Threats to the Polar Bear Reading Answers

Threats to the Polar Bear

Polar bears are classified as marine mammals because they spend most of their lives on the sea ice of the Arctic Ocean. They have a thick layer of body fat and a water-repellent coat that protects them from the cold air and water. Considered talented swimmers, they can sustain a pace of six miles per hour by paddling with their front paws and holding their hind legs flat to act like a rudder.

Iconic symbols of the Arctic, polar bears are distributed across the five Arctic coastal

countries of Canada, Denmark (Greenland), Norway, Russia, and the United States. The worldwide population is currently estimated to be between 22,000 and 25,000 bears. Scientists have divided the total polar bear population into 19 units or subpopulations. Of those, the latest data from the IUCN Polar Bear Specialist Group show that three subpopulations are in decline and that there is a high estimated risk of future decline due to climate change.

Polar bears live throughout the ice-covered waters of the circumpolar Arctic, particularly in near shore annual ice over the continental shelf, where productivity is highest. The most significant threat facing the long-term survival of polar bears is the loss of this habitat due to climate change. Projected reductions in the extent and thickness of sea ice in the polar bear's range will have direct and indirect effects on polar bears, with habitat loss and degradation and reduced prey availability respectively.

The latter is reduced, because polar bears rely on sea ice to hunt and store energy for the summer and autumn, when food can be scarce. The bears need sea ice for hunting, as they cannot outswim seals, their preferred prey. They get around this by waiting near holes in the ice and employing ambush to kill the seals as they come up for air. Polar

bears spend over 50 per cent of their time hunting for food, yet they might catch only one or two out of ten seals they hunt, depending on the time of year and other variables. Their diet mainly consists of ringed and bearded seals, because they need large quantities of fat to stay alive.

In the short term, climatic warming may improve bear and seal habitats in higher latitudes over continental shelves if currently thick multiyear ice is replaced by annual ice with more leads, making it more suitable for seals. However, a cascade of impacts from reduced sea ice will take place. Firstly, reduced fat stores will lead to lowered reproductive rates, because females will have less fat to invest in cubs during the winter fast. Secondly, non-pregnant bears may have to fast on land or offshore on the remaining multiyear ice through progressively longer periods of open water while they await freeze- up and a return to hunting seals.

Thirdly, as sea ice thins and becomes more fractured and easily changed, it is likely to move more in response to currents, so that polar bears will need to walk or swim more and thus use greater amounts of calories to maintain contact with the remaining preferred habitats. Fourthly, as the bears spend longer periods without food, their health declines. For example, for every week earlier the ice breaks up in Hudson Bay, bears come ashore roughly 10 kilograms lighter and in poorer condition. Unhealthy bears can lead to even fewer cubs being born into these threatening circumstances.

Another threat to polar bears is the oil and gas business, which is increasingly moving into the Arctic as more accessible reserves in the south dry up. This is a danger, as contact with oil spills can reduce the insulation of the bears' fur. In addition, polar bears can also ingest oil through grooming and through eating contaminated prey. The ingested oil can cause liver and kidney damage, and has long term toxicity; bears can be poisoned by even a limited amount of oil on their fur. Offshore operations pose the greatest risk, since spills will be discharged directly into the sea or on the sea ice.

Polar bear populations are expected to come under increased pressure if oil developments in the Arctic go ahead according to industry plans. Other pollution also threatens polar bears. Because of their role as the apex predator, polar bears are exposed to high levels of pollutants through their food. The popular image of polar bears living in a pure, frozen wilderness is misleading, as the Arctic food chain contains high levels of some toxic chemicals.

Bears with high levels of some persistent organic pollutants have low levels of vitamin A, thyroid hormones, and some antibodies. These are important for a wide range of biological functions, such as growth, reproduction, and the ability to fight off diseases. In some areas, the mother bears' milk contains particularly high concentrations of these chemicals and so the milk can actually poison the cubs, leading to even lower survival rates.

It is the loss of habitat, however, that really threatens polar bears. The effects of climate change are likely to show large geographic, temporal and even individual differences and be highly variable, making it difficult to develop adequate monitoring and research programs. All bears show behavioral plasticity, but given the rapid pace of ecological change in the Arctic, the long generation time, and the highly specialized nature of polar bears, it is unlikely that polar bears will survive as a species if the sea ice disappears completely, as has been predicted by some scientists.