According to new research, nearly two-thirds of the sharks and rays that live around the world’s coral reefs are threatened with extinction with potentially catastrophic impacts on coastal ecosystems and communities.
Overfishing has been the main cause of declines over the past half century, with sharks and larger rays particularly hard hit.
“These sharks and rays have evolved over 450 million years and survived six mass extinctions but they just can’t handle this hunting pressure,” said Professor Colin Sempfendorfer, a global expert on sharks and rays and one of the study’s lead authors from Australia’s James Cook. University.
“This is not just a few species. This is a massive extinction crisis.”
With the disappearance of sharks and rays, the study said there would be cascading effects on other species with “growing ecological consequences for coral reefs, which would be difficult or impossible to reverse,” the team of more than 30 researchers wrote.
The authors said that as global warming threatens the future of coral reefs worldwide, the pressures facing sharks will only get worse.
Without urgent and widespread global action to reduce the numbers of sharks caught, there will be “increasingly severe consequences for the health of the coral reef ecosystem and the coastal communities that depend on it.”
the A new study in Nature Communicationsis based on the findings of a 2020 study that concluded sharks are “functionally extinct” on 20% of the world’s coral reefs.
The authors of the new study examined assessments of the conservation status of all 1,200 species of sharks and rays Orchestrated in 2021 by the International Union for Conservation of Nature. 143 of these species inhabit or use coral reefs.
Using a combination of previous studies and catch data, the authors said reef sharks and rays were more at risk than other sharks and rays.
Larger species that travel long distances were more at risk because they traveled through different jurisdictions that had different levels of protection.
Of the 134 species, only one—the blue-spotted ribbon ray—was known to be increasing globally.
Larger species such as bull, tiger and hammerhead sharks and manta rays were at greater risk because they tend to get easily caught in nets, said lead author Dr Samantha Sherman, of Simon Fraser University in Canada.
“But they also don’t mature until they’re about 20 years old,” she said, “so when they’re caught, it takes a long time for the population to increase. When they’re caught before they can reproduce, we see these drastic declines.”
Fourteen of the 134 species reviewed are already at risk of extinction; Nine of them were rays. She said, “The future doesn’t look great unless we act now. It has to be a global effort. For example, bull sharks are found in more than 150 countries, but if they are protected in only a few, it will have severe impacts on their populations.”
While climate change is degrading coral reef habitats, Simpfendorfer said, fishing was a more immediate threat that – if not controlled – could drive many species to extinction within a decade.
“It will lead to the next mass extinction if we don’t act soon,” he said.
Removing top predators from any ecosystem can have devastating effects on entire ecosystems, said Professor Judy Romer, a marine biologist and expert on sharks and rays at James Cook University who was not involved in the research.
She said preventing the species from being overfished — or caught as “bycatch” in nets — was possible, but a challenge across different geopolitical borders.
She said creating marine parks where fish are protected from fishing should also be seen as a bridge to protect them from global warming.
Coral reef habitats for sharks and rays have already been degraded by global warming, with sharks and rays having to either move, adapt, or die.
“The homes of sharks and rays attached to the reef have seen a rapid succession of mass coral bleaching events, heat waves, and several intense tropical cyclones,” she said.
“Putting dotted lines around the water doesn’t mean those waters won’t get warmer and those corals won’t spawn.”