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True seals

True seals

Published:
Updated: September 8, 2011, 7:34 pm
Topics: Oceans and seas Marine Ecology Conservation Biology Species
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This article has been reviewed by the following Topic Editor: C Michael Hogan

True seals (scientific name: Phocidae) are a family of nineteen species of marine mammals. Together with the families of Eared seals and Walruses, True seals form the group of marine mammals known as pinnipeds. Alternative names for this family are: Earless seals, Crawling seals and Phocid. seals. Collectively this family of seals is broadly distributed along the coastal waters and shorelines of the world's seas and oceans. They are carnivores, who prey chiefly upon fish and crustaceans.

Scientific Classification

Kingdom: Animalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Carnivora (Carnivores)
Family:-------- Phocidae (True Seals)

Family morphology

True seals differ from Eared seals in that they do not have external earflaps: hence the common name Earless seals.  True seals also do not have the strong front flippers and flexible hind flippers which enable Eared seals to be quite moble on land, leading to the alternative common family name, Crawling seals

While True seals are less mobile on land, they more streamlined than Eared seals and very efficient swimmers, usually capable of covering large distances. The rear flippers propel the animal through the water while the front flippers provide balance and steer.

True seals vary considerably in size from the smallest, the Ringed seal are 1.1 to 1.7 meters in length, and 45 to 100 kilograms (kg) in weight. The largest, the male Southern elephant seal, has been documented to reach over six meters long and weighing over 4,000 kg. This is in sharp contrast to the female Southern elephant seal which seldomly exceeds 800 kg or four meters in length.

Taxonomy

True seals break down into thirteen genera:

 
Hooded seal. Source:Sea Mammal Research Unit (SMRU)/WoRMS/Encyclopedia of Life. Hooded seal. Source:Sea Mammal Research Unit (SMRU)/WoRMS/Encyclopedia of Life.
Bearded seal with satellite-linked data recorder attached to it for research purposes. Source: NOAA. Bearded seal with satellite-linked data recorder attached to it for research purposes. Source: NOAA.
Grey seal. Source: Cynthia Sims Parr, Animal Diversity Web/Encyclopedia of Life Grey seal. Source: Cynthia Sims Parr, Animal Diversity Web/Encyclopedia of Life
Ribbon seal. Source: M. Cameron/NOAA Ribbon seal. Source: M. Cameron/NOAA
 
Leopard seal. Source: Yan Ropert-Coudert/WoRMS/Encyclopedia of Life Leopard seal. Source: Yan Ropert-Coudert/WoRMS/Encyclopedia of Life
 
Weddell sea. Source: José Luis Orgeira/WoRMS/Encyclopedia of Life Weddell sea. Source: José Luis Orgeira/WoRMS/Encyclopedia of Life
Crabeater seal. Source: Mike Cameron/NOAA Crabeater seal. Source: Mike Cameron/NOAA
 
Northern elephant seal. Source: Fred Sorenson/BioLib/Encyclopedia of Life Northern elephant seal. Source: Fred Sorenson/BioLib/Encyclopedia of Life
 
Southern elephant seal. Source: José Luis Orgeira/WoRMS/Encyclopedia of Life Southern elephant seal. Source: José Luis Orgeira/WoRMS/Encyclopedia of Life
 
Mediterranean monk seal. Source: Giovanni Dall'Orto Mediterranean monk seal. Source: Giovanni Dall'Orto
 
Hawaiian monk seals. Source: U.S. Fish and Wildlife Service Hawaiian monk seals. Source: U.S. Fish and Wildlife Service
 
Carribean monk seal. Carribean monk seal.
 
Ross seal. Source: NOAA Ross seal. Source: NOAA
 
Harp seal. Harp seal.
 
Spotted seal. Source:M. Cameron/NOAA Spotted seal. Source:M. Cameron/NOAA
 
Harbor seal. Source: Petr Baum/BioLib/Encyclopedia of Life Harbor seal. Source: Petr Baum/BioLib/Encyclopedia of Life
 
Caspian seal. Caspian seal.
 
Ringed seal. Ringed seal.
 
Baikal seal. Baikal seal.
 

True seals are found in many regions of the earth from the Arctic to the Antarctic and a frequently observed in coastal regions. The Hawaiian monk seal is noteworthy for its presence in tropical waters. Before it became extinct, the Caribbean Monk Seal was similarly noteworthy. The Caspian Seal is noteworthy for being endemic to an inland sea, though two subspecies of Ringed Seal, the Lagoda ringed seal and the Saimaa ringed seal have similar inland ranges.

There has been no confirmed sighting of a Caribbean monk seal since 1952, and the species is now considered extinct. The other two species of monk seal, the Mediterranean monk seal and the Hawaiian monk seal both have a conservation status of Critically Endangered  and survive in low numbers in habitat that is highly impacted by human activity. The Caspian Seal is also considered an endangered species. The conservation status of the individual species within this family is as follows:

  • Hooded seal                                 Vulnerable
  • Bearded seal                                Least Concern
  • Grey seal                                      Least Concern
  • Ribbon seal                                  Least Concern
  • Leopard seal                                Least Concern
  • Weddell seal                                Least Concern
  • Crabeater seal                             Least Concern
  • Northern elephant seal                 Least Concern
  • Southern elephant seal                Least Concern
  • Mediterranean monk seal            Critically Endangered
  • Hawaiian monk seal                   Critically Endangered
  • Caribbean monk seal                  Extinct
  • Ross seal                                   Least Concern
  • Harp seal                                    Least Concern
  • Spotted seal                                Least Concern
  • Harbor seal                                 Least Concern
  • Caspian seal                               Endangered
  • Ringed seal                                 Least Concern (ssp Lagoda and Saimaa are of concern)
  • Baikal seal                                   Least Concern


For details regarding individual species, consult the article on each individual seal.

Further Reading

  1. Encyclopedia of Life (accessed April 21,2009) 
  2. WoRMS, World Registry of Marine Species (accessed March 21, 2009)
  3. IUCN Red List (accessed April 21, 2009)
  4. Seal Conservation Society (accessed April 21, 2009)
  5.  Zalophus, MarineBio.org (accessed, April 8, 2009)
  6. The Pinnipeds: Seals, Sea Lions, and Walruses, Marianne Riedman, University of California Press, 1991 ISBN: 0520064984 
  7. Encyclopedia of Marine Mammals, Bernd Wursig, Academic Press, 2002 ISBN: 0125513402
  8. 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
  9. Walker's Mammals of the World, Ronald M. Nowak, Johns Hopkins University Press, 1999 ISBN: 0801857899

Citation

Encyclopedia of Life (Lead Author);Peter Saundry (Contributing Author);C Michael Hogan (Topic Editor) "True seals". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth July 20, 2010; Last revised Date September 8, 2011; Retrieved May 24, 2012 <http://www.eoearth.org/article/True_seals>

The Author

Encyclopedia of LifeThe Encyclopedia of Life (EOL) is an ambitious, even audacious project to organize and make available via the Internet virtually all information about life present on Earth. At its heart lies a series of Web sites—one for each of the approximately 1.8 million known species—that provide the entry points to this vast array of knowledge. The entry-point for each site is a species page suitable for the general public, but with several linked pages aimed at more specialized users. The sites spark ... (Full Bio)

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