Reef sharks play a vital role in the coral ecosystems where they live. The predators, which include such species as the whitetip and Caribbean reef sharks, help maintain healthy prey fish populations by killing sick fish and keeping population numbers in check. But they are also in serious danger of extinction, according to a new study published last week in Nature.
Led by Aaron MacNeil, a biologist at Dalhousie University in Canada, researchers conducted a survey of 371 tropical reefs across 58 countries, reports Riley Black for National Geographic.
No adult sharks were recorded at 69 reefs, about 20 percent of all locations surveyed, which suggests that reef sharks are “functionally extinct” at those sites, the researchers write. More than half of the stations recorded 50 percent fewer sharks than expected, reports Natalie Parletta for Cosmos magazine. Reef shark populations were most depleted in reefs close to poorer countries with fewer government restrictions on fishing and areas with a high density of humans, as Erik Stokstad reports for Science magazine.
The study was part of the Global FinPrint project, which marine biologists Mike Heithaus and Demian Chapman launched more than five years ago to survey marine life on the world’s coral reefs. Researchers placed more than 15,000 baited camera traps and combed through about 18,000 hours of footage to conduct the survey.
“It’s the most comprehensive study that’s ever been done to look at shark abundance,” Ellen Pikitch, a marine biologist at Stony Brook University not involved in the study, tells Science magazine.
According to the Smithsonian Institution, sharks are highly susceptible to extinction because they grow and reproduce slowly. Many reef shark populations have been threatened in recent decades by overfishing and shark finning, the practice of killing sharks to sell their valuable dorsal fins.
“The good news is that if we fully protect areas from fishing, marine life and sharks can bounce back,” study co-author Enric Sala tells National Geographic. Whereas the study recorded low reef shark populations off the coasts of Qatar, the Dominican Republic, Colombia, Sri Lanka, and Guam, they recorded strong populations in the Bahamas and French Polynesia. The researchers created a computer model that showed that the countries with thriving reef shark populations also tended to have conservation rules in place, such as protected waters and enforced fishing regulations, per Science.
“These nations are seeing more sharks in their waters because they have demonstrated good governance on this issue,” says MacNeil in a statement. “From restricting certain gear types and setting catch limits, to national-scale bans on catches and trade, we now have a clear picture of what can be done to limit catches of reef sharks throughout the tropics.”
Nick Dulvy, a marine ecologist at Simon Fraser University not involved in the study, tells Science magazine that the study underscores the need for urgent conservation measures to protect reef shark populations: “We really need to substantively move toward conservation and recovery in the next decade, or else we’re going to be in real trouble,” says Dulvy.