No-fishing zones breed stronger fish

By Karl Gruber 1 April 2015
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Numbers of fish in no-take zones of the Great Barrier Reef have increased to levels not seen since European colonisation of Australia.

SOME SPECIES OF fish are thriving in no-fishing zones across the Great Barrier Reef, and are better able to cope with stress from cyclones, according to a new study.

The study monitored the health of coral trout across 150,000sq.km of the Great Barrier Reef Marine Park over the past 35 years, including fishing zones as well as green zones –areas where fishing is totally prohibited.

The research, led by Dr Michael Emslie at the Australian Institute of Marine Science (AIMS), found that coral trout from green zones are up to 12 per cent bigger than those of fishing zones, and also that green zones host more than twice as much trout biomass as fishing areas.

No-fishing zones in the Great Barrier Reef

This trend was noted in the 1980s, when green zones where first established, but the most significant increases have occurred since 2004, when the zones were expanded to include more than 40 per cent of the marine park.

“It’s heartening to know the green zones are working,” Michael told reporters. “Among the world’s coral reefs, fishing on the Great Barrier Reef is relatively light but it has still reduced the number and average size of the few fish species that are taken by fishers.”

One unexpected finding, the authors say, was the survival of larger trout in the green zones after tropical cyclone Hamish, which hit the reef in 2009.

In the immediate aftermath, trout numbers declined in both fishing and green zones. But green zones had the upper hand when it came to recovery, as they held to a larger trout biomass, explains Dr Hugh Sweatman, also at AIMS.

Coral trout numbers rebounding

“Biomass of coral trout dropped substantially on the fished reefs but not on the no-take reefs, indicating that the coral trout that remained…were larger.”

He believes that larger fish may be better at dodging the turbulence caused by cyclones or finding a safe place to hide – or they are less dependent on the reef structure that survives after the storm.

“Size is important in fishes, because larger individuals produce disproportionately more larvae,” Hugh says. “The greater size of coral trout on [no-take] reefs following the cyclone means that these reefs should supply more larvae, both locally and to surrounding reefs.”

As a consequence, green zones may help drive a speedy recovery after cyclones, he adds.

The research was published in the March edition of the journal Current Biology.