Polar Bears and the Ice of Hudson Bay

About 20,000 years ago, during the last ice age, the area that is now Hudson Bay lay under a layer of ice hundreds of meters thick. As the climate warmed, the ice thinned, and lakes in the middle of Canada joined the Arctic Ocean to form a huge inland bay. Today it is home to polar bears, whales, walruses, seals and many other animals.

Because it is shallow and surrounded by land, the bay freezes completely in winter and melts in summer. Usually all the ice has gone by August, and the water starts to freeze again in October or November. On June 29, 2017, a NASA satellite captured an image of the bay while the ice was breaking up, and much of the remaining ice was drifting along the western coast.

This timing matters a lot to polar bears. When the bay is covered with ice, they walk out onto it to hunt seals. When the ice melts, they swim to land, where they eat almost nothing until the ice returns. Andrew Derocher, a scientist who tracks the bears with GPS, said that the bears in the west had stayed on the ice longer than normal that year, because they had found patches of ice that still worked for them.

Most experts believe that the loss of Arctic sea ice in recent decades puts these bears at risk. In the western part of the bay, the bear population has fallen by 30 percent in the past ten years, while in the north it has stayed stable. “Sea ice loss is simply habitat loss for polar bears,” Derocher said. He explained that if the ice-free period was too long, an area could no longer support a healthy population of bears.