There have been reports of fisherman cutting fins off live sharks and throwing the poor creatures back into the sea. Indiscriminate fishing - some fishing competitions are judged simply on the basis of the weight of fish caught resulting in many sharks being killed, weighed and discarded. As a result they are starved of fresh, oxygen-rich water for their gills, and die. Environmental deterioration - the oceans have long been regarded as the planet's refuse bin and many sorts of waste have been released into them, both accidentally and deliberately. The resulting pollution, e.g. oil, pesticides and plastics, affects all life in the oceans, including sharks.
Most sharks live in tropical and temperate inshore waters.
Relatively few live in Arctic and sub-Antarctic waters, the open sea and water deeper than 2km. All sharks are predators. The diet of different species ranges from tiny crustaceans to large fishes, other sharks, rays, dolphins, seals, sea birds and marine reptiles. Sharks may also scavenge, but most eat live animals. All sharks reproduce by internal fertilization.