Although sharks are streamlined swimmers and ferocious predators in the water, they lack the ability to swim backwards and the ability to stop swimming suddenly. This is due to the fact that a shark’s pectoral fins cannot bend upwards like a fish can. This limits their swimming ability to a forward motion. Thus, if a shark needs to move backwards, it uses gravity to fall. In order for a shark to come to an abrupt stop they must swerve to the side in order to hit something as they cannot just simply stop themselves. For the shark swimming for them is more like flying.
Some sharks are fast swimmers that can swim anywhere up to 40 miles per hour. The great white shark swims by propelling itself through the water using its tail. Their fins are only used for balance. Other sharks such as the whale shark, move their bodies from side to side to propel themse lves through the water. If sharks do not keep swimming they will sink. The reasoning for this being that unlike other fish they are not equipped with a gas filled bladder to help keep them afloat. Their large, oily liver provides some buoyancy but even so, they are still heavier than the water and will sink unless they propel themselves through the water properly.