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For other uses, see Polar bear (disambiguation).
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Ursus eogroenlandicus |
The polar bear (Ursus maritimus) is a bear native to the Arctic. The world\'s largest land carnivore, an adult male generally weighs 300–600 kg (660–1320 lb), while an adult female is about half that size. Its fur is hollow and translucent, but usually appears as white or cream colored, thus providing the animal with effective camouflage, though its skin is actually black. Its thick blubber and fur insulate it against the cold. The bear has a short tail and small ears that help reduce heat loss, as well as a relatively small head and long, tapered body to streamline it for swimming.
A semi-aquatic marine mammal, the polar bear is adapted for a life on land, sea, and ice,Gunderson, Aren (2007). Ursus Maritimus. Animal Diversity Web. University of Michigan Museum of Zoology. Retrieved on 2007-10-27. and is the apex predator within its range.Polar Bears International It feeds mainly on seals, young walruses, and whales, although it is an opportunistic feeder and will eat anything it can kill.
The polar bear is classified as a vulnerable species. Some zoologists and climatologists believe that the projected decreases in the polar sea ice due to global warming will reduce their population by two thirds by 2050.Derocher, Andrew E.; Lunn, Nicholas J. & Stirling, Ian (April 2004), "Polar Bears in a Warming Climate", Integrative and Comparative Biology 44 (2): pp. 163-176, ISSN 1540-7063, <http://www.biology.ualberta.ca/faculty/andrew_derocher/uploads/abstracts/Deroche_%20Lunn_Stirling_Warming_climate_2004.pdf>. Retrieved on 12 October 2007 Long-term studies show that 7 of the 19 recognized subpopulations are declining or are already severely reduced, 8 are stable, increasing or not reduced, and 7 do not have sufficient data to make a determination. (June 2005) "Status of the Polar Bear" (PDF) in Polar Bears. Compiled and edited by Jon Aars, Nicholas J. Lunn and Andrew E. Derocher Proceedings of the 14th Working Meeting of the IUCN/SSC Polar Bear Specialist Group 32: pp. 33-55, Gland, Switzerland: IUCN. ISBN 2-8317-0959-8. Retrieved on 2007-09-15. See also HTML excerpts: population status reviews and Table 1 summarizing polar bear population status per 2005.Polar Bears and Conservation and Polar Bear FAQ. Polar Bears International. Retrieved on 2007-09-15. The U.S. Fish and Wildlife Service formally proposed listing the polar bear as a threatened species on January 9, 2007. A final decision was due on January 9, 2008 but has been delayed.
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Constantine John Phipps was the first to describe the polar bear as a distinct species. He chose the scientific name Ursus maritimus, the Latin for \'maritime bear\',Kidd, D.A. (1973). Collins Latin Gem Dictionary. London: Collins. ISBN 0-00-458641-7. due to the animal\'s native habitat. The Inuit, the indigenous peoples inhabiting the Arctic region and sharing much of the same habitat as the polar bear, refer to the animal as Nanuk (occasionally rendered as Nanook, or Nanuuq in the Inupiat language).The Marine Mammal CenterThe Arctic Sounder
For some time, the polar bear was considered to belong to its own genus, Thalarctos, combining the Ancient Greek words thalassa/θαλασσα \'sea\', and arctos/αρκτος \'bear\' and also, with reference to Ursa Major, \'northern\' or \'of the north pole\'.Liddell, Henry George and Robert Scott (1980). A Greek-English Lexicon (Abridged Edition). United Kingdom: Oxford University Press. ISBN 0-19-910207-4. However, evidence of hybrids between polar bears and brown bears, and of the relatively recent evolutionary divergence of the two species, does not support the establishment of this separate genus, and the accepted scientific name is now therefore Ursus maritimus, as Phipps originally proposed.IUCN Red List: Ursus maritimus. Retrieved on 2008-02-15.
In Romance languages, the animal is referred to by local cognates of \'polar bear\', for example the French Ours Polaire, or the Spanish Oso Polar. By contrast, in many Germanic languages (although not in English), the animal is referred to by a cognate of \'ice bear\'; for example, the German Eisbär, or the Swedish Isbjörn.M. Gorgas (1999). in A.J. Mitchell-Jones, et. al.: Atlas of European Mammals. London: T & AD Poyser Ltd., 324-325. ISBN 0-85661-130-1. .
The bear family, ursidae, is believed to have differentiated from other carnivorans about 38 million years ago. The ursinae subfamily originated some 4.2 million years ago. According to both fossil and DNA evidence, the polar bear diverged from the brown bear, Ursus arctos, roughly 200 thousand years ago. The oldest known polar bear fossil is less than 100 thousand years old. Fossils show that between 10 and 20 thousand years ago, the polar bear\'s molar teeth changed significantly from those of the brown bear. Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene.
