9:59 AM Mon 24 Nov 2008 GMT
The world's coral reef fish are caught in a double whammy of intensifying fishing pressure and spreading reef destruction, a team of leading international coral scientists has warned.
In a new paper in the journal Global Change Biology the team from five international institutions warns of dangers to future fish populations from the combination of top-down fishing pressure and bottom-up habitat degradation.
A major research program carried out off Fiji's Lau islands has investigated the impacts on fish and corals as human and environmental forces interact and intensify in all the world's tropical oceans.
'On the one hand you have reefs being hit with events such as coral bleaching and Crown-of-Thorns starfish (COTS) attacks leading to a loss of the dominant Acropora corals. This mainly affects the smaller coral-dependent fish and small herbivores,' says Dr Shaun Wilson of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, and the Department of Environment and Conservation in WA. 'And on the other, you have fishing methods, targetted at the larger predatory fish like emperors, coral trout and snappers,' he explains.
In the Fiji study, the team found coral cover had declined off some of the Lau islands by as much as 50 per cent between 2000-06, due mainly to bleaching and a COTS plague. However the number of large fish had showed signs of recovery off islands where human numbers and fishing activity had decreased. While previous studies have looked at fishing pressure and habitat decline independently, this is the first major study of its type to analyse their combined impact and attribute their effects on different fish groups.
'Over-exploitation and climate change are two major drivers of global environmental change and are responsible for local extinctions and declining ecosystem services,' the team says. 'Overall, fishing continues to have an influence on Fijian fish communities; however, habitat loss is currently the overriding agent of change on some reefs' they conclude.
The team is concerned for what all this may mean for human communities throughout the Pacific, the Asian Coral Triangle and Indian Ocean who depend on coral reefs for their food and economic survival. Reefs are estimated to support around 500 million people in Asia, the Pacific, the Indian subcontinent, Middle East and Africa.
They conclude that climate-induced coral losses could have significant effects on fish populations - even on remote reefs in the Pacific where there is little or no fishing pressure.
However the Fiji study also showed some encouraging trends as well: reefs which had been badly hit by COTS in 2000 showed signs of coral recovery over the six year period, and fish populations showed improvement wherever local fishing pressures had declined, Dr Nick Graham said.
'In Fiji the fishery is often controlled by the local community under traditional governance, which means there is more scope to restrict the fish catch or the use of unsustainable methods than in places where ownership over the reefs are less clear,' he adds.
'This suggests strongly that devolving the power to control fisheries to local people is one of the best ways to put the management of the reef and its fish on a sound footing.'
The main conclusion from the research is that coral reef fish everywhere are under sustained pressure from above and below, and the key to ensuring their survival is to manage local pressures to reefs so that they can better withstand the effects of climate change.
Wilson, SK, Fisher, R, Pratchett, MS, Graham, NAJ, Dulvy, NK, Turner, RA, Cakacaka, A, Polunin, NVC and Rushton, SP (2008). Exploitation and habitat degradation as agents of change within coral reef fish communities. Global Change Biology 14(12): 2796-2809.
dx.doi.org/10.1111/j.1365-2486.2008.01696.x
www.coralcoe.org.au
by ARC Centre of Excellence Coral Reef Studies
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