Polar bear - Ursus maritimus

It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak bear, which can reach approximately the same size. An adult male polar bear weighs around 350–680 kg, while an adult female is about half that size, normally weighing 150–249 kg. When pregnant, however, females can weigh as much as 500 kg.

Adult males measure 2,4–3 m in length, while adult females measure 1,8–2,4 m in length. The polar bear is among the most sexually dimorphic of large mammals.

Polar bears are superbly insulated by up to 10 cm of blubber, their hide and their fur, but they overheat at temperatures above 10°C. Polar bears gradually moult from May to August, but, unlike other Arctic mammals, they do not shed their coat for a darker shade to camouflage themselves in the summer conditions.

Polar bear

Polar bears occur at low densities throughout their range and are most abundant in shallow water areas near shore or where currents or upwellings increase biological productivity near ice areas associated with open water or lead systems.

The polar bear is sometimes regarded as a marine mammal because it spends many months of the year at sea. 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. 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. 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.

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. In the Chukchi Sea, polar bears retreat each summer to the ice further north that remains frozen year-round. In the summer open water season in the Svalbard, and in recent years during the fall in Russian Chukotka, polar bears may be found on land in higher densities.

The polar bear plays an important ecological role as the apex predator within its range. Several animal species, particularly the arctic fox and the glaucous gull, routinely scavenge polar bear kills.

Polar bears rarely live beyond 25 years. The oldest wild bears on record died at the age of 32, whereas the oldest captive was a female who died in 1991 at the age of 43. The causes of death in wild adult polar bears are poorly understood, as carcasses are rarely found in the species's frigid habitat. 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.

Breeding occurs in March to May, implantation is delayed until autumn, and birth is generally thought to occur from late November to mid-January. Although some cubs are born in earth dens, most births occur in snow dens that may be occupied between 5 and 6 months during the maternal event. The average litter size is less than two and cubs are dependent upon mothers until after the start of their third year of life. Age of first reproduction is normally 5 to 6 years for females. These factors contribute to the low reproductive potential for the species.

There are nineteen hypothesized sub-populations or stocks which number in total 20,000 to 25,000 polar bears. Only four of the sub-populations are pertinent to the Eurasian landmass (Barents Sea sub-population, Kara Sea sub-population, Laptev Sea sub-population, Chukchi Sea sub-population). However, considerable overlap of putative populations occurs and genetic differences among them are small.

Globally, polar bar numbers are thought to be decreasing.

• Barents Sea sub-population: An aerial line-transect was carried out in Russia and Norway in 2004. Population estimate is 2,650. The trend of the population is unknown.
• Kara Sea sub-population: Population size and trend are unknown.
• Laptev Sea sub-population: Population size and trend are unknown.
• Chukchi Sea sub-population: Unknown population size. The sub-population is thought to decline based on reductions in sea ice and unknown rates of illegal harvest.

Polar bears are native in the following Eurasian countries and territories:

• Norway
• Russian Federation (Krasnoyarsk, North European Russia, West Siberia, Yakutiya)
• Svalbard
• Jan Mayen

The presence of polar bears is uncertain in Iceland.

• Norway
• Russia

Due to the absence of human development in most of its remote habitat, the polar bear retains more of its original range than any other existing large carnivore. While regional and global shifts in climate patterns may have affected its range over the past centuries, the polar bear's range never extended significantly further south during historic times, due to its poor tolerance of higher temperatures.

Polar bears live throughout the ice-covered waters of the circumpolar Arctic, and their range is limited by the southern extent of sea ice. 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 bears are forced to spend several months on land fasting on stored fat reserves until freeze-up. Use of land by polar bears during the ice-free season appears to be increasing in certain locations.

The species is found in Canada, Greenland, Norway (including Svalbard), the Russian Federation (North European Russia, Siberia, Chukotka, Sakha (Yakutia), Krasnoyarsk) and the United States. Vagrants occasionally reach Iceland.

The Intergovernmental Panel on Climate Change and the Arctic Climate Impact Assessment have both predicted that the Arctic is extremely vulnerable to projected climate change. Polar bears will likely be shifted pole-ward if the sea ice retreats. According to some estimates the polar ice cap will disappear almost entirely during summer in the next 100 years.

