The link below is to an article that looks at overfishing sharks and the threat to sharks from humans.
For more visit:
http://www.guardian.co.uk/environment/2013/mar/02/shark-killings-humans-become-predators
Kevin's Walk on the Wild Side
Environment, Wildlife and Wilderness – Articles and News
Kevin's Walk on the Wild Side 
The entire oceans are over fished about 15 years ago, now its crunchtime. you just have look at the amount of fish the Asians go through in a week.