Most people know dolphins from films or zoos. In the sea they live together in groups, so-called schools, in warm waters. These schools can consist of 15 to 100 individuals, sometimes up to 1,000. Dolphins are mammals and have an average length of 2.40 metres and weigh roundabout 230 kilograms. They feed on crabs, eels, squids and other species of fish. Foraging is done with the help of echolocation. They also make sounds to communicate with their fellow dolphins. Among each other these marine mammals keep company very fondly. They frequently keep good company with humans too. The U.S. Navy trains these clever animals to recognise underwater mines or to use them for other dangerous missions.