More recent genetic studies have shown that some clades of brown bear are more closely related to polar bears than to other brown bears, meaning that the polar bear is not a true species according to some species concepts.Marris, E. 2007. Nature 446, 250-253. Linnaeus at 300: The species and the specious In addition, polar bears can breed with black bears to produce fertile hybrids,DeMaster, Douglas P. & Stirling, Ian (May 8, 1981), "Ursus Maritimus", Mammalian Species (American Society of Mammalogists) 145: pp. 1-7, ISSN 0076-3519, OCLC 46381503, doi:10.2307/3503828, <http://links.jstor.org/sici?sici=0076-3519(19810508)2%3A145%3C1%3AUM%3E2.0.CO%3B2-D>. Retrieved on 21 January 2008.Schliebe, Scott; Evans, Thomas & Johnson, Kurt et al. (December 21, 2006), Range-wide Status Review of the Polar Bear (Ursus maritimus), Anchorage, Alaska: U.S. Fish and Wildlife Service, <http://alaska.fws.gov/fisheries/mmm/polarbear/pdf/Polar_Bear_%20Status_Assessment.pdf>. Retrieved on 31 October 2007 indicating that they have only recently diverged and are not yet truly distinct species, although neither species can survive long in the other\'s ecological niche, and with distinctly different morphology, metabolism, social and feeding behaviors, and other phenotypic characters, the two bears are generally classified as separate species.
A comparison of the DNA of various brown bear populations showed that the brown bears of Alaska\'s ABC islands shared a more recent common ancestor with polar bears than with any other brown bear population.Lisette P. Waits, Sandra L. Talbot, R.H. Ward and G. F. Shields (April 1998). Mitochondrial DNA Phylogeography of the North American Brown Bear and Implications for Conservation pp. 408-417. Conservation Biology. Retrieved on August 1, 2006. Polar bears still have a vestigial hibernation induction trigger in their blood, but they do not hibernate in the winter as the brown bear does. Only female polar bears enter a dormant state (referred to as "denning") during pregnancy, though their body temperature does not decrease during this period as it would for a typical mammal in hibernation.Bruce, D. S.; Darling, N. K. & Seeland, K. J. et al. (March 1990), "Is the polar bear (Ursus maritimus) a hibernator?: Continued studies on opioids and hibernation", Pharmacology Biochemistry and Behavior 35 (3): pp. 705-711, ISSN 0091-3057.
A polar bear in Churchill, Manitoba
When the polar bear was originally documented, two subspecies were identified: Ursus maritimus maritimus by Constantine J. Phipps in 1774, and Ursus maritimus marinus by Peter S. Pallas in 1776.Rice, Dale W. (1998), Marine Mammals of the World: Systematics and Distribution, vol. 4, Special Publications of the Society for Marine Mammals, Lawrence, Kansas: The Society for Marine Mammalogy, ISBN 1-891276-03-4. This distinction has since been invalidated. The IUCN/SSC Polar Bear Specialist Group (PBSG), the pre-eminent international scientific body for research and management of polar bears, recognizes only one extant species distributed in 19 discrete subpopulations across five areas:
The 19 subpopulations show seasonal fidelity to geographic areas, but DNA studies show significant interbreeding among them.Paetkau, S.; Amstrup, C. & Born, E. W. et al. (October 1999), "Genetic structure of the world\'s polar bear populations", Molecular Ecology (Blackwell Science) 8 (10): pp. 1571-1584, ISSN 1471-8278, <http://www.biology.ualberta.ca/faculty/andrew_derocher/uploads/abstracts/Paetkau_et_al_1999.pdf>. Retrieved on 17 November 2007.
One fossil subspecies has been identified. Ursus maritimus tyrannus—descended from Ursus arctos—became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies.
Polar bears are the largest living land carnivores. Males are generally 25–45% larger than females.Brown, Gary (1996). Great Bear Almanac, pp. 340. ISBN 1558214747. Most adult males weigh 350–650 kg (770–1500+ lb) and measure 2.5–3.0 m (8.2–9.8 ft) in length. Adult females are roughly half the size of males and normally weigh 150–250 kg (330–550 lb), measuring 2–2.5 m (6.6–8.2 ft), but double their weight during pregnancy.Stirling makes no mention of length, these are from SeaWorld The great difference in body size makes the polar bear among the most sexually dimorphic of mammals, surpassed only by the eared seals.Derocher, Andrew E.; Magnus Andersen, and Øystein Wiig (October 2005). "Sexual dimorphism of polar bears". Journal of Mammalogy 86 (5): pp. 895–901. ISSN 1545-1542. At birth, cubs weigh only 600–700 g (1.3–1.5 lb). The largest polar bear on record was a huge male, allegedly weighing 1002 kg (2200 lb), which was shot at Kotzebue Sound in northwestern Alaska in 1960.Wood, G.L. (1981). The Guinness Book of Animal Records, 240. Their tail is 7–12 cm (2.8–4.8 in) long.Brown, Gary (1996). Great Bear Almanac, p. 340. ISBN 1558214747.
