Sharks 'functionally extinct' from one in five coral reefs

A global study has found sharks are "functionally extinct" on nearly one in five coral reefs.

The research involving James Cook University academics studied 370 reefs in 58 countries over several years.

Queensland researcher Professor Colin Simpfendorfer says the decrease in numbers has a severe impact on marine ecosystems.

"There are some places where you saw almost no sharks on coral reefs and that's not normal," he said.

"While there may still be some sharks there, their numbers are so low in terms of their function in the ecosystem, it's disappeared.

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"So the roles that they play have gone and that has consequences for the rest of the system... it's not until we can get these shark populations back, that these reefs will function as normal."

But there is hope yet, the study revealing a number of reefs on the northern Great Barrier Reef remain thriving, with solid shark populations.

The data collected will guide conservation plans for protecting what reef sharks remain.