The first study to assess the worldwide status of 21 species of pelagic sharks and rays -- those living and hunting in open seas -- found that more than half are rapidly being fished out of existence.
Particularly vulnerable species include the short-finned mako, the thresher and the silky, said the report, to be published in the journal Aquatic Conservation: Marine and Freshwater Ecosystems.
"Despite mounting evidence of decline and increasing threats to these species, there are no international catch limits for oceanic sharks," said co-author Sonja Fordham, a researcher at the Oceans Conservancy and Shark Alliance in Brussels.
"Our research shows that action is urgently needed on a global level if these fisheries are to be sustainable."
Many big shark species have fallen prey to booming Asian economies where shark-fin soup is prized as a must-have delicacy at weddings and other banquet occasions. The fins are often sliced off of living fish which are then discarded in the sea.
Accidental "by-catch" by industrial fishing operations have also decimated shark populations, the study said.
Sharks and big rays are especially vulnerable to overfishing because they take many years to reach sexual maturity and have relatively few offspring.
"We are losing species at a rate 10 to 100 times greater than historic rates," said the study's lead author, Nicholas Dulvy, a professor at Sime Fraser University in Vancouver, Canada.
The report, presented at a major UN conference on biodiversity in Bonn, calls for the establishment and enforcement of science-based catch limits for sharks and rays, and a ban on the practice of "shark finning."
The 11-day Bonn conference seeks to prevent the destruction of countless plant and animal species.It is the ninth of its kind of countries who signed up to the UN Convention on Biological Diversity at the 1992 Rio Earth Summit.