Beluga whales are distributed throughout seasonally ice-covered arctic and subarctic waters of the Northern Hemisphere and are closely associated with open leads in ice-covered regions. Depending on season and region, beluga whales may occur in both offshore and coastal waters, with concentrations in Cook Inlet, Bristol Bay, Norton Sound, Kasegaluk Lagoon, and the Mackenzie Delta. It is assumed that most beluga whales from these summering areas over winter in the Bering Sea, excluding those found in the northern Gulf of Alaska. Seasonal distribution is affected by ice cover, tidal conditions, access to prey, temperature, and human interaction. During the winter, beluga whales occur in offshore waters associated with pack ice. In the spring, they migrate to warmer coastal estuaries, bays, and rivers for molting and calving. Annual migrations may cover thousands of kilometers. Belugas grow as long as 4.5 m and weigh up to 1500kg. Calves are born in the summer and remain with their mothers for about 24 months. They are slate gray to pinkish brown at birth but become completely white by the time they are adults.