Oceans and seas

Pinniped

Content Cover Image

Common seal. Source: François, Roland

Pinnipeds ("finned-feet") are are group of marine mammals, that includes seals, sea lions, and walruses. The word pinniped is sometimes treated as a synonym for "seal" since all pinnipeds except for the the sole species of Walrus are seals (sea lions are eared seals).

 

caption Harbor (or

 

Scientific Classification

Kingdom: Animalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Carnivora (Carnivores)
Family:-------- Otariidae (Eared seals)

Pinnipeds differ form other marine mammals like whales, dolphins and porpoises in that they do not spend their entire lives in water. Pinnipeds "haul out" onto land and ice to mate, give birth, moult, and rest.

Pinnipeds were agressively hunted until the early twentieth century for their skins, oil, meat and, in the case of walruses, their tusks. As a result of this, combined with habitat loss, and negative interactions with commercial fishing,  the populations of most pinnipeds were severely depleted and two species (Japanese sea lion and Caribbean monk seal) are now believed to be extinct, while several other species are threatened with extinction. However, laws have been passed throughout the world to protect pinnipeds and many species have made strong come backs over recent decades.

Pinnipeds includes species (two of which are considered extinct since the 1950s) in three taxonomic families:

Pinnipeds are frequently organized taxonomically as a superfamily termed pinnipedia.

The name pinniped is derived from the Latins words pinna, meaning "fin", "flap", or "wing", and ped, meaning "foot". This reflects that fact that these mammals have fins rather than the feet, hooves or paws of land mammals.

Physical Description

caption Male and female Southern Elephant seals have a pronounced difference in size. An example of

Pinnipeds are torpedo shaped with a broad middle and tapered at the head and fins. This streamlined shape combined with thick layers of blubber and a large volume of blood for their body size enable pinnipeds to move efficiently through water and capable of deep and sustained dives under water in search of food. Elephant seals regularly dive deeper that 1,000 meters and can reach 1,500 meters (one mile). These species can also regularly stay under water regularly for in excess of a hour before surfacing to breath.

Pinnipeds vary in size considerably. The smallest, Ringed seals are 1.1-1.7 meters in length, and 45 - 100 kg in weight as adults. The largest, the male Southern Elephant seal, has been documented to reach over six meters long and weighing over 4,000 kg.

Many pinnipeds exhibit huge difference between the size of males and females, sometimes males being as much as five times the size of the female. For example, in sharp contrast to the large size of male Southern Elephant seal, females are rarely over 800 kg or four meters long. The nine species of fur seals, in particular, exhibit this type of pronounced sexual dimorphism. The Weddell Seal is notable inthat the male is slightly smaller than the female.

True seals differ from Eared seals in a number of ways. First, True seals have no external ear flaps, simply small holes. Eared seals have ear flaps.

Eared seals have hind flippers that can be turned to face forwards. Together with strong front flippers, this gives them extra mobility on land. They also use their front flippers for swimming, whereas true seals use their rear flippers only to propel themselves through the water while the front flippers provide balance and steer. While True seals are less mobile on land, they more streamlined than Eared seals and very efficient swimmers, usually capable of covering large distances. However, on land, True seals are far  less mobile than Eared seals, which is reflected in another common name they have -"Crawling seals".

Walruses have features that are a mix of True seals and Eared seals. Like true seals, walruses have no external ear flaps. Like eared seals, walruses have reversible hind flippers that give them greater mobility on land.

Species/Taxonomy

Pinnipeds includes 33-36 species in three taxonomic families. There is some disagreement about whether the New Zealand fur seal and the Galapagos fur seal are to be considered as distinct species or as subspecies of the South African fur seal. There is also scientific debate about whether the Juan Fernandez fur seal and Guadalupe fur seal are in fact both subspecies of a single species of fur seal. Here these seals are considered species, but indented to indicate there questioned status. Two species, the Japanese sea lion and the Caribbean Monk Seal, are now believed to be extinct. Thus there are 31-34 living species of pinnipeds. Pinnipeds are frequently organized taxonomically as a "superfamily" named "Pinnipedia" in the following way:

       Family: Otariidae (Eared Seals)

