Polar bears are classified as marine mammals because they spend most of their lives on the frozen Arctic sea ice. Males can weigh up to 1,430 pounds and grow as long as 10 feet in length.  But only 20,000-25,000 of these powerful animals remain in the wild, and their survival is in jeopardy. Climate change, which leads to the loss of Arctic sea ice, is the leading threat to polar bears. The survival of polar bears and the protection of their marine habitat are urgent issues for WWF and other conservationists.