One-Quarter Of The World's Sharks And Rays Are At Risk Of Extinction, IUCN Study Finds

By Josh Lieberman on January 21, 2014 7:14 PM EST

shark
Twenty-five percent of all shark and ray species will become threatened or extinct in the coming decades, says a new IUCN study. Above, a thresher shark, which faces a high risk of extinction. (Photo: Wikimedia Commons)

The first-ever study assessing the fate of all the world's cartilaginous fish has found that a quarter of all shark and ray species could be wiped out in the coming decades. According to the International Union for the Conservation of Nature study, of the 1,041 species, 25 are "critically endangered"--the last level before extinction. Overall, just 23 percent of species were found to be of "least concern." Thresher sharks, sawfishes and angel sharks face the highest risk of extinction. 

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"Our analysis shows that sharks and their relatives are facing an alarmingly elevated risk of extinction," said Nick Dulvy, a co-chair of the IUCN's Shark Specialist Group. "In greatest peril are the largest species of rays and sharks, especially those living in shallow water that is accessible to fisheries."  The "hotspot" areas, where shark and ray depletion is worst, are in the Gulf of Thailand and the Mediterranean Sea.

What's killing the world's sharks and rays? Overfishing, mainly. Catches of sharks, rays and chimaeras (also known as ghost sharks) peaked in 2003, and catches are likely to be widely underreported, says the IUCN. Fish are often caught unintentionally in catches, but fishermen may even welcome such bycatches, as sharks are desirable in China for use in shark fin soup (though the popularity of the soup is apparently declining), and because some traditional medicines use various parts from sharks and rays. Compounding the overfishing problem is the fact that sharks, rays and chimaeras grow slowly and don't produce a lot of offspring. 

Losing so many species of sharks and rays is problematic for a number of reasons. One is that they represent important links in evolutionary history, says Dulvy: "They are the only living representatives of the first lineage to have jaws, brains, placentas and the modern immune system of vertebrates." Another, more immediate reason to fear the loss of so many sharks and rays is that the largest of them are apex predators, meaning they're at the top of their food chain. When apex predators are lost, they can hugely disrupt ecosystems. 

Despite the study's vast participation--302 researchers in 64 countries worked on it--there was still by necessity a bit of guesswork used to determine that 25 percent of sharks and rays (about 249 species) are likely to face extinction in the coming decades. There was insufficient data on 487 species in the study (accounting for about half of the species studied). For these fish, the researchers extrapolated their findings from fish that had more data available.  

"Significant policy strides have been made over the last two decades but effective conservation requires a dramatic acceleration in pace as well as an expansion of scope to include all shapes and sizes of these exceptional species," said Sonja Fordham, deputy chair of the IUCN's Shark Specialist Group. "Our analysis clearly demonstrates that the need for such action is urgent."

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