Harp seal
| Harp seal | |
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| Scientific classification | |
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Pagophilus
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| Species: |
P. groenlandicus
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| Binomial name | |
| Pagophilus groenlandicus Erxleben, 1777
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Phoca groenlandica |
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The harp seal or saddleback seal (Pagophilus groenlandicus) is a species of earless seal native to the northernmost Atlantic Ocean and parts of the Arctic Ocean. It now belongs to the monotypic genus Pagophilus. Its scientific name means "ice-lover from Greenland", and its synonym, Phoca groenlandica means "Greenland seal".[2] Originally in the genus Phoca with a number of other species, it has since been reclassified into its own genus Pagophilus.
Contents
Description
The harp seal has a silvery-gray body. Its eyes are pure black. It has black harp or wishbone-shaped markings on the back.[2] The baby harp seal (pup) has a yellow-white coat at birth, but after three days, the coat turns white and stays white for about 12 days. Adult harp seals grow up to be 1.7 to 2.0 m (5 ft 7 in to 6 ft 7 in) long and weigh from 140 to 190 kg (310 to 420 lb).
Physiology
Thermoregulation
Harp seals combine anatomical and behavioural approaches to managing their body temperatures, instead of elevating their metabolic rate and energy requirements.[2] A thick coat of blubber insulates its body and provides energy when food is scarce or during fasting. 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 just-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]
Senses
Vision is its critical sense. Its eyes are proportionally large and contain a large spherical lens, improving 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 rods best sense blue-green, while its cones help with bright light and may provide some colour discrimination. Its cornea is sometimes tear-covered, to protect it from salt. Lacking tear ducts, it "cries" to remove its tears.[2] On ice, the mother identifies her offspring by smell. This sense may also warn of an approaching predator. Underwater, this seal closes its nostrils and smells nothing.[2] Its whiskers, called vibrissae, lie in horizontal rows on either side of its snout. They may provide a touch sense, and underwater, also respond to low-frequency vibrations, such as movement.
Life history
Harp seals prefer to swim in the ocean, spending relatively little time on land.[3] These are extremely social animals and they can be very noisy, as well. They will form large colonies where they spend a great deal of time. Within that loose structure, smaller groups with their own hierarchy are believed to form. Sometimes, these large groups will have to go their separate ways there. Many harp seals are able to live up to 30 years in the wild. After 12 days the mothers abandon their babies.
On the ice, pups call their mothers by "bawling" and "mumble" while playing with others. Adults "growl" and "warble" to warn off others. Underwater, adults express themselves with more than 19 call types during courting and mating.[2]
Reproduction
Females mature sexually at age five to six. Annually thereafter, they bear one pup, usually in late February. The fertilized egg grows into a spherical embryo that implants in the uterus only after three or so months, to allow birth to take place while sufficient pack ice is available.[2]
Newborn pups weigh around 11 kilograms (24 lb) and are 80–85 centimetres (31–33 in) long. After birth, the mother only feeds that pup. During the 12 day nursing period, the mother does not eat, losing up to 3 kilograms (7 lb) per day. Harp seal milk contains up to 60% fat, so pups gain over 2.2 kilograms (4.9 lb) per day. During this time, the juvenile's "greycoat" grows in beneath the white neonatal coat, and it weighs 80 pounds (36 kg). 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.[2]
The stranded pup cries at first, and then becomes sedentary to conserve body fat. Within a few days, it sheds its white coat, reaching the "beater" stage.[2]
Pups are unable to swim or find food until seven to eight weeks old or until the ice melts, leaving them vulnerable to polar bears and other predators. This fast costs them up to 50% of their weight. As many as 30% of pups die during their first year, due in part to their early immobility because they learn to swim only slowly.
At about 13–17 months old, the pup molts again, becoming a "bedlamer". Juveniles molt several times, producing a "spotted harp", before the adult's harp-marked pelt fully emerges after several years (or not all in females).[2]
Seals congregate annually on the ice to molt before migrating to summer feeding grounds. Their lifespan extends for about 20 years.[2]
Distribution
The harp seal population is found in three separate populations, each of which uses a specific breeding site. The western North Atlantic stock, which is the largest, is located off eastern Canada. 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.[4][5]
There are two recognised subspecies:[6]
- Pagophilus groenlandicus groenlandicus – Eastern Canada to Norway
- Pagophilus groenlandicus oceanicus – White 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;[7] one individual was located off the north Norwegian coast, 4,640 kilometres (2,880 mi) east northeast of its tagging location.[8] Their navigational accuracy is high, with good eyesight an important factor.[7][9] 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,[10]
More recently, they reached Lindisfarne in Northumberland in September 1995,[11] 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.[12]
Seal hunting
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All 3 populations are hunted commercially, mainly by Canada, Norway, Russia and Greenland.[2]
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.[2]
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.[2]
The 2004 West Ice TAC was 15,000 "1+" animals (2 pups = 1+), almost double the sustainable catch of 8,200. Actual catches were 9,895 in 2004 and 5,808 in 2005.[2]
The 2004 White Sea TAC was 45,000 1+ (2.5 pups = 1+). The catch was 22,474.[2]
References
- ↑ Kovacs, K. (2008). Pagophilus groenlandicus. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 29 January 2009.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 Lua error in package.lua at line 80: module 'strict' not found.
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- ↑ 7.0 7.1 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.
- ↑ Sergeant, D.E. (1973). Transatlantic migration of a Harp Seal, Pagophilus groenlandicus. J. Fish. Res. Board Canada. 30:124-125.
- ↑ King, J. E. (2015). Seals of the World, 2nd. ed. British Museum, London.
- ↑ Corbet, G. B., & Harris, S., eds. (1991). The Handbook of British Mammals. 3rd ed. Blackwell, Oxford.
- ↑ 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.
- ↑ Anon. (1987). Harp Seals, Brunnich's Guillemots and White-billed Divers Twitching 1(3):58.
Further reading
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. 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. 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.