The polar bear\'s ears and tail are smaller than other bears, and its legs are stocky, as predicted by Allen\'s rule for a northerly animal. Its feet are very large: 36 cm (12 in) across in an adult, to distribute load when walking on snow or thin ice (as with snowshoes).Lockwood, pp. 10 - 16 Stiff hairs on the pads of the paws provide insulation and traction on the ice. Despite a recurring internet meme that all polar bears are left-handed,Are polar bears left-handed or right-handed?, September 2006, <http://www.blurtit.com/q497068.html>. Retrieved on 25 November 2007.Bear Facts: Myths and Misconceptions, 2007, <http://www.polarbearsinternational.org/bear-facts/myths-and-misconceptions/>. Retrieved on 25 November 2007. there is no scientific evidence to support such a contention. Researchers studying polar bears have failed to find any evidence of left-handedness in all bears and one study of injury patterns in polar bear forelimbs found injuries to the right forelimb to be more frequent than those to the left, suggesting, perhaps, right-handedness. Fractures of the Radius and Ulna secondary to possible Vitamin \'D\' deficiency in Captive Polar Bears (Ursus maritimus), <http://www.polarbearsinternational.org/pbhc/fractures.htm>. Retrieved on 25 November 2007.
A polar bear resting
Polar bear fur consists of a layer of dense underfur and an outer layer of guard hairs, which appear white to tan but are actually translucent. The guard hair is 5–15 cm (2–6 in) over most of the body.Uspenskii, S. M. (1977). The Polar Bear. Moscow: Nauka. Polar bears are superbly insulated by their 10 cm (4 in) of blubber, their hide and their fur; they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography, in which only their breath and muzzles can be easily seen.
Polar bears gradually molt from May to August,Kolenosky G. B. 1987. Polar bear. pp. 475–485 in Wild furbearer management and conservation in North America (M. Novak, J. A. Baker, M. E. Obbard, and B. Malloch, eds.). Ontario Fur Trappers Association, North Bay, Ontario, Canada. but, unlike other Arctic mammals, they do not shed their coat for a darker shade to camouflage themselves in the summer conditions. It was once conjectured that the hollow guard hairs of a polar bear coat acted as fiber-optic tubes to conduct light to its black skin, where it could be absorbed—a theory disproved by recent studies.Koon, Daniel W. (1998), "Is Polar Bear Hair Fiber Optic?", Applied Optics (Optical Society of America) 37 (15): pp. 3198-3200, ISSN 0003-6935, <http://www.opticsinfobase.org/abstract.cfm?URI=ao-37-15-3198>.
An infrared image of a polar bear
Usually the white coat yellows with age. When kept in captivity in warm, humid conditions, it is not unknown for the fur to turn a pale shade of green. This is due to algae growing inside the guard hairs: in unusually warm conditions, the hollow tubes provide an excellent home for algae. While the algae is harmless to the bears, it is often a worry to the zoos housing them, and affected animals are sometimes washed in a salt solution, or mild peroxide bleach to make the fur white again.
In addition to camouflage and insulation, a polar bear\'s fur provides other functions: the males have significantly longer hairs in their forelegs which increase in length until the bear reaches 14 years of age. It is suggested that the male\'s ornamental foreleg hair serves to attract females—the feature which has been likened to the lion\'s mane.
Polar bears are aggressive and curious, and, as such, potentially dangerous to humans. Wild polar bears, unlike most other bears, are poorly habituated to humans and will quickly assess any animal they encounter as potential prey. Males are normally solitary except for mating season, and females are usually social towards one another.
The long muzzle and neck of the polar bear help it to search in deep holes for seals, while powerful hindquarters enable it to drag massive prey.
The polar bear is the most carnivorous member of the bear family: 95% of its diet consists of ringed and bearded seals."". PBS Nature. 2008-02-17. The Arctic is home to millions of seals, which become prey when they surface in holes in the ice in order to breathe, or when they haul out on the ice to rest.Matthews, pp. 73-88 The polar bear\'s most common hunting method is called still-hunting:Hemstock, pp. 24-27 The bear uses its excellent sense of smell to locate a seal breathing hole, and crouches nearby in silence for a seal to appear. When the seal exhales, the bear smells its breath, reaches into the hole with a forepaw, and drags it out onto the ice. The polar bear kills the seal by biting its head to crush its skull. The polar bear also hunts by stalking seals resting on the ice: Upon spotting a seal, it walks to within 100 yards, and then crouches. If the seal does not notice, the bear creeps to within 30 or 40 feet of the seal and then suddenly rushes forth to attack. A third method of hunting seals is to raid the snow caves created by female seals which are about to give birth. Mature bears eat only the skin and blubber of the seal, whereas younger bears consume the protein-rich red meat.
