Sharks have evolved in a tight inter-dependency with their ecosystem. They tend to eat very efficiently, going after the old, sick, or slower fish in a population that they prey upon, keeping that population healthier. Sharks groom many populations of marine life to the right size so that those prey species don’t cause harm to the ecosystem by becoming too populous. 

The ocean ecosystem is made up of very intricate food webs.  Sharks are at the top of these webs and are considered by scientists to be “keystone” species, meaning that removing them causes the whole structure to collapse.  For this reason, the prospect of a food chain minus its apex predators may mean the end of the line for many more species.  A number of scientific studies demonstrate that depletion of sharks results in the loss of commercially important fish and shellfish species down the food chain, including key fisheries such as tuna, that maintain the health of coral reefs.