National Geographic : 2011 Jul
• In August the naturalist John Muir was sailing o Alaska aboard the steamer omas Corwin, searching for three vessels that had gone missing in the Arctic. O Point Barrow he spotted three polar bears, "magni cent fellows, fat and hearty, rejoicing in their strength out here in the bosom of the icy wilderness." Were Muir to sail o Point Barrow in August today, any polar bears he'd see would not be liv- ing in a wilderness of ice but swimming through open water, burning precious fat reserves. at's because the bears' sea-ice habitat is disappear- ing. And it's going fast. Polar bears ply the Arctic niche where air, ice, and water intersect. Superbly adapted to this harsh environment, most spend their entire lives on the sea ice, hunting year-round, visiting land only to build maternal birthing dens. ey prey mainly on ringed and bearded seals (it's been said that they can smell a seal's breathing hole from more than a mile away) but sometimes catch walruses and even beluga whales. Sea ice is the foundation of the Arctic marine environment. Vital organisms live underneath and within the ice itself, which is not solid but pierced with channels and tunnels large, small, and smaller. Trillions of diatoms, zooplank- ton, and crustaceans pepper the ice column. In spring, sunlight penetrates the ice, triggering algal blooms. e algae sink to the bottom, and in shallow continental shelf areas they sustain a food web that includes clams, sea stars, arctic cod, seals, walruses---and polar bears. Experts estimate the world's polar bear num- bers at , to ,, in 19 subpopulations. Bears in Svalbard (the Norwegian archipelago where Florian Schulz made most of these pho- tographs), the Beaufort Sea, and Hudson Bay have been studied the longest. It was in western Hudson Bay, where ice melts in the summer and freezes back to shore in the fall, that the crea- tures' predicament rst came to light. Ian Stirling, now retired from the Canadian Wildlife Ser vice, has monitored polar bears there since the late 1970s. He found that they gorged on seals in the spring and early summer, before breakup, then retreated to land as the BY SUSAN MCGRATH PHOTOGRAPHS BY FLORIAN SCHULZ Impervious to a dive-bombing arctic tern, a hungry bear on the shore of Hudson Bay uses up energy prowling for tern eggs. Summers dry-dock bears around the bay, where biologist Ian Stirling has linked shrinking sea ice to skinnier bears and smaller litters.