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Mixed News for the Great Barrier Reef

By Stephen Luntz

The Great Barrier Reef is suffering the effects of overfishing, but progress is being made to curb the threat of herbicide run-off, according to two studies released in the same week.

Run-off of PSII herbicides has been cited as one of the main causes of decline in the health of the reef. “The geography of the region means that almost the entire flow from the Burdekin River Irrigation Area in the dry season (from July to January) is made up of irrigation water from sugarcane and other cropping,” says Ms Danni Oliver of CSIRO Water for a Healthy Country. With herbicide concentrations often exceeding Australian water quality guidelines, the run-off poses a threat to the seagrass meadows on which the reef ecosystem depends.

Herbicides are normally applied using boom sprayers. Irrigation water carries them into drainage channels and then creeks. By using a shielded sprayer with herbicide applied only to raised beds rather than irrigation furrows, Oliver achieved 90% reductions in herbicide flows.

“Given the importance of improving GBR water quality, additional testing and demonstration of these technologies across different soil types, farming systems and possibly different combinations of chemicals would provide valuable additional testing of the approach from an industry perspective,” says team leader Dr Rai Kookana of the results published in Science of the Total Environment.

The news is worse for sea cucumber populations in the Great Barrier Reef Marine Park. “Sea cucumbers play a vital role in reef health, and our previous research indicates they may help reduce the harmful impact of ocean acidification on coral growth,” says Prof Maria Byrne of the University of Sydney’s School of Biological Sciences.

Sea cucumbers are used to produce trepang, which is popular in China, but overfishing has closed 24 Pacific fisheries, often followed by switching to lower value species.

“We conducted the study on this fishery on the Great Barrier Reef to see what Australia could share with low-income developing countries that lack management capacity,” Byrne says. “Sadly we found striking similarities with low-income countries. Catch reports over a 20-year period (1991–2011) showed the same pattern of exploitation.” The high value teatfish has become too rare on the reef for fishing, with lower value species fished instead.

“While most fisheries in developing countries struggle to monitor catches, in Australia the data exist but are confidential. We have to question whether this confidentiality in catch data – the main source of information for fishery management – is best practice,” Byrne says.