PRECISION MANAGEMENT FOR NORTHERN PRAWNS
17 February 2003

For the first time, researchers will be able to measure the real effects of prawn trawling on the seabed.

A new study of the impact of prawn trawling will involve full-scale experiments in (and under) the Gulf of Carpentaria, according to Dr Burke Hill of CSIRO Marine Research.

"Prawn trawling has a range of effects on seabed habitats, but these are poorly understood," says Dr Hill.

"This project will quantify the rate at which seabed organisms are removed by trawls and the rate at which they recover after trawling," he says.

The trawling experiments will be conducted in a full-scale 'outdoor laboratory', on an area of seabed within the Northern Prawn Fishery that hasn't been trawled since 1985.

"The plots will be surveyed, and then trawled up to 20 times," Dr Hill says.

"Researchers will measure how much of the seabed fauna is removed by the trawling and resurvey the plots after the trawling is completed to find out how much of the fauna remains.

"The plots will be monitored over the next two years to measure the rate at which the seabed fauna recovers from trawling."

Findings from the undersea trials will be linked with satellite-derived maps of fleet movements across the fishery.

This will boost the accuracy of a 'trawl simulation' model developed by CSIRO to predict the consequences of trawling on a variety of seabed organisms, and evaluate different management options.

"Australia's $120 million Northern Prawn Fishery (NPF) will be able to demonstrate that it can achieve its environmental goals," says Dr Hill.

The number of trawlers in the NPF has decreased from about 250 to 100 in past 20 years.

Trawling is highly concentrated in areas of highest catch rates and presently takes place in less than 25% of the area available.

Because of this patchy distribution of fishing, it has been difficult to assess the effect of trawling on the seabed fauna as a whole.

"The project will take us a long way forward in our ability to predict the effects of management initiatives on the marine environment," Dr Hill says.

"For example, the model will be used to evaluate the consequences for seabed fauna of a 33% reduction in trawl effort imposed by the Australia Fisheries Management Authority (AFMA) in 2002.

"This capacity to evaluate management initiatives is crucial as Australian fisheries are being required by federal legislation and international accreditors to demonstrate their environmental sustainability.

"It is particularly important to the NPF, which exports 90% of the its catch."

The project will also map the distribution of trawl effort, using data collected by AFMA using satellites. This Vessel Monitoring System of the NPF fleet, provides very-high-resolution information on where the trawlers fish.

"Previous studies have been based on fishing logbooks kept by skippers," Dr Hill says.

"VMS-derived maps have a resolution 36 times higher than the logbook information, showing researchers exactly which areas of the NPF are trawled.

"The maps will enable us to increase the accuracy with which we model the impacts of trawling on the seabed communities in the NPF and will assist in the planning of future research dealing with trawl impacts."

The three-year project, beginning in January 2003, is funded by the NPF, the Fisheries Research and Development Corporation and CSIRO. It is led by CSIRO Marine Research.

More information from:
Dr Burke Hill, CSIRO Marine Research 07-3826 7229
Bryony Bennett, CSIRO Marine Research 03-6232 5261 bryony.bennett@marine.csiro.au
Kylie Paulsen, FRDC 02-6285 0415

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