They also help other members of the group that are in trouble. Dolphins sometimes use their backs or flippers to keep an ill or injured dolphin near the surface. Dolphins communicate with one another in a variety of ways. For example, they may use a complex series of whistles and clicks called phonations. The animals make these sounds in air-filled sacs connected to their blowholes.
Dolphins also communicate by slapping their flukes on the surface of the water.
Swimming and diving. Dolphins swim by moving their flukes up and down. This action differs from that of most fish, which propel themselves through the water by swinging their tail fins from side to side. Dolphins use their flippers to make sharp turns and sudden stops. But they can maintain those speeds for only a short time.