The increasing changes in the sea ice that affect access to prey will have a negative effect on the bears. With less food, polar bears will fail to reproduce more often and give birth to smaller young that have higher mortality rates.

Polar bears may be forced on shore for extended periods and rely on fat reserves deposited the previous spring for survival. In such a situation they will be increasingly vulnerable to hunting if not regulated. If these periods become excessively long, mortality will increase. Sea ice is also used for access to den areas, and if ice patterns change, existing den areas may become unreachable. Warmer temperatures and higher winds may reduce ice thickness and increase ice drift. Because polar bears must walk against the moving ice (like walking the wrong way on an escalator) increased ice movements will increase energy use and reduce growth and reproduction.

Polar bears are the apex predator and are exposed to high levels of pollutants that are magnified with each step higher in the food web. A key characteristic of the pollutants is that they tend to persist in the environment and resist degradation. Many of the organochlorine pollutants are lipophilic or "fat loving" and bond tightly to fat molecules. Polar bears are particularly vulnerable to organochlorines because of their 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.

Certain areas of the Eurasian Arctic, such as the Barents Sea and the Kara Sea, have higher levels of pollutants. Based on studies in other species, it is reasonable to believe that the pollutant load of polar bears in some areas are negatively affecting the immune system, hormone regulation, growth patterns, reproduction, and survival rates of polar bears. Recent studies have suggested that the immune system is weaker in polar bears with higher levels of PCBs. A major concern with polar bears pertains to their reproductive system. There are suggestions that species with delayed implantation are more vulnerable to the effects of pollution through endocrine (hormone) disruption. Furthermore, female polar bears are food deprived during gestation their pollution loads increase because as they use their fat stores, where pollutants are stored, for energy. Because the cubs are nursed on fat rich milk, the cubs are exposed to very high pollution loads from their mother.

Oil development in the Arctic poses a wide 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 polar bears and their main prey being directly exposed to oil. Other studies suggest that polar bears are sensitive to disturbance at maternity den sites. Disturbance could occur both when a pregnant female is selecting a den site and during the winter-spring after the cubs are born.

Over-harvest is an ongoing concern for some polar bear populations: particularly in areas where there is no information on population size (such as the Chukchi Sea) and no quotas.

Utilisation

The principle use of polar bears in the circumpolar arctic is for subsistence purposes. These include consumption of meat; use of hides in the construction of clothing such as mittens, boots, fur ruffs for parkas, and fur pants. Norway and Russia prohibit harvest of polar bears. However, in Russia during the early 1990s an unsanctioned harvest of polar bears began following dissolution of the Soviet Union.

Public viewing and photography are another form of utilization and occur locally at specific locals in Svalbard, Norway.

• IUCN/SSC Polar Bear Specialist Group
  The PBSG is the authoritative source for information on the world’s polar bears, and one of IUCN/SSC’s more than 100 specialist groups that work to produce and to compile scientific knowledge about the world’s species and give independent scientific advice to decision-makers and management authorities.
• Polar Bears International
  Our research, stewardship, and education programs address the issues that are endangering polar bears.
• WWF: A Leader in Polar Bear Conservation
  Of all of the wildlife species in the Arctic, the polar bear is perhaps the most fitting icon for this ecoregion. Its amazing adaptations to life in the harsh Arctic environment and dependence on sea ice make them so impressive, and yet so vulnerable. Large carnivores are sensitive indicators of ecosystem health. Polar bears are studied to gain an understanding of what is happening throughout the Arctic as a polar bear at risk is often a sign of something wrong somewhere in the arctic marine ecosystem.
• Polarbears International
  Polarbears International
• Polar Bears International
  Polar Bears International is an organization dedicated to the conservation of polar bears and their habitat. In an effort to raise awareness of the challenges polar bears face in their environment, Polar Bears International designated 2008 as the Year of the Polar Bear.

Please email photos and figures that may be used in further publications to info at largeherbivore dot org

To illustrate this webpage (and for the sake of the protection of these animals) we have made use of photos of which it is not always clear who is the possessor of the credits and rights. If you feel yourself infringed in your rights or if you know the source of a photo, please let us know.