Polar bears are one of the most sensitive Arctic marine mammals to climate warming because they spend most of their lives on sea ice.35 Declining sea ice in northern Alaska is associated with smaller
bears, probably because of less successful hunting of seals, which are themselves ice - dependent and so are projected to decline with diminishing ice and snow cover.36, 37,38,39 Although
bears can give birth to cubs on sea ice, increasing
numbers of female
bears now come ashore in Alaska in the summer and fall40 and den on land.41 In Hudson Bay, Canada, the most studied population in the Arctic, sea ice is now absent for three weeks longer than just a few decades ago, resulting in less body fat,
reduced survival of both the youngest and oldest
bears, 42 and a population now estimated to be in decline43 and projected to be in jeopardy.44 Similar
polar bear population declines are projected for the Beaufort Sea region.45