  1. South African fur seal (also Cape fur seal, Australian fur seal; Arctocephalus pusillus)
  2. Antarctic fur seal (Arctocephalus gazella)
  3. Subantarctic fur seal (Arctocephalus tropicalis)
  4. South American fur seal (Arctocephalus australis)
  5.   - New Zealand fur seal (Arctocephalus forsteri)
  6.   - Galapagos fur seal (Arctocephalus galapagoensis)
  7.   - Juan Fernandez fur seal (Arctocephalus philippii)
  8.   - Guadalupe fur seal (Arctocephalus townsendi)
  9. Pribilof fur seal (also Northern fur seal; Callorhinus ursinus)
  10. Japanese sea lion (Zalophus japonicus)
  11. California sea lion (Zalophus californianus)
  12. Galápagos sea lion (Zalophus wollebaeki)
  13. Steller Sea Lion (also Northern sea lion; Eumetopias jubatus)
  14. Australian sea lion (Neophoca cinerea)
  15. New zealand sea lion (Phocarctos hookeri)
  16. South American sea lion (Otaria flavescens)

    Family: Phocidae (True or "earless" seals)
  17. Bearded Seal (Erignathus barbatus)
  18. Harbor Seal (also Common Seal; Phoca vitulina)
  19. Spotted Seal (Phoca largha)
  20. Ringed Seal (Pusa hispida)
  21. Caspian Seal (Pusa caspica)
  22. Baikal Seal (Pusa sibirica)
  23. Grey Seal (Halichoerus grypus)
  24. Ribbon Seal (Histriophoca fasciata)
  25. Harp Seal (Pagophilus groenlandicus)
  26. Hooded Seal (also Bladdernose seal) (Cystophora cristata)
  27. Caribbean Monk Seal (Monachus tropicalis)
  28. Mediterranean Monk Seal (also Pied monk seal) (Monachus monachus)
  29. Hawaiian Monk Seal (Monachus schauinslandi)
  30. Southern Elephant Seal (Mirounga leonina)
  31. Northern Elephant Seal (Mirounga angustirostris)
  32. Weddell Seal (also Weddell's seals) (Leptonychotes weddellii)
  33. Ross Seal (Ommatophoca rossii)
  34. Crabeater Seal (also White Antarctic seal) (Lobodon carcinophaga)
  35. Leopard Seal (Hydrurga leptonyx)

    Family: Odobenidae (Walruses)
     
  36. Walrus Odobenus rosmarus

Images

 
caption South American fur seal. Source: Wikipedia
caption New Zealand Fur Seal. Source: Petr Baum/BioLib/Encyclopedia of Life
 
caption Antarctic Fur Seal. Source: José Luis Orgeira/WoRMS/Encyclopedia of Life
caption South African fur seal. Source: Petr Baum/BioLib/Encyclopedia of Life
  
 
caption Guadalupe fur seal. Source:NOAA
 
caption Sub Antarctic fur seal. Source:Yan Ropert-Coudert/WoRMS/Encyclopedia of Life
  
caption Pribilof fur seal. Source: Anne Morkill/BioLib/Encyclopedia of Life
 
caption Stellar Sea Lion. Source: Tom Early/BioLib/Encyclopedia of Life
caption Australian Sea Lion. Source: Cody Pope
 
caption New Zealand sea lion. Source: Roger Kirkwood/WoRMS/Encyclopedia of Life
 
caption South American sea lion. Source: Biopix/ Encyclopedia of Life
 
caption California sea lion. Source: David Corby/Wikipedia
 
caption Galápagos sea lion. Source: Kelley Kane/Wikipedia
 
caption Japanese sea lion (stuffed specimen at Tenn?ji Zoo, Osaka, Japan.) Source: Nkensei/Wikipedia)
 
caption Hooded seal. Source:Sea Mammal Research Unit/WoRMS/Encyclopedia of Life
 
caption Bearded seal with satellite-linked data recorder attached to it for research purposes. Source: NOAA
 
caption Grey seal. Source: Cynthia Sims Parr, Animal Diversity Web/Encyclopedia of Life
 
caption Ribbon seal. Source: M.Cameron/NOAA
 
caption Leopard seal. Source: Yan Ropert-Coudert/WoRMS/Encyclopedia of Life
 
caption Weddell seal. Source:José Luis Orgeira/WoRMS/Encyclopedia of Life
 
caption Crabeater seal. Source: Mike Cameron/NOAA
 
caption Northern elephant seal. Source: Fred Sorenson/BioLib/Encyclopedia of Life
 
caption Southern elephant seal. Source: José Luis Orgeira/WoRMS/Encyclopedia of Life
 
caption Mediterranean monk seal. Source: Giovanni Dall'Orto/Wikipedia
 
caption Hawaiian monk seal. Source: U.S. Fish and Wildlife Service
 
caption Caribbean monk seal in 1910. Source: New York Zoological Society.
 
