the primary use of the caudal fin is to provide a "push" while the shark swims. the upper lobe of the caudal fin produces the most amount of the push, and usually forces the shark downwards. the pectoral fins and the shape of the body (like an airfoil) work together to counter this force. the strong, non-lunate caudal fin in most benthic shark species allows the shark to swim close to the seabed (such as the nurse shark). however, the fastest swimming sharks (such as the mako sharks) tend to have lunate-shaped (crescent-shaped) caudal fins.