Harp seal

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Harp seal
Harp seal.jpg
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Phocidae
Genus: Pagophilus
Gray, 1844
Species: P. groenlandicus
Binomial name
Pagophilus groenlandicus
Erxleben, 1777
Sattelrobbe-Phoca groenlandica-World.png
Synonyms

Phoca groenlandica

The harp seal or saddleback seal, Pagophilus groenlandicus is a species of earless seal, or true seal, native to the northernmost Atlantic Ocean and Arctic Ocean. Originally in the genus Phoca with a number of other species, it was reclassified into the monotypic genus Pagophilus in 1844. In Latin, its scientific name translates to "ice-lover from Greenland," and its taxonomic synonym, Phoca groenlandica translates to "Greenlandic seal."[2]

Description

Whitecoated pup

The mature harp seal has pure black eyes. It has a silver-gray fur covering its body, with black harp or wishbone-shaped markings dorsally. Adult harp seals grow to be 1.7 to 2.0 m (5 ft 7 in to 6 ft 7 in) long and weigh from 115 to 140 kg (254-308 lbs).[3] The harp seal pup often has a yellow-white coat at birth due to staining from amniotic fluid, but after one to three days, the coat whitens and remains white for 2–3 weeks, until the first molt.[2] Adolescent harp seals have a silver-gray coat spotted with black.

Physiology

Harp seals are considered sexually dimorphic, as the males are slightly larger, and more decorated . Males weigh an average of 135 kg (298 lbs.), and reach a length up to 1.9 meters (6.2 ft.), while females weigh an average of 120 kg (264 lbs.) and reach up to 1.8 meters (5.9 ft.). Males generally have a more defined dorsal harp marking and a darker head, while some females never develop the marking and remain spotted.[2]

Thermoregulation

Harp seals combine anatomical and behavioral approaches to managing their body temperatures, instead of elevating their metabolic rate and energy requirements [4]. A thick coat of blubber insulates its body and provides energy when food is scarce or during fasting[5]. Blubber also streamlines its body for more efficient swimming. Brown fat warms blood as it returns from the body surface as well as providing energy, most importantly for newly-weaned pups.[2]

Flippers act as heat exchangers, warming or cooling the seal as needed. On ice, the seal can press its fore-flippers to its body and its hind-flippers together to reduce heat loss.[2] They can also redirect blood flow from the periphery to minimize heat loss.[5]

Senses

The harp seals' eyes are large for its body size and contain a large spherical lens, which improves its focusing ability. Its pupil is mobile to help it adapt to the intense glare of the Arctic ice. Its retina is rod-dominated and backed by a cat-like and reflective tapetum lucidum, enhancing its low light sensitivity. Its cones are most sensitive to blue-green spectra, while its rods help sense light intensity and may provide some color discrimination. Its cornea is lubricated by lacrimal glands, to protect the eye from sea water damage. The lack of tear glands to drain secretions to the nasal passages contribute to the harp seals "eye rings" on land. This can be an indication of the hydration level of the seal. [2]

Seal showing hydration rings around the eyes due to lacrimal gland secretions. (Note: the animal pictured is Halichoerus grypus rather than Pagophilus groenlandicus.)

On ice, the mother identifies her offspring by smell. This sense may also warn of an approaching predator. Underwater, the seal closes its nostrils and smells nothing.[2]

Its whiskers, called vibrissae, lie in horizontal rows on either side of its snout. They provide a touch sense with labeled line coding, and underwater, also respond to low-frequency vibrations, such as movement.[2]

Diet

The harp seal is carnivorous.[6] They have a diverse diet which includes several dozen species of fish and invertebrates.[7]

Life history

Harp seals spend relatively little time on land compared with time at sea. These are social animals and can be quite vocal in groups. They form large colonies, within which, smaller groups with their own hierarchy are believed to form.[2] Groups of several thousand form during pupping and mating season.[8] Harp seals are able to live over 30 years in the wild.[2]

On the ice, pups call their mothers by "yelling," and "mumble" while playing with others. Adults "growl" and "warble" to warn off conspecifics and predators.[2] Underwater, adults have been recorded using more than 19 types of vocalization during courting and mating.[2]

