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Trawling for insights about the North West shelf

By Asaesja Young

October 11, 2017

trawling ship at sea
Image: Shutterstock

Following decades of heavy trawling off the north-west shelf of Australia in the 1970s and 1980s, researchers will assess how the region has recovered, providing scientific advice to guide sustainable fishing practices both in Australia and internationally.

Since as early as the 1950s the NW shelf has been a focus for national and international trawling, which reached a peak in 1974 when Taiwanese vessels landed around 40,000 tonnes of fish from the area. The Australia-wide catch for the continent that year was 58,000 tonnes.

Almost ten years later, when catches had started to decline and concerns about the impact to seabed organisms had been raised, CSIRO sent a team of scientists to assess the region’s recovery.

The team found it was too early to make a full assessment of recovery rates, but did discover that the reductions in targeted fish species was associated with a loss of 3-dimensional seabed habitats.

Now, thirty-five years later, we are going back aboard the Marine National Facility research vessel Investigator, to reassess and compare our early findings.

man onboard ship
John Keesing investigating trawling in the NW shelf, onboard the RV Investigator. Image: Max McGuire

Voyage chief scientist and CSIRO researcher Dr John Keesing says the team will also investigate how areas that remain trawled have comparatively recovered to areas closed to trawling.

“Since the early trawling by foreign fleets, some areas along the north-west shelf have been closed to trawling, while others have continued to be trawled by Australian fishers,” says Keesing.

“To understand the recovery, we will look at the species and size of fish in the region, the types of organisms living on the sea floor and the amount of phytoplankton and zooplankton in the water, which along with providing food for fish are key indicators of productivity in a region.”

Various species of fish are found along the NW shelf including Australian seafood favourites the red emperor and blue-spotted emperor.

“Seafood is an important part of our diet and is a major contributor to our economy, so it’s important that we understand how fishing can occur as sustainably as possible,” says Keesing.

This balance of economic and environmental ocean sustainability is often referred to as the “blue economy” and was the focus of Foreign Minister Julia Bishop’s recent speech to an international conference focussed on Australian-US-Asia relations.

The voyage comes after CSIRO research reported that at a national scale, seven per cent of sea floor organisms were at risk from trawling, while 55 per cent were found in areas which were not trawled or protected.

“Trawling which contacts the seabed is often criticised because it has a direct impact on sea floor organisms like sea sponges and sea fans, which contribute significantly towards the 3D structure and function of an ocean eco-system,” says Keesing.

“Foreign vessels have not trawled on the region since 1989 and the current Australian fishery is operated over a much smaller area with fewer vessels and in 2015 caught 1779 tonnes.

“The absence of trawling for many years on parts of the north-west shelf makes it an ideal place to carry out this research.

“This issue of how animals on the sea bed recover from trawling is an important global issue and the research will provide the latest science to both Australian and international management agencies.”

The voyage leaves Broome on 11 October and arrives in Fremantle on 9 November.

Findings from the study are expected to be available within the next year and will be shared with industry, management agencies and the general public.

The Marine National Facility is owned and operated by CSIRO for the benefit of the nation.

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