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.

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:

• Cystophora
  1. Hooded seal, Cystophora cristata (Bladdernose seal)

• Erignathus
  2. Bearded seal, Erignathus barbatus (Square Flipper seal)
• Halichoerus
  3. Grey seal, Halichoerus grypus (Atlantic grey seal, Atlantic seal, Baltic gray seal, Gray seal, and Horsehead seal)
  4. Ribbon seal, Histriophoca fasciata
• Hydrurga
  5. Leopard seal, Hydrurga leptonyx
• Leptonychotes
  6. Weddell seal, Leptonychotes weddellii (Weddell's seal)
• Lobodon
  7. Crabeater seal, Lobodon carcinophaga (White Antarctic seal) 
• Mirounga (Elephant seals)
  8. Northern elephant seal, Mirounga angustirostris
  9. Southern elephant seal, Mirounga leonina
• Monachus (Monk Seals)
  10. Mediterranean monk seal, Monachus monachus (Pied monk seal)
  11. Hawaiian monk seal, Monachus schauinslandi
  12. Caribbean monk seal, Monachus tropicalis (West Indian monk seal or West Indian seal) 
• Ommatophoca
  13. Ross seal, Ommatophoca rossii
• Pagophilus
  14. Harp seal, Pagophilus groenlandicus
• Phoca
  15. Spotted seal, Phoca largha
  16. Harbor seal, Phoca vitulina (Common seal, Eastern Atlantic harbor seal, Western Atlantic harbour seal, Ungava seal, Eastern Pacific harbor seal, Western Pacific harbour seal or Kuril seal
• Pusa
  17. Caspian seal, Pusa caspica
  18. Ringed seal, Pusa hispida
  19. Baikal seal, Pusa sibirica '
  
  

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.	Grey seal. Source: Cynthia Sims Parr, Animal Diversity Web/Encyclopedia of Life	Ribbon seal. Source: M. Cameron/NOAA
Leopard seal. Source: Yan Ropert-Coudert/WoRMS/Encyclopedia of Life	Weddell sea. Source: José Luis Orgeira/WoRMS/Encyclopedia of Life	Crabeater seal. Source: Mike Cameron/NOAA	Northern elephant seal. Source: Fred Sorenson/BioLib/Encyclopedia of Life
Southern elephant seal. Source: José Luis Orgeira/WoRMS/Encyclopedia of Life	Mediterranean monk seal. Source: Giovanni Dall'Orto	Hawaiian monk seals. Source: U.S. Fish and Wildlife Service	Carribean monk seal.
Ross seal. Source: NOAA	Harp seal.	Spotted seal. Source:M. Cameron/NOAA	Harbor seal. Source: Petr Baum/BioLib/Encyclopedia of Life
Caspian seal.	Ringed 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