Turtles escape trawls using TEDs

A major study has found that the Northern Prawn Fishery has reduced its impact on bycatch species.

• 24 January 2006 | Updated 14 October 2011

• What the study involved
• Good news for turtles
• Smaller fish
• Faster handling

Turtles, large sharks and rays can escape from prawn trawls, but greater efforts are needed to protect smaller species from incidental capture.

Australia’s Northern Prawn Fishery (NPF) has taken a major step towards minimising its impact on unwanted species.

The fishery made the use of Turtle Excluder Devices (TEDs) and Bycatch Reduction Devices (BRDs) compulsory in 2000, to reduce the catch of non-target or ‘bycatch’ species.

TEDs are hard grids placed in trawl nets to exclude turtles and other large animals. BRDs are escape grids designed to enable smaller animals to swim out of the net.

What the study involved

The study involved CSIRO, the Australian Maritime College and NPF operators, with funding from the Fisheries Research and Development Corporation.

It combined the skills of:

• fishers
• fisheries technologists
• scientists
• economists
• statisticians
• conservationists. 

Together they assessed and improved the operational and economic performance of Turtle Excluder Devices and Bycatch Reduction Devices.

Scientific observers compared catches on 23 NPF vessels. They surveyed a further 75 trawlers, covering 80 per cent of the fleet in all.

Good news for turtles

Mr David Brewer led the CSIRO research team. 

‘We found that the effect of these devices varied widely between species groups,’ Mr Brewer said. ‘The impact of trawling on turtles and many of the highest risk sharks and rays, however, had been dramatically reduced.

‘The greatest bycatch reduction was recorded for turtles, whose capture was reduced from about 5 500 in 1999 to less than 50 in 2000 with total mortalities reduced from about 1 200 to less than 12, following the introduction of TEDs and BRDs. All species of turtle are excluded equally.’

Smaller fish

Sea snakes, sawfish, and small fish, sharks and rays are still at risk of unintentional capture.

‘Continuous improvement in the design and use of TEDs and BRDs will be critical, and new devices or technologies may be needed for some species,’ Mr Brewer said.

‘This may require a greater understanding of prawn and fish behaviour during the capture process so that BRD designs can be improved to allow fish to swim to freedom while retaining the prawns.’

Faster handling

The exclusion of larger animals:

• made catches easier to handle and sort
• reduced danger to the crew
• increased the value of the catch by reducing the crushing of prawns.

‘While catches of commercially important prawns were reduced by 3–6 per cent, damage to prawns by heavy animals was reduced by 40 per cent,’ said Mr Brewer.

The NPF is one of Australia’s most valuable commonwealth fisheries and one of the most progressive fisheries in dealing with environmental issues. It covers more than one million square kilometres of ocean, from north of Weipa in Queensland to Cape Londonderry in Western Australia.

This was the first major assessment of bycatch reduction practices conducted in a tropical fishery.

Read more about the research by CSIRO Marine and Atmospheric Research.