Reproduction

The harp seal is believed to have a promiscuous mating system.[9] Breeding occurs between mid-February and April.[10]

Females mature sexually between ages five to six.[2] Annually thereafter, they bear one pup, usually in late February.[2] There have been reported cases of twin births, but singletons are vastly more common.[11] The fertilized egg grows into an embryo which remains suspended in the womb for up to three months before implantation, to delay birth until sufficient pack ice is available.[2]

Newborn pups weigh 11 kilograms (24 lbs) on average and are 80–85 centimetres (31–33 in) long.[2] After birth, the mother feeds only her own pup. During the approximately 12-day long nursing period, the mother does not hunt, and loses up to 3 kilograms (7 lb) per day.[2] Harp seal milk contains nearly 60% fat, and pups gain over 2.2 kilograms (4.9 lb) per day while nursing, quickly thickening their blubber layer. During this time, the juvenile's "greycoat" grows in beneath the white neonatal coat, and the pup increases its weight to 36 kg (80 lbs). Weaning is abrupt; the mother turns from nursing to promiscuous mating, leaving the pup behind on the ice. While courtship starts on the ice, mating usually takes place in the water.

The stranded pup cries out for its mother, then becomes sedentary to conserve body fat. Within a few days, it sheds its white coat, reaching the "beater" stage.[2] This name comes from the sound a beater's tail makes as the seal learns to swim.[11] Pups are unable to swim or find food until seven to eight weeks old, around the same time at which the ice melts leaving them vulnerable to polar bears and other predators. This fast can reduce their weight up to 50%. As many as 30% of pups die during their first year, due in part to their early immobility on land.[2]

Juvenile harp seal- a "bedlamer."

Around 13–14 months old, the pup molts again, becoming a "bedlamer".[11] Juveniles molt several times, producing a "spotted harp", before the adults' harp-marked pelt fully emerges after several years (or not all in females).[2]

Seals congregate annually on the ice to molt, pup and breed before migrating to summer feeding grounds. Their lifespan can be over 30 years.[2]

Distribution

The harp seal population is found in three distinct stocks, each of which uses a specific breeding site. The western North Atlantic stock, which is the largest, is located off eastern Canada.[11] This population is further divided into two separate herds based on the breeding location. The Front herd breeds off the coast of Labrador and Newfoundland, and the Gulf herd breeds near the Magdalen Islands in the middle of the Gulf of St. Lawrence. A second stock breeds on the "West Ice" off eastern Greenland. A third stock breeds on the "East Ice" in the White Sea, which is off the coast of Russia. Breeding occurs between mid-February and April, and varies somewhat for each stock.[10] The three stocks are allopatric and don't interbreed.[12]

There are two recognised subspecies:[12]

  • Pagophilus groenlandicus groenlandicus – Eastern Canada to Norway
  • Pagophilus groenlandicus oceanicusWhite and Barents seas

Migration and vagrancy

Harp seals are strongly migratory. The northwest population regularly moves up to 4,000 kilometres (2,500 mi) northeast outside of the breeding season;[13] one individual was located off the north Norwegian coast, 4,640 kilometres (2,880 mi) east northeast of its tagging location.[14] Their navigational accuracy is high, with good eyesight an important factor.[13][15] They are occasionally found as vagrants, south of their normal range. In Great Britain, a total of 31 vagrants were recorded between 1800 and 1988,[16]

More recently, they reached Lindisfarne in Northumberland in September 1995,[17] and the Shetland Islands in 1987. The latter was linked to a mass movement of harp seals into Norwegian waters; by mid-February 1987, 24,000 were reported drowned in fishing nets and perhaps 30,000,000 (about 10% of the world population) had invaded fjords as far south as Oslo. The animals were emaciated, likely due to humans competing for their prey.[18]

Harp seals can strand on Atlantic coasts, often in warmer months, due to dehydration and parasite load.[19] Harp seals often consume snow to stay hydrated, but in mild winters may not have enough available. Several centers are active in seal rescue and rehabilitation, including IFAW, NOAA, and the New England Aquarium. Harp seals are protected by the Marine Mammal Protection Act in the United States.