The polar bear will also eat anything it can kill: birds, eggs, rodents, shellfish, crabs, beluga whales, walrus calves, muskox, reindeer, and other polar bears. Although carnivorous, it has been observed to eat plants, including berries, roots, and kelp, however these do not form a significant part of its diet. Its biology is specialized for the digestion of fat from marine mammals and it cannot derive much nutrition from terrestrial food.Ramsay, M. A. & Hobson, K. A. (May 1991), "Polar bears make little use of terrestrial food webs: evidence from stable-carbon isotope analysis", Oecologia (Berlin / Heidelberg: Springer) 86 (4): pp. 598-600, ISSN 0029-8549Best, R. C. (1985), "Digestibility of ringed seals by the polar bear", Canadian Journal of Zoology (Ottawa: National Research Council of Canada) 63 (5): pp. 1033-1036, ISSN 0008-4301 Most terrestrial animals can outrun the polar bear on land, most marine animals can outswim it in open water, and polar bears overheat quickly. As a result, the polar bear subsists almost entirely on live seals and walrus calves taken at the edge of sea-ice in the winter and spring, or on the carcasses of dead adult walruses or whales. It lives off fat reserves through the late summer and early fall when the sea-ice is at a minimum. Although it is an enormously powerful predator it will rarely kill an adult walrus, which can be twice the bear\'s weight. However, an adult walrus kill has been recorded on tape.
Polar bear diving in a zoo
Polar bears are excellent swimmers and have been seen in open Arctic waters as far as 60 miles (100 km) from land. In some cases they spend half their time on ice floes. Their 12 cm (5 in) layer of fat adds buoyancy in addition to insulating them from the cold. Recently, polar bears in the Arctic have undertaken longer than usual swims to find prey, resulting in four recorded drownings in the unusually large ice pack regression of 2005.Monnett, Charles & Gleason, Jeffrey S. (July 2006), "Observations of mortality associated with extended open-water swimming by polar bears in the Alaskan Beaufort Sea", Polar Biology (Berlin: Springer) 29 (8): pp. 681-687, ISSN 0722-4060, DOI 10.1007/s00300-005-0105-2.
Being both curious animals and scavengers, polar bears will investigate and consume garbage where they come into contact with humans. This was documented at the dump in Churchill, Manitoba before its closure.Lunn, N. J. & Stirling, Ian (1985), "The significance of supplemental food to polar bears during the ice-free period of Hudson Bay", Canadian Journal of Zoology (Toronto: NRC Research Press) 63 (10): pp. 2291-2297, ISSN 1480-3283. Polar bears may attempt to consume almost anything they can find, including hazardous substances such as styrofoam, plastic, car batteries, ethylene glycol, hydraulic fluid, and motor oil.Clarkson, Peter L. & Stirling, Ian (1994), "Polar Bears", in Hygnstrom, Scott E.; Timm, Robert M. & Larson, Gary E., Prevention and Control of Wildlife Damage, Lincoln: University of Nebraska, pp. pp. C-25 to C-34, <http://icwdm.org/handbook/carnivor/ca_c25.pdf>. Retrieved on 13 November 2007.Manning, T. H. (March 1961), "Comments on "Carnivorous walrus and some Arctic zoonoses"", Arctic 14 (1): pp. 76-77, ISSN 0004-0843, <http://pubs.aina.ucalgary.ca/arctic/Arctic14-1-76.pdf>. Retrieved on 13 November 2007. The Churchill dump was closed in 2006 to protect the bears, and waste is now recycled or transported to Thompson, Manitoba.Hudson Bay Post
Mother with cub at Svalbard
A mother and cubs in Churchill, Manitoba
Polar bears are polygynous, however mated partners stay together for an entire week.Rosing, pp. 42-48 Courtship and mating take place on the sea ice in April and May; the mating ritual induces ovulation in the female. The fertilized egg then remains in a suspended state until August or September. During these four months, the females eat prodigious amounts of food in preparation for pregnancy, often more than doubling their body weight. When food becomes scarce in the fall because of ice floe breakup, females dig a maternity den in a snow drift and enter a dormant state similar to hibernation. This hibernation-like state does not consist of continuous sleeping, however the bear\'s heart rate slows from 46 to 27 beats per minute.Lockwood, pp.17-21 Between November and February, cubs are born blind, covered with a light down fur, and weighing less than 2 lb. The typical litter size is two or three cubs. The mother maintains her fast while nursing her cubs on a fat-rich milk until March, when the family emerges from the den.
Cubs are weaned at two or three years of age and are separated from their mother. In the 1990s, less than 20% of cubs in the Western Hudson Bay were weaned at 18 months, as opposed to 40% of cubs in the early 1980s. Cubs may fall prey to wolves, to adult males who kill cubs in order to make their mother sexually receptive, or to starvation. In Alaska, the United States Geological Survey (USGS) reports that 42% of cubs now reach 12 months of age, down from 65% 15 years ago.
