Eared Seals
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Eared Seals (scientific name: Otariidae) are a family of sixteen species of marine mammals 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.
Scientific Classification Kingdom: Anamalia (Animals) |
Eared Seal Species
There are sixteen species of Eared seals in seven genera:
- Arctocephalus (Southern fur seals)
1. South American fur seal (Arctocephalus australis)
2. New Zealand fur seal (also Antipodean fur seal, Australasian fur seal, Black fur seal, and South Australian fur seal.) (Arctocephalus forsteri)
3. Galápagos fur seal (Arctocephalus galapagoensis)
4. Antarctic fur seal (also Kerguelen fur seal) (Arctocephalus gazella)
5. Juan Fernandez fur seal (Arctocephalus philippii)
6. South African fur seal (also Cape fur seal, Australian fur seal, Brown fur seal, Giant fur seal, Tasmanian fur seal, and Afro-Australian Fur Seal) (Arctocephalus pusillus)
7. Guadalupe fur seal (also Lower californian fur seal) (Arctocephalus townsendi)
8. Subantarctic fur seal (also Amsterdam fur seal) (Arctocephalus tropicalis) - Callorhinus (Northern fur seal)
9. Pribilof fur seal (also Northern fur seal and Alaska fur seal) (Callorhinus ursinus) - Eumetopias
10. Steller Sea Lion (also Northern sea lion, Sea king, Stellar sea lion, and Steller's sea lion) (Eumetopias jubatus) - Neophoca
11. Australian sea lion (also White-capped sea lion) (Neophoca cinerea) - Otaria
12. South American sea lion (also Southern Sea Lion, Patagonian Sea Lion, and Maned sea lion. (Otaria flavescens) - Phocarctos
13. New zealand sea lion (Phocarctos hookeri) - Zalophus
14. California sea lion (Zalophus californianus)
15. Japanese sea lion (Zalophus japonicus)
16. Galápagos sea lion (Zalophus wollebaeki)
Physical Description
Eared seals differ from true seals in that they have 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.
Eared seals show a considerable size difference between the sexes. The males are considerably larger than the female; in some instances, up to five times as large. This makes them among the most sexually dimorphous mammals.
Sea lions differ from fur seal in that they have coarse, short fur in contrast to a dense underfur characteristic of fur seal. Sea lions are also generally larger than fur seals. The Galapagos fur seal is the smallest species of eared seal and the Steller Sea Lion is the largest.
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Reproduction
Eared seals are polygynous, meaning that males will establish territories (often created and protected through fighting or shows of aggression) within which they establish a harem and breed with a number of females (the range varies with species). Males will come ashore and establish their territories at the beginning of the mating season.
Most eared seals mate annually at certain times of the year. The Australian sea lion is an exception to this with a breeding cycle of 17.6 months. Females typically arrive a few weeks after the males and select their mates for the coming season. Before mating, the females will first give birth to a pup conceived during the mating season of the prior year. Mating occurs typically 6-12 days after the birth of the pup.
The fertilized egg within the female fur seal undergoes a three to four month period of delayed implantation. This ensures that that the developing pup will be born at the right time the following year when the animals return to their breeding grounds. For the Australian sea lion the period of delayed implantation may be longer reflecting the longer duration of its breeding cycle.
Distribution
Fur seals are primarily found in the southern hemisphere. Two species, the Pribilof fur seal and Guadalupe fur seal, are found in the northern hemisphere, and a third, the Galapagos fur seal, is found on the equator. Sea lions are more broadly distributed.
Conservation Status
Six eared seal species are included in the IUCN Red List of Threatened Species, four of those, the Galapagos fur seal, Steller Sea Lion, Australian sea lion, and Galápagos sea lion are listed as Endangered. One species, the Japanese sea lion, is believed to have gone extinct in the 1950s.
- South American fur seal Least Concern
- New Zealand fur seal Least Concern
- Galapagos fur seal Endangered
- Antarctic fur seal Least Concern
- Juan Fernandez fur seal Near Threatened
- South African fur seal (Afro Australian fur seal) Least Concern
- Guadalupe fur seal Near Threatened
- Subantarctic fur seal Least Concern
- Pribilof fur seal (Northern fur seal) Vulnerable
- Steller Sea Lion Endangered
- Australian sea lion Endangered
- South American sea lion Least Concern
- New zealand sea lion Vulnerable
- California sea lion Least Concern
- Japanese sea lion Extinct
- Galápagos sea lion Endangered
Further Reading
- Encyclopedia of Life (accessed April 11,2009)
- WoRMS, World Registry of Marine Species (accessed March 28, 2009)
- IUCN Red List (accessed April 2, 2009)
- <em>Zalophus japonicus</em> Aurioles, D. & Trillmich, F., 2008, IUCN (accessed April 8, 2009)
- Zalophus, Seal Conservation Society (accessed April 8, 2009)
- MarineBio.org (accessed, April 8, 2009)
- Galápagos and Californian sea lions are separate species: Genetic analysis of the genus ''Zalophus'' and its implications for conservation management, Wolf, JB; Tautz, D; Trillmich, F, Frontiers in zoology, 2007.
- Archaeology and holocene sand dune stratigraphy on Chatham Island, B. G. McFadgen, Journal of the Royal Society of New Zealand, 1994.
- 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