The world's reef shark population has plummeted with the five dominant species in far more trouble than previously thought.
Australian researchers have led a landmark study that points to overfishing and poor regulation as the culprits.
Australia seems to be doing relatively well at managing its reef sharks, in contrast to the broad trend with global stocks of grey, blacktip, whitetip, nurse and Caribbean reef sharks plunging by an average of 63 per cent.
James Cook University professor Colin Simpfendorfer, who is lead author of the five-year study, says the depletion estimates are among the best ever produced.
That's because so many reefs were sampled across so many countries, including 22,000 hours of footage taken at baited video stations on 391 reefs in 67 nations and territories.
"This tells us the problem for reef sharks on coral reefs is far worse and more widespread than anyone thought," Professor Simpfendorfer said.
But there was some good news. Reef sharks were still common in marine protected areas and locations where shark fishing was banned or highly regulated.
Australia's east coast was a bright spot in that regard, said study co-author and JCU professor Joshua Cinner.
"Only four places in our study had reef shark populations that were in better shape. We can be proud of how well we've managed our reef sharks, but there is still room for improvement."
Researchers said reefs that were more heavily fished tended to become stripped of sharks, leaving them dominated by rays which could have broad consequences for the overall health of coral reef ecosystems.
Results from the study have been used to update the status of four of the species to more threatened categories by the International Union for the Conservation of Nature.
The study's findings were presented at a recent international gathering on the trade in endangered species that saw governments agree to better regulate the shark trade.
"This means no trade should come from nations where the take of the species will threaten its survival," Prof Simpfendorfer said.
"This study can be used to help identify those nations where such catches would be detrimental. We need to act now to stop widespread extinction of shark species in many parts of the world."
More than 150 researchers from over 120 institutions across the world contributed to the research, which has been published in the journal Science.
