Marine Ecology

Bearded seal

May 21, 2011, 10:21 am
Content Cover Image

Bearded seal. source: NOAA

The Bearded seal (also Square flipper seal; Scientific name: Erignathus barbatus) is one of nineteen species of marine mammals in the family of true seals. Together with the families of eared seals and Walruses, True seals form the group of marine mammals known as pinnipeds. The name Bearded seal derives from the long bushy facial whiskers of the species.  There are two recognized subspecies of this seal, (although there is some debate on these designatiions):

  • Atlantic Bearded seal (Erignathus barbatus barbatus) 
  • Pacific Bearded seal (Erignathus barbatus nauticus) 

Physical Description

caption Bearded seal with satellite-linked data recorder attached to it for research purposes. Source: NOAA
Conservation Status

Scientific Classification

Kingdom: Animalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Carnivora (Carnivores)
Family:-------- Phocidae (True Seals)
Genus:--------- Erignathu
Species:-------- Erignathus barbatus (Erxleben, 1777)

Bearded seals have a gray or brown coat that is darker on their back than their underside. They are heavier in the winter and early spring, when they can attain peak body weight around 360 kg; a pregnant female also reaches the apex of weight.  In the spring, this seal decreases  food intake, reducing blubber and mass to about 216 kg to 239 kilograms (kg). Adults are generally the same size, though females may be slightly longer (adults average about 2.4 m to 2.5 m). The large body mass makes their round head and flippers appear small by comparison. Their large, wide muzzle contrasts with their small close set eyes. Bearded seals have long white whiskers, hence their name. At the end of each flipper are equal length digits (sometimes the third digit is slightly larger) which results in a square appearance. The claws on the digits are very strong, unlike those on the hind flippers. Differing from most other species of earless seals,Bearded seals have four rather than two retractable teats.

Pups are similar in color to adults but have a lighter face and a back that has broad,light colored stripes. A dark line extending from the head to between the eyes is sometimes apparent. They are about half of the size of the adults when born (about 1.3 metres) and weigh much less (about 30 to 40kg).

Reproduction

caption Geographic distribution of the Bearded seal.

Bearded seals give birth on pack ice in mid-March to late April. Males produce whistling sounds that are audible underwater. Some studies suggest Bearded seals male practice a form of "lek" polygyny, where the females select their mates.  During breeding season, the mature males sing an audible, underwater song - a long, oscillating warble that may last for more than one minute, followed by a short, low-frequency moan - which may be a proclamation of territory or breeding condition. It is thought, that based on these displays, which occur in a common area, females select their mates.

Bearded seals are primarily solitary animals except during breeding seasons, or when females are raising their pups. The gestation period is 11 months including a dormancy period of 2.5 to 3.0 months after conception. This dormancy occurs until July when the embryo starts developing rapidly. Their reproductive cycle is annual and females usually breed a fortnight after their pups are weaned.

Shortly after birth, pups are able to swim and can dive 75 meters below the sea surface to escape polar bears. Pups put on weight quickly, especially during the 12 to 18 days of nursing. Pups molt into the adult coat around the time of weaning, which occurs when it reaches approximately 85 kg. "After the breeding season, many seals migrate northward with the retreating ice, returning southward again as the ice advances in autumn and winter".

Lifespan/Longevity

Female life spans can be up to 31 years, while males usually live about 25 years.

Behavior

Often solitary individuals are observed resting on floating ice with their head facing downward into the water. This posture facilitates quick escape into the sea, if a predator appears. A Bearded seal can ram its head into thin ice in order to create breathing apertures.Individuals have been known to dive to a depth of 200 meters, however, they chiefly feed in shallow waters.

Distribution

Throughout the Arctic and sub-Arctic, south of latitude 85º North:

  • Atlantic Bearded seal-- central Canadian Arctic east to the central Eurasian Arctic, includes all of Hudson Bay, Greenland, the north shore of Iceland, and the Svalbard Archipelago
  • Pacific Bearded Seal- - Canadian Arctic in the West and the Laptev Sea in the East, Bering Sea, a separated population iunhabits the Sea of Okhotsk, ranging south to the islands of Hokkaido, Japan

They have also been known to go as far as China, Tokyo Bay, Portugal and Cape Cod, Massachusetts.

caption Geographic distribution of the Bearded seal.

Habitat

Bearded seals prefer shallow, arctic waters less than 200 meters in depth. They also prefer broken, drifting patches of ice, although they readily adapt to dense, slow moving ice by making breathing holes. During the warmer months they sometimes climb ashore to gravel beaches.

Predators

The dominant predators of bearded seals are polar bears. These seals, when on shore, stay close to the edge of the water for a quick escape if disturbed. They are also hunted in the water by killer whales.

Food Habits

Bearded seals prey upon invertebrates and fish that occur in the shallow marine areas they inhabit. By using their sensitive whiskers, they are able to easily track their favorite food items such as crab, shrimp, clams and snails.

Conservation Status

Bearded seal populations appear stable, with an estimated global population size, excluding Canada and Norway, of 500,000. However, they are difficult to count and there are some concerns that the population may be declining as a result of habitat loss and other disturbances. Their habitats are in danger from global warming, pollution from oil and gas extraction and boat traffic. Also, there is a potential for conflict between Bearded seals and commercial fishermen, particularly in the central Bering Sea for species such as tanner crabs, pink shrimp and clams, all components of the bearded seal diet.

Economic Importance for Humans

Bearded seals are often hunted for their hides and are an important component of Arctic peoples' diet. Bearded seal meat is the most desirable of the seals, and the hides are sometimes used for boat covers, rawhide line, boot soles and  other uses. This species is most successfully hunted in the spring when boats are able to move through the broken ice and when seals are migrating north. Bearded seals were previously hunted for their intestines to make waterproof clothing and blubber to obtain lamp oil.

Further Reading

  1. Erignathus barbatus (Erxleben, 1777), Encyclopedia of Life (accessed May 13, 2010)
  2. Erignathus barbatus , Lutz, H., 2000, Animal Diversity Web (accessed May 13, 2010)
  3. Bearded Seal, Seal Conservation Society (accessed May 13, 2010)
  4. Erignathus barbatus, IUCN 2008 Red List (accessed May 13, 2010)
  5. The Pinnipeds: Seals, Sea Lions, and Walruses, Marianne Riedman, University of California Press, 1991 ISBN: 0520064984
  6. Encyclopedia of Marine Mammals, Bernd Wursig, Academic Press, 2002 ISBN: 0125513402
  7. 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
  8. Walker's Mammals of the World, Ronald M. Nowak, Johns Hopkins University Press, 1999 ISBN: 0801857899
  9. Bearded Seal, MarineBio.org (accessed May 13, 2010)
  10. Burns, J. 1994. "Bearded Seal" (On-line). Alaska Department of Fish & Game Wildlife Notebook Series.
  11. Haley, D. 1978. Marine Mammals of Eastern North Pacific and Arctic Waters. Seatle, Washington: Pacific Search Press.
  12. Jefferson, T., S. Leatherwood, M. Webber. 1993. Marine Mammals of the World. Rome, Italy: Food and Agriculture Organization of United Nations.
  13. Macdonald, D. 1985. Encyclopedia of Mammals. New York, NY: Facts on File Publications.
  14. Parker, S. 1990. Grzimek's Encyclopedia Mammals Vol.4. New York,NY: McGraw-Hill Publishing Co.
  15. Erignathus barbatus Wilson and Reeder's Mammals of the World (accessed  May 13, 2010)
Glossary

Citation

Life, E. (2011). Bearded seal. Retrieved from http://www.eoearth.org/view/article/150454

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