Most sharks live in the ocean at depths no greater than 7,000 feet; very few sharks live below 10,000 feet. Sharks are found in all the world's oceans, from the Arctic to the Antarctic, and in some rivers and lakes.
Sharks are an ancient group of fish related to skates and rays. There are over 470 species ranging in size from the dwarf lanternshark at 6.7 inches to the whale shark at 39 feet. They feed on a wide range of aquatic life ranging from plankton to large fish and marine mammals. Benthic or bottom-dwelling sharks usually forage for creatures such as crabs, clams or sea urchins on the ocean floor, while pelagic or ocean-dwelling species are divided between active hunters of fish, squid, birds, mammals and filter feeders that subsist on plankton and small, free-swimming creatures.