Sea ice is critical for all parts of the walrus’s life cycle. Adults dive and eat on these frigid platforms, and females give birth and raise their pups there. But as sea ice retreats during Arctic summers, walruses are being driven ashore.

“In the summer we’ve seen the sea ice recede far to the north,” said Chadwick V. Jay, a research ecologist for the United States Geological Survey. That change is “making it very difficult for walruses to make a living.”

In five of the last seven summers, tens of thousands of female Pacific walruses and their pups have come ashore in Alaska, farther from their preferred prey: the clam, worm and snail beds in the deep waters of the Bering and Chukchi Seas.