Polar bears, despite the fact they live on land and ice, are classified as marine mammals due to the fact that their survival is strongly dependent on the sea. Every adult, to survive, must eat about 70 seals a year. Bears hunt them in the openings of ice cover, through which the animals breathe. When the seal leans out, the predator kills it with one blow of the paw. Unfortunately, polar bears are threatened with extinction due to climate warming and water pollution. A team of Harvard University scientists found that the main reason for the extinction of these animals is the melting of the Arctic ice that they use for hunting.