caption Ross seal. Source: NOAA
 
caption Harp seal. Source: NOAA
 
caption Spotted seal. Source:M. Cameron/NOAA
 
caption Harbor seal. Source: Petr Baum/BioLib/Encyclopedia of Life
 
caption Caspian seal. Source:Nanosanchez/Wikipedia
 
caption Ringed seal. Source:Steve Amstrup/USGS
 
caption Baikal seal. Source:Uryah/Wikipedia
 
caption Walrus at Togiak National Wildlife Refuge. Source: U.S. Fish and Wildlife Service
 
caption Juan Fernandez fur seal. Source: Collection Georges Declercq/WWF/Encyclopedia of Life
 

Reproduction

Pinnipeds are semi-aquatic mammals, in that, while they spend much of their time in water, they nearly always give birth on land or on stable ice. While most pinnipeds also mate on land or ice, some (e.g., Walrus and many True seals) mate at sea. Until recently the difficulty of observing aquatic-mating pinnipeds, meant that most information obtained referred to pinnipeds that mated on land or fixed ice.

Pinnipeds 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 avergae number varies with species). In some species, females join harems as a matter of chance based upon their location on the beach. In some species, males engage in displays in which they produce sounds to attract mates and the females chose their mates. Males typically will come ashore and establish their territories at the beginning of the mating season.

Most, but not all, species of pinnipeds mate annually at certain times of the year. Typically, before mating, the females will first give birth to a pup conceived during the mating season of the prior year. Mating occurs typically a week or two after the birth of the pup. Sometimes two pups are born. In these cases just usually survives. Males pinnipeds do not assist inthe rearing of their offspring.

The fertilised egg within the female undergoes a period of delayed implantation (from 1.5 to 5.0 months). 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.

Females pinnipeds typically reach sexual maturity at three to six years (though Weddell seals and Ringed seals mature slight slower). Female become fertile slightly quicker on average than males. However, males typically do not activity mate until eight to nine years when they become large enough to successfully challenge other males and defend harems in the polygynous mating system.

Lifespan/Longevity

The average lifespan of pinnipeds is a subject about which there is uncertainty and continuing study. However, for most pinniped species in the wild, an individual that survives the first few years will live 13-23 years in the wild typical, with some variation among species, and with females living to the upper part of the range and males living to the lower part of the range. In captivity, pinnipeds have been know to live to 30 years. A few species like the Caspian seal and the Walrus live somewhat longer lives.

Behavior

caption Walrus Colony. Source: U.S. Fish and Wildlife Service

Some pinniped species are extremely social, living in groups that can be quite large (especially in the case of Walruses) and particularly so during periods of mating. In some pinniped species (e.g., Subantarctic fur seal), the females to continually return to their rookerly throughout the year. In other species (e.g., Harbor seal), individuals live quite solitary lives outsideof the mating period.

Pinnipeds invoke a number of behaviors to attract and retain mates. Males will often fight on engage in aggressive behavior to establish and maintain a teritory within which they gather females for mating. Pinnipeds often use grunts, snorts or other sounds to attract mates or scare competitors of mates. The Hooded seal has a rather unique addition to this type of behavior. When mating, excited, or threatened, the male Hooded seal can close one of his nostrils, an inflate its trunk. The inflated trunk forms a crest or a hood on top of the head.

Pinnipeds are efficient swimmers and  capable of deep and sustained dives. Southern elephant seals, in particular, are amazing divers and will usually spend at least thirty minutes underwater, come up for a brief two-minute period, and then return underwater for another thirty minutes. While most dives are only between 300 and 800 m, dives of over 1,500 m have been recorded, nearing depths only surpassed in mammals by sperm whales. Dives can last well over an hour. Some researchers think they may enter a sleep-like state when diving. Not very much is known about the habits of foraging southern elephant seals due to the solitary nature and the extreme depths to which they dive.  During most trips at sea, they are underwater for 90% of the time, day and night.

 

Distribution

caption Southern elephant seals fighting. Source: Yan Ropert-Coudert/WoRMS/Encyclopedia of Life Pinnipeds are found primarily in polar and temperate waters. Eared seals are most common in the Southern Hemisphere, although the Pribilof fur seal is an exception. There are also tropical pinnipeds (Galapagos fur seal and Monk seals). 

Their distribution, when viewed in terms of breeding locations, tends to be patchy with certain specific locations serving as rookeries over a long time frame. However, most species forage for food over large areas in ways that are not yet well understood. Research using satellite telemetry track to location and movement of pinnipeds is beginning to bring a much better understanding of certain species.

Predation

Pinnipeds are of at or near the top of the food chain in most situations. However, they are prey to sharks like the great white sharks (Carcharodon carcharias), and to [[Killer Whale|Killer whales}} (orcas - Orcinus orca). Ocassionally, they are prey to other pinnipeds like Stellar sea lions, Leopard seals, or walruses. You are naturally more vulnerable to predation that mature pinnipeds. The most significant predation historically has been by humans for commercial purposes.

