These are evolutionary upstarts. Their ancestors would have been omnivorous, like most modern bears, eating leaves, fruit and roots, together with a little fish, small prey and carrion. But in the high Arctic it is too cold, and for several months of the year, too dark, to sustain plants and the animals that feed on them. The sea is the only larder for a large, active mammal, and not a very accessible one for a doggy-paddling bear. By concentrating their hunting efforts on ringed seals, polar bears make the most of their talents.
Seals have to surface to breathe every few minutes, and their pups are born and suckled on the ice.
Therein lie the bears' best chances. Where the sea is frozen, the seals make their own breathing holes by gnawing or scraping against the underside of the ice with their teeth and claws. A polar bear may stalk a seal while it is resting on the ice, or wait quietly beside a breathing hole, sometimes for hours. When a seal surfaces, the bear grabs it by the nose and hauls it onto the ice, where it cannot move fast or put up much resistance. Seal pups make even easier prey.