Fur seals, as their name implies, are highly valued for their pelts, which exhibit a dense, waterproof underfur that typically consists of more than 350,000 hairs per square inch. Several different species of fur seal have been classified, all of which are members of the family Otariidae, which is comprised of the eared seals. Most fur seal species inhabit the southern hemisphere, but the northern fur seal is the variety that migrates each year to the islands of Alaska. This sociable and notably vocal variety of seal possesses hind flippers that can rotate forward, enabling them to move sufficiently well on dry land. Weighing as much as 600 pounds, males are considerably larger than females, which typically weigh about 100 pounds. The fur of the animals varies somewhat, but generally appears black when wet and brown when dry.