Oceans: Study highlights threats to sharks and rays

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Majestic manta rays are among the species identified as facing a significant threat. Photo courtesy NOAA.

‘Unless binding commitments to protect these fish are made now, there is a real risk that our grandchildren won’t see sharks and rays in the wild …’

By Summit Voice

FRISCO — Overfishing is putting about 25 percent of the world’s sharks and rays at risk of extinction, according to ocean experts who took a close look at the global distribution, catch, abundance, population trends, habitat use, life histories, threats and conservation measures.

Previous studies have documented local overfishing of some populations of sharks and rays, but this is the first survey of their status throughout coastal seas and oceans. According to the findings, 249 of 1,041 known shark, ray and chimaera species globally fall under three threatened categories on the IUCN Red List.

“We now know that many species of sharks and rays, not just the charismatic white sharks, face extinction across the ice-free seas of the world,” said Nick Dulvy, a Simon Fraser University Canada Research Chair in Marine Biodiversity and Conservation. “There are no real sanctuaries for sharks where they are safe from overfishing,” Dulvy said.

Sharks and rays are at substantially higher risk of extinction than many other animals and have the lowest percentage of species considered safe. Using the IUCN Red List, the authors classified 107 species of rays (including skates) and 74 species of sharks as threatened. Just 23 percent of species were in the IUCN least concern category.

The two key hotspots for shark and ray depletion are the Indo-Pacific (particularly the Gulf of Thailand), the Red Sea and the Mediterranean Sea.

“In the most peril are the largest species of rays and sharks, especially those living in relatively shallow water that is accessible to fisheries. The combined effects of over-exploitation … especially for the lucrative shark fin soup market … and habit degradation are most severe for the 90 species found in freshwater,” Dulvy said.

“A whole bunch of wildly charismatic species is at risk. Rays, including the majestic manta and devil rays, are generally worse off than sharks. Unless binding commitments to protect these fish are made now, there is a real risk that our grandchildren won’t see sharks and rays in the wild.”

Losing these fish will be like losing whole chapters of our evolutionary history, according to Dulvy. “They are the only living representatives of the first lineage to have jaws, brains, placentas and the modern immune system of vertebrates.”

The potential loss of the largest species is frightening for many reasons, Dulvy said.

“The biggest species tend to have the greatest predatory role. The loss of top or apex predators cascades throughout marine ecosystems,” he said.

The IUCN’s shark specialist group is calling on governments to safeguard sharks, rays and chimaeras through a variety of measures, including the following: Prohibition on catching the most threatened species, science-based fisheries quotas, protection of key habitats and improved enforcement.

The stidy was published last week in eLife.

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