 All whales are carnivorous and predatory . Odontocetes , as a whole , mostly feed on fish and cephalopods , and then followed by crustaceans and bivalves . All species are generalist and opportunistic feeders . Mysticetes , as a whole , mostly feed on krill and plankton , followed by crustaceans and other invertebrates . A few are specialists . Examples include the blue whale , which eats almost exclusively krill , the minke whale , which eats mainly schooling fish , the sperm whale , which specialize on squid , and the gray whale which feed on bottom @-@ dwelling invertebrates . The elaborate baleen " teeth " of filter @-@ feeding species , mysticetes , allow them to remove water before they swallow their planktonic food by using the teeth as a sieve . Usually whales hunt solitarily , but they do sometimes hunt cooperatively in small groups . The former behaviour is typical when hunting non @-@ schooling fish , slow @-@ moving or immobile invertebrates or endothermic prey . When large amounts of prey are available , whales such as certain mysticetes hunt cooperatively in small groups . Some cetaceans may forage with other kinds of animals , such as other species of whales or certain species of pinnipeds . 
