How Much can Polar Bears Bear?

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Polar bears are an icon of the Arctic, but even more than that, they have come to embody the perils of climate change. These charismatic predators intrinsically depend on the presence of sea ice for daily life, and without it, these bears may not be able to adapt to the warming world of our near future. Based on climate change models, scientists have predicted that projected reductions of critical sea ice habitat will be responsible for the loss of two-thirds (about 16,000) of the world’s polar bear population by 2050 and that the species may be extinct by the end of the century.

 

Without sea ice, polar bears would be deprived of their main source of food, pinnipeds (meaning fin or flipper-footed and refering to the marine mammals that have front and rear flippers), and forced to migrate onto land where they are known to be inefficient hunters, leading to high cub mortality rates and underweight bears that cannot reproduce. Reduced ice cover as well as early break-up and rapid movement of sea ice also require bears to expend more energy travelling between their preferred home range and the sea-ice-air interface where they hunt, exhausting them and negatively impacting their reproductive capabilities. They were officially listed as “Threatened” under the Endangered Species Act in 2008 and are the first vertebrate species to gain this classification because of the imminent threat climate change poses to their survival.

 

Polar bears, Ursus maritimus, are uniquely adapted to life on the ice. Their white, water-repellent fur camouflages them against a snowy backdrop, making it easier for them to hunt, while a thick layer of subcutaneous fat helps insulate them against the frigid waters and bitter cold. Their particularly large size reduces the overall surface area to body mass ratio, minimizing exposure to the elements and consequently, energy loss. These huge carnivores can weigh up to 770kg in the case of adult males, while large females do not get much bigger than 450kg. The diet of a polar bear consists almost exclusively of ringed and bearded seals, supplemented by the occasional walrus, beluga whale, and other seal species. This is where loss of arctic sea ice poses the greatest threat.

Essay by Alex Rose & photographs by Michael AW  ( see OG Issue 30)

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