The variety of rays is rising in coral reef ecosystems around the globe as overfishing obliterates shark populations.
The findings come from a worldwide research utilizing hundreds of underwater cameras to survey shark and ray prevalence at 391 coral reefs in 67 nations.
It discovered far fewer sharks than could be anticipated, with populations of species together with blacktip reef sharks, whitetip reef sharks, nurse sharks and gray reef sharks having utterly disappeared from reefs in some locations.
The populations of 5 of the commonest reef shark species had been 60 to 75 per cent beneath their anticipated abundance, primarily based on a modelled situation with no human pressures, the research discovered.
Colin Simpfendorfer at James Prepare dinner College in Townsville, Australia, who led the analysis, says the declines had been most likely attributable to overfishing. In distant reefs, or in areas the place reefs had been inside efficient marine protected areas (MPAs), the sharks are much more ample, he says – and this was extra usually the case in higher-income nations.
In lots of reefs the place shark numbers have plummeted, ray numbers have elevated, the research discovered. Numbers of yellow and southern stingrays within the Atlantic, and blue-spotted maskrays and blue-spotted ribbontail rays within the Indo-Pacific, had been increased in locations the place a number of reef shark species had been depleted. “We go from very shark-dominated communities to ray-dominated communities,” says Simpfendorfer.
These traits have a “cascading” impact all through all the reef ecology, he says. For instance, with out sharks to prey on them, the numbers of herbivorous fish soar. “They eat algae, and so we’ve truly seen on coral reefs that lose reef sharks, loads much less carbon is sequestered within the algae,” says Simpfendorfer.
On account of the reef surveys, at the least one species – the gray reef shark – has been reclassified by the Worldwide Union for Conservation of Nature as endangered.
Simpfendorfer says international locations with coral reefs ought to be given extra help to implement MPAs. “One of many issues that comes by way of very clearly is that MPAs that are effectively enforced are capable of truly get well reef shark populations pretty shortly,” he says.