Due to an explosion in shark fishing across the globe, shark numbers have declined by a staggering 90% throughout our oceans.

Sharks and rays are top level predators. So, once fully grown, most sharks and rays naturally live for a long time. Also, they produce only small numbers of young at a very late age.

Therefore overfishing has severe impacts on the numbers of animals that are not able to reproduce as fast as they get killed.
Recent research found that almost one third of open ocean sharks and rays are threatened with extinction, primarily due to overfishing.

http://aqua-marine-life.com/underwater-fact-63/