The diets of sharks vary according to species, but most sharks eat fish, squid and crustaceans. Although they have preferences, sharks tend to be opportunistic hunters, eating what is available according to where they are at a given time.
Blue sharks eat a significant amount of squid, while tiger sharks are known to eat sea turtles. Smooth dogfish sharks eat crabs and lobsters, and hammerhead sharks prefer stingrays. Some sharks that are quick and large enough also hunt sea mammals. Great white sharks, tiger sharks and mako sharks have been known to eat sea lions, seals, dolphins, porpoises and sea birds. They also prey on large fish like mackerel and tuna. The largest shark, the whale shark, doesn't hunt for its food. Instead, it uses specialized gills to filter plankton, which is made from algae and microscopic sea creatures. Some bottom-dwelling sharks spend the majority of their time scouring the ocean floor for clams and mollusks.
Because many sharks feed indiscriminately, some have been found with non-food items, including coal, trash, oil and clothing, in their stomachs. Sharks very rarely prey on humans and usually release them after realizing that what they caught is not among its typical food sources.
Sharks don't require as much food as their size suggests, mainly because they're cold-blooded and don't burn energy quickly.