Feeding Habits

Pinnipeds eat a large number of different species which means that they are considered to be  carnivores that are "generalized predators" or "opportunistic feeders." However, most pinnipeds get most of their diet from a small number of prey species, such as a fish and cephalopods like octopuses and squid (e.g., Grey seal), krill (e.g., Crabeater seal), and crustaceans (e.g., Harp seal).

In a few cases certain species of pinniped prey upon other pinniped species.  Stellar sea lions will prey on Harbor seals, Bearded seals, ringed seals, Spotted seals and young Pribilof fur seals; Leopard seals will eat Weddell seals; and, Walruses often prey on ringed seals, Spotted seals and young Bearded seals.

Conservation Status

Pinnipeds were agressively hunted until the early twentieth century for their skins, oil, meat and, in the case of Walruses, their tusks. As a result of this, combined with habitat loss, and negative interactions with commercial fishing,  the populations of most pinnipeds were severely depleted and two species (Japanese sea lion and Caribbean Monk Seal) are now believed to be extinct, while several other species are threatened with extinction. However, laws have been passed throughout the world to protect pinnipeds and many species have made strong come backs over recent decades (especially Grey seals, Harbor seals, Antarctic fur seals, and Pribilof fur seals. The species that are of concern ranked in order of risk are as follows:

Extinct:

Critically Endangered:

Endangered:

Vulnerable:

 Near Threatened:

Data Deficient                                                 

Note

  • While the Ringed Seal is considered of "Least Concern", two of its subspecies Lagoda ringed seal and Saimaa ringed seal are of concern

The most abundant pinniped is the Crabeater seal (a misnomer as it actually eats krill) with a population estimated at between 15 and 40 million. The least abundant is the Mediterranean monk seals, of which there are fewer than 500 individuals in the world today, probably 350-450. It is estimated that there were twice this number 20 years ago. The number of mature Mediterranean monk seals in thought to be less than 250.

15 species of True or Earless seals have numbers in excess of 100,000 while 8 species of Eared seals have such large numbers.

Economic Importance for Humans

Pinnipeds were agressively hunted until the early twentieth century for their skins, oil, meat and, in the case of walruses, their tusks. Since then most commerical hunting has ceased.  Harp seals continue to be hunted commercially in the Newfoundland and Labrador Seas of Northeastern Canada. This hunting is managed in such a away thay it does not seem to be adversely impacting athe health population of {harp Seal|Harp seals]], estimated to be about 8 million. 

Pinnipeds are a very popular tourist attraction in many parts of the world. California sea lions in particular are a highly social and intelligent species that is widely used in educational programs in zoos and aquariums throughout the world because of their agility and trainability.

Evolution

It is generally held that Eared seals and walruses evolved from species that also gave rise to bears, while True seals evolve from species that also gave rise to weasels, skunks and Otters. The fossil record indicates that there were many species of pinniped which lived  in prior times but do not exist today.

caption Image by Ansgar Walk (Wikimedia Commons)

Further Reading

  1. Encyclopedia of Life (accessed April 30, 2009)
  2. Animal Diversity Web (accessed April 30, 2009)
  3. Seal Conservation Society (accessed April 30, 2009)
  4. The Pinnipeds: Seals, Sea Lions, and Walruses, Marianne Riedman, University of California Press, 1991 ISBN: 0520064984
  5. Encyclopedia of Marine Mammals, Bernd Wursig, Academic Press, 2002 ISBN: 0125513402
  6. 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
  7. IUCN Red List of Threatened Species (accessed April 30, 2009)
  8. Heath, C.B. (2002) California, Galapagos, and Japanese sea lions. In: Perrin, W.F., Wursig, B. and Thewissen, J.G.M. Eds. Encyclopedia of Marine Mammals. Academic Press, San Diego.
  9. Walker's Mammals of the World, Ronald M. Nowak, Johns Hopkins University Press, 1999 ISBN: 0801857899 
  10. MarineBio.org (accessed April 30, 2009)
  11. Encyclopedia of Marine Mammals, by William F. Perrin (Author, Editor), J. G.M. Thewissen (Editor), Bernd Wursig (Editor), Academic Press; 2 edition (2008) ISBN: 012373553X
  12. “Committee on Taxonomy. 2009. List of marine mammal species and subspecies. Society for Marine Mammalogy, consulted on May 16, 2011.”

 

Glossary

Citation

Saundry, P. (2014). Pinniped. Retrieved from http://www.eoearth.org/view/article/51cbeea27896bb431f699402

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