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Overview

Brief Summary

Description

Polar Bears prey mostly on Ringed Seals. In the spring, the pups are easy prey. They also hunt Bearded and Harp Seals, Walruses, Beluga, Narwhals, and sea ducks, and very occasionally eat small amounts of plant matter. They travel long distances to stay with pack ice, and fast for long periods of time if food is not available. In Hudson Bay, the ice melts by late July and the bears fast until November, when it freezes again. They do not drink water or urinate the whole time. Pregnant females, who enter dens to give birth, continue fasting for another four months, living only on stored fat for eight months. Cubs are born in December, and are ready to follow their mother out of the den and learn to hunt by March or April. They are independent when they are about two-and-a-half years old, at which point the female mates again.

Links:
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Biology

Polar bears are solitary mammals throughout most of the year, with the exception of breeding pairs and family groups (3). Populations, or stocks, of polar bears are distributed throughout the Arctic and have overlapping home ranges which are not defended, and may vary in size from a few hundred to over 300,000 square kilometres (3) (4). The main food source is ringed seals P. hispida, and, to a lesser degree, bearded seals (Erignathus barbatus). The polar bears capture seals when they surface to breathe, or hunt them in their lairs, where young seals are nurtured (3). Polar bears show some amazing adaptations to their Arctic life and are able to detect prey that are almost a kilometre away and up to a metre under the compacted snow, using their heightened sense of smell (2). They also feed opportunistically on walruses, belugas, narwhals, waterfowl and seabirds (2). When food is available these bears have a remarkable ability to devour large amounts of food rapidly, and are also metabolically unique in their ability to switch from a normal state to a slowed-down, hibernation-like condition at any time of year when there is less food available (3). For example, in Hudson Bay the ice melts completely by mid-July and, as it does not re-freeze until mid-November, pregnant females do not feed for 8 months. During this fasting time, they metabolise their fat and protein stores and recycle metabolic by-products. During periods of particularly cold weather polar bears may also fast, and are known to conserve energy by occupying temporary dens (3). Polar bears breed from late March to late May (2). Females nurse and care for their cubs for 2.5 years and are therefore only available for mating once the cubs are independent, every three years. As this means that only a third of females can breed each season there is intense competition by the males for females, which may explain why males are so large in size (3). Females must mate many times over a period of several weeks before ovulation and fertilisation are stimulated (induced ovulation), and breeding pairs remain together for one to two weeks to ensure successful mating. If the female's partner is displaced she may mate with more than one male at this time. Implantation of the fertilised egg is delayed until mid-September to mid-October, and the female gives birth to the young in a snow den some two to three months later (3). Two-thirds of litters are twins, and single litters and triplets are also born (3). Though the polar bear has low reproductive potential, individuals do live for a long time, and have been known to live for up to 30 years (3).
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Description

The polar bear is the largest living land carnivore in the world today, with adult males growing up to 2.6 meters in length (2). The most well known of all bears, the polar bear is immediately recognisable from the distinctive white colour of its thick fur (2). The only unfurred parts of the body are the foot pads and the tip of its nose, which are black, revealing the dark colour of the skin underneath the pelt (3). The neck of the polar bear is longer than in other species of bears, and the elongated head has small ears. Polar bears have large strong limbs and huge forepaws which are used as paddles for swimming (3). The toes are not webbed, but are excellent for walking on snow as they bear non-retractable claws which dig into the snow like ice-picks (3). The soles of the feet also have small projections and indents which act like suction cups and help this bear to walk on ice without slipping (2). Females are about half the size of males, although a pregnant female with stored fat can exceed 500 kg in weight. Polar bear cubs weigh up to 0.7 kilograms at birth. They look similar in appearance to adults, though they have much thinner fur (2).
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Comprehensive Description

Description of Ursus maritimus

Ursus maritimus is one scientific name for the polar bear. These white bears are native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world\'s largest land carnivore along with the omnivorous Kodiak Bear. An adult male weighs around 350–680 kg (770–1,500 lb), while an adult female is about half that size. It can interbreed with the brown bear, leading some to conclude that this is not a separate species but falls inside Ursos arctos (brown or grizzly bears). Polar bears occupy a distinctive narrow ecological niche, well adapted to cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet. Although most polar bears are born on land, they spend most of their time at sea. Polar bears can hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present. The polar bear is classified as a vulnerable species, with eight of the nineteen polar bear subpopulations in decline. For decades, large scale hunting raised international concern for the future of the species but populations rebounded after controls and quotas began to take effect. For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of Arctic indigenous peoples, and polar bears remain important in their cultures.
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Distribution

Range Description

Polar Bears live throughout the ice-covered waters of the circumpolar Arctic (Obbard et al. 2010, www.pbsg.npolar.no). Although some occur in the permanent multi-year pack ice of the central Arctic basin, they are most common in the annual ice over the continental shelf and inter-island archipelagos that surround the polar basin. Polar Bears that have continuous access to sea ice are able to hunt throughout the year. However, in those areas where the sea ice melts completely each summer,Polar Bearsare forced to spend several months on land, where they primarily fast on stored fat reserves until freeze-up. Use of land byPolar Bearsduring the ice-free season appears to be increasing at least in some areas where sea ice duration has declined (e.g., Schliebe et al. 2008, Herreman and Peacock 2013).The southern extent of the range ofPolar Bearsoccurs off the coast of Newfoundland, Canada in the northwest Atlantic Ocean. The northernmost documented observation of aPolar Bearwas at 8946N, 25 km from the North Pole (van Meurs and Splettstoesser 2003).Currently, the most southerly known denning area is on Akimiski Island in James Bay, Canada, at about 5235N (Kolenosky and Prevett 1983).

The species is found in Canada (Manitoba, Newfoundland, Labrador, Nunavut, Northwest Territories, Quebec, Yukon Territory, Ontario), Greenland/Denmark, Norway (including Svalbard), Russian Federation (North European Russia, Siberia, Chukotka, Sakha (Yakutia), Krasnoyarsk), United States (Alaska). Also, vagrants occasionally reach Iceland.

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Polar bears have a circumpolar distribution. They range throughout the arctic region surrounding the North Pole. The limits of their range are determined by the ice pack of the Arctic Ocean and the landfast ice of surrounding coastal areas. Bears have been reported as far south as the southern tips of Greenland and Iceland. During the winter, polar bears will range along the southern edge of the ice pack or northern edge of ice formed off the coasts of the continents. Pregnant females will overwinter on the coastlines where denning habitat is available for bearing young. During the summer, bears will remain at the edge of the receding ice pack or on islands and coastal regions that retain landfast ice. Six different populations are recognized as: Wrangel Island and western Alaska, northern Alaska, the Canadian Arctic archipelago, Greenland, Svalbard-Franz Josef Land, and Central Siberia.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); arctic ocean (Native )

Other Geographic Terms: holarctic

  • DeMaster, D., I. Stirling. 1981. *Ursus maritimus*. Mammalian Species, 145: 1-7.
  • Nowak, R. 1999. Walker's Mammals of the World. Baltimore and London: The Johns Hopkins University Press.
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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Polar bears have a circumpolar distribution in the northern hemisphere, including the East Siberian, Laptev, Kara, and Barents seas of Russia; Fram Strait (the narrow strait between northern Greenland and Svalbard), Greenland Sea and Barents Sea of northern Europe (Norway and Greenland); Baffin Bay, which separates Canada and Greenland, through most of the Canadian Arctic archipelago and the Canadian Beaufort Sea; and the Chukchi and Beaufort seas west and north of Alaska (Amstrup 2003, USFWS 2008). The range encompasses portions of northern Canada (Northwest Territories to Labrador and Newfoundland), Greenland, Norway, northern Russian Federation (Krasnoyarsk, North European Russia, West Siberia, Yakutiya), Svalbard and Jan Mayen, and the United States (northern Alaska). Distribution in most areas changes with the seasonal extent of sea-ice cover. The species in now excluded by humans from some parts of the historical southern portion of the range.

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Historic Range:
U.S.A. (AK), Canada, Russia, Denmark (Greenland), Norway

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Range

This bear is found throughout the circumpolar Arctic on ice-covered waters, from Canada, to Norway, parts of the US, the former USSR and Greenland (Denmark). The furthest south the polar bears occur all year round is James Bay in Canada, which is about the same latitude as London (2). During the winter, when the ice extends further south, polar bears move as far south as Newfoundland and into the northern Bering Sea (2). They rarely enter the zone of the central polar basin as there is thick ice all year round and there is little to eat (2).
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Physical Description

Morphology

The body of a polar bear is large and stocky, similar to that of a brown bear, except it lacks the shoulder hump. The head is relatively smaller than the heads of other bears and the neck is elongated. At the shoulder a polar bear can measure 1.6 m in height. Adult males weigh between 300-800 kg (660-1760 lbs) and can reach 2.5 m in length from tip of nose to tip of tail. Females are smaller, weighing 150 to 300 kg (330 to 660 lbs) and measuring 1.8 to 2 m in length. The pelage generally has a white appearance, but it can be yellowish in the summer due to oxidation or may even appear brown or gray, depending on the season and light conditions. Polar bear skin is black and the fur is actually clear, lacking in pigment. The white appearance is the result of light being refracted from the clear hair strands. The forepaws are broad and make excellent paddles while swimming. The soles of both hind and fore feet are furred for insulation and traction while walking on ice and snow. Polar bears have a plantigrade gait. Females have four functional mammae.

Range mass: 150 to 800 kg.

Range length: 180 to 250 cm.

Other Physical Features: endothermic ; heterothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

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Size

Size in North America

Sexual Dimorphism: Males are about twice the size of females.

Length:
Range: 2,300-2,600 mm males; 1,900-2,100 mm females

Weight:
Range: "400-600 kg males; 175-300 kg females (350-500 kg when pregnant) "
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Polar Bears occur at low densities throughout the circumpolar Arctic and are more abundant in shallower, ice-covered waters associated with the continental shelf where currents or upwellings increase biological productivity. Seasonally, in the summer open water season, Polar Bears may be found on land in higher densities.

The Polar Bear is a K-selected species with late sexual maturity, small litter size, high maternal investment and high adult survival. The Polar Bears reproductive rate is among the lowest in all mammals (Bunnell and Tait 1981) although similar to that of other ursids. Females generally mature at 4-5 years, and enter a prolonged oestrus between late March and early June, although most mating occurs in April and early May. Ovulation is induced by mating (Stirling 2009), and implantation is delayed until autumn. The total gestation period ranges between 195-265 days (Uspenski 1977, Amstrup 2003). Whether or not the embryo implants and proceeds to develop is likely determined by body condition. Pregnant females enter dens in snow drifts or slopes on land, close to the sea (Andersen et al. 2012), or on sea ice (in the Chukchi and Beaufort seas) as early as September/October, but more typically in late autumn (Lentfer and Hensel 1980, Amstrup and Gardner 1994, Wiig 1998). Females give birth inside the den, usually in late December to early January (Derocher et al. 1992, Amstrup 2003). Polar Bears most often give birth to twin cubs; singleton and triplet litters are less frequent. Newborn Polar Bears are blind, sparsely haired and weigh approximately 0.6 kg (Blix and Lentfer 1979). They grow rapidly, fed on rich milk from their mother (36% fat; Derocher et al. 1993), and when they emerge from the den sometime between early March and late April (Pedersen 1945, Wiig 1998), they weigh 10-12 kg (Amstrup 2003). In some regions, after emerging from the den, the female may not have fed for a period up to 8 months, which may be the longest period of food deprivation for any mammal (Watts and Hansen 1987).

Cub mortality is high in the first year (Larsen 1985, Amstrup and Durner 1995, Wiig 1998), with the probability of cub survival largely determined by maternal condition. Mothers with larger fat stores in the fall emerge in the spring with larger cubs which are more likely to survive (Atkinson and Ramsay 1995, Derocher and Stirling 1998, Robbins et al. 2012a). The young usually stay with their mother for two years (Ln 1970, Stirling et al. 1976, Amstrup and Durner 1995, Wiig 1998), and consequently females on average do not enter a new reproductive cycle more often than every third year most places (Amstrup 2003). In contrast to their low reproductive rates, adult Polar Bears have high survival rates (Obbard et al. 2010).

Polar Bears are the most carnivorous of the extant species of bears. Throughout their range, Ringed Seals (Phoca hispida), preferably young-of-the-year, and to a lesser extent Bearded Seals (Erignathus barbatus) are their primary prey (Derocher et al. 2002, Thiemann et al. 2008). In some areas they are also known to take Harp Seals (Pagophilus groenlandicus), Hooded Seals (Cystophora cristata), and even larger species such as Walrus (Odobenus rosmarus) and Beluga (Delphinapterus leucas) (Thiemann et al. 2008). Polar Bears digest fat more efficiently than protein (Best 1984). Polar Bears are large when compared to other ursid species, which is a consequence of their energy-rich diet. Although birds, fish, vegetation and kelp are eaten where locally available during the ice free-season (Pedersen 1945, Russell 1975, Dyck and Romberg 2007, Born et al. 2011, Gormezano and Rockwell 2013), it is unlikely that Polar Bears would be capable of gaining enough nutritional benefit to survive on a primarily terrestrial diet (Ramsay and Hobson 1991, Hobson et al. 2009, Rode et al. 2010b, Rode et al. 2015).

Systems
  • Terrestrial
  • Marine
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Polar bears are considered by many to be marine mammals. The name Ursus maritimus means maritime bear. Their preferred habitat is the pack ice of the Arctic Ocean. The ice edge and pressure ridges where fractures and refreezing occur provide the best hunting ground. Bears will travel as much as 1,000 km north and south, as the ice melts and freezes. During summer bears may remain on islands or coastlines with landfast ice, drift on ice flows, or get stranded on land where they are forced to endure warm weather.

Range elevation: 0 (low) m.

Average elevation: 0 m.