Seal hunting

All 3 populations are hunted commercially, mainly by Canada, Norway, Russia and Greenland.[20]

In Canada, commercial hunting season is from November 15 to May 15. Most sealing occurs in late March in the Gulf of St. Lawrence, and during the first or second week of April off Newfoundland, in an area known as "the Front". This peak spring period is generally what is referred to as the "Canadian seal hunt". Hunting Canadian whitecoats has been banned since 1987. In 2006, the St. Lawrence hunt officially started on March 25 due to thin ice caused by the year's milder temperatures. Inuit people living in the region hunt mainly for food and, to a lesser extent, commerce.[20]

In 2003, the three-year quota granted by the Department of Fisheries and Oceans was increased to 975,000, with a maximum of 350,000 in any two consecutive years. In 2006, 325,000 harp seals, as well as 10,000 hooded seals and 10,400 grey seals were killed. An additional 10,000 animals are allocated to First Nations hunters.

The Canadian seal hunt is monitored by the Canadian government. Although approximately 70% of the hunt occurs on "the Front", most private monitors focus on the St. Lawrence hunt, due to its more convenient location.

About 70,000–90,000 animals are taken from the population off the coast of Greenland.[20]

The 2004 West Ice total allowable catch (TAC) was 15,000, almost double the sustainable catch of 8,200. Actual catches were 9,895 in 2004 and 5,808 in 2005.[20] The 2004 White Sea TAC was 45,000. The catch was 22,474.[20]

References

  1. ^ Kovacs, K.M. (2015). Pagophilus groenlandicus. The IUCN Red List of Threatened Species doi:10.2305/IUCN.UK.2015-4.RLTS.T41671A45231087.en
  2. ^ a b c d e f g h i j k l m n o p q r s t u Encyclopedia of marine mammals. Perrin, William F., Würsig, Bernd G., Thewissen, J. G. M. (2nd ed ed.). Amsterdam: Elsevier/Academic Press. 2009. ISBN 9780123735539. OCLC 316226747. 
  3. ^ Kovacs, K.M. 2015. Pagophilus groenlandicus. The IUCN Red List of Threatened Species 2015: e.T41671A45231087. http://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T41671A45231087.en. Downloaded on 03 April 2018.
  4. ^ Lavigne, D., Innes, S., Worthy, G., Kovacs, K., Schmitz, O., & Hickie, J. (1986). Metabolic rates of seals and whales. Canadian Journal of Zoology, 64(2), 279-284.
  5. ^ a b "Adaptation of the Harp Seal". bioweb.uwlax.edu. Retrieved 2018-04-03. 
  6. ^ "Harp Seal | National Geographic". 2011-03-10. Retrieved 2018-04-10. 
  7. ^ "Harp Seal". Oceana. Retrieved 2018-04-10. 
  8. ^ Fisheries, NOAA. "Harp Seal (Pagophilus groenlandicus) :: NOAA Fisheries". www.nmfs.noaa.gov. Retrieved 2018-04-03. 
  9. ^ Miller, Edward H. and Burton, Lauren E. (2001). "It's all relative: allometry and variation in the baculum (os penis) of the harp seal, Pagophilus groenlandicus (Carnivora: Phocidae)" (PDF). Biological Journal of the Linnean Society. 72 (3): 345–355. doi:10.1111/j.1095-8312.2001.tb01322.x.
  10. ^ a b Fisheries, NOAA. "Harp Seal (Pagophilus groenlandicus) :: NOAA Fisheries". www.nmfs.noaa.gov. Retrieved 2018-04-03. 
  11. ^ a b c d "Harp seal | mammal". Encyclopedia Britannica. Retrieved 2018-04-03. 
  12. ^ a b BERTA, Annalisa; CHURCHILL, Morgan (2012-07-01). "Pinniped taxonomy: review of currently recognized species and subspecies, and evidence used for their description". Mammal Review. 42 (3): 207–234. doi:10.1111/j.1365-2907.2011.00193.x. ISSN 1365-2907. 
  13. ^ a b Ronald, K., & Healey, P. J. (1981). Harp Seal. Chapter 3 in Ridgeway, S. H., & Harrison, R. J., eds. Handbook of Marine Mammals, vol. 2 Seals. Academic Press, London.
  14. ^ Sergeant, D.E. (1973). "Transatlantic migration of a Harp Seal, Pagophilus groenlandicus". Journal of the Fisheries Research Board of Canada. 30: 124–125. doi:10.1139/f73-020. 
  15. ^ King, J. E. (2015). Seals of the World, 2nd. ed. British Museum, London.
  16. ^ Corbet, G. B., & Harris, S., eds. (1991). The Handbook of British Mammals. 3rd ed. Blackwell, Oxford.
  17. ^ Frankis, M. P.; Davey, P. R. & Anderson, G. Q. A. (1997). "Harp Seal: a new mammal for the Northumberland fauna". Trans. Nat. Hist. Soc. Northumbria. 57 (4): 239–241. 
  18. ^ Anon (1987). "Harp Seals, Brunnich's Guillemots and White-billed Divers". Twitching. 1 (3): 58. 
  19. ^ "Rounds Notes | National Marine Life Center". nmlc.org. Retrieved 2018-04-10. 
  20. ^ a b c d e Lavigne, David M. (2009). Perrin, William F.; Wursig, Bernd; Thewissen, J.G.M., eds. Encyclopedia of Marine Mammals (2nd ed.). 30 Corporate Drive, Burlington Ma. 01803: Academic Press. ISBN 978-0-12-373553-9. 

