Coral trout. Image: AIMS Long-term Monitoring Program.

Marine scientists working on the Great Barrier Reef have found evidence that protected fish populations can bounce back rapidly from the impact of years of heavy fishing.

They have documented a spectacular recovery in coral trout numbers on unfished reefs following the imposition of a strict no-fishing policy across 33 per cent of the GBR in 2004, to form the world's largest network of no-take reserves.

A team led by Professor Garry Russ of the ARC Centre of Excellence for Coral Reef Studies at James Cook University and Dr Hugh Sweatman of AIMS, supported by the Australian Government's Marine and Tropical Sciences Research Facility (MTSRF), found coral trout numbers rebounded by 31 to 75 per cent on most of the reefs that had been closed to fishing for 1.5 to 2 years.

Closing reefs to fishing has been controversial, both politically and socially, and there has been much public interest in the outcome, making accurate assessment of the effects of closure essential.

Closed inshore reefs in the Palm and Whitsunday islands showed increases in coral trout population densities of 65 and 75 per cent respectively compared with paired reefs left open to fishing. Closed reefs offshore of the cities of Townsville (64 per cent), Cairns (53 per cent) and Mackay (57 per cent) also showed marked improvements.

Densities of coral trout on the reefs left open to fishers showed little or no change in fish density after the rezoning, suggesting that these fish stocks were not impacted by fishing effort displaced from the reefs that were closed to fishing. Only one recently closed reef area showed a decline in the abundance of coral trout after the rezoning but this was attributed to widespread coral bleaching experienced in the Keppel Islands.

In time, the higher fish populations on closed reefs may lead to improvements in fish numbers on open reefs, as juveniles from closed areas settle on open ones.