Sexual maturity typically comes at the age of four, but may be delayed by up to two years. A study in Hudson Bay indicated that both the reproductive success and the maternal weight of females peaked in their mid-teens.Maternal success appeared to decline after this point, possibly because of an age-related impairment in the ability to store the fat necessary to rear cubs. Derocher, A.E.; Stirling, I. (1994). "Age-specific reproductive performance of female polar bears (Ursus maritimus)". Journal of Zoology 234 (4): 527-536. Retrieved on 2008-02-15. Polar bears rarely live beyond 25 years. The oldest wild bear on record died at the age of 32, and the oldest captive at 41.Hemstock, pp. 29-35
The bears sometimes have problems with various skin diseases which may be caused by mites or other parasites. The bears are especially susceptible to Trichinella, a parasitic roundworm they contract through cannibalism.Larsen, Thor & Kjos-Hanssen, Bjørn (October 1983), Goldman, Helle V., ed., "Trichinella sp. in polar bears from Svalbard, in relation to hide length and age", Polar Research (Oslo: Norwegian Polar Institute) 1 (1): pp. 89-96, ISSN 0800-0395, DOI 10.1111/j.1751-8369.1983.tb00734.x. Sometimes excess heavy metals have been observed, as well as ethylene glycol (antifreeze) poisoning. Bears exposed to oil and petroleum products lose the insulative integrity of their coats, forcing metabolic rates to dramatically increase to maintain body heat in their challenging environment. Bacterial Leptospirosis, rabies and Morbillivirus have been recorded. The bears are thought by some to be more resistant than other carnivores to viral disease.[citation needed] The pollutant effect on the bears\' immune systems, however, may end up decreasing their ability to cope with the naturally present immunological threats they encounter, and in such a challenging habitat even minor weaknesses can lead to serious problems and rapid mortality.
Polar bear
The polar bear is a circumpolar species found in and around the Arctic Ocean. Though it spends time on land and ice, the polar bear is regarded as a marine mammal due to its intimate relationship with the sea. In order to hunt the seals that make up most of its diet, it requires sea ice containing fissures and areas of open water, such as polynyas.Stirling, Ian (January 1997), "The importance of polynyas, ice edges, and leads to marine mammals and birds", Journal of Marine Systems (Elsevier) 10 (1-4): pp. 9-21, ISSN 0924-7963, DOI 10.1016/S0924-7963(96)00054-1. Polar bears are therefore found along the perimeter of the polar ice pack, where there are cracks in which seals can breathe, rather than in the Polar Basin close to the North Pole.Matthews, p. 15
The main population centers are Wrangell Island and western Alaska; Northern Alaska; the Canadian Arctic archipelago; Greenland; Svalbard-Franz Josef Land; and North-Central Siberia. Their southernmost point is James Bay in Canada. There is a photographically confirmed case from the beginning of the 20th century of a Svalbard polar bear drifting on ice as far south as the northern coast of the Norwegian mainland. It was found and killed near the village of Berlevag. More recent sightings in Berlevag, including one in the summer of 2005, remain unconfirmed.[citation needed] While their numbers thin north of 88°, there is evidence of polar bears all the way across the Arctic. Population is estimated to be between 20,000 to 25,000. About 60% of the world\'s polar bears live in Canada.
The destruction of its habitat on the Arctic ice threatens the species\' survival.Stirling, Ian; and Claire L. Parkinson (September 2006). "Possible Effects of Climate Warming on Selected Populations of Polar Bears (Ursus maritimus) in the Canadian Arctic" (in English) (PDF). Arctic 59 (3): pp. 261-275. ISSN 0004-0843. Retrieved on 2007-09-15. Stirling, Ian; N.J. Lunn, John Iacozza, Campbell Elliott and Martyn Obbard (March 2004). "Polar Bear Distribution and Abundance on the Southwestern Hudson Bay Coast During Open Water Season, in Relation to Population Trends and Annual Ice Patterns" (in English) (PDF). Arctic 57 (1): pp. 15-26. ISSN 0004-0843. Retrieved on 2007-09-15. Barber, D.G.; J. Iacozza (March 2004). "Historical analysis of sea ice conditions in M\'Clintock Channel and the Gulf of Boothia, Nunavut: implications for ringed seal and polar bear habitat." (in English) (PDF). Arctic 57 (1): pp. 1-14. ISSN 0004-0843. T. Appenzeller and D. R. Dimick, "The Heat is On," National Geographic 206 (2004): 2-75. cited in Flannery, Tim (2005). The Weather Makers. Toronto, Ontario: HarperCollins, 101-103. ISBN 0-00-200751-7.
