Sharks are apex predators, feeding on turtles, fish, seals, crabs and mollusks. They have adapted to feed on virtually everything in their environment. Their predation is a crucial element in maintaining population in different areas of the ocean, preventing prey animals from overgrazing any one area.
Different species of sharks eat different amounts. Some eat a large meal and do not eat for weeks after, while others need a large volume of food and eat constantly. However, large sharks benefit any area they live in even without hunting; prey animals, such as turtles, are intimidated by their presence and range further away to feed, grazing over a larger region.
When sharks kill, they target the sickest and weakest members of any group of prey. Some sharks also scavenge from carcasses. By doing so, they prevent outbreaks of disease among prey groups and keep gene pools strong, resulting in larger numbers of healthier fish.
In the long run, removal of sharks from an ecosystem affects both humans and marine animals. The removal of sharks from the ocean's ecosystem has, in the past, led to the collapse of fisheries and the destruction of coral reefs. Without sharks preying on other animals, their populations spike, and they overfeed.