Nearly two-thirds of coral reef shark and ray species worldwide are threatened with extinction, reports a new study in Nature Communications. This build on a study in 2020 that found that reef sharks across the globe are in decline, missing from 19% of the world’s coral reefs. At the time, this was the greatest decline of reef sharks ever recorded, but these recent results suggest that the extinction risk of coral reef sharks and rays, as a percentage of threatened species, is almost double that of all 1,199 known shark and ray species.
“The findings highlight the need for immediate conservation action for these species through local protections, fisheries management and enforcement, and Marine Protected Areas,” stress the authors of the new study.
Coral reef ecosystems are among the most vulnerable to global climate change. These grand structures are composed of tiny animals called polyps, which live, reproduce, die, and eventually leave behind their skeletons. These skeletons are the basis of coral reefs like the Great Barrier Reef. While they only occupy less than 0.1% of our ocean’s floor, they are home to more than a quarter of all marine life, making them even more populated than rainforests.
It’s not just animals who reap the rewards from this ecosystem – people benefit from reefs, too. They protect coastlines from storms and waves, which can cause land erosion and destruction, as well as providing food and employment for many millions. But due to destructive fishing practices, pollution, coastal development, and climate change, corals have been dying in mass numbers.
A coral reef is an oasis of biodiversity and food for reef sharks, and it has been found that sharks and rays are also vital for coral reef health (i.e. helping it to function as these predators cover a range of ecological niches, from filter feeders to apex predators). We are still learning about the various ecological roles that reef sharks play, but scientists believe that there are still numerous mutual benefits to be discovered between these animals and coral reefs. However, it is gradually becoming evident that their absence has consequences.
Previous research has highlighted that reef sharks influence their prey’s behavior just by existing! Herbivorous, grazing fishes have been shown to dramatically reduce how much seaweed they eat when reef sharks are around, which can change the landscape of the reef as a whole. Take those predators away and it’s unclear what will happen. Declines in sharks has also been shown to influence the behavior of stingrays and increase their local numbers, but what ecological consequences this has… who knows. Although overfishing has previously been attributed to steep declines in some populations, there are still questions over the global status of sharks and rays living in coral reefs.
Dr. Samantha Sherman and colleagues used the International Union for Conservation of Nature (IUCN) Red List of Threatened Species to evaluate the extinction risk of all 134 coral reef associated shark and ray species, and compared their status with all other coral reef species. The authors uncovered that 59% of coral reef shark and ray species are threatened with extinction, such as the whitefin topeshark (Hemitriakis leucoperiptera) and the coach whipray (Himantura uarnak). These results make them the most threatened group in the world, other than marine mammals. ‘The findings suggest that without action to improve the conservation of sharks and rays on coral reefs, declines could have serious consequences for the health of coral reefs and the hundreds of millions of people in coastal communities that rely on them,” the authors said.
According to the IUCN, a quarter of the world’s shark species are threatened with extinction due to overfishing. The scientists found this to also apply to coral reef species, with fishing also being their main threat, compounded by habitat loss and climate change. Extinction risk was found to be greatest in nations with greater fishing pressure and weaker governance (e.g. Brazil, Tanzania, and Indonesia) and for widely distributed large species, such as the bull shark (Carcharhinus leucas) and the reef manta ray (Mobula alfredi), both found in the waters of over 60 countries. The authors say the solution is clear: “To achieve recovery, fishing mortality from subsistence, artisanal, and industrial fisheries needs to be controlled, with the best way forward being science-based fisheries management (both traditional and ‘western’) with strong enforcementand increased use of well-implemented and enforced, marine protected areas (MPAs).”