Sharks are apex predators, meaning they are at the top of the food chain. Their appetites and presence are integral for maintaining population control of their prey, which in turn prevents overgrazing of habitats and the spreading of disease or illness.
Many sharks prey on fish, eating the old, sick or weak, and strengthening the gene pool while stopping the fish from demolishing their habitats. Some species feed on seals or other marine mammals. While sharks have different appetites based on species, even their presence can intimidate prey species enough to disperse the population, avoiding overgrazing of the habitat. Because of this, scientists have classified them as keystone species, meaning that their removal can destroy the entire ecosystem, affecting not just the animals that live in the ocean but humans as well. The loss of commercially important fish and shellfish, including tuna, has been observed to negatively affect fisheries after the elimination of sharks.
Sharks are at risk of becoming endangered. They have low reproduction rates, worsened by the destruction of mangroves and reefs where they reproduce and pollution of their habitats. They are hunted by humans for their fins. Their populations are also severely damaged by accidental capture in fisheries.