Overfishing biggest threat to reef sharks
PROVIDENCE — A newly published study about sharks living on coral reefs collected a staggering amount of video, which led to a sobering conclusion: Overfishing is pushing reef sharks to the brink of extinction.
More than 150 researchers from around the world collaborated on the five-year initiative led by researchers at Florida International University’s Global FinPrint project, founded in 2015. It is the first shark and ray survey of its kind.
A recent report in Science reveals that the population of five major reef shark species has decreased by 60 percent to 70 percent in about five years. Other shark species that could no longer be found on 34 percent to 47 percent of surveyed reefs had been listed in lower-risk extinction categories by the International Union of Conservation of Nature, a group that fights to save species from extinction.
Colin Simpfendorfer, the lead author of the study and an adjunct professor of marine and aquaculture science at James Cook University in Australia said, “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. This tells us the problem for sharks on coral reefs is far worse and more widespread than anyone thought.”
According to the study, areas with marine-protected areas, which are located more frequently in the waters of wealthy nations, had increased reef shark populations, while less wealthy nations with weak conservation measures had depleted reef shark populations. Countries with lower shark populations had a high potential for repopulation if they became shark sanctuaries, or invested in shark fisheries management.
“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,” said Demian Chapman, lead scientist of Global FinPrint and director of the Sharks and Rays Conservation Program at Mote Marine Laboratory. “Reef sharks can be important for human livelihoods through dive tourism, and if fished very carefully. An investment in reef shark conservation can . . . be good for people, too.”
Researchers studied over 22,000 hours of video to identify different species of sharks, rays, and other coral inhabitants. They recorded each shark sighting, counted species, and avoided duplicate data.
Jon Dodd, executive director of the Atlantic Shark Institute in South Kingstown, said his organization uses the same video systems to monitor white sharks in New England waters. He called the colossal reef study “rock-solid, not-much-to-debate” research, and a “monumental undertaking” that would impact all shark research.
The US boasts one of the bestmanaged and sustainable shark fisheries in the world, but still has declining shark numbers, according to Dodd.
NOAA Fisheries said that none of the 43 Atlantic shark species they manage are endangered in US waters under the Endangered Species Act.
“While on the surface it may sound good . . . that none of the sharks are considered endangered [in US waters], many of these sharks, their populations are decreasing,” Dodd said. “They are getting to levels that are going to be very difficult to come back from in our lifetime.”
The Atlantic Shark Institute monitors great white, mako, thresher, porbeagle, blue, spinner, and blacktip. All of them have declined in recent years, Dodd told the Globe.
“It’s difficult to feel good or to feel we accomplished something because it is local,” Dodd said. “None of these sharks have roads to stay on; they don’t run into state or country boundaries.”
Dodd said as sea temperatures have risen, the range of sharks in New England waters is drastically changing. “Sharks typically move north because that’s where cooler water is,” he said. “Sharks that weren’t here before have started to come out.”
Dodd said that marine-protected areas are still subject to changes in a shark’s habitat, which drastically changes with rising sea temperatures. He told the Globe last year that since the 1980s, the northern edge of the high-catch density line for tiger sharks — the area where sharks can be caught in abundance — has moved northward by 250 miles. Fishermen have been catching yellowfin tuna 25 miles offshore — that’s about 75 miles closer than in previous years.
A marine-protected area that was full of sharks one season could be gone the next.
“When tiger sharks migrate 300 miles north of those areas and give birth, what happens then?” Dodd said. “Are those protected areas or not? It’s one of the reasons we do this research. What we knew 10 years ago might not be the case now.”