There are approximately 470 known species of shark in the world, but it's impossible to count the exact number of individual sharks on the planet. World Wildlife Fund estimates that more than 100 million sharks are killed each year for their fins.
As part of its shark monitoring program, WWF has identified more than 450 whale sharks and has tagged almost 30. Sharks, like other predatory species, reproduce slowly and in smaller quantities than other fish, which are prey species that rely on high reproductive rates to continue their species. Shark populations are dropping because of pollution, over-fishing of their food sources and habitat alteration.