The gray whale (Eschrichtius robustus),[1] also known as the grey whale,[4] gray back whale, Pacific gray whale, or California gray whale[5] is a baleen whale that migrates between feeding and breeding grounds yearly. It reaches a length of 14.9 meters (49 ft), a weight of 36 tonnes (40 short tons), and lives between 55 and 70 years.[6] The common name of the whale comes from the gray patches and white mottling on its dark skin.[7] Gray whales were once called devil fish because of their fighting behavior when hunted.[8] The gray whale is the sole living species in the genus Eschrichtius, which in turn is the sole living genus in the family Eschrichtiidae. This mammal descended from filter-feeding whales that appeared at the beginning of the Oligocene, over 30 million years ago.