Overfishing is driving the sharks based on coral reefs towards extinction faster than previously realised, with the five main species so familiar to scuba divers – grey reef, blacktip reef, whitetip reef, nurse and Caribbean reef sharks – already having declined globally by an average of 63%.
This is the worrying conclusion of scientists working on Global FinPrint, a five-year international study supported by the Paul G Allen Family Foundation. Led by researchers at Florida International University, it involves investigating sharks, rays and other coral-reef life using baited remote underwater video systems (BRUVS) on a wide scale.
“These are some of the best estimates of population decline of widespread shark species because of the very large number of reefs and countries sampled,” says lead author Colin Simpfendorfer, adjunct professor of Marine & Aquaculture Science at Australia’s James Cook University. “This tells us the problem for sharks on coral reefs is far worse and more widespread than anyone thought.”
The research, which includes 22,000 hours of video footage from baited underwater video stations across 391 reefs in 67 nations and territories, indicates that widespread overfishing is the main cause of the problem.
As reefs are more heavily fished, they are either stripped of both shark and ray species or stripped of only shark species to leave the ecosystem dominated by rays. Losing sharks could have an impact on the overall health and function of the coral reef ecosystem.
“Sharks can play many different roles on reefs, including influencing their prey and even transporting important nutrients from offshore waters to the reefs,” says co-author Dr Michael Heithaus, marine ecologist with Florida International University. “Losing specific species of reef sharks could remove roles that are important to the health of reefs.
“The changes we see in the shark and ray communities as human pressures mount is concerning, because we are losing pieces of the puzzle. Luckily, there are ways for people to stop and reverse declines to ensure we have healthy shark populations and healthy reefs.”
Dive tourism
“While overfishing and poor governance is associated with the absence of these species, they are still common in Marine Protected Areas and places where shark fishing was banned or highly regulated,” says Demian Chapman, lead scientist of Global FinPrint and director of the Sharks & Rays Conservation Programme at Florida’s Mote Marine Laboratory.
“Reef sharks can be important for human livelihoods through dive tourism and if fished carefully. An investment in reef shark conservation can therefore be good for people, too.”
Early results from the study have already been used to update the status of four of the shark species to more threatened IUCN Red List categories. They were also presented during the most recent CITES convention, helping world governments in making the ground-breaking decision to improve regulation of trade in these and more than 50 other shark species.
“This means no trade should come from nations where the take of the species will threaten its survival,” said Simpfendorfer. “This study can be used to help identify those nations where such catches would be detrimental. We need to act now to stop widespread extinction of shark species in many parts of the world.”
More than 150 researchers from more than 120 institutions across the world contributed to the research, which has just been published in Science.
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