A new study has found that unsustainable fishing practices have led to declining shark numbers in coral reefs across the world, upsetting the ecological balance of marine ecosystems. In fact, sharks are already “functionally extinct” from 20 percent of the coral reefs studied.
Published in Nature last week, the study involved over a 100 scientists, who used a network of remote underwater cameras across 58 countries, states, and territories, covering 371 coral reefs, to observe sharks in their natural habitat over a span of four years. The 15,000 hours of underwater video footage showed that sharks had vanished from almost one out of every five coral reefs.
Sharks are integral to coral reefs. As the apex predators of these ecosystems, directly, they help in maintaining diversity through their role in the food chain, and indirectly, help maintain healthy seagrass meadows by preventing overgrazing. Essentially, sharks act as the indicator species that provide insights into the all-round health of the ecosystems they exist in. Ecologists are worried that the disappearance of sharks could potentially trigger a phenomenon called the ‘mesopredator release,’ wherein other large, predatory fish would dramatically increase to replace the apex predator in the food chain, and feed extensively on herbivores, which are necessary to preserve the marine ecosystems by eating algae that otherwise overwhelms and kills young corals.
“At a time when corals are struggling to survive in a changing climate, losing reef sharks could have dire long-term consequences for entire reef systems,” Dr. Mike Heithaus from the Department of Biological Sciences at Florida International University, and a leader of the Global FinPrint project, which funded the study, told The Guardian.
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But, it’s not too late. The researchers found that in the Bahamas, the US, Australia, French Polynesia, and the Maldives, among others, conservation efforts are working and sharks are in abundance. Practices like banning certain fishing gear, limiting the number of sharks that can be caught, or banning shark-fishing completely, has worked in these regions.
“Reducing fishing mortality is key to protecting existing shark populations and rebuilding populations where they have declined. We found that there are several management options for effectively rebuilding shark populations including banning gillnets and longlegs, setting catch limits, and creating large protected areas or shark sanctuaries,” Dr. Heithaus told Forbes. But, he added that there’s no one-size-fits-all solution, and countries need to figure out how best to address the dwindling numbers in their territories by understanding which area-specific factors, or combinations of factors, are responsible for the decline.
“We really need to substantively move toward conservation and recovery in the next decade, or else we’re going to be in real trouble,” Nick Dulvy, Co-Chair of the IUCN SSC Shark Specialist Group and a conservation biologist at Simon Fraser University, who peer-reviewed the study, told Science.
“Stopping destructive fishing practices and getting some good governance into these fisheries could change the situation almost overnight,” Dr. Mark Meekan, who was also involved in the study, said.