Further reading

Paro, a medical robot pet based on the harp seal

The Northwest population:

  • Hammill, M.O. and Stenson, G.B., (2000). Estimated Prey Consumption by Harp seals (Phoca groenlandica), Hooded seals (Cystophora cristata), Grey seals (Halichoerus grypus) and Harbour seals (Phoca vitulina) in Atlantic Canada.[permanent dead link] J. Northw. Atl. Fish. Sci., Vol. 26:1–23
  • Lawson, J.W., Anderson, J.T., Dalley, E.L. and Stenson, G.B. (1998). Selective foraging by harp seals Phoca groenlandica in nearshore and offshore waters of Newfoundland, 1993 and 1994. Marine Ecology Progress Series 163:1–10.
  • Shelton, P.A. and Healey, B.P. (1999). Should depensation be dismissed as a possible explanation for the lack of recovery of the northern cod (Gadus morhua) stock? Can. J. Fish. Aquat. Sci. 56:1521–1524.
  • Stenson, G.B., Hammill, M.O., and Lawson, J.W. (1997). Predation by Harp Seals in Atlantic Canada: Preliminary Consumption Estimates for Arctic Cod, Capelin and Atlantic Cod.[permanent dead link] J. Northw. Atl. Fish. Sci. 22:137–154

The White Sea and West Ice populations:

  • Hamre, J.(1994). Biodiversity and exploitation of the main fish stocks in the Norwegian- Barents Sea ecosystem. Biodiversity and Conservation 3:473–492.
  • Haug, T., Kroeyer, A.B., Nilssen, K.T., Ugland, K.I. and Aspholm, P.E., (1991). Harp seal (Phoca groenlandica ) invasions in Norwegian coastal waters: Age composition and feeding habits. ICES journal of marine science. 48(3):363–371
  • ICES 2001. Report of the Joint ICES/NAFO Working Group on Harp and Hooded Seals, ICES Headquarters, 2–6 October 2000. ICES CM, 2001, ACFM:8, 40 pp.
  • Nilssen, K.T., Pedersen, O.-P., Folkow, L.P., & Haug. T. (2000). Food consumption estimates of Barents Sea harp seals. NAMMCO Sci. Publ. 2:9–28.

External links

  • ICES/NAFO Working Group on Harp and Hooded Seals
  • Smithsonian Institution – North American Mammals: Pagophilus groenlandicus
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