Despite their fearful features, sharks are highly endangered animals. In fact, some of the most vulnerable species are the great white and the whale shark. A new study by the British journal, Nature, states that shark populations have declined by a shocking 71% since 1970. But what is causing this massive population decline for sharks?

The largest factor leading to the rapid population decline is over-fishing—many places kill sharks only for their fins. Some places use them for medicine, others as food. About 73 million sharks are killed each year, just for their fins.

Oftentimes, sharks are not even the intended target when fishing lines are placed in the water—they are the first to come, and end up getting killed when the intended target was other fish. Also, because sharks mature relatively slowly, many young ones are also more vulnerable to over-exploration.

Other factors have led to sharp decreases in shark populations, including pollution and climate change, but none have done more damage than over-fishing. And, if something is not done soon, the global shark population is likely to collapse.

Many scientists say governments need to create catch limits to aid in the recovery of the shark population, but there are many other steps that should or must be taken to help get the numbers of sharks on the road to recovery.