"The vast majority of the impact is in the northern third of the reef, from Port Douglas to Cape York, with the central and southern regions escaping significant mortality," the statement said. Three-quarters of the Barrier Reef is alive, says the Great Barrier Reef Marine Park Authority. "While bleaching caused by heat stress affected most of the reef, the most severe mass bleaching and the greatest mortality has been restricted." The move follows revelations that environment bureaucrats intervened to remove references to Australia in a United Nations report on the risk that climate change poses to World Heritage sites, including the Great Barrier Reef, because it feared the impact on tourism. The statement came just hours after Prime Minister Malcolm Turnbull was accosted in Adelaide by a protester dressed as the animated film character Nemo, who called on the government to do more to save the reef, which has suffered under the effects of global warming and agricultural run-off.

GBRMPA chairman Russell Reichelt said the mortality assessment was based on hundreds of "comprehensive in-water surveys" conducted across the reef since March. Dr Reichelt said the results had been released before final surveys were completed to address "misinterpretation of how much of the reef has died". "We've seen headlines stating that 93 per cent of the reef is practically dead. We've also seen reports that 35 per cent, or even 50 per cent, of the entire reef is now gone. "However, based on our combined results so far, the overall mortality is 22 per cent — and about 85 per cent of that die-off has occurred in the far north," he said, adding the southern part of the reef had experienced little mortality. "We know the Great Barrier Reef, which is larger than Italy, is still resilient with the ability to recover from major events, given enough time," he said.

Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, pointed to recent commentary that suggested reef statistics had been exaggerated. "When we say .... 'only 7 per cent [of the reef] has no bleaching', that sometimes gets reported as '93 per cent of the reef is dead'," he said. AIMS chief executive John Gunn said the reef was undergoing "the most serious bleaching event" on record, which related to both warming oceans and a major El Niño event. "The biological impacts of bleaching stress are still playing out across the reef … while we know many corals in the northern sector will die, others will recover from bleaching over the coming months," he said. The authority says average coral loss ranged from 50 per cent in the far north – stretching from the tip of Cape York to north of Lizard Island – to no damage in the area off Mackay and Bundaberg.