Amazing grace

Sharks are graceful swimmers propelling themselves through the water by beating their tails from side to side. The pectoral fins are held out from the body and as water flows over them, lift is generated to keep the shark from sinking. Further lift is produced by the upper lobe of the tail, which tends to push the head down, so that the shark can swim on the level. Shark fins are not nearly as flexible as those of bony fish, but adjustments to the angle at which the fins are held, control whether the shark goes up, down, left, or right. Pectoral fins are also used for braking. Some sharks that live on the sea bed, such as horn sharks and epaulette sharks, can use their pectoral fins to crawl along the bottom. Unlike bony fish, sharks cannot move their pectoral fins like paddles so are unable to swim backwards or hover in the water. They also lack swim bladders which act as buoyancy aids in bony fish. However, they do have oil-rich livers which help reduce their weight in water.