Sharks have disappeared from nearly a fifth of the world’s reefs, leaving them “functionally extinct”, and too rare to fulfil their normal role in the ecosystem, according to a new study.
Researchers placed more than 15,000 underwater video cameras in 371 reefs off the coast of 58 countries to track the sharks over three years, in the most in-depth study of the global population.
They found that 63 per cent of the of the video stations did not record a shark and at 69 out of 371 reefs, or 19 per cent, no sharks were seen at all.
Sharks have an important role in balancing reef ecosystems as one of the biggest predators, keeping levels of other fish in check.
But they have been subjected to overfishing for their meat and fins, both to supply a market in south-east Asia, and to feed local fishing communities, and are often caught up accidentally in fishing gear.
“These are places where we're saying that reef sharks are essentially functionally absent from the ecosystem,” said Aaron MacNeil, the lead author of the study, which was published in the journal Nature. “They play no role in the ecosystem there and they're functionally extinct.”
“We expect that there should be sharks on every reef in the world, and to find 20 per cent of the reefs we surveyed that didn't have sharks on and is very concerning,” he said.
Six of the countries have virtually no sharks in any of their reefs. Over 800 survey hours, the cameras tracked only 3 sharks in the Dominican Republic, the French West Indies, Kenya, Vietnam, the Windward Dutch Antilles and Qatar.
But the study did show a glimmer of hope for the sharks. Places that had shark sanctuaries, where shark fishing and trade was banned, had relatively high numbers.
Among the countries where reef sharks were relatively thriving were the Maldives and the Bahamas, where they play a vital role in the tourism industry.
“While it's clear that people are a big part of the problem affecting reef sharks, the global FinPrint data tell us that it's very clear that people are a big part of the solution too,” co-lead author Dr Demian Chapman, of Florida International University, said. “Our results show that reef sharks can under the right conditions live alongside people and thrive just fine.”
Mr Chapman warned against a full on ban on shark fishing in places where local populations rely on the trade for food and income. But he said there were easier gains by banning fishing gear such as gillnets and longlines that are more likely to pick up reef sharks by accident.
Commenting on the study, Dr Simon Walmsley, the chief marine adviser at WWF-UK said, “This study provides more evidence of the growing shark crisis - where almost a third of all species are now threatened with extinction. We must take the pressure off by reducing accidental capture and overfishing. Sharks are yet another victim of the dramatic decline in ocean health.
“We also need to do more to protect the oceans and make them more resilient as temperatures increase and the seas become more acidic. WWF is calling for properly managed marine protected areas to give nature the space to recover and for at least 30% of the ocean to be in these areas by 2030.”
The Global FinPrint project is funded by the Paul G. Allen Family Foundation.