Habitat Regions: polar ; terrestrial ; saltwater or marine

Terrestrial Biomes: tundra ; icecap

Aquatic Biomes: coastal

  • Stirling, I., E. McEwan. 1975. The caloric value of whole ringed seals (*Phoca hispida*) in relation to polar bear (*Ursus maritimus*) ecology and hunting behavior. Canadian Journal of Zoology, 53: 1021-1027.
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Comments: Polar bears are closely tied to arctic pack ice. They prefer areas with ice that is periodically active, such as at the interface of landfast ice and drifting pack ice along the arctic coasts or near polynyas. Polar bears show a preference for sea ice located over and near the continental shelf, likely due to higher biological productivity in these areas and greater accessibility to prey in near-shore shear zones and polynyas (areas of open sea surrounded by ice) compared to deep-water regions in the central polar basin; they are most abundant near the shore in shallow-water areas, and also in other areas where currents and ocean upwelling increase marine productivity and serve to keep the ice cover from becoming too consolidated in winter (see USFWS 2008 for specific sources of this information).

Sometimes polar bears wander inland as much as 150 km from the coast. In the Bering and Chukchi Seas, Alaska, where sea ice melts in summer, bears migrate up to 1,000 km to remain with the southern ice boundary (Garner et al. 1990, 1994 in Amstrup 2003); in Hudson Bay, James Bay and parts of the Canadian Arctic, bears may be forced onto land for up to several months when sea ice melts in summer (Jonkel et al. 1976, Lunn et al. 1997 in Amstrup 2003). During ice-free period along western Hudson Bay, adult males occupy the coast while family groups and pregnant females occur farther inland. Pregnant females remain on or near land in dens through winter while males and non-breeders winter on sea ice. On land, range of subadults overlaps that of adult males (Derocher and Stirling 1990).

Female denning habitat may be found in mountain, fjord, or even relatively flat tundra areas, but generally it is near the coast and contains microhabitats which catch and collect snow in fall and early winter (Amstrup 2003). While most denning occurs on coastlines, bears may also den on drifting pack ice and on land-fast ice adjacent to shore (Amstrup and Gardner 1994). Females typically dig maternity dens in a hillside snowbank (in southwestern Hudson Bay, however, pregnant females commonly overwinter in earth dens 20-100 km from the coast). Dens often are built within 8 km of coast and rarely more than 48 km offshore (though sometimes in active offshore pack ice as much as 550 km north of Alaskan coast). Polar bears exhibit a general fidelity to denning areas and even after months of long-distance passive transportation on sea ice females often return to specific den habitats (Amstrup 2003).

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Pan-Arctic, associated with sea ice; Seasonal movement (north with receding ice edge)
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The preferred habitat is the annual ice near the coastlines of continents and islands, where there are large numbers of ringed seals (Phoca hispida), on which these bears feed (2).
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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Movements associated with distribution and movement of sea ice. In some areas makes extensive north-south migrations (DeMaster and Stirling 1981) that are dependent on seasonal melting and freezing of nearshore ice (Amstrup 2003). Moves south with drifting ice flows in spring/summer, north along shore in summer after ice breakup. See Amstrup (1995) for extensive information on movements in the Chukchi and Beaufort Seas.

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Trophic Strategy

Polar bears are carnivores. In the summer, they may consume some vegetation but gain little nutrition from it. Their primary prey are ringed seals (Pusa hispida). They also hunt bearded seals (Erignathus barbatus), harp seals (Pagophilus groenlandicus), hooded seals (Cystophora cristata), walruses (Odobenus rosmarus), sea birds and their eggs, small mammals, fish and scavenge on carrion of seals, walruses, or whales. Bears often leave a kill after consuming only the blubber. The high caloric value of blubber relative to meat is important to bears for maintaining an insulating fat layer and storing energy for times when food is scarce. Polar bears do not store or cache unconsumed meat as other bears do.

Polar bears have two hunting strategies. Still-hunting is used predominately. This involves finding a seal's breathing hole in the ice and waiting for the seal to surface to make the kill. When a bear sees a seal basking out of the water it will use a stalking technique to get close, then make an attempt at catching it. One stalking technique is crouching and staying out of sight while creeping up on the seal. Another technique is to swim through any channels or cracks in the ice until it is close enough to catch the seal. Using this technique a bear may actually dive under the ice and surface through the breathing hole in order the surprise the seal and eliminate its escape route. Feeding usually occurs immediately after the kill has been dragged away from the water. Polar bears consume the skin and blubber first and the rest is often abandoned. Other polar bears or arctic foxes then scavenge these leftovers. After feeding, polar bears will wash themselves by licking and rinsing their fur.

Animal Foods: birds; mammals; fish; eggs; carrion

Plant Foods: leaves

Primary Diet: carnivore (Eats terrestrial vertebrates)

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Comments: Seals are primary food source; especially ringed, also bearded and harp seals. May hunt larger animals such as beluga whales and walruses and consumes fish, small mammals, bird eggs and sometimes vegetation, especially in summer when other food is unavailable. Pregnant females may fast for 8 months while in maternal dens (Derocher et al. 1992, Amstrup 2003). Reportedly are surplus killers, but do not normally cache prey they have killed. They consume the highest-fat portions of seals first and young or smaller bears may be driven away from kills by larger bears (Amstrup 2003). This species apparently digests fat more easily than protein and uses metabolic water released from fat metabolism, an efficient adaptation to the arctic environment where energy is otherwise required to melt ice and snow to make water available (Amstrup 2003).

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Associations

Polar bears are a top carnivore of the arctic. The remains of seal kills left unconsumed by bears are likely an important source of food for younger, less-experienced polar bears and for Artic foxes.

Ecosystem Impact: keystone species

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Humans and other polar bears are the only predators of Ursus maritimus. Male polar bears may prey on cubs if they come into contact. Females with cubs tend to avoid other bears for this reason. Historically, polar bears have been hunted by the native peoples of the arctic for fur and meat. Commercial and sport hunting of polar bears increased in the 1900s as the price of pelts reached as much as $3000.

Known Predators:

  • humans (Homo sapiens)
  • male polar bears (Ursus maritimus)

Anti-predator Adaptations: cryptic

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Known predators

Ursus maritimus is prey of:
Homo sapiens
Ursus maritimus

This list may not be complete but is based on published studies.
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Known prey organisms

Ursus maritimus preys on:
Phocidae
Actinopterygii
Aves
Mammalia
Delphinapterus leucas
Monodon monoceros
Ursus maritimus
Phoca largha

Based on studies in:
Norway: Spitsbergen (Coastal)

This list may not be complete but is based on published studies.
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
  • V. S. Summerhayes and C. S. Elton, Contributions to the ecology of Spitsbergen and Bear Island, J. Ecol. 11:214-286, from p. 232 (1923).
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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 6 - 20

Comments: Based on movement patterns and spatial segregation with limited interchange, the IUCN/SSC Polar Bear Specialist Group and USFWS (2008) recognized 19 relatively discrete (but variously overlapping) populations or management units (Stirling 1991, Amstrup 2003), which correspond with major occupied ecogeographic units.

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Global Abundance

10,000 - 100,000 individuals

Comments: Total population is 20,000-25,000 (see USFWS 2008).

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General Ecology

Generally solitary or in female-offspring groups; aggregations of adult males occur during ice-free period along western Hudson Bay. Sometimes wanders long distances but usually stays in one general area from one year to the next (Reeves et al. 1992). Few predators except man, sometimes killer whale. Unlike other bears, only pregnant females winter in dens; denning is seen as a reproductive strategy (providing a protective environment for young) as opposed to a foraging strategy as it is with other bears, since seal prey is available year-round (Amstrup 2003).

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Life History and Behavior

Behavior

Like other bear species, polar bears have a keen sense of smell and use their sensitive lips and whiskers to explore objects. They vision and hearing are not exceptionally well developed. Polar bears use a "chuffing" sound as a form of greeting.

Communication Channels: tactile ; acoustic ; chemical

Perception Channels: visual ; tactile ; acoustic ; chemical

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Cyclicity

Comments: Most active during the first third of the day (DeMaster and Stirling 1981). Pregnant females are dormant in winter dens from autumn to spring, when young are able to survive outside. Variable snow and ice conditions determine when females enter and exit den sites (Amstrup 2003). In the Beaufort Sea, den entry dates averaged mid-November and den exit dates were late March/early April (Amstrup and Gardner 1994 in Amstrup 2003). Mean den entry for the Canadian Arctic was September 17 and mean den exit March 21 (Messier et al. 1994, in Amstrup 2003). Molting commences in April to May and shorter summer coats are achieved by late summer (Amstrup 2003).

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Life Cycle

0.3m (10 inch) at birth, 0.5-1kg (1-2 lbs); Sexually mature at 4-8 years; Cubs born in dens midwinter; 28 months lactation; Longevity 25-30 years; Behavior; Usually solitary, except female-cub groups; Pregnant females den in winter; Dive to approach basking seals at floe edge
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Life Expectancy

In the wild polar bears are estimated to live 25 to 30 years. Annual adult mortality is estimated to be 8-16%. In captivity a female was still alive at 45 years in old at the Detroit Zoo in 1999.

Range lifespan

Status: wild:
25 to 30 years.

Average lifespan

Status: wild:
30.0 years.

Average lifespan

Status: captivity:
38.2 years.

Average lifespan

Status: wild:
25.0 years.

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Lifespan, longevity, and ageing

Maximum longevity: 43.8 years (captivity) Observations: Like in other species of bears, there is a delayed implantation of the fertilized eggs. That extends the pregnancy to 195-265 days (Ronald Nowak 1999). A wild born female kept in captivity at the Detroit Zoo was about 43.8 years of age when she died (Richard Weigl 2005).
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Reproduction

Polar bears have a sequential polygynous mating system. Male and female breeding pairs remain together for a short time while females are in estrus (3 days).

Mating System: polygynous

Mating occurs in late winter and early spring, from March to June. Delayed implantation extends gestation to 195 to 265 days. Pregnant females establish a winter den on land dug into the snow usually within 8 km of the coast in October or November. An average of 2 cubs are born in the mother's den between November and January, litter sizes can range from 1 to 4. She remains in hibernation, nursing her cubs until April. The mortality rate for cubs is estimated to be 10-30%. The average annual rate of reproduction calculated by DeMaster and Stirling (1981) was 0.274 females per adult female.

Breeding interval: Females breed yearly.

Breeding season: Breeding occurs from March to June.

Range number of offspring: 1 to 4.

Average number of offspring: 2.

Range gestation period: 195 to 265 days.

Range weaning age: 24 to 36 months.

Range age at sexual or reproductive maturity (female): 3.5 (low) years.

Average age at sexual or reproductive maturity (female): 5-6 years.

Range age at sexual or reproductive maturity (male): 3.5 (low) years.

Average age at sexual or reproductive maturity (male): 5-6 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous ; delayed implantation

Average birth mass: 665 g.

Average number of offspring: 2.

Cubs are born with their eyes closed; they have a good coat of fur and weigh about 600 grams. They will emerge from the den in spring weighing 10 to 15 kg. Mothers provide all parental care of their offspring. The cubs remain with their mother for 2 to 3 years. They will not reach sexual maturity until 5 to 6 years old.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); extended period of juvenile learning

  • DeMaster, D., I. Stirling. 1981. *Ursus maritimus*. Mammalian Species, 145: 1-7.
  • Nowak, R. 1999. Walker's Mammals of the World. Baltimore and London: The Johns Hopkins University Press.
  • Ramsey, M., I. Stirling. 1988. Reproductive biology and ecology of female polar bears (*Ursus maritimus*). Journal of Zoology, 214: 601-634.
  • Stirling, I., E. McEwan. 1975. The caloric value of whole ringed seals (*Phoca hispida*) in relation to polar bear (*Ursus maritimus*) ecology and hunting behavior. Canadian Journal of Zoology, 53: 1021-1027.
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Males reach sexual maturity at 3 years in Alaska, at age 4 in many parts of the Canadian Arctic, and at age 5 in the Beaufort Sea, but these younger males may not actually breed due to competition with prime males (>10 years old) (Stirling et al. 1976, 1977b, 1980, 1984 in Amstrup 2003); few males breed successfully until about 6 years old. Females generally are sexually mature in 3-6 years. Breeding occurs from late March to mid-May, with implantation delayed until autumn; gestation period is 195-265 days (DeMaster and Stirling 1981). Two cubs (sometimes 1 or 3) are born December-January (mid-November to mid-December along western Hudson Bay). Newborn cubs are totally helpless, among the least developed of placental mammal young, weighing 600-700 grams. Emergence from maternity dens occurs toward the end of March in Hudson and James bays, in April in Alaska. Young are weaned at approximately 24-28 months. Reproductive rate is low; adult females produce young every 3 years in most areas, in alternate years at lower Hudson Bay (Stirling 1991). Along western Hudson Bay, there was a high degree of reproductive failure; 33% of females classified as pregnant were not accompanied by cubs the following year; annual pregnancy rate of solitary females was 82-100%; pregnancy rates drop off for most females of 21 years or older, but some older females retain reproductive competency through life (Derocher et al. 1992). Generation time is about 15 years (see USFWS 2008).

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Fur provides insulation: polar bear
 

Hair of polar bear insulates it from cold because it has low emissivity in infrared.

     
  "Polar bears are masters at conserving energy. During their eight-month fast, breeding females can lose as much as 45 percent of their weight. So heat retention is important, to avoid spending too much energy to keep warm. The bears' fur is dense, made of clear hairs that scatter light, creating a white effect. Underneath the fur lies black skin that absorbs the sun's rays…polar bears are nearly invisible in the far infrared, the frequency range in which bodies radiate heat. Researchers from Berkeley's Department of Mechanical Engineering, led by professors Boris Rubinsky and Ralph Greif, found that the conventional explanation, that the bears are so well-insulated that their surfaces are the same temperature as the snow, is correct but incomplete: the hair's emissivity in the infrared is also nearly equal to that of snow and that this low emissivity could help to insulate the bears by lowering the amount of infrared heat that the bears radiate away." (Courtesy of the Biomimicry Guild)
  Learn more about this functional adaptation.
  • Preciado JA; Rubinsky B; Otten D; Nelson B; Martin MC; Greif R. 2002. Radiative properties of polar bear hair. Proceedings of the ASME International Mechanical Engineering Congress and Exposition. BED-53: 1-2.
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Functional adaptation

Paws have non-slip grip: polar bears
 

The paws of polar bears grip ice well due to the rough surface of their pads.

