Tails and more tails

The shape of a shark’s tail suits its lifestyle. Many sharks have tail fins where the upper lobe is larger than the lower, and as the tail swings from side to side, this lobe produces lift which tends to push the head down. This is compensated by lift from the pectoral fins, which stops the shark from sinking at the bottom. In fast sharks, like the mako and great white, these two lobes are almost equal in size. Lift may also come form the base of the tail which, in the mako, has small, horizontal keels. The extra height of these more symmetrical-shaped tails gives a more powerful thrust. Slow bottom-dwellers, like the nurse, have less powerful tails and their swimming motion is more eel-like, with obvious waves passing down to their tails.