Harp seals have good eyesight, which is very useful in the dimly lit Arctic waters. They also use their sharp ears and sensitive whiskers, which can sense vibrations in the water caused by the swimming action of their prey. Fish such as capelin, herring and cod make up most of an adult seal's diet. They are able to dive to depths of 150-200m in search of prey. Once caught, small fish are eaten whole underwater, but for larger catches, the harp seal will swim to the surface before eating.