     
  "A polar bear spends the winter living on sea ice—ice formed when the ocean freezes. But the bear has no trouble keeping its footing on slippery ground. Its paws are perfect for getting around on a slick, cold surface. Rough pads give it a nonslip grip, and thick fur between the pads keeps the bear’s feet warm. It uses the sharp, curved claws on its front paws like hooks to climb onto the ice from the water. Polar bears' claws also help them dig in the ice when they hunt seals." (Kranking 2001)
  Learn more about this functional adaptation.
  • Kathy Kranking. 2001. Bear Necessities: How Polar Bears Survive the Deep Freeze. National Geographic Kids Magazine [Internet], Accessed 9/24/2007.
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Ursus maritimus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 6 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

ATGTTCATAAACCGGTGATTATTCTCTACGAACCATAAAGACATTGGCACCCTTTATCTTCTGTTCGGTGCATGAGCCGGAATAGTGGGCACTGCCCTCAGCCTTTTAATTCGTGCCGAGCTGGGTCAGCCCGGGGCTCTGTTGGGGGATGATCAGATCTACAATGTAGTCGTAACTGCCCATGCATTCGTGATAATCTTCTTCATAGTTATGCCTATTATAATTGGGGGATTCGGGAACTGATTAGTGCCTTTGATGATCGGTGCCCCCGACATAGCGTTCCCTCGAATAAATAACATAAGCTTCTGGTTGCTGCCACCATCTTTCTTACTGCTTCTGGCCTCCTCTATGGTAGAAGCAGGTGCAGGGACTGGATGAACTGTCTACCCTCCTCTAGCGGGTAATCTGGCCCATGCAGGAGCATCAGTAGACTTAACAATCTTTTCTCTGCACCTAGCAGGCATCTCTTCTATTCTGGGGGCTATCAATTTCATCACTACTATTATTAACATGAAACCCCCTGCAATATCTCAATATCAAACCCCTCTGTTTGTATGATCAGTCCTAATCACAGCAGTACTTCTTCTTTTATCTCTGCCAGTCTTAGCAGCTGGGATTACTATACTACTTACAGATCGAAACCTTAACACTACCTTTTTTGATCCAGCTGGAGGAGGAGATCCTATTTTATATCAACACTTGTTCTGATTCTTCGGACACCCTGAGGTTTACATTCTAATCCTTCCTGGGTTCGGAATGATCTCTCACATTGTTACTTATTATTCAGGAAAAAAAGAACCTTTTGGCTATATAGGAATAGTCTGAGCGATAATATCCATTGGATTCTTAGGATTTATCGTGTGAGCTCATCATATGTTTACCGTAGGTATAGACGTTGACACACGAGCTTACTTCACTTCAGCTACCATAATTATTGCTATCCCGACAGGAGTCAAAGTATTTAGCTGACTAGCCACTCTGCACGGAGGGAATATTAAATGATCTCCCGCTATGATGTGAGCCCTGGGCTTTATTTTCCTGTTTACAGTAGGAGGCCTTACGGGAATTGTCCTAGCTAATTCATCTCTAGACATCGTTCTCCATGACACGTACTATGTGGTAGCCCATTTTCACTACGTGCTGTCAATGGGAGCTGTTTTCGCCATCATAGGAGGATTTGTCCACTGATTCCCACTATTCTCAGGCTACACACTTAATAACACATGAGCAAAAATTCACTTTATAATTATATTCATTGGGGTTAATATGACATTCTTTCCTCAGCATTTTCTAGGCCTGTCAGGAATACCTCGGCGATATTCCGACTATCCAGATGCCTATACAACATGAAACACAGTATCTTCTATAGGCTCATTTATTTCACTAACAGCAGTTATGCTAATAATTTTCATGATTTGGGAGGCCTTCGCATCAAAACGAGAGGTGGCAGTGGTAGAACTTACCTCAACCAACATTGAATGACTACACGGATGCCCTCCTCCATATCACACATTCGAAGAACCTGCCTACGTTACACTAAAATAA
-- end --

Download FASTA File

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Statistics of barcoding coverage: Ursus maritimus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 29
Specimens with Barcodes: 32
Species With Barcodes: 1
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Conservation

Conservation Status

Polar bear populations were recently considered to be stable or growing in some areas. In 1993, the estimated world population was 21,470 to 28,370 bears. In 1972, the United States Marine Mammal Protection Act prohibited all hunting, except for subsistence, of polar bears in the U.S. In 1973 the United States, Russia, Norway, Canada, and Denmark came to an agreement to protect polar bear habitat, limit hunting, and cooperate on research. Polar bear populations are currently threatened by trends in global warming, which continues to decrease the extent of their habitat (pack ice) and their prey base. In 2008 the U.S. Fish and Wildlife Service listed polar bears as threatened. The IUCN lists Ursus maritimus as vulnerable.

US Federal List: threatened

CITES: appendix ii

IUCN Red List of Threatened Species: vulnerable

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National NatureServe Conservation Status

Canada

Rounded National Status Rank: N3 - Vulnerable

United States

Rounded National Status Rank: N3 - Vulnerable

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NatureServe Conservation Status

Rounded Global Status Rank: G3 - Vulnerable

Reasons: Restricted to high northern latitudes; total population size 20,000-25,000, in about 19 relatively discrete major populations; global warming effects on sea ice are projected to result in major declines in polar bear distribution and abundance over the foreseeable future.

Intrinsic Vulnerability: Highly vulnerable

Environmental Specificity: Narrow. Specialist or community with key requirements common.

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Current Listing Status Summary

Status: Threatened
Date Listed: 05/15/2008
Lead Region:   Alaska Region (Region 7) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: T

For most current information and documents related to the conservation status and management of Ursus maritimus , see its USFWS Species Profile

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Status

Vulnerable.
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Status

Classified as Vulnerable (VU) on the IUCN Red List (1).
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IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A3c

Version
3.1

Year Assessed
2015

Assessor/s
Wiig, ., Amstrup, S., Atwood, T., Laidre, K., Lunn, N., Obbard, M., Regehr, E. & Thiemann, G.

Reviewer/s
Rondinini, C.

Contributor/s
Akakaya, H.R., Holmes, E., Reynolds, J., Stern, H., Schliebe, S. & Derocher, A.E

Justification
Loss of Arctic sea ice due to climate change is the most serious threat to Polar Bears throughout their circumpolar range (Obbard et al. 2010, Stirling and Derocher 2012, USFWS 2015). We performed a data-based sensitivity analysis with respect to this threat by evaluating the potential response of the global Polar Bear population to projected sea-ice conditions. Our analyses included a comprehensive assessment of generation length (GL) for Polar Bears; development of a standardized sea-ice metric representing important habitat characteristics for the species; and population projections, over three Polar Bear generations, using computer simulation and statistical models representing alternative relationships between sea ice and Polar Bear abundance.

Our analyses highlight the potential for large reductions in the global Polar Bear population if sea-ice loss continues, which is forecast by climate models and other studies (IPCC 2013). Our analyses also highlight the large amount of uncertainty in statistical projections of Polar Bear abundance and the sensitivity of projections to plausible alternative assumptions. Across six scenarios that projected polar bear abundance three generations forward in time using the median and 95th percentile of estimated GL, the median probability of a reduction in the mean global population size greater than 30% was approximately 0.71 (range 0.20-0.95; see Table 4 in the attached Supporting Material). The median probability of a reduction greater than 50% was approximately 0.07 (range 0-0.35), and the probability of a reduction greater than 80% was negligible. The International Union for the Conservation of Nature Red List Guidelines suggests that assessors consider nearly the full range of uncertainty in potential outcomes, and adopt a precautionary but realistic attitude toward risk tolerance (Section 3.2.3, IUCN 2014). In light of the significant probability, across scenarios, of a reduction in mean global population size greater than 30%, and the relatively low probability of a reduction greater than 50%, we conclude that Polar Bears currently warrant listing as Vulnerable under criterion A3c (IUCN 2014).

History
  • 2008
    Vulnerable (VU)
  • 2006
    Vulnerable (VU)
  • 1996
    Lower Risk/conservation dependent (LR/cd)
  • 1994
    Vulnerable (V)
  • 1990
    Vulnerable (V)
  • 1988
    Vulnerable (V)
  • 1986
    Vulnerable (V)
  • 1982
    Vulnerable (V)
  • 1965
    Less rare but believed to be threatened-requires watching
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Population

Population
At present, 19 subpopulation units of Polar Bears are recognized by the Polar Bear Specialist Group (PBSG) of the International Union for the Conservation of Nature (Obbard et al. 2010). Genetic studies have shown that gene flow occurs among the various subpopulations (Paetkau et al. 1999, Crompton et al. 2008, Peacock et al. 2015) and there is no evidence that any of the units have been evolutionarily separated for significant periods of time. Although demographic exchange may be limited between subpopulations (Mauritzen et al. 2002, Crompton et al. 2008, Peacock et al. 2015), some demographic and genetic exchange occurs. Consequently, the Polar Bear subpopulations cannot be considered as distinct demographic units and the term management units may be more accurate. Ongoing reductions in the duration, distribution, and quality of sea ice due to climate change (Sahanatien and Derocher 2012) may result in different levels of genetic and demographic exchange among subpopulations in the future (Derocher et al. 2004, Molnr et al. 2010), which could lead to new metapopulation dynamics or to functionally isolated subpopulations.

The PBSG summarized the best-available scientific information on the status of the 19 subpopulations of Polar Bears in 2014 (PBSG 2015) including an assessment of current trend (i.e., estimated change in population size over a 12-year period, centred on the time of assessment). The PBSG concluded that one subpopulation (MClintock Channel) has increased, six were stable (Davis Strait, Foxe Basin, Gulf of Boothia, Northern Beaufort Sea, Southern Hudson Bay, and Western Hudson Bay), three were considered to have declined (Baffin Bay, Kane Basin, and Southern Beaufort Sea) and, for the remaining nine (Arctic Basin, Barents Sea, Chukchi Sea, East Greenland, Kara Sea, Lancaster Sound, Laptev Sea, Norwegian Bay, and Viscount Melville Sound) there were insufficient data to provide an assessment of current trend. The type, precision, and time span of data used to estimate trends varies among subpopulations (PBSG 2015).

Estimating Polar Bear abundance is expensive and difficult because the animals often occur at low densities in remote habitats. Although abundance estimates have generally improved in recent decades (Obbard et al. 2010), information remains poor or outdated for some subpopulations. Summing across the most recent estimates for the 19 subpopulations (Table 3 in the Supplementary Material) results in a total of approximately 26,000 Polar Bears ( 95% CI = 22,000-31,000 ). We note that this number differs from what would be obtained by summing abundance estimates in PBSG (2015), because criteria were not the same for including abundance estimates in the two sources (section Population projections). The total number presented here does not include the Arctic Basin subpopulation, for which no information on abundance is available. The 95% confidence intervals presented here were generated using simulation based on estimates of uncertainty in Table 3 and an assumption that the abundance of every subpopulation is independent of the others (see the section Population projections in the Supplementary Material). The mixed quality and even lack of available information on each subpopulation means caution is warranted when establishing and reporting a single estimate of the number of polar bears across the circumpolar Arctic. Therefore we used the abundance data in Table 3 in a relative manner, to scale subpopulation-specific changes to changes in the global population size, rather than in an absolute manner.


Population Trend
Unknown
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Global Short Term Trend: Relatively stable to decline of 30%

Comments: USFWS (2008) reviewed available trend data and concluded that two polar bear populations are increasing (Viscount Melville Sound and M'Clintock Channel; both were severely reduced in the past and are recovering under conservative harvest limits); six populations are stable (Northern Beaufort Sea, Southern Hudson Bay, Davis Strait, Lancaster Sound, Gulf of Bothia, Foxe Basin); five populations are declining (Southern Beaufort Sea, Norwegian Bay, Western Hudson Bay, Kane Basin, Baffin Bay); and six populations are designated as data deficient (Barents Sea, Kara Sea, Laptev Sea, Chukchi Sea, Arctic Basin, East Greenland) with no estimate of trend. The two populations with the most extensive time series of data, Western Hudson Bay and Southern Beaufort Sea, were both considered to be declining.

Within the foreseeable future (determined by USFWS 2008 to be 45 years, which is equivalent to three generations), the polar bear is likely to experience a significant decline, primarily as a result of loss of sea ice (USFWS 2008). The projected rate of decline is uncertain but likely will exceed 30 percent over three generations (IUCN SSC Polar Bear Specialist Group).

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Threats

Major Threats
Anthropogenic and natural changes in Arctic environments, as well as recognition of the shortcomings of our knowledge of Polar Bear ecology, are increasing the challenges for Polar Bear conservation and management. Higher ambient temperatures and erratic weather fluctuations, symptoms of anthropogenic climate change, are increasing across the range of polar bears. Polar Bears are dependent upon Arctic sea ice for access to their prey. Their dependence on an ephemeral habitat that exists as a function of sea surface and atmospheric temperatures means that climate warming poses the single most important threat to the long-term persistence of Polar Bears (Obbard et al. 2010). Arctic sea ice loss has thus far progressed faster than most climate models have predicted (Stroeve et al. 2007) with September sea extent declining at a linear rate of 14% per decade from 1979 through 2011 (Stroeve et al. 2012, Stroeve et al. 2014). Because changes in sea-ice are known to alter Polar Bear abundance, productivity, body condition, and distribution (Stirling et al. 1999, Fischbach et al. 2007, Schleibe et al. 2008, Durner et al. 2009, Regehr et al. 2010, Rode et al. 2010a, 2012, 2014b, Bromaghin et al. 2015), continued climate warming will increase future uncertainty and pose severe risks to the welfare of Polar Bear subpopulations (Stirling and Derocher 2012, Derocher et al. 2013). Arctic sea ice extent is linearly related to global mean temperature, which in turn, is directly related to atmospheric greenhouse gas concentrations (Amstrup et al. 2010). Population and habitat models predict substantial declines in the distribution and abundance of Polar Bears in the future (Durner et al. 2009, Amstrup et al. 2008, Hunter et al. 2010, Castro de la Guardia et al. 2013, Hamilton et al. 2014). Although Polar Bears living in historically colder regions of the Arctic might derive transient benefit from a climate-driven transition away from multi-year ice (Derocher et al. 2004), the annual sea ice must persist long enough for Polar Bears to derive benefit from associated changes in seal availability and biological productivity. Recent sea ice simulations suggest large regions of the Canadian Arctic Archipelago will be ice free for >5 months by the late 21st century (Hamilton et al. 2014). In other parts of the Arctic, the 5-month ice-free threshold may be reached by the middle of the 21st century (Atwood et al. 2015). These studies are based on sea-ice data obtained from the World Climate Research Programme's Coupled Model Intercomparison Project phase 5 (CMIP5) (http://cmip-pcmdi.llnl.gov/cmip5/). An annual ice-free period of 5 months is likely to lead to extended fasting, which is predicted to lead to increased reproductive failure and starvation (Molnr et al. 2011, 2014a, Robbins et al. 2012b). Nevertheless, uncertainty and regional variability in the near-term effects of climate change must be included in Polar Bear management and conservation plans.