The U.S. Geological Survey has also published research which purports to show that the percentage of Alaskan polar bears that den on sea ice has changed from 62% between the years 1985–1994, to 37% over the years 1998–2004. The Alaskan population thus now more resembles the world population, in that it is more likely to den on land.Fischbach, A. S.; Amstrup, S. C. & Douglas, D. C. (October 2007), "Landward and eastward shift of Alaskan polar bear denning associated with recent sea ice changes", Polar Biology (Berlin: Springer) 30 (11): pp. 1395-1405, ISSN 0722-4060, DOI 10.1007/s00300-007-0300-4.
Projected change in polar bear habitat from 2001–2010 to 2041–2050. From USGS
The World Conservation Union (IUCN) listed polar bears as a vulnerable species in May 2006.Release of the 2006 IUCN Red List of Threatened Species reveals ongoing decline of the status of plants and animals. World Conservation Union. Retrieved on 2006-02-01. It cited a "suspected population reduction of >30% within three generations (45 years)", due primarily to global warming. Other risks to the polar bear include pollution in the form of toxic contaminants, conflicts with shipping, stresses from recreational polar-bear watching, and oil and gas exploration and development. The IUCN also cited a "potential risk of over-harvest" through legal and illegal hunting.
Warnings about the future of the polar bear are often contrasted with the fact that worldwide population estimates have increased over the past 50 years and are relatively stable today. [1]Polar Bear - Population & Distribution. World Wildlife Foundation. Retrieved on 2008-03-11. Some estimates of the global population are around 5,000–10,000 in the early 1970sKrauss, Clifford. Bear Hunting Caught in Global Warming Debate. New York Times. Retrieved on 2008-03-11.Polar Bear. Young People\'s Trust for the Environment. Retrieved on 2008-03-11.; other estimates were 20,000–40,000 during the 1980s.Stirling, Ian (1988), Polar Bears, Ann Arbor: University of Michigan Press, ISBN 0-472-10100-5 Current estimates put the global population at between 20,000 and 25,000. There are several reasons for the apparent discordance between past and projected population trends: Estimates from the 1950s and 1960s were based on stories from explorers and hunters rather than on scientific surveys.Derocher, Andrew. Ask the Experts: Are Polar Bear Populations Increasing?. Polar Bears International. Retrieved on 2008-03-09.Bruemmer, p. 101. In an meeting of the five circumpolar nations on September 6, 1965, estimates of the worldwide poplation ranged from 5,000 to 19,000. "The truth was, no one knew... Scientific research had been sketchy and knowledge of the polar bear was based largely on stories brought back by explorers and hunters." Second, controls of harvesting were introduced that allowed this previously-overhunted species to recover. Third, the recent effects of global warming have affected sea ice abundance in different areas to varying degrees. Long-term studies of local populations of polar bears show they have been shrinking in the Western Hudson Bay and Baffin Bay areas, and are under stress in the Southern Beaufort Sea area. In the Western Hudson Bay region, for example, there were an estimated 1,194 polar bears in 1987, and 935 in 2004Regehr, E. V.; Lunn, N. J. & Amstrup, N. C. et al. (November 2007), "Effects of earlier sea ice breakup on survival and population size of polar bears in western Hudson Bay", Journal of Wildlife Management (Bethesda: The Wildlife Society) 71 (8): pp. 2673–2683, ISSN 0022-541X, DOI 10.2193/2006-180.–though there were an estimated 500 polar bears there in 1981.Lunn, N. J.; Iacozza, J. C. & Stirling, I. (1999), "Long-term Trends in the Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climate Change", Arctic 52 (3): pp. 294-306
The accuracy of current population estimates has been challenged. The tracking of bears requires flying a helicopter in a difficult climate, shooting a tranquilizer dart at the bear to sedate it, and then tagging the bear. Modern tracking techniques, which have been implemented only since the mid-1980s, are therefore extremely expensive and difficult to perform consistently over a large area. Some Inuit are skeptical of conservation concerns because of increases in bear sightings near settlements in recent years. Scientists have responded by noting that hungry bears may be congregating around human settlements, leading to the illusion that populations are higher than they actually are.Campbell, Colin; Lunau, Kate. "The war over the polar bear: Who\'s telling the truth about the fate of a Canadian icon?", Maclean\'s, 2008-01-25. Retrieved on 2008-03-09.
