The earliest known sharks date from more than 420 million years ago. Since that time, sharks have diversified into 440 species. They range in size from the small dwarf lanternshark, a deep sea species of only 17 centimeters in length, to the whale shark, the largest fish in the world, which reaches approximately 12 meters. Despite its size, the whale shark feeds only on plankton, squid, and small fish by filter feeding. Well-known species such as the great white shark, tiger shark, blue shark, mako shark, and the hammerhead shark are apex predators – organisms at the top of their underwater food chain. Their predatory skill fascinates and frightens humans, even though their survival is threatened by human-related activities.
It is estimated that 100 million sharks are killed by people every year, due to commercial and recreational fishing. Sharks are a common seafood in many places, including Japan and Australia. They are often killed for shark fin soup. Fishermen capture live sharks, fin them, and dump the finless animal back into the water which soon dies from suffocation or predators. Shark fin has become a major trade within black markets all over the world.
Sharks generally reach sexual maturity only after many years and produce few offspring in comparison to other fish. Major declines in shark stocks have been recorded—some species have been depleted by over 90% over the past 20–30 years. If these top predators disappear, it is the entire equilibrium of the marine ecosystem which is threatened.