Although there have been local and regional studies on polar bear denning habitat (Kolenosky and Prevett 1983, Messier et al. 1994, Lunn et al. 2004, Richardson et al. 2005, Durner et al. 2003, 2006, 2013, Andersen et al. 2012), large scale mapping of Polar Bear denning habitat across the Arctic has not occurred. It is also unknown how climate change will change denning locations and habitats, though predicted increases in forest fires may have adverse effects on maternity denning habitat in sub-Arctic regions (Richardson et al. 2007). Declining sea ice availability can impair the ability of pregnant females to reach traditional denning areas (Derocher et al. 2011, Cherry et al. 2013) and increases of rain events will be detrimental for denning Polar Bears (Stirling and Derocher 1993, Derocher et al. 2004).

The occurrence of diseases and parasites in Polar Bears is rare compared with occurrences in other ursids. However, with warming Arctic temperatures, altered climate could influence infectious disease epidemiology through mechanisms such as novel pathogen introduction due to range expansion of carrier animals and arthropod vectors; modification of host susceptibility; changes in pathogen evolution, transmission, and number of generations per year; host immunosuppression; shifts in main food sources; altered behaviour; and co-infections with multiple agents (Harvell et al. 2002, Parmesan 2006, Burek et al. 2008, Hueffer et al. 2011). As a result, the potential for exposure to pathogens and resulting disease outbreaks may become more significant threats as Polar Bears experience the cumulative effects of multiple stressors (Patyk et al. 2015).

The warming climate has been associated with an increase in pathogens in other Arctic marine and terrestrial organisms. Parasitic agents that have developmental stages outside the bodies of warm-blooded hosts (e.g., nematodes: Laaksonen et al. 2010) will likely benefit from the warmer and wetter weather projected for the Arctic. Improved conditions for such parasites have already adversely affected the health of some Arctic mammals (Kutz et al. 2013). Bacterial parasites also are likely to benefit from a warmer and wetter Arctic (e.g., Vibrio parahaemolyticus; Baker-Austin et al. 2012). As the effects of climate change become more prevalent, there is concern about the emergence of new pathogens within polar bear range, new threats from existing pathogens that may be able to infect immuno-compromised/stressed bears, and the potential for new and existing pathogens to cross humananimal boundaries (e.g., giardia). Because of the previous limited exposure of Polar Bears to diseases and parasites (Fagre et al. 2015), researchers have as yet been unable to determine whether they will be more susceptible to new pathogens. However, concern is exacerbated by the fact that Polar Bears appear to have a nave immune system (Weber et al. 2013), which may make them particularly vulnerable to infection. Many different pathogens have been found in seal species that are Polar Bear prey; the potential therefore exists for transmission of these diseases to Polar Bears (Kirk et al. 2010). If Polar Bears become nutritionally stressed, altered foraging behaviours such as increased feeding on the internal organs of their primary prey and use of alternative foods (e.g., Prop et al. 2015) may increase the potential for exposure to pathogens. Ensuring the long-term persistence of Polar Bears will necessitate understanding how a rapidly changing physical environment modulates exposure to disease risk factors and, ultimately, population health.

Persistent organic pollutants, which reach Arctic regions via long range transport by air and ocean currents as well as river run off, also increase uncertainty for the welfare of polar bears (Obbard et al. 2010, www.pbsg.npolar.no). Although Polar Bears live in relatively pristine Arctic regions, a variety of industrial toxic substances are brought into Polar Bear management areas from human anthropogenic activities around the world. Polar Bears are apex predators and are therefore exposed to high levels of pollutants, which magnify with each step in the food web resulting in high concentrations in polar bear tissue (Letcher et al. 2010). A key characteristic of these pollutants is that they persist in the environment due to low biotic and abiotic degradation. The contaminant burdens among Polar Bears are known to vary among regions (e.g., Letcher et al. 2010, McKinney et al. 2011). Even where contaminant burdens may be known, their effects on Polar Bear physiology and health are not well understood (Letcher et al. 2010, Sonne et al. 2012). However, Dietz et al. (2015) showed that the risk for reproductive, immune suppressive and carcinogenic effects in polar bear subpopulations across the Arctic are high due to PCB and perflourinated compounds (PFCs) exposure.

Many of the contaminants are lipophilic and bond tightly to lipophilic tissues. Polar Bears are particularly vulnerable to organochlorines because they eat a fat rich diet. Ringed, bearded, and harp seals comprise the main food of Polar Bears and the blubber layer is preferentially eaten by the bears and subsequently, the intake of pollutants is high (Letcher et al. 2010). Recent studies have documented new pollutants in polar bear tissues which expose the species to even more toxic and complex combination of industrial chemicals (Verreault et al. 2005, 2006; Muir et al. 2006; Smithwick et al. 2006; McKinney et al. 2009, 2011; Gebbink et al. submitted). The potential for contaminants to impact Arctic systems is predicted to increase as climate warming alters global circulation and precipitation patterns (Macdonald et al. 2005, Jenssen et al. 2015) and predicting local and regional effects will become more complicated and uncertain.

A three decade study (1983-2010) of East Greenland Polar Bears revealed both declines of conventional POPs and increases in brominated flame retardants (BFRs) and PFCs (Dietz et al. 2008, 2013a,b; Riget et al. 2013). The last decade has showed climate related increases in PCBs as well as peaks of BFRs and PFCs due to recent industrial reductions (Dietz et al. 2013b McKinney et al. 2013).

Although the effects of pollutants on polar bears are only partially understood, levels of such pollutants in some subpopulations are already sufficiently high that they may interfere with hormone regulation, immune system function, and possibly reproduction (Wiig et al. 1998; Bernhoft et al. 2000; Skaare et al. 2000, 2001; Gustavson et al. 2015; Henriksen et al. 2001; Derocher et al. 2003; Derocher 2005; Dietz et al. 2015; Sonne et al. 2015). There are suggestions that species with delayed implantation are more vulnerable to the effects of pollution through endocrine (hormone) disruption (Knott et al. 2011). Further, because female Polar Bears are food deprived during gestation, their pollution load increases in their blood, when energy and pollutants are mobilized from their adipose tissue. Because the cubs are nursed on fat rich milk they are exposed to very high pollution loads from their mother (Polishuk et al. 2002, Bytingsvik et al. 2012). This may pose the greatest threat to the species as the vulnerability of pre- and neonatal polar bears is the most sensible to life-long health effects from long-range transported pollution which decreases immunity, survival and reproductive success (Letcher et al. 2010, Sonne 2010).

An additional emerging threat to Polar Bears is the increase in resource exploration and development in the Arctic along with increased ice-breaking and shipping. There are currently no data on the effects of ice-breaking on habitat use by Polar Bears. Although some studies suggest that Polar Bears are sensitive to localized disturbance at maternity den sites (Lunn et al. 2004, Durner et al. 2006), our knowledge about potential effects of large scale development is lacking.

Oil development in the Arctic poses a wide of range of threats to Polar Bears ranging from oil spills to increased human-bear interactions. It is probable that an oil spill in sea ice habitat would result in oil being concentrated in leads and between ice floes resulting in both Plar Bears and their main prey (Ringed Seal and Bearded Seal) being directly exposed to oil. Polar Bears are often attracted by the smells and sound associated with human activity. Polar Bears are known to ingest plastic, styrofoam, lead acid batteries, tin cans, oil, and other hazardous materials with lethal consequences in some cases (Lunn and Stirling 1985, Amstrup et al. 1989, Derocher and Stirling 1991). Another concern is that seals covered in oil may be a major source of oil to polar bears. Although the biological threats and impacts of oil and gas activities on Polar Bears are reasonably well understood (ritsland et al. 1981; Hurst and ritsland 1982; Stirling 1988, 1990; Isaksen et al. 1998; Amstrup et al. 2006), mitigation and response plans are currently lacking (but see Wilson et al. 2014). Moreover, how Polar Bears will be affected by other types of human activity are less well known (Vongraven et al. 2012).

Significant portions of the Polar Bears range already are being developed and exploration is proposed for many other areas. With warming induced sea ice decline, previously inaccessible areas will be exposed to development and other forms of anthropogenic activities (e.g., trans-Arctic shipping, tourism). The direct effects of human activities, the increased potential for negative human-bear encounters, and the potential for increased local pollution are all concerns that must be understood if we are to understand and manage impacts on the future for Polar Bears.

Our understanding of Polar Bear population dynamics has improved with ongoing development and refinement of analytical methods (e.g., Taylor et al. 1987, 2002, 2005, 2006, 2008a,b, 2009; Amstrup et al. 2001; McDonald and Amstrup 2001; Regehr et al. 2007, 2010, 2015; Aars et al. 2009; Stapleton et al. 2014). These improved and new tools suggest that previous estimates of population parameters and numbers can be biased. Vital rates are subpopulation specific, and different from the generalized rates that were often used to generate previous status reports (Taylor et al. 1987). For the two subpopulations (Southern Beaufort Sea, Western Hudson Bay) that are known to have been impacted by climate change and where a long time series of abundance exist, harvest represents an additive impact. Illegal take of polar bears in Russia, combined with legal subsistence harvest in the U.S., may exceed sustainable limits for the Chukchi subpopulation (pbsg.npolar.no). In many cases harvest documentation and the population data necessary to assess the impact of harvest both are insufficient to allow managers to provide the desired balance between potential yield and take. Given the cultural and economic importance of Polar Bear hunting in many regions, understanding the potential for and the impact of hunting continues to be a critical part of management (Obbard et al. 2010, Vongraven et al. 2012, pbsg.npolar.no).

It is important that subpopulation estimates and projections are based on substantiated scientific data. In some areas, studies to estimate abundance occur infrequently so if the harvest rate is either initially set above the sustainable level or it becomes so, the subpopulation may be reduced before the next inventory is made. In addition, harvest practices may have to be reconsidered given recent knowledge about long-term environmental trends and fluctuations that can affect sustainable removal rates. In some jurisdictions in Canada, the governance system includes aboriginal co-management boards and aboriginal hunting organizations. In some of these co-management systems, both local knowledge and science are to be considered equally in both management and research decisions. Although scientific studies have concluded that the long-term effects of capturing and collaring polar bears are minimal (Ramsay and Stirling 1986, Messier 2000, Thiemann et al. 2013, Rode et al. 2014a), some local groups nevertheless consider these techniques disrespectful or harmful to the animals. As a result, population inventory and ecological studies have been delayed or not permitted. On the other hand, alternative research techniques such as aerial surveys and genetic biopsy capture-recapture methods were designed and implemented. Reduced monitoring will constrain governments ability to assess sustainability of harvest especially if abundance is estimated from aerial surveys which cannot provide data on vital rates (Aars et al. 2009, Stapleton et al. 2014).

Human caused habitat change and increasing human-bear interactions also must be incorporated into polar bear population projections (e.g., Hunter et al. 2010) and polar bear harvest management in the future. Due to increased access to previously isolated areas, Polar Bears will face increased risks from a variety of humanbear interactions. New settlements are possible with industrial development, and expansion of tourist visitations is assured. Although the fact of humanbear interactions can be reasonably measured, we have a long way to go to understand the effect of such interactions. The added stresses, resulting from a more crowded Arctic, may play an important role in the future welfare of Polar Bears.
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Degree of Threat: Very high - high

Comments: Loss of the polar bear's primary habitat (sea ice) is the primary threat. Sea ice is rapidly diminishing throughout the Arctic, and the best available evidence is that Arctic sea ice will continue to be affected by climate change for the foreseeable future (see USFWS 2008 for extensive discussion).

USFWS (2008) determined that harvest is likely exacerbating the effects of habitat loss in several populations. In addition, polar bear mortality from harvest and negative bear-human interactions may in the future approach unsustainable levels for several populations, especially those experiencing nutritional stress or declining population numbers as a consequence of habitat change. Continued efforts are necessary to ensure that harvest or other forms of removal do not exceed sustainable levels. However, USFWS (2008) concluded that overutilization does not currently threaten the polar bear throughout all or a significant portion of its range.

USFWS (2008) evaluated the best available scientific information on disease and predation and determined that disease and predation (including intraspecific predation) do not threaten the species throughout all or any significant portion of its range. Potential for disease outbreaks, an increased possibility of pathogen exposure from changed diet or the occurrence of new pathogens that have moved northward with a warming environment, and increased mortality from cannibalism all warrant continued monitoring and may become more significant threat factors in the future for polar bear populations experiencing nutritional stress or declining population numbers.

Industrial development may hinder natural movement, feeding and breeding patterns, and could expose bears to chemical contaminants. Persistent organic pollutants, such as PCBs, may be adversely affected bear immune systems, thyroid function, and reproduction (Siegel and Cummings 2005: Appendix D). However, USFWS (2008) determined that contaminants, ecotourism, and shipping do not threaten the polar bear throughout all or any significant portion of its range. Some of these, particularly contaminants and shipping, may become more significant threats in the future for polar bear populations experiencing declines related to nutritional stress brought on by sea ice and environmental changes.

Low reproductive rate makes this species slow to recover from declines (Stirling 1991).

