"Below 300 kilograms per hectare we see a series of dramatic changes on reefs. This is where you get on a real slippery slope," McClanahan noted. "Strangely, the metric used by most managers to gauge the health of reef systemscoral coveris the last threshold before ecosystem failure. Overfished reefs can appear healthy and then shift to algae dominated seascapes."
The authors recommend measuring the biomass of fish instead of coral cover to identify the early warning rather than the final sign of reef collapse.
"The good news is that a reef can likely provide sustainable fisheries even after the first three warning switches are turned off, but it becomes increasingly difficult to maintain a healthy fishery and restore reefs when the final five switches have been turned off," said Dr. McClanahan. "This study provides managers and policy makers with a tangible target of where to maintain their fishery."
Dr. Joshua Cinner from James Cook University in Australia added: "Of course, having a target is one thing, but achieving it is, well, another kettle of fish. So we also assessed how well different reef management schemes did at maintaining reefs."
Reef fisheries with no regulations tended to perform poorly, with some passing all the switches and completely collapsing. No-take marine reserves, where fishing was prohibited, were the best performers and tended to maintain key ecosystem processes such as predation.
"People depend on reefs for their livelihoods, so we can't prohibit fishing everywhere," noted Dr. Cinner. "A key finding from our study was that even easily enforceable regulations that restrict gear or the types of species that can be caught helped maintain biomass. These regulations are often more agreeable to fishermen than no-take closures and consequ
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Wildlife Conservation Society