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Beluga whale (or white whale, ^IDelphinapterus^i ^Ileucas^i) bull. In summer, belugas migrate into river estuaries, where they moult. The whale's yellowish skin colour in this picture is typical of moulting adults. Belugas are normally a creamy white. Their skin is 100 times thicker than a human's, mainly for insulation. To encourage shedding of the old skin, they roll on the river bottom to rub against rocks and mud. Belugas inhabit the Arctic coastal waters of Europe, Asia and North America. They live in pods (groups) of 20-200. They dive to the seabed to feed on bottom- dwelling fish and invertebrates. Photographed in July in Cunningham Inlet, Canadian Arctic. (KEYSTONE/SCIENCE PHOTO LIBRARY/DOUG ALLAN/SCIENCE PHOTO LIBRARY)