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More than half of the tropical coral reefs in the world where governments collect data on fishing levels are being degraded beyond repair, according to a global survey of reef fisheries.
The findings suggest that it would take an additional area of tropical coral nearly four times the size of the Great Barrier Reef - the biggest reef system in the world - to sustain current levels of fishing.
If the commercial exploitation of tropical corals continues at present rates, many reefs will be irreversibly degraded and millions of people will have to look for other sources of food, scientists say.
"Millions of people are dependent on coral reef fisheries. We are facing a global crisis among communities which have limited alternative livelihoods or major food sources," said Katie Newton of the University of East Anglia in Norwich.
"We're facing a food-security crisis - 30 million people on the planet depend entirely on coral reefs for their income and for the food," she said.
The study found that 55 per cent of the 49 island nations who register their fish catch are fishing unsustainably by taking more fish, molluscs and crustaceans than the reefs are able to replace. The scientists estimated that the amount of fish being caught on tropical coral reefs is 64 per higher than can be reasonably sustained.
This meant that it would require an added area of tropical coral amounting to 75,000 square kilometres - 3.7 times the size of the Great Barrier Reef - to make current fishing levels sustainable, the scientists said.
By 2050, the growth of the human population in tropical areas would triple the fishing pressures, yet coral reefs will continue to suffer from other threats, notably pollution and global warming, which are causing the "bleaching" of corals.
The study, published in the online journal Current Biology, suggests that the threat to the wellbeing of tropical corals will lead to many inhabited island atolls being abandoned this century. It also warns the figures on overfishing may be underestimates because it is possible that fish catches being recorded are underreported.
Nick Dulvy of the Centre for Environment, Fisheries and Aquaculture in Lowestoft, said the unchecked exploitation of coral fisheries could only lead to long-term social and economic hardship.
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