Polar bears at risk of survival: is the situation now irreversible?

Model estimates predict a decline in the size of Hudson Bay polar bear litters by 22-67% by mid-century

by Lorenzo Ciotti
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Polar bears at risk of survival: is the situation now irreversible?
© Carter Acton

The survival of polar bears is at risk. In Hudson Bay, near ⁤Manitoba⁢ in Canada, the southernmost extent of polar bear habitat, the ice-free period increased by three weeks between 1979 and 2015. This forced polar bears to live on land for about 130 days in the last decade.

Model estimates predict a decline in the size of Hudson Bay polar bear litters by 22-67% by mid-century, if female polar bears are forced onto the mainland one month earlier than in the 1990s. Others⁢ have predicted that up to 24% of adult ⁢males⁢ would starve if summer fasting increased to 180 days.

The scientists⁤, who equipped 20 polar bears in⁢ Hudson Bay with collar cameras, followed them during the summer, monitoring the bears' behaviors. Approximately 70% of bears began eating or hunting on land and sea to increase their calorie intake or entered a hibernation-like state of rest to conserve energy. A bear swam nearly 320 kilometers to find a beluga carcass in the sea, but couldn't eat it while swimming or drag it onto land.

Climate warming is increasing the duration of the ice-free period in some areas of the Arctic, forcing polar bears in these regions to move to land.
Polar bears get most of their energy resources during a short period in late spring and early summer, when seals give birth and wean their pups.

The polar bears in the study continued to lose weight. The researchers calculated that two of the ⁢younger females would have starved to death‍ before the ice returned, typically around November 30.

Polar bear
Polar bear© Creative Commons Attribution-Share Alike 4.0
 

The enemies of the polar bear

The most famous hunting method of polar bears is the one used for seals: the plantigrade hears the noise of its prey under the ice, lurks near a crack and, as soon as the prey comes out to breathe, kills it with a violent paw.

Only males have such powerful musculature and the size to attack belugas and narwhals, both up to five and a half meters long, easily exceeding 1000 kg in weight and the latter with the long tusk typical of males. Having identified the prey, often a young or female narwhal, the white bear enters the water and nimbly attacks the cetacean in delicate points, such as the fins and belly, avoiding fatal blows.

The polar bear is an alpha predator, so being at the top of the food chain it has few enemies. Only the cubs can be attacked by wolves and even other polar bears; this happens when the family disperses during the second summer and the mother leaves her children alone. The cubs then become victims of hunters and winter. Naturally, man remains the real danger for this species: every year more than 1000 bears are killed, both by the Eskimos, who feed on their meat and exploit their fur, and by simple hunters.