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Polar bears are not endangered, though if hunting was not regulated they would be, due to their slow rates of population growth. They do face threats however, that must be constantly monitored (4). The Polar Bear Specialist Group reported in their 2005 meeting that the greatest challenge to the conservation of polar bears may be large-scale ecological change resulting from climatic warming, if the trend documented in recent years continues (5). Other threats to this species include pollution, poaching, and disturbances from industrial activities (4) (5). While the effects of climate change are not certain, it is recognised that even minor climate changes can have profound effects on polar bears and their sea-ice habitat (4). For example, if climate change results in increased snow in the Arctic, polar bears may be less able to hunt prey by entering seal birth lairs, which will affect the survival of both polar bear adults and cubs. On the other hand, if there is reduced snow and increased seasonal rain, seal productivity may be reduced as the lairs may not be thick enough to protect the pups as they develop, or lairs may collapse and kill the seals. In turn this would reduce prey for the polar bears. Unusual warm weather could also impact the polar bear's denning activity (6). Persistent Organic Pollutants (POP) also pose a threat to polar bears. Studies on the accumulation of organochlorines (caused by pollutants) through food chains have shown that polar bears, as top predators, are at risk of accumulating elevated levels of these compounds. These levels are associated with a range of effects, including neurological, reproductive and immunological changes, which may, for example, reduce ability to fight diseases and reproduce (6). In the 1960s and 1970s, extensive hunting of polar bears had pushed them to the brink of extinction. This threat had a considerable impact on polar bear populations, and, though hunting is now controlled, populations are still recovering (4).
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Management

Conservation Actions

Conservation Actions
Conservation actions for Polar Bears vary by jurisdiction and detailed information can be found in Obbard et al. (2010) and at www.pbsg.npolar.no. The International Agreement on the Conservation of Polar Bears that was signed in 1973 by the five nations Canada, Denmark (Greenland) Norway, Soviet Union (Russian Federation) and USA, provides guidance. Article II of the Agreement states that each contracting party shall manage polar bear populations in accordance with sound conservation practices based on the best available scientific data, and according to Article VII, The Contracting Parties shall conduct national research programs on Polar Bears and ...consult with each other on the management of migrating Polar Bear populations.... These articles have been important for stimulating governments to support applied research to answer management questions regarding Polar Bears throughout their range.

In light of the growing concern over Polar Bear conservation in relation to climate change and a number of other issues, such as oil- and gas activities, shipping and tourism, the five Parties have agreed to initiate a process that would lead to a coordinated approach to conservation and management strategies for Polar Bears. A key aspect of this approach is the recognition that plans for action should be developed at a national level leading up to development of comprehensive circumpolar plan for action that address Polar Bear conservation. The Circumpolar Action Plan for Polar Bear is planned to be signed by the parties in autumn 2015.

The Parties recognize that Article VII of the Agreement calls for all Parties to conduct national research programs, particularly relating to the conservation and management of Polar Bears, and that they shall coordinate such research and exchange information on research programs, results, and data on bears taken. The Parties continue to be committed to carrying out research in support of Polar Bear conservation. The Parties also recognize that the technical support and scientific advice on Polar Bear conservation provided by the PBSG supports the 1973 Agreement and is a vital part of the decision making process that the competent authorities should consider in making management decisions. The PBSG has accepted to serve as an independent science advisory body to the Parties.

The PBSG regards the 1973 Agreement as the cornerstone and basis for any action plan on Polar Bears. The PBSG has identified the following research elements to be included in all action plans (Vongraven et al. 2012):
  • Assessment of subpopulation size and/or trend and projection of future status
  • Monitoring harvest and other removals
  • Understanding movements and distribution patterns and how they are changing with ongoing habitat changes
  • Establishing trends in physical condition and why they are changing
  • Documenting human-bear conflicts
  • Documenting trends in habitat use, availability and trends
  • Documenting trends in pollution and disease
  • Vital rates estimation, evaluating trends and projection
The PBSG recognizes that particular elements (for example, monitoring of pollution and sea ice habitat) are of inter-jurisdictional concern and would benefit from multi-jurisdictional cooperation. Further, the Parties shall consult with each other on the management of shared Polar Bear subpopulations, and exchange information on research and management programs. The PBSG has reiterated that all management actions be based on the best scientific information. The PBSG has identified these management elements to be included in all action plans (Vongraven et al. 2012):
  • Protection of essential habitats
  • Use of scientific evidence
  • Monitoring, prevention and sound management of human-bear conflicts
  • Development of inter-jurisdictional agreements for shared populations
  • Development of management strategies to minimize impacts of human activities (e.g. mining, shipping, oil and gas activities, tourism and other human-caused disturbance)
  • Management of sustainable harvest
  • Ensure the active involvement of the local public living in polar bear areas in developing and achieving the goals of the action plan

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Management Requirements: The following management needs were identified in "Alaska's Western Arctic: a summary and synthesis of resources" (Schoen and Senner 2002): Cooperative management between USFWS, Alaska Natives, and other nations, including joint international studies with Canada and Russia would facilitate more complete conservation efforts. Management should endeavor to fully implement the International Polar Bear Agreement, the Habitat Conservation Strategy for Polar Bears in Alaska (USFWS 1995a), and the pending U.S. and Russia Polar Bear Agreement. Polar Bear and human interactions should be minimized. Important habitats should be protected, including "ice-edge" habitats and polynyas, barrier beaches, and denning sites.


Harvest management should focus on protecting females (Armstrup et al. 1986).

See Herrero (1985) for prevention of attacks on humans.

See USFWS (1997) for information on application requirements and permit procedures for the issuance of permits to import trophies of polar bears sport hunted in Canada.

Biological Research Needs: Research is needed on movements of male bears; currently, no satisfactory method for long-term attachment of radio transmitters has been designed. Better estimates of abundance and harvest are also necessary, especially harvest counts for Russia and Greenland.

Relationships between polar bears, seals, and sea ice needs study (Amstrup and DeMaster 1988). Effects of industry should be assessed, particularly the effects of seismic exploration on denning bears. An evaluation of direct and indirect effects of marine oil spills should be conducted.

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Conservation

Following the drastic population losses of polar bears in the 1960s and 1970s, an international accord was reached between the five nations with polar bears (Canada, Norway, US, the former USSR and Denmark, which governed Greenland at that time) (4). These nations signed the 'International Agreement on the Conservation of Polar Bears', and agreed to prohibit unregulated hunting and to outlaw the hunting of the bears from aircrafts and icebreakers (4). The agreement also obliged each nation to protect polar bear denning sites and migration routes, as well as undertake and share information on polar bear research (4). This was one of the first and most successful international conservation measures of the 21st century and was responsible for the recovery of the polar bear (4). The threats caused by climate change are now the main concern, especially as the rate at which environmental changes could occur may be faster than the rate at which many species can adapt. More than ever, the complexity of these issues and their global nature will demand international cooperation if this species and other wildlife is to survive (4).
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Relevance to Humans and Ecosystems

Benefits

Polar bears are viewed as potentially dangerous to humans. Contact between humans and bears is rare due to the large home range of individual bears and the sparse human population throughout their distribution. Two deaths resulting from polar bear encounters have been reported.

Negative Impacts: injures humans (bites or stings)

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Polar bear materials have historically been used by native people of the arctic for fur, meat, and medicines. Hunting by those groups is still allowed in the United States, Canada, and Greenland (Denmark). Trophy and commercial hunters have taken bears for pelts that sold for $3000 in the past.

Positive Impacts: food ; ecotourism ; source of medicine or drug ; research and education

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Economic Uses

Comments: Hunted and trapped for meat and hides for thousands of years; mainly subsistence havest by native arctic peoples. Harvested by natives in Canada, principally within the Northwest Territories; the present annual harvest is about 700, which is probably close to the maximum sustainable yield (Stirling 1991). See USFWS (Federal Register, 17 July 1995) for information on sport harvest in Canada. Subsistence hunting by natives also continues in Alaska. Subjected to sport hunting, mostly by non-natives, in Alaska from the late 1940s to 1972 (Reeves et al. 1992).

Some believe that study of polar bear fur could lead to improvements in solar panels for homes and industry; reportedly the fur is excellent at absorbing ultraviolet radiation (Boston Globe, 4 June 1990).

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Wikipedia

Polar bear

This article is about the animal. For other uses, see Polar bear (disambiguation).

The polar bear (Ursus maritimus) is a carnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is a large bear, approximately the same size as the omnivorous Kodiak bear (Ursus arctos middendorffi).[3] A boar (adult male) weighs around 350–700 kg (770–1,540 lb),[4] while a sow (adult female) is about half that size. Although it is the sister species of the brown bear,[5] it has evolved to occupy a narrower ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet.[6] Although most polar bears are born on land, they spend most of their time at sea. Their scientific name means "maritime bear", and derives from this fact. Polar bears hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present.

The polar bear is classified as a vulnerable species, with eight of the nineteen polar bear subpopulations in decline.[7] For decades, large scale hunting raised international concern for the future of the species but populations rebounded after controls and quotas began to take effect.[citation needed] For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of Arctic indigenous peoples, and polar bears remain important in their cultures.

Naming and etymology[edit]

Constantine John Phipps was the first to describe the polar bear as a distinct species in 1774.[1] He chose the scientific name Ursus maritimus, the Latin for 'maritime bear',[8] due to the animal's native habitat. The Inuit refer to the animal as nanook[9] (transliterated as nanuq in the Inupiat language).[10] The Yupik also refer to the bear as nanuuk in Siberian Yupik.[11] The bear is umka in the Chukchi language. In Russian, it is usually called бе́лый медве́дь (bélyj medvédj, the white bear), though an older word still in use is ошку́й (Oshkúj, which comes from the Komi oski, "bear").[12] In French, the polar bear is referred to as ours blanc ("white bear") or ours polaire ("polar bear").[13] In the Norwegian-administered Svalbard archipelago, the polar bear is referred to as Isbjørn ("ice bear").

The polar bear was previously considered to be in its own genus, Thalarctos.[14] However, evidence of hybrids between polar bears and brown bears, and of the 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.[1]

Taxonomy and evolution[edit]

Polar bears have evolved adaptations for Arctic life, for example, large furry feet and short, sharp, stocky claws give them good traction on ice.

The bear family, Ursidae, is believed to have split off from other carnivorans about 38 million years ago.[15] The Ursinae subfamily originated approximately 4.2 million years ago.[16] The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004.[17] Fossils show that between ten to twenty thousand years ago, the polar bear's molar teeth changed significantly from those of the brown bear.[18] Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene[19] or from the eastern part of Siberia, (from Kamchatka and the Kolym Peninsula).[20]

The evidence from DNA analysis is more complex. The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear, Ursus arctos, roughly 150,000 years ago.[17] Further, some clades of brown bear, as assessed by their mtDNA, are more closely related to polar bears than to other brown bears,[21] meaning that the polar bear is not a biological species.[22] The mtDNA of Extinct Irish brown bears is particularly close to polar bears.[23] A comparison of the nuclear genome of polar bears with that of brown bears revealed a different pattern, the two forming genetically distinct clades that diverged approximately 603,000 years ago,[24] although the latest research is based on analysis of the complete genomes (rather than just the mitochondria or partial nuclear genomes) of polar, brown and black bears, and establishes the divergence of polar and brown bears at 4–5 million years ago.[25]

However, the two species have mated intermittently for all that time, most likely coming into contact with each other during warming periods, when polar bears were driven onto land and brown bears migrated northward. Most brown bears have about 2 percent genetic material from polar bears, but one population, the ABC Islands Bears has between 5 percent and 10 percent polar bear genes, indicating more frequent and recent mating.[26] Polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids,[19][27] rather than indicating that they have only recently diverged, the new evidence suggests more frequent mating has continued over a longer period of time, and thus the two bears remain genetically similar.[26] However, because neither species can survive long in the other's ecological niche, and because they have different morphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.[28]

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 Simon Pallas in 1776.[29] This distinction has since been invalidated. 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.[19]

Population and distribution[edit]

Polar bears investigate the submarine USS Honolulu 450 kilometres (280 mi) from the North Pole.

The polar bear is found in the Arctic Circle and adjacent land masses as far south as Newfoundland Island. Due to the absence of human development in its remote habitat, it retains more of its original range than any other extant carnivore.[30] While they are rare north of 88°, there is evidence that they range all the way across the Arctic, and as far south as James Bay in Canada. Their southernmost range is near the boundary between the subarctic and humid continental climate zones. They can occasionally drift widely with the sea ice, and there have been anecdotal sightings as far south as Berlevåg on the Norwegian mainland and the Kuril Islands in the Sea of Okhotsk. It is difficult to estimate a global population of polar bears as much of the range has been poorly studied; however, biologists use a working estimate of about 20,000 to 25,000 polar bears worldwide.[1][31]

There are 19 generally recognized, discrete subpopulations.[31][32] The subpopulations display seasonal fidelity to particular areas, but DNA studies show that they are not reproductively isolated.[33] The thirteen North American subpopulations range from the Beaufort Sea south to Hudson Bay and east to Baffin Bay in western Greenland and account for about 70% of the global population. The Eurasian population is broken up into the eastern Greenland, Barents Sea, Kara Sea, Laptev Sea, and Chukchi Sea subpopulations, though there is considerable uncertainty about the structure of these populations due to limited mark and recapture data.

Polar bears play-fighting

The range includes the territory of five nations: Denmark (Greenland), Norway (Svalbard), Russia, the United States (Alaska) and Canada. These five nations are the signatories of the International Agreement on the Conservation of Polar Bears, which mandates cooperation on research and conservation efforts throughout the polar bear's range.

