hofmeyr and Kovacs, 2011)

Contributors

Hannah Walsh (author), Michigan State University, Barbara Lundrigan (editor), Michigan State University, Laura Podzikowski (editor), Special Projects.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

References

2012. "CITES" (On-line). Accessed April 19, 2012 at http://www.cites.org/eng/app/appendices.php.

Beauplet, G., L. Dubroca, C. Guinet, Y. Cherel, W. Dabin. 2004. Foraging ecology of subantarctic fur seals Arctocephalus tropicalis breeding on Amsterdam Island: seasonal changes in relation to maternal characteristics and pup growth. Marine Ecology Progress Series, 273: 211-225.

Bester, M. 1990. Reproduction in the male sub-Antarctic fur seal Arctocephalus tropicalis. Journal of Zoology, London, 222: 177-185.

Bester, M., G. Kerley. 1983. Rearing of twin pups to weaning by sub-Antarctic fur-seal Arctocephalus tropicalis female. South African Journal of Wildlife Research, 13: 86-87.

Bester, M., G. Rossouw. 1994. Time budgets and activity patterns of sub-Antarctic fur seals at Gough Island. South African Journal of Zoology, 29 (2): 168-174.

Charrier, I., N. Mathevon, P. Jouventin. 2002. How does a fur seal mother recognize the voice of her pup? An experimental study of Arctocephalus tropicalis. The Journal of Experimental Biology, 205: 603-612.

Dabin, W., G. Beauplet, E. Crespo, C. Guinet. 2004. Age structure, growth, and demographic parameters in breeding-age female Subantarctic fur seals, Arctocephalus tropicalis. Canadian Journal of Zoology, 82 (7): 1043-1050.

Georges, J., F. Bonadonna, C. Guinet. 2000. Foraging habitat and diving activity of lactating Subantarctic fur seals in relation to sea-surface temperatures at Amsterdam Island. Marine Ecology Progress Series, 196: 291-304.

Guinet, C., N. Servera, T. Deville, G. Beauplet. 2005. Changes in subantarctic fur seal pups' activity budget and diving behaviours throughout the rearing period. Canadian Journal of Zoology, 83 (7): 962-970.

Hofmeyr, G., K. Kovacs. 2011. "Arctocephalus tropicalis" (On-line). IUCN Red List of Threatened Species. Accessed April 14, 2012 at http://www.iucnredlist.org/apps/redlist/details/2062/0.

McKenzie, J., B. Page, M. Hindell. 2007. Age and reproductive maturity of New Zealand fur seals (Arctocephalus forsteri) in Southern Australia. Journal of Mammalogy, 88 (3): 639-648.

Reisinger, R., P. de Bruyn, M. Bester. 2011. Predatory impact of killer whales on pinniped and penguin populations at the Subantarctic Prince Edward Islands: fact and fiction. Journal of Zoology, 285: 1-10.

Souto, L., J. Abrao-Oliveira, R. Maia-Nogueira, L. Dorea-Reis. 2009. Interactions between subantarctic fur seal (Arctocephalus tropicalis) and cookiecutter shark (Isistius plutodus) on the coast of Bahia, north-eastern Brazil. Marine Biodiversity Records, 2: 1-2.

Strahan, R. 1995. Mammals of Australia. Washington DC: Smithsonian Institution Press.

Zanre, R., M. Bester. 2011. Vagrant Subantarctic fur seal on the Mayumba National Park, Gabon. African Zoology, 46 (1): 185-187.

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