- Shark populations in the world’s oceans have declined by an “alarming” 71% since 1970.
- “The last 50 years have been pretty devastating for global shark populations.”
- Of the 31 oceanic species of sharks and rays analyzed in the study, 24 are now threatened with extinction.
The predators of the seas are in trouble.
“The last 50 years have been pretty devastating for global shark populations,” said Nathan Pacoureau, a biologist at Simon Fraser University in Canada and a co-author of the study.
“We document an alarming, ongoing, worldwide decline in oceanic shark populations across the world’s largest ecosystem over the past half-century, resulting in an unprecedented increase in the risk of extinction of these species,” the authors write in the study.
The new research also looked at rays as well as sharks, and found that more than three-quarters of the shark and ray species the scientists studied are now threatened with extinction. Specifically, of the 31 oceanic species of sharks and rays analyzed in the study, 24 are now threatened with extinction.
In fact, three species of sharks (the oceanic whitetip, the scalloped hammerhead and the great hammerhead sharks) have declined so sharply that they are now classified as critically endangered – the highest threatened category in a list that is produced by the International Union for Conservation of Nature.
The risk of extinction is primarily caused by overfishing, study authors said. Although sharks are sometimes intentionally caught by fishing fleets, more often they are reeled in incidentally as “bycatch,” in the course of fishing for other species such as tuna and swordfish.
“You drop a fishing line in the open ocean, and often it’s sharks that are there first – whether or not they’re the primary target,” said marine biologist Stuart Sandin, who works at the Scripps Institution of Oceanography.
The number of fishing vessels trolling the open ocean has risen steeply since the 1950s, as engine power expanded ships’ range. And while climate change and pollution also imperil shark survival, increased fishing pressure is the greatest threat for every oceanic shark species.
The authors say relative fishing pressure – a measure of the proportion of sharks and rays caught relative to their global population – is 18 times higher today than it was 50 years ago. They argue that immediate action is needed to prevent collapses in shark and ray populations. Specifically, they call on governments to implement catch limits to help promote recovery of the threatened species.
Contributing: The Associated Press