Modern methods of tracking polar bear populations have been implemented only since the mid-1980s, and are expensive to perform consistently over a large area.[34] The most accurate counts require flying a helicopter in the Arctic climate to find polar bears, shooting a tranquilizer dart at the bear to sedate it, and then tagging the bear.[34] In Nunavut, some Inuit have reported increases in bear sightings around human settlements in recent years, leading to a belief that populations are increasing. 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.[34] The Polar Bear Specialist Group of the IUCN takes the position that "estimates of subpopulation size or sustainable harvest levels should not be made solely on the basis of traditional ecological knowledge without supporting scientific studies."[35]

Of the 19 recognized polar bear subpopulations, eight are declining, three are stable, one is increasing, and seven have insufficient data, as of 2009.[7][31]

Habitat[edit]

Polar bear jumping on fast ice

The polar bear is a marine mammal because it spends many months of the year at sea.[36] However, it is the only living "marine mammal" with powerful, large limbs and feet that allow them to cover miles on foot and run on land.[37] Its preferred habitat is the annual sea ice covering the waters over the continental shelf and the Arctic inter-island archipelagos. These areas, known as the "Arctic ring of life", have high biological productivity in comparison to the deep waters of the high Arctic.[30][38] The polar bear tends to frequent areas where sea ice meets water, such as polynyas and leads (temporary stretches of open water in Arctic ice), to hunt the seals that make up most of its diet.[39] Polar bears are therefore found primarily along the perimeter of the polar ice pack, rather than in the Polar Basin close to the North Pole where the density of seals is low.[40]

Annual ice contains areas of water that appear and disappear throughout the year as the weather changes. Seals migrate in response to these changes, and polar bears must follow their prey.[38] In Hudson Bay, James Bay, and some other areas, the ice melts completely each summer (an event often referred to as "ice-floe breakup"), forcing polar bears to go onto land and wait through the months until the next freeze-up.[38] In the Chukchi and Beaufort seas, polar bears retreat each summer to the ice further north that remains frozen year-round.

Biology and behavior[edit]

Physical characteristics[edit]

Skull, as illustrated by N. N. Kondakov
Polar bear skeleton
Captive polar bear swimming

The only other bear of a similar size to the polar bear is the Kodiak bear, which is a subspecies of brown bear.[41] The polar and Kodiak bears are considered the largest terrestrial carnivores alive today, unless the more extensively aquatic saltwater crocodile is included.[42][43] Adult male polar bears weigh 350–700 kg (770–1,540 lb) and measure 2.4–3 metres (7 ft 10 in–9 ft 10 in) in total length.[44][45] The Guinness Book of World Records listed the average male as having a body mass of 385 to 410 kg (849 to 904 lb) and a shoulder height of 133 cm (4 ft 4 in), slightly smaller than the average male Kodiak bears.[46] Around the Beaufort Sea, however, mature males reportedly average 450 kg (1,000 lb).[47] Adult females are roughly half the size of males and normally weigh 150–250 kg (330–550 lb), measuring 1.8–2.4 metres (5 ft 11 in–7 ft 10 in) in length. Elsewhere, a slightly larger estimated average weight of 260 kg (570 lb) was claimed for adult females.[48] When pregnant, however, females can weigh as much as 500 kg (1,100 lb).[44] The polar bear is among the most sexually dimorphic of mammals, surpassed only by the pinnipeds such as elephant seals.[49] The largest polar bear on record, reportedly weighing 1,002 kg (2,209 lb), was a male shot at Kotzebue Sound in northwestern Alaska in 1960.[46] This specimen, when mounted, stood 3.39 m (11 ft 1 in) tall on its hindlegs.[46] The shoulder height of an adult polar bear is 122 to 160 cm (4 ft 0 in to 5 ft 3 in).[46][50] While all bears are short-tailed, the polar bear's tail is relatively the shortest amongst living bears, ranging from 7 to 13 cm (2.8 to 5.1 in) in length.[51]

Compared with its closest relative, the brown bear, the polar bear has a more elongated body build and a longer skull and nose.[28] As predicted by Allen's rule for a northerly animal, the legs are stocky and the ears and tail are small.[28] However, the feet are very large to distribute load when walking on snow or thin ice and to provide propulsion when swimming; they may measure 30 cm (12 in) across in an adult.[52] The pads of the paws are covered with small, soft papillae (dermal bumps) which provide traction on the ice.[28] The polar bear's claws are short and stocky compared to those of the brown bear, perhaps to serve the former's need to grip heavy prey and ice.[28] The claws are deeply scooped on the underside to assist in digging in the ice of the natural habitat. Research 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.[53] Unlike the brown bear, polar bears in captivity are rarely overweight or particularly large, possibly as a reaction to the warm conditions of most zoos.

The 42 teeth of a polar bear reflect its highly carnivorous diet.[28] The cheek teeth are smaller and more jagged than in the brown bear, and the canines are larger and sharper.[28] The dental formula is 3.1.4.23.1.4.3[28]

Polar bears are superbly insulated by up to 10 cm (4 in) of blubber,[52] their hide and their fur; they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography.[54] 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 transparent.[52] The guard hair is 5–15 cm (2–6 in) over most of the body.[55] Polar bears gradually moult from May to August,[56] but, unlike other Arctic mammals, they do not shed their coat for a darker shade to camouflage themselves in the summer conditions. The hollow guard hairs of a polar bear coat were once thought to act as fiber-optic tubes to conduct light to its black skin, where it could be absorbed; however, this theory was disproved by recent studies.[57]

The white coat usually yellows with age. When kept in captivity in warm, humid conditions, the fur may turn a pale shade of green due to algae growing inside the guard hairs.[58] Males have significantly longer hairs on their forelegs, which increase in length until the bear reaches 14 years of age. The male's ornamental foreleg hair is thought to attract females, serving a similar function to the lion's mane.[59]

The polar bear has an extremely well developed sense of smell, being able to detect seals nearly 1.6 km (1 mi) away and buried under 1 m (3 ft) of snow.[60] Its hearing is about as acute as that of a human, and its vision is also good at long distances.[60]

The polar bear is an excellent swimmer and often will swim for days.[61] One bear swam continuously for 9 days in the frigid Bering Sea for 400 mi (687 km) to reach ice far from land. She then traveled another 1,100 mi (1,800 km) [62] With its body fat providing buoyancy, the bear swims in a dog paddle fashion using its large forepaws for propulsion.[63] Polar bears can swim 10 km/h (6 mph). When walking, the polar bear tends to have a lumbering gait and maintains an average speed of around 5.6 km/h (3.5 mph).[63] When sprinting, they can reach up to 40 km/h (25 mph).[64]

Hunting and diet[edit]

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.[65]

The polar bear is the most carnivorous member of the bear family, and throughout most of its range, its diet primarily consists of ringed (Pusa hispida) and bearded seals (Erignathus barbatus).[66] 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.[65][67] Polar bears hunt primarily at the interface between ice, water, and air; they only rarely catch seals on land or in open water.[68]

The polar bear's most common hunting method is called still-hunting:[69] The bear uses its excellent sense of smell to locate a seal breathing hole, and crouches nearby in silence for a seal to appear. The bear may lay in wait for several hours. 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 90 m (100 yd), and then crouches. If the seal does not notice, the bear creeps to within 9 to 12 m (30 to 40 ft) of the seal and then suddenly rushes forth to attack.[65] A third hunting method is to raid the birth lairs that female seals create in the snow.[69]

A widespread legend tells that polar bears cover their black noses with their paws when hunting. This behavior, if it happens, is rare – although the story exists in native oral history and in accounts by early Arctic explorers, there is no record of an eyewitness account of the behavior in recent decades.[63]

Polar bear at a whale carcass

Mature bears tend to eat only the calorie-rich skin and blubber of the seal, which are highly digestible,[70] whereas younger bears consume the protein-rich red meat.[65] Studies have also photographed polar bears scaling near-vertical cliffs, to eat birds' chicks and eggs.[71][72][73] For subadult bears which are independent of their mother but have not yet gained enough experience and body size to successfully hunt seals, scavenging the carcasses from other bears' kills is an important source of nutrition. Subadults may also be forced to accept a half-eaten carcass if they kill a seal but cannot defend it from larger polar bears. After feeding, polar bears wash themselves with water or snow.[63]

The polar bear is perhaps unequaled by any other living land predator in its enormous physical power. However, its primary prey species, the ringed seal, is much smaller than itself, and many of the seals hunted are pups rather than adults. Ringed seals are born weighing 5.4 kg (12 lb) and grown to an estimated average weight of only 60 kg (130 lb).[74][75] They also in places prey heavily upon the harp seal (Pusa groenlandica) or the harbor seal.[76] The bearded seal, on the other hand, can be nearly the same size as the bear itself, averaging 270 kg (600 lb).[75] Adult male bearded seals, at 350 to 500 kg (770 to 1,100 lb) are believed to be too large for a female bear to overtake,[77] and so are potential prey only for mature male bears.[78] Enormously powerful large males also occasionally attempt to hunt and kill even larger prey items.[79] It can kill an adult walrus (Odobenus rosmarus),[76][80] although this is rarely attempted. At up to 2,000 kg (4,400 lb) and a typical adult mass range of 600 to 1,500 kg (1,300 to 3,300 lb), a walrus can be more than twice the bear's weight,[81] and has up to 1-metre (3 ft)-long ivory tusks that can be used as formidable weapons. A polar bear may charge a group of walruses, with the goal of separating a young, infirm, or injured walrus from the pod. They will even attack adult walruses when their diving holes have frozen over or intercept them before they can get back to the diving hole in the ice. Yet, polar bears will very seldom attack full-grown adult walruses, with the largest male walrus probably invulnerable unless otherwise injured or incapacitated. Since an attack on a walrus tends to be an extremely protracted and exhausting venture, bears have been known to back down from the attack after making the initial injury to the walrus.[82] Polar bears have also been seen to prey on beluga whales (Delphinapterus leucas)[76] and narwhals (Monodon monoceros),[76] by swiping at them at breathing holes. The whales are of similar size to the walrus and nearly as difficult for the bear to subdue.[83][84] Most terrestrial animals in the Arctic can outrun the polar bear on land as polar bears overheat quickly, and most marine animals the bear encounters can outswim it. In some areas, the polar bear's diet is supplemented by walrus calves and by the carcasses of dead adult walruses or whales, whose blubber is readily devoured even when rotten.[85] Polar bears sometimes like to go fishing where they swim underwater to catch fish like the arctic charr or the Fourhorn sculpin.[67]

Some characteristic postures:
1. – at rest;
2. – at an estimated reaction;
3. – when feeding

With the exception of pregnant females, polar bears are active year-round,[86] although they have a vestigial hibernation induction trigger in their blood. Unlike brown and black bears, polar bears are capable of fasting for up to several months during late summer and early fall, when they cannot hunt for seals because the sea is unfrozen.[86] When sea ice is unavailable during summer and early autumn, some populations live off fat reserves for months at a time.[54] Being both curious animals and scavengers,[81][87] polar bears investigate and consume garbage where they come into contact with humans.[76][81] 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.[81][87] The dump in Churchill, Manitoba was closed in 2006 to protect bears, and waste is now recycled or transported to Thompson, Manitoba.[88][89]

Dietary flexibility[edit]

Although seal predation is the primary and an indispensable way of life for most polar bears, when alternatives are present they are quite flexible. Polar bears will consume a wide variety of other wild foods, including muskox (Ovibos moschatus), reindeer (Rangifer tarandus),.[90] birds, eggs, rodents, crabs, other crustaceans and other polar bears. They may also eat plants,.[90] including berries, roots, and kelp,[90] however none of these are a significant part of their diet,[81] except that beachcast marine mammal carcasses are an exception.[91] When stalking land animals, such as muskox, reindeer.[90] and even willow ptarmigan (Lagopus lagopus), polar bears appear to make use of vegetative cover and wind direction to bring them as close to their prey as possible before attacking. Polar bears have been observed to hunt the small Svalbard reindeer (R. t. platyrhynchus), which weigh only 40 to 60 kg (90 to 130 lb) as adults, as well as the Barren-ground caribou (R. t. groenlandicus), which is about twice as heavy as that.[92][93][94] Adult muskox, which can weigh 450 kg (1,000 lb) or more, are a more formidable quarry.[95] Although ungulates are not typical prey, the killing of one during the summer months can greatly increase the odds of survival during that lean period. Like the brown bear, most ungulate prey of polar bears is likely to be young, sickly or injured specimens rather than healthy adults.[93] The polar bear's biology is specialized to require large amounts of fat from marine mammals, and it cannot derive sufficient caloric intake from terrestrial food.[96][97]

In their southern range, especially near Hudson Bay and James Bay Canada polar bears live all summer without sea ice.[90] Here their food ecology shows their dietary flexibility. They still manage to consume some seals, but they are food-deprived in summer as only marine mammal carcasses are an important alternative without sea ice,[98] especially carcasses of the bowhead whale.[99] These alternatives may reduce the rate of weight loss of bears when on land.[100] One scientist found that 71% of the Hudson Bay bears had fed on seaweed (marine algae) and that about half were feeding on birds [76] like sea ducks, especially the oldsquaw (53%), common eider, long-tailed duck or dovekieby swimming underwater to catch them. They were also diving to feed on blue mussels and other underwater food sources like the green sea urchin. 24% had eaten moss recently, 19% had consumed grass, 34% had eaten black crowberry and about half had consumed willows.[90] This study illustrates the polar bear's dietary flexibility but it does not represent its life history elsewhere. Most polar bears elsewhere will never have access to these alternatives, except for the marine mammal carcasses that are important wherever they occur.

Behavior[edit]

Polar bear males frequently play-fight. During the mating season, actual fighting is intense and often leaves scars or broken teeth.

