 Whales are creatures of the open ocean ; they feed , mate , give birth , suckle and raise their young at sea . So extreme is their adaptation to life underwater that they are unable to survive on land . Whales range in size from the 2 @.@ 6 metres ( 8 @.@ 5 ft ) and 135 kilograms ( 298 lb ) dwarf sperm whale to the 34 metres ( 112 ft ) and 190 metric tons ( 210 short tons ) blue whale , which is the largest creature that has ever lived . The sperm whale is the largest toothed predator on earth . Several species exhibit sexual dimorphism , in that the females are larger than males . Baleen whales have no teeth ; instead they have plates of baleen , a fringe @-@ like structure used to expel water while retaining the krill and plankton which they feed on . They use their throat pleats to expand the mouth to take in huge gulps of water . Balaenids have heads that can make up 40 % of their body mass to take in water . Toothed whales , on the other hand , have conical teeth designed for catching fish or squid . Baleen whales have a well developed sense of " smell " , whereas toothed whales have well @-@ developed hearing − their hearing , that is adapted for both air and water , is so well developed that some can survive even if they are blind . Some species , such as sperm whales , are well adapted for diving to great depths to catch squid and other favoured prey . 
