Overfishing is causing shark and ray populations to plummet It's an apolcayptic scenario, but researchers say it's still possible to reverse the trend with proper policies Populations of oceanic sharks and rays have crashed by more than 70% over the past half a century, and it’s our fault. The decline is mostly owed to overfishing, a new study shows — but conservation policies can help. Image credit: Wikipedia Commons The Union of Conservation of Nature (IUCN) has listed half of the world’s oceanic shark species as engendered or critically threatened. The giant manta ray is also endangered. Yet, this doesn’t seem to be nearly enough to protect these creatures.