Unlike grizzly bears, polar bears are not territorial. Although stereotyped as being voraciously aggressive, they are normally cautious in confrontations, and often choose to escape rather than fight.[101] Satiated polar bears rarely attack humans unless severely provoked. However, due to their lack of prior human interaction, hungry polar bears are extremely unpredictable, fearless towards people and are known to kill and sometimes eat humans.[85] Many attacks by brown bears are the result of surprising the animal, which is not the case with the polar bear. Polar bears are stealth hunters, and the victim is often unaware of the bear's presence until the attack is underway.[102] Whereas brown bears often maul a person and then leave, polar bear attacks are more likely to be predatory and are almost always fatal.[102] However, due to the very small human population around the Arctic, such attacks are rare. Michio Hoshino, a Japanese wildlife photographer, was once pursued briefly by a hungry male polar bear in northern Alaska. According to Hoshino, the bear started running but Hoshino made it to his truck. The bear was able to reach the truck and tore one of the doors off the truck before Hoshino was able to drive off.[103]

In general, adult polar bears live solitary lives. Yet, they have often been seen playing together for hours at a time and even sleeping in an embrace,[85] and polar bear zoologist Nikita Ovsianikov has described adult males as having "well-developed friendships."[101] Cubs are especially playful as well. Among young males in particular, play-fighting may be a means of practicing for serious competition during mating seasons later in life.[104] Polar bears have a wide range of vocalisations, including bellows, roars, growls, chuffs and purrs.[105]

In 1992, a photographer near Churchill took a now widely circulated set of photographs of a polar bear playing with a Canadian Eskimo Dog (Canis lupus familiaris) a tenth of its size.[106][107] The pair wrestled harmlessly together each afternoon for ten days in a row for no apparent reason, although the bear may have been trying to demonstrate its friendliness in the hope of sharing the kennel's food.[106] This kind of social interaction is uncommon; it is far more typical for polar bears to behave aggressively towards dogs.[106]

Reproduction and lifecycle[edit]

Cubs are born helpless and typically nurse for two and a half years

Courtship and mating take place on the sea ice in April and May, when polar bears congregate in the best seal hunting areas.[108] A male may follow the tracks of a breeding female for 100 km (60 mi) or more, and after finding her engage in intense fighting with other males over mating rights, fights which often result in scars and broken teeth.[108] Polar bears have a generally polygynous mating system; recent genetic testing of mothers and cubs, however, has uncovered cases of litters in which cubs have different fathers.[109] Partners stay together and mate repeatedly for an entire week; the mating ritual induces ovulation in the female.[110]

After mating, the fertilized egg remains in a suspended state until August or September. During these four months, the pregnant female eats prodigious amounts of food, gaining at least 200 kg (440 lb) and often more than doubling her body weight.[108]

Maternity denning and early life[edit]

Female emerging from her maternity den

When the ice floes break up in the fall, ending the possibility of hunting, each pregnant female digs a maternity den consisting of a narrow entrance tunnel leading to one to three chambers.[108] Most maternity dens are in snowdrifts, but may also be made underground in permafrost if it is not sufficiently cold yet for snow.[108] In most subpopulations, maternity dens are situated on land a few kilometers from the coast, and the individuals in a subpopulation tend to reuse the same denning areas each year.[30] The polar bears that do not den on land make their dens on the sea ice. In the den, she enters 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.[111] Her body temperature does not decrease during this period as it would for a typical mammal in hibernation.[54][112]

Between November and February, cubs are born blind, covered with a light down fur, and weighing less than 0.9 kg (2.0 lb),[110] but in captivity they might be delivered in the earlier months. The earliest recorded birth of polar bears in captivity was on 11 October 2011 in the Toronto Zoo.[113] On average, each litter has two cubs.[108] The family remains in the den until mid-February to mid-April, with the mother maintaining her fast while nursing her cubs on a fat-rich milk.[108] By the time the mother breaks open the entrance to the den, her cubs weigh about 10 to 15 kilograms (22 to 33 lb).[108] For about 12 to 15 days, the family spends time outside the den while remaining in its vicinity, the mother grazing on vegetation while the cubs become used to walking and playing.[108] Then they begin the long walk from the denning area to the sea ice, where the mother can once again catch seals.[108] Depending on the timing of ice-floe breakup in the fall, she may have fasted for up to eight months.[108]

Cub nursing

Cubs may fall prey to wolves[citation needed]or to starvation. Female polar bears are noted for both their affection towards their offspring[citation needed], and their valiance in protecting them[citation needed]. One case of adoption of a wild cub has been confirmed by genetic testing.[109] Adult male bears occasionally kill and eat polar bear cubs,[114] for reasons that are unclear.[115] As of 2006, in Alaska, 42% of cubs now reach 12 months of age, down from 65% 15 years ago.[116] In most areas, cubs are weaned at two and a half years of age,[108] when the mother chases them away or abandons them. The western coast of Hudson Bay is unusual in that its female polar bears sometimes wean their cubs at only one and a half years.[108] This was the case for 40% of cubs there in the early 1980s; however by the 1990s, fewer than 20% of cubs were weaned this young.[117] After the mother leaves, sibling cubs sometimes travel and share food together for weeks or months.[85]

Later life[edit]

Females begin to breed at the age of four years in most areas, and five years in the Beaufort Sea area.[108] Males usually reach sexual maturity at six years; however, as competition for females is fierce, many do not breed until the age of eight or ten.[108] A study in Hudson Bay indicated that both the reproductive success and the maternal weight of females peaked in their mid-teens.[118]

Polar bears appear to be less affected by infectious diseases and parasites than most terrestrial mammals.[115] Polar bears are especially susceptible to Trichinella, a parasitic roundworm they contract through cannibalism,[119] although infections are usually not fatal.[115] Only one case of a polar bear with rabies has been documented, even though polar bears frequently interact with Arctic foxes, which often carry rabies.[115] Bacterial Leptospirosis and Morbillivirus have been recorded. Polar bears sometimes have problems with various skin diseases which may be caused by mites or other parasites.

Life expectancy[edit]

Polar bears rarely live beyond 25 years.[120] The oldest wild bears on record died at age 32, whereas the oldest captive was a female who died in 1991, age 43.[121] The causes of death in wild adult polar bears are poorly understood, as carcasses are rarely found in the species's frigid habitat.[115] In the wild, old polar bears eventually become too weak to catch food, and gradually starve to death. Polar bears injured in fights or accidents may either die from their injuries or become unable to hunt effectively, leading to starvation.[115]

Ecological role[edit]

The polar bear is the apex predator within its range. Several animal species, particularly Arctic Foxes (Vulpes lagopus) and Glaucous Gulls (Larus hyperboreus), routinely scavenge polar bear kills.[63]

The relationship between ringed seals and polar bears is so close that the abundance of ringed seals in some areas appears to regulate the density of polar bears, while polar bear predation in turn regulates density and reproductive success of ringed seals.[68] The evolutionary pressure of polar bear predation on seals probably accounts for some significant differences between Arctic and Antarctic seals. Compared to the Antarctic, where there is no major surface predator, Arctic seals use more breathing holes per individual, appear more restless when hauled out on the ice, and rarely defecate on the ice.[63] The baby fur of most Arctic seal species is white, presumably to provide camouflage from predators, whereas Antarctic seals all have dark fur at birth.[63]

Polar bears rarely enter conflict with other predators, though recent brown bear encroachments into polar bear territories have led to antagonistic encounters.[citation needed] Brown bears tend to dominate polar bears in disputes over carcasses,[122] and dead polar bear cubs have been found in brown bear dens.[123] Wolves are rarely encountered by polar bears, though there are two records of Arctic wolf (Canis lupus arctos) packs killing polar bear cubs.[124] A rather unlikely killer of a grown polar bear has reportedly included a wolverine (Gulo gulo), anecedotely reported to have suffocated a bear with a bite to the throat during a conflict over food.[125] Polar bears are sometimes the host of arctic mites such as Alaskozetes antarcticus.[63]

Long distance swimmer[edit]

Researchers tracked 52 sows in the southern Beaufort Sea off Alaska with GPS system collars; no boars were involved in the study due to males' necks being too thick for the GPS-equipped collars. Fifty long-distance swims were recorded; the longest at 354 kilometres (220 mi), with an average of 155 kilometres (96 mi). The length of these swims ranged from most of a day to ten days. Ten of the sows had a cub swim with them and after a year six cubs survived. The study did not determine if the others lost their cubs before, during, or some time after their long swims. Researchers do not know whether or not this is a new behavior; before polar ice shrinkage, they opined that there was probably neither the need nor opportunity to swim such long distances.[126]

Hunting[edit]

Indigenous people[edit]

Skins of hunted polar bears

Polar bears have long provided important raw materials for Arctic peoples, including the Inuit, Yupik, Chukchi, Nenets, Russian Pomors and others. Hunters commonly used teams of dogs to distract the bear, allowing the hunter to spear the bear or shoot it with arrows at closer range.[127] Almost all parts of captured animals had a use.[128] The fur was used in particular to sew trousers and, by the Nenets, to make galoshes-like outer footwear called tobok; the meat is edible, despite some risk of trichinosis; the fat was used in food and as a fuel for lighting homes, alongside seal and whale blubber; sinews were used as thread for sewing clothes; the gallbladder and sometimes heart were dried and powdered for medicinal purposes; the large canine teeth were highly valued as talismans.[129] Only the liver was not used, as its high concentration of vitamin A is poisonous.[130] Hunters make sure to either toss the liver into the sea or bury it in order to spare their dogs from potential poisoning.[129] Traditional subsistence hunting was on a small enough scale to not significantly affect polar bear populations, mostly because of the sparseness of the human population in polar bear habitat.[131]

History of commercial harvest[edit]

In Russia, polar bear furs were already being commercially traded in the 14th century, though it was of low value compared to Arctic Fox or even reindeer fur.[129] The growth of the human population in the Eurasian Arctic in the 16th and 17th century, together with the advent of firearms and increasing trade, dramatically increased the harvest of polar bears.[54][132] However, since polar bear fur has always played a marginal commercial role, data on the historical harvest is fragmentary. It is known, for example, that already in the winter of 1784/1785 Russian Pomors on Spitsbergen harvested 150 polar bears in Magdalenefjorden.[129] In the early 20th century, Norwegian hunters were harvesting 300 bears a year at the same location. Estimates of total historical harvest suggest that from the beginning of the 18th century, roughly 400 to 500 animals were being harvested annually in northern Eurasia, reaching a peak of 1,300 to 1,500 animals in the early 20th century, and falling off as the numbers began dwindling.[129]

In the first half of the 20th century, mechanized and overpoweringly efficient methods of hunting and trapping came into use in North America as well.[133] Polar bears were chased from snowmobiles, icebreakers, and airplanes, the latter practice described in a 1965 New York Times editorial as being "about as sporting as machine gunning a cow."[133] The numbers taken grew rapidly in the 1960s, peaking around 1968 with a global total of 1,250 bears that year.[134]

Contemporary regulations[edit]

Road sign warning about the presence of polar bears

Concerns over the future survival of the species led to the development of national regulations on polar bear hunting, beginning in the mid-1950s. The Soviet Union banned all hunting in 1956. Canada began imposing hunting quotas in 1968. Norway passed a series of increasingly strict regulations from 1965 to 1973, and has completely banned hunting since then. The United States began regulating hunting in 1971 and adopted the Marine Mammal Protection Act in 1972. In 1973, the International Agreement on the Conservation of Polar Bears was signed by all five nations whose territory is inhabited by polar bears: Canada, Denmark, Norway, the Soviet Union, and the United States. Member countries agreed to place restrictions on recreational and commercial hunting, ban hunting from aircraft and icebreakers, and conduct further research.[135] The treaty allows hunting "by local people using traditional methods". Norway is the only country of the five in which all harvest of polar bears is banned. The agreement was a rare case of international cooperation during the Cold War. Biologist Ian Stirling commented, "For many years, the conservation of polar bears was the only subject in the entire Arctic that nations from both sides of the Iron Curtain could agree upon sufficiently to sign an agreement. Such was the intensity of human fascination with this magnificent predator, the only marine bear."[136]

Agreements have been made between countries to co-manage their shared polar bear subpopulations. After several years of negotiations, Russia and the United States signed an agreement in October 2000 to jointly set quotas for indigenous subsistence hunting in Alaska and Chukotka.[137] The treaty was ratified in October 2007.[138]

Russia[edit]

The Soviet Union banned the harvest of polar bears in 1956, however poaching continued and is believed to pose a serious threat to the polar bear population.[32] In recent years, polar bears have approached coastal villages in Chukotka more frequently due to the shrinking of the sea ice, endangering humans and raising concerns that illegal hunting would become even more prevalent.[139] In 2007, the Russian government made subsistence hunting legal for Chukotka natives only, a move supported by Russia's most prominent bear researchers and the World Wide Fund for Nature as a means to curb poaching.[139]

Greenland[edit]

In Greenland, hunting restrictions were first introduced in 1994 and expanded by executive order in 2005.[32] Until 2005 Greenland placed no limit on hunting by indigenous people. However, in 2006 it imposed a limit of 150, while also allowed recreational hunting for the first time.[140] Other provisions included year-round protection of cubs and mothers, restrictions on weapons used, and various administrative requirements to catalogue kills.[32]

Canada[edit]

Dogsleds are used for recreational hunting of polar bears in Canada. Use of motorized vehicles is forbidden.

About 500 bears are killed per year by humans across Canada,[141] a rate believed by scientists to be unsustainable for some areas, notably Baffin Bay.[31] Canada has allowed sport hunters accompanied by local guides and dog-sled teams since 1970,[142] but the practice was not common until the 1980s.[143] The guiding of sport hunters provides meaningful employment and an important source of income for native communities in which economic opportunities are few.[34] Sport hunting can bring CDN$20,000 to $35,000 per bear into northern communities, which until recently has been mostly from American hunters.[144]

The territory of Nunavut accounts for the location 80% of annual kills in Canada.[141] In 2005, the government of Nunavut increased the quota from 400 to 518 bears,[144] despite protests from some scientific groups.[145] In two areas where harvest levels have been increased based on increased sightings, science-based studies have indicated declining populations, and a third area is considered data-deficient.[146] While most of that quota is hunted by the indigenous Inuit people, a growing share is sold to recreational hunters. (0.8% in the 1970s, 7.1% in the 1980s, and 14.6% in the 1990s)[143] Nunavut polar bear biologist, Mitchell Taylor, who was formerly responsible for polar bear conservation in the territory, insists that bear numbers are being sustained under current hunting limits.[147] In 2010, the 2005 increase was partially reversed. Government of Nunavut officials announced that the polar bear quota for the Baffin Bay region would be gradually reduced from 105 per year to 65 by the year 2013.[148] The Government of the Northwest Territories maintain their own quota of 72 to 103 bears within the Inuvialuit communities of which some are set aside for sports hunters.[citation needed] Environment Canada also banned the export from Canada of fur, claws, skulls and other products from polar bears harvested in Baffin Bay as of 1 January 2010.[148]

Because of the way polar bear hunting quotas are managed in Canada, attempts to discourage sport hunting would actually increase the number of bears killed in the short term.[34] Canada allocates a certain number of permits each year to sport and subsistence hunting, and those that are not used for sport hunting are re-allocated to Native subsistence hunting. Whereas Native communities kill all the polar bears they are permitted to take each year, only half of sport hunters with permits actually manage to kill a polar bear. If a sport hunter does not kill a polar bear before his or her permit expires, the permit cannot be transferred to another hunter.[34]

United States[edit]

The Marine Mammal Protection Act of 1972 afforded polar bears some protection in the United States. It banned hunting (except by indigenous substinence hunters), banned importing of polar bear parts (except polar bear pelts taken legally in Canada), and banned the harassment of polar bears. On 15 May 2008, the United States department of Interior listed the polar bear as a threatened species under the Endangered Species Act and banned all importing of polar bear trophies. Importing products made from polar bears had been prohibited from 1972 to 1994 under the Marine Mammal Protection Act, and restricted between 1994 and 2008. Under those restrictions, permits from the United States Fish and Wildlife Service (FWS) were required to import sport-hunted polar bear trophies taken in hunting expeditions in Canada. The permit process required that the bear be taken from an area with quotas based on sound management principles.[149] Since 1994, more than 800 sport-hunted polar bear trophies have been imported into the U.S.[150]

Conservation status, efforts and controversies[edit]

This map from the U.S. Geological Survey shows projected changes in polar bear habitat from 2001 to 2010 and 2041 to 2050. Red areas indicate loss of optimal polar bear habitat; blue areas indicate gain.