The most severe and topically recognized threats to the polar bear are the drastic changes taking place in their natural habitat, which is literally melting away as a result of global warming.Hassol, Susan Joy (2004), Impact of a Warming Arctic: Arctic Impact Climate Assessment, Cambridge: Cambridge University Press, ISBN 0 521 61778 2, OCLC 56942125, <http://amap.no/workdocs/index.cfm?dirsub=%2FACIA%2Foverview>. The United States Geological Survey stated in November 2006, that the Arctic shrinkage in the Alaskan portion of the Beaufort Sea has led to a higher death rate for polar bear cubs.Regehr, Eric V.; Amstrup, Steven C. & Stirling, Ian (2006), written at Anchorage, Alaska, Polar Bear Population Status in the Southern Beaufort Sea, Reston, Virginia: U.S. Geological Survey, Open-File Report 2006-1337, <http://pubs.usgs.gov/of/2006/1337/pdf/ofr20061337.pdf>. Retrieved on 15 September 2007
Three polar bears investigate the submarine USS Honolulu 280 miles (450 km) from the North Pole.
Mother and two cubs climbing up Guillemot Island, Ukkusiksalik National Park
A 1999 study by scientists from the Canadian Wildlife Service of polar bears in the Hudson Bay area showed that global warming is threatening polar bears with starvation. Rising temperatures cause the sea-ice from which the bears hunt to melt earlier in the year, driving them to shore weeks before they have caught enough food to survive the period of scarce food in the late summer and early fall,Stirling, Ian; Lunn, N. J. & Iacozza, J. (September 1999), "Long-term Trends in the Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climatic Change", Arctic 52 (3): pp. 294-306, ISSN 0004-0843, <http://pubs.aina.ucalgary.ca/arctic/Arctic52-3-294.pdf>. Retrieved on 11 November 2007 and leading to a 22% decline in the local subpopulation.
The United States Geological Survey forecasts that two-thirds of the world\'s polar bears will disappear by 2050, based on moderate projections for the shrinking of summer sea ice caused by global warming.Amstrup, Steven C.; Marcot, Bruce G. & Douglas, David C. (2007), Forecasting the Range-wide Status of Polar Bears at Selected Times in the 21st Century, Reston, Virginia: U.S. Geological Survey, <http://www.usgs.gov/newsroom/special/polar_bears/docs/USGS_PolarBear_Amstrup_Forecast_lowres.pdf>. Retrieved on 29 September 2007 The bears would disappear from Europe, Asia, and Alaska, and be depleted from the Arctic archipelago of Canada and areas off the northern Greenland coast. By 2080, they would disappear from Greenland entirely and from the northern Canadian coast, leaving only dwindling numbers in the interior Arctic archipelago. Global warming has already had an impact on polar bear population health and size. Recent declines in polar bear numbers can be linked to the retreat of sea ice and its formation later in the year."Starving polar bears shame Bush to act" Ice is also breaking up earlier in the year, forcing bears ashore before they have time to build up sufficient fat stores, or forcing them to swim long distances, which may exhaust them, leading to drowning. The result of the effects of global warming are thinner bears, a decrease in reproduction rates, and lower survival rates in juvenile bears."Polar Bears in a Warming Climate" The latest estimate of the IUCN is that 7 out of 19 subpopulations are declining or already severely reduced.
Predictions differ on the extent to which polar bears could adapt to climate change by switching to terrestrial food sources. Mitchell Taylor, the Nunavut Government Manager of Wildlife Research, wrote to the U.S. Fish and Wildlife Service arguing that local studies are insufficient evidence for global protection at this time. The letter stated, "At present, the polar bear is one of the best managed of the large Arctic mammals. If all Arctic nations continue to abide by the terms and intent of the Polar Bear Agreement, the future of polar bears is secure…. Clearly polar bears can adapt to climate change. They have evolved and perisisted for thousands of years in a period characterized by fluctuating climate."Taylor, Mitchell K. (April 6th, 2006). "Review of CBD Petition" (PDF). Letter to the U.S. Fish and Wildlife Service. Retrieved on 2007-09-08. Ken Taylor, deputy commissioner for Alaska\'s Department of Fish and Game, has said, "I wouldn\'t be surprised if polar bears learned to feed on spawning salmon like grizzly bears." However, many scientists consider these theories to be naive.; it is noted that black and brown bears at high latitudes are smaller than elsewhere, because of the scarcity of terrestrial food resources.Stirling, Ian & Derocher, Andrew E. (Fall 2007), "Melting Under Pressure: The Real Scoop on Climate Warming and Polar Bears", The Wildlife Professional (Lawrence, Kansas: The Wildlife Society) 1 (3): pp. 24-27, 43, <http://www.biology.ualberta.ca/faculty/andrew_derocher/uploads/abstracts/Stirling_Derocher_Wildlife_Professional_PB_climate_2007.pdf>. Retrieved on 17 November 2007. The IUCN wrote:
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First polar bear shot in the S. A. Andrée\'s Arctic balloon expedition of 1897
Humans are the only regular predators of polar bears. For the Inuit, hunting of the polar bear, or Nanuk has been an important aspect of survival and culture for thousands of years.Lockwood, pp 6-9 Polar remains have been found at hunting sites dating to 2,500 to 3,000 years ago.Lockwood, pp. 31-36 A traditional hunt in the harsh Arctic could take several days, and like most native people, the Inuit made use of the entire bear, including its fur, meat, sinew, and bones. Only the liver was not used, as its high concentration of vitamin A is poisonous to humans.As a carnivore which feeds largely upon fish-eating carnivores, the polar bear ingests large amounts of vitamin A, which is stored in their livers. The resulting high concentrations cause Hypervitaminosis A. Rodahl, K. & Moore, T. (July 1943), "The vitamin A content and toxicity of bear and seal liver", The Biochemical Journal (London: Portland Press) 37 (2): pp. 166-168, ISSN 0264-6021, <http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1257872&blobtype=pdf>. Retrieved on 11 November 2007.
