Western Arctic bowhead whales are distributed in ice-covered waters of the Arctic and near-Arctic, generally north of 60*N and south of 75*N in the western Arctic Basin. The largest population is in the Bering Sea. The majority of the Bering Sea bowheads migrate from wintering areas in the northern Bering Sea (November to March), through the Chukchi Sea in the spring (March through June), to the Beaufort Sea where they spend much of the summer (mid-May through September) before returning to the Bering Sea in the fall (September through November) to overwinter. Most of the year, bowhead whales are closely associated with sea ice. The bowhead spring migration follows fractures in the sea ice around the coast of Alaska, generally in the shear zone between the shorefast ice and the mobile pack ice. However, during the summer, most of the population is in relatively ice-free waters in the southern Beaufort Sea. All bowheads were commercially exploited for oil and baleen in the eighteenth and nineteenth centuries, reducing the population significantly. Today, only subsistence hunting by a few Alaska natives occurs. Bowhead whales can reach lengths of 19.8 m and weigh up to 100 metric tons.