Estimates of the status of the global population of polar bears vary widely. As of 2008, the World Conservation Union (IUCN) reports that the global population of polar bears is 20,000 to 25,000, and is declining.[1] In 2006, the IUCN upgraded the polar bear from a species of least concern to a vulnerable species.[151] It cited a "suspected population reduction of >30% within three generations (45 years)".[1] However, a report published in July 2013, estimates that the global population of polar bears increased by an average of almost 4,200 bears since 2001.[152] Risks to the polar bear include climate change, pollution in the form of toxic contaminants, conflicts with shipping, stresses from recreational polar-bear watching, and oil and gas exploration and development.[1] The IUCN also cited a "potential risk of over-harvest" through legal and illegal hunting.[1]

According to the World Wildlife Fund, the polar bear is important as an indicator of arctic ecosystem health. Polar bears are studied to gain understanding of what is happening throughout the Arctic, because at-risk polar bears are often a sign of something wrong with the arctic marine ecosystem.[153]

Climate change[edit]

The IUCN, Arctic Climate Impact Assessment, United States Geological Survey and many leading polar bear biologists have expressed grave concerns about the impact of climate change, including the belief that the current warming trend imperils the survival of the species.[30][154][155][156][157][158] The polar bear has survived several periods warmer than at present.[159]

The key danger posed by climate change is malnutrition or starvation due to habitat loss. Polar bears hunt seals from a platform of sea ice. Rising temperatures cause the sea ice to melt earlier in the year, driving the bears to shore before they have built sufficient fat reserves to survive the period of scarce food in the late summer and early fall.[117] Reduction in sea-ice cover also forces bears to swim longer distances, which further depletes their energy stores and occasionally leads to drowning.[160] Thinner sea ice tends to deform more easily, which appears to make it more difficult for polar bears to access seals.[68] Insufficient nourishment leads to lower reproductive rates in adult females and lower survival rates in cubs and juvenile bears, in addition to poorer body condition in bears of all ages.[30]

Mothers and cubs have high nutritional requirements, which are not met if the seal-hunting season is too short.

In addition to creating nutritional stress, a warming climate is expected to affect various other aspects of polar bear life: Changes in sea ice affect the ability of pregnant females to build suitable maternity dens.[27] As the distance increases between the pack ice and the coast, females must swim longer distances to reach favored denning areas on land.[30] Thawing of permafrost would affect the bears who traditionally den underground, and warm winters could result in den roofs collapsing or having reduced insulative value.[30] For the polar bears that currently den on multi-year ice, increased ice mobility may result in longer distances for mothers and young cubs to walk when they return to seal-hunting areas in the spring.[30] Disease-causing bacteria and parasites would flourish more readily in a warmer climate.[68]

Problematic interactions between polar bears and humans, such as foraging by bears in garbage dumps, have historically been more prevalent in years when ice-floe breakup occurred early and local polar bears were relatively thin.[154] Increased human-bear interactions, including fatal attacks on humans, are likely to increase as the sea ice shrinks and hungry bears try to find food on land.[154][161]

Swimming

The effects of climate change are most profound in the southern part of the polar bear's range, and this is indeed where significant degradation of local populations has been observed.[158] The Western Hudson Bay subpopulation, in a southern part of the range, also happens to be one of the best-studied polar bear subpopulations. This subpopulation feeds heavily on ringed seals in late spring, when newly weaned and easily hunted seal pups are abundant.[146] The late spring hunting season ends for polar bears when the ice begins to melt and break up, and they fast or eat little during the summer until the sea freezes again.[146]

Due to warming air temperatures, ice-floe breakup in western Hudson Bay is currently occurring three weeks earlier than it did 30 years ago, reducing the duration of the polar bear feeding season.[146] The body condition of polar bears has declined during this period; the average weight of lone (and likely pregnant) female polar bears was approximately 290 kg (640 lb) in 1980 and 230 kg (510 lb) in 2004.[146] Between 1987 and 2004, the Western Hudson Bay population declined by 22%.[162]

In Alaska, the effects of sea ice shrinkage have contributed to higher mortality rates in polar bear cubs, and have led to changes in the denning locations of pregnant females.[116][163] In recent years, 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.[160]

Pollution[edit]

Polar bears accumulate high levels of persistent organic pollutants such as polychlorinated biphenyl (PCBs) and chlorinated pesticides. Due to their position at the top of the food pyramid, with a diet heavy in blubber in which halocarbons concentrate, their bodies are among the most contaminated of Arctic mammals.[164] 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. PCBs have received the most study, and they have been associated with birth defects and immune system deficiency.[165]

The most notorious of these chemicals, such as PCBs and DDT, have been internationally banned. Their concentrations in polar bear tissues continued to rise for decades after the ban as these chemicals spread through the food chain. But the trend seems to have abated, with tissue concentrations of PCBs declining between studies performed from 1989 to 1993 and studies performed from 1996 to 2002.[166]

Oil and gas development[edit]

Oil and gas development in polar bear habitat can affect the bears in a variety of ways. An oil spill in the Arctic would most likely concentrate in the areas where polar bears and their prey are also concentrated, such as sea ice leads.[1] Because polar bears rely partly on their fur for insulation and soiling of the fur by oil reduces its insulative value, oil spills put bears at risk of dying from hypothermia.[86] Polar bears exposed to oil spill conditions have been observed to lick the oil from their fur, leading to fatal kidney failure.[86] Maternity dens, used by pregnant females and by females with infants, can also be disturbed by nearby oil exploration and development. Disturbance of these sensitive sites may trigger the mother to abandon her den prematurely, or abandon her litter altogether.[1]

Predictions[edit]

The U.S. Geological Survey predicts 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 climate change.[68] 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.[68]

Predictions vary on the extent to which polar bears could adapt to climate change by switching to terrestrial food sources. Mitchell Taylor, who was director of Wildlife Research for the Government of Nunavut, 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 persisted for thousands of years in a period characterized by fluctuating climate."[147] Ken Taylor, deputy commissioner for the Alaska Department of Fish and Game, has said, "I wouldn't be surprised if polar bears learned to feed on spawning salmon like grizzly bears."[34]

However, many scientists consider these theories to be naive;[34] it is noted that black and brown bears at high latitudes are smaller than elsewhere, because of the scarcity of terrestrial food resources.[146] An additional risk to the species is that if individuals spend more time on land, they will hybridize with brown or grizzly bears.[158] The IUCN wrote:

Polar bears exhibit low reproductive rates with long generational spans. These factors make facultative adaptation by polar bears to significantly reduced ice coverage scenarios unlikely. Polar bears did adapt to warmer climate periods of the past. Due to their long generation time and the current greater speed of climate change, it seems unlikely that polar bear will be able to adapt to the current warming trend in the Arctic. If climatic trends continue polar bears may become extirpated from most of their range within 100 years.[1]

Controversy over species protection[edit]

Captive polar bear

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.[167][168] Some estimates of the global population are around 5,000 to 10,000 in the early 1970s;[169] other estimates were 20,000 to 40,000 during the 1980s.[38][54] Current estimates put the global population at between 20,000 and 25,000.[32]

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.[170][171] Second, controls of harvesting were introduced that allowed this previously overhunted species to recover.[170] Third, the recent effects of climate change have affected sea ice abundance in different areas to varying degrees.[170] Finally, the prediction methods used to predict the decline in the future population of bears excluded key forecasting principles and included questionable assumptions.[172]

Debate over the listing of the polar bear under endangered species legislation has put conservation groups and Canada's Inuit at opposing positions;[34] the Nunavut government and many northern residents have condemned the U.S. initiative to list the polar bear under the Endangered Species Act.[173][174] Many Inuit believe the polar bear population is increasing, and restrictions on sport-hunting are likely to lead to a loss of income to their communities.[34][175]

Protection in the North America[edit]

The polar bear is protected by many US laws, most notably the Marine Mammal Protection Act and the Endangered Species Act

U.S. Marine Mammal Protection Act[edit]

Polar bears are protected under the Marine Mammal Protection Act, which prohibits the take (i.e., harass, hunt, capture, or kill) of all marine mammals.[176]

U.S. Endangered Species Act[edit]

On 14 May 2008 the U.S. Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act, citing the melting of Arctic sea ice as the primary threat to the polar bear.[176]

Canadian endangered species legislation[edit]

In Canada, the Committee on the Status of Endangered Wildlife in Canada recommended in April 2008 that the polar bear be assessed as a species of special concern under the federal Species at Risk Act (SARA). A listing would mandate that a management plan be written within five years, a timeline criticized by the World Wide Fund for Nature as being too long to prevent significant habitat loss from climate change.[177]

In culture[edit]

Engraving, made by Chukchi carvers in the 1940s on a walrus tusk, depicts polar bears hunting walrus.

Indigenous folklore[edit]

For the indigenous peoples of the Arctic, polar bears have long played an important cultural and material role.[128][129] Polar bear remains have been found at hunting sites dating to 2,500 to 3,000 years ago[131] and 1,500 year old cave paintings of polar bears have been found in the Chukchi Peninsula.[129] Indeed, it has been suggested that Arctic peoples' skills in seal hunting and igloo construction has been in part acquired from the polar bears themselves.[129]

The Inuit and Alaska Natives have many folk tales featuring the bears including legends in which bears are humans when inside their own houses and put on bear hides when going outside, and stories of how the constellation which is said to resemble a great bear surrounded by dogs came into being.[127] These legends reveal a deep respect for the polar bear, which is portrayed as both spiritually powerful and closely akin to humans.[127] The human-like posture of bears when standing and sitting, and the resemblance of a skinned bear carcass to the human body, have probably contributed to the belief that the spirits of humans and bears were interchangeable.[127] Eskimo legends tell of humans learning to hunt from the polar bear.

Among the Chukchi and Yupik of eastern Siberia, there was a longstanding shamanistic ritual of "thanksgiving" to the hunted polar bear. After killing the animal, its head and skin were removed and cleaned and brought into the home, a feast was held in the hunting camp in its honor. In order to appease the spirit of the bear, there were traditional song and drum music and the skull would be ceremonially fed and offered a pipe.[178] Only once the spirit was appeased would the skull be separated from the skin, taken beyond the bounds of the homestead, and placed in the ground, facing north.[129] Many of these traditions have faded somewhat in time, especially in light of the total hunting ban in the Soviet Union (and now Russia) since 1955.

The Nenets of north-central Siberia placed particular value on the talismanic power of the prominent canine teeth. They were traded in the villages of the lower Yenisei and Khatanga rivers to the forest-dwelling peoples further south, who would sew them into their hats as protection against brown bears. It was believed that the "little nephew" (the brown bear) would not dare to attack a man wearing the tooth of its powerful "big uncle" (the polar bear).[129] The skulls of killed polar bears were buried at specific sacred sites and altars, called sedyangi, were constructed out of the skulls. Several such sites have been preserved on the Yamal Peninsula.[129]

Symbols and mascots[edit]

Coat of arms of the Chukotka Autonomous Okrug in the Russian Federation
Coat of arms of the Greenlandic Self-Rule government (Kalaallit Nunaat)

Their distinctive appearance and their association with the Arctic have made polar bears popular icons, especially in those areas where they are native. The Canadian Toonie (two-dollar coin) features the image of a polar bear and both the Northwest Territories and Nunavut license plates in Canada are in the shape of a polar bear. The polar bear is the mascot of Bowdoin College in Maine and the University of Alaska Fairbanks (see also Alaska Nanooks) and was chosen as mascot for the 1988 Winter Olympics held in Calgary. The Eisbären Berlin professional hockey team, playing in the DEL top-level pro hockey league of Germany also uses a roaring polar bear (seen head-on) as their team logo.

Companies such as Coca-Cola, Polar Beverages, Nelvana, Bundaberg Rum or Good Humor-Breyers have used images of the polar bear in advertising,[179] while Fox's Glacier Mints have featured a polar bear named Peppy as the brand mascot since 1922.

Fiction[edit]

Polar bears are also popular in fiction, particularly in books aimed at children or teenagers. For example, The Polar Bear Son is adapted from a traditional Inuit tale.[180] Polar bears feature prominently in East (also released as North Child) by Edith Pattou,[181] The Bear by Raymond Briggs (adapted into an animated short in 1998),[182] and Chris d'Lacey's The Fire Within series.[183] The panserbjørne of Philip Pullman's fantasy trilogy His Dark Materials are sapient, dignified polar bears who exhibit anthropomorphic qualities, and feature prominently in the 2007 film adaptation of The Golden Compass.[184] The television series Lost features polar bears living on the tropical island setting.[185]

See also[edit]


Notes[edit]

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Names and Taxonomy

Taxonomy

Comments: Ursus maritimus appears to share a common ancestor with the present-day grizzly/brown bear (Ursus arctos), branching off the brown bear lineage during the late Pleistocene (Amstrup 2003). Various evidence sources indicate these species are sister taxa, more closely related to each other than either is to the black bear (Ursus americanus); mtDNA sequences of brown bears from the Alexander Archipelago, southeast Alaska, were even found to be more closely related to mtDNA of polar bears than of other brown bears (Cronin et al. 1991). Cronin et al. (1991) found low divergence in mtDNA haplotypes among polar bear populations from Alaska and Canada.

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