Overfishing Is Pushing Coral Reef Sharks Toward Extinction, Study Finds
Reef sharks are the top predators in Caribbean reef communities and play a large role in maintaining the delicate balance of the reef environment’s food webs.
However, they are under threat from overfishing, as their meat and fins are highly valuable in international markets, according to WWF.
Each year, hundreds of reef sharks are killed or injured after being caught unintentionally as bycatch. They can also fall victim to ingesting or becoming entangled in marine debris such as plastic bags, bottles and cans.
“Sharks have a very vulnerable life history. They don’t reproduce very quickly, and so when you start to fish them out, they decline very quickly and recover very slowly,” Colin Simpfendorfer, lead author of the study and adjunct professor of marine and aquaculture science at James Cook University in Australia, told Mongabay.
The coral reef habitat of reef sharks and other marine animals is becoming increasingly degraded and destroyed by coastal pollution and development.
The study, “Widespread diversity deficits of coral reef sharks and rays,” was published in the journal Science.
Reef sharks act as managers of the coral reef marine ecosystem, which is relied on by hundreds of millions of people, reported AFP.
For the study, more than 22,000 hours of footage was collected by the researchers from coral reefs across the Middle East, Africa, Australasia, Asia and the Americas.
The scientists found that, of the most common reef shark species, five of them — blacktip reef, whitetip reef, Caribbean reef, gray reef and nurse — had declined by 60 to 73 percent.
The team of more than 100 scientists derived the depletion data from a computer model estimating how many sharks there would have been without human influences.
In 14 percent of reefs where sharks had previously been documented, there were no longer any to be found.
Simpfendorfer told AFP that before the study the sharks weren’t believed to be doing badly.
“But when you sat down and looked at the overall results, it was quite stunning,” Simpfendorfer said.
Simpfendorfer pointed out that the biggest factor in the sharks’ decline was overfishing, both through intentional targeting of the species for their meat and fins and unintentional bycatch, AFP reported.
Loss of reef sharks results in ripple effects for the entire food chain. As the numbers of their prey increase, the species on the next rung down decreases and on down the chain. These disruptions can have unforeseen effects on human food security.
For the study, the researchers baited remote underwater cameras with oily fish to attract and observe the sharks.
They surveyed a total of 391 reefs in 67 countries and territories with 22,756 cameras, accumulating three years of video footage.
The findings showed that reefs with more robust populations of reef sharks had a tendency to be in high-income nations with stricter regulations and more democratic participation.
The research did find “hope spots” in developing countries, like Lighthouse Reef in Belize and Sipadan Island in Malaysia.
“In and around them, things are fairly depleted—but in those areas where you have strong MPAs (marine protected areas) and really good ways to enforce them, you have robust shark populations,” Mike Heithaus, co-author of the study and executive dean of the College of Arts, Sciences & Education at Florida International University, told AFP.
Heithaus said this showed there was hope for heavily depleted areas being repopulated as long as there was a source population of reef sharks and precise management programs were adhered to.
“People need healthy coral reefs,” said Heithaus, as Mongabay reported. “We are seeing that when sharks disappear, that causes other changes in these ecosystems. Keeping shark populations healthy, or rebuilding them, is important for maintaining their roles for healthy reefs.”