Bowhead whales are protected from predators by their large size. They are also known to take shelter under ice drifts. As the oceanic waters of the polar regions become frozen, bowhead whales will swim beneath the extending polar ice cap. In order to survive under the ice cap, B. mysticetus can break through the ice in order to breathe without making themselves accessible to other marine predators (Stover 2001). In a study in 1995, it was found that one-third of the animals of the Davis Strait stock showed scars from killer whale attacks (Shelden and Rugh 1995).