Traditional subsistence hunting was of a small enough scale to not significantly affect polar bear populations, however commercial hunting of the polar bear for its fur began in the 1500s to 1700s. Hunters from around the Arctic have harvested hundreds of polar bears annually since at least the 18th century. The numbers taken grew rapidly in the 1960s, peaking around 1968 with a global total of 1,250 bears that year. (February 1970) "Proceedings of the 2nd Working Meeting of Polar Bear Specialists" (HTML) in Polar Bears. {{{booktitle}}}, Morges, Switzerland: IUCN. Retrieved on 2007-10-24. Although the polar bear was not deemed endangered at the time, the growing threat encouraged countries to regulate polar bear hunting around that time. Norway passed a series of increasingly strict regulations from 1965 to 1973. Canada began imposing hunting quotas in 1968. The U.S. began regulating in 1971 and adopted the Marine Mammal Protection Act in 1972. In 1973, the International Agreement on the Conservation of Polar Bears (known as the Oslo Agreement) was signed by the five nations whose Arctic territory is inhabited by polar bears: U.S., Canada, Norway, Denmark (via its territory Greenland) and Russia (then the Soviet Union). Although the agreement is not enforceable in itself, member countries agreed to place restrictions on recreational and commercial hunting, completely ban hunting from aircraft and icebreakers, and conduct further research.International Agreement on the Conservation of Polar Bears, November 15, 1973, Oslo The treaty allows hunting "by local people using traditional methods," although this has been liberally interpreted by member nations. All nations except Norway allow hunting by the Inuit, and Canada and Denmark allow trophy hunting by tourists.[citation needed]
The Government of the Northwest Territories maintain their own quota of 72–103 bears within the Inuvialuit communities of which some are set aside for sports hunters. The Soviet Union declared a complete protection in 1955, but allows hunting by the indigenous people on the basis that it is part of their culture. It signed the "Agreement between the Government of the United States of America and the Government of the Russian Federation on the Conservation and Management of the Alaska-Chukotka Polar Bear Population" in October 2000.
Skin of hunted polar bears in Ittoqqortoormiit (NE Greenland)
In Greenland, regulations for the species were first introducted in 1994 and expanded by executive order in 2005. Until 2005, Greenland placed no limit on hunting by indigenous people. It imposed a limit of 150 for 2006. It also allowed recreational hunting for the first time.The Humane Society of the United States "Hitting Polar Bears When They Are Down" Other provisions included year-round protection of cubs and mothers, restrictions on weapons used, and various administrative requirements to catalogue kills. Since 1973, Norway has had a complete ban on polar bear hunting.
Polar bears at the Detroit Zoo
Polar bears accumulate high levels of artificial halocarbons such as PCBs and pesticides because of their diet. Their position at the top of the food pyramid tends to concentrate pollutants, particularly halocarbons because of their lipophilicity: halocarbons are soluble in the blubber which makes up the bulk of the polar bear\'s diet. Halocarbons are known to be toxic to other animals because they mimic hormone chemistry, and biomarkers such as immunoglobulin G and retinol suggest similar effects on polar bears. The overall significance to population health is uncertain because of unique features of polar bear biology such as summertime fasting. PCBs have received the most study, and they have been associated with birth defects and immune system deficiency.Skaare, Janneche Utne; Larsen, Hans Jørgen & Lie, Elisabeth et al. (December 2002), "Ecological risk assessment of persistent organic pollutants in the arctic", Toxicology (Shannon, Ireland: Elsevier Science) 181-182: pp. 193-197, ISSN 0300-483X, <http://www.biology.ualberta.ca/faculty/andrew_derocher/uploads/abstracts/Skaare_et_al_2002.pdf>. Retrieved on 17 November 2007. Polar bears in Svalbard have the highest concentrations of PCBs, and biologists suggest this may explain the high incidence of hermaphroditic bears in the area.Wiig, Oystein; Derocher, Andrew E. & Cronin, Matthew M. et al. (October 1998), "Female Pseudohermaphrodite Polar Bears at Svalbard", Journal of Wildlife Diseases (Lawrence, Kansas: Wildlife Disease Association) 34 (4): pp. 792-796, ISSN 0090-3558, <
