AN ASSESSMENT OF BYCATCH REDUCTION DEVICES IN A TROPICAL AUSTRALIAN PRAWN TRAWL FISHERY

Our study assessed 16 different Bycatch Reduction Devices (BRDs) for u se in Australia's Northern Prawn Fishery (NPF), during three cruises i n the Gulf of Carpentaria. The study was a response to pressure from c onservation and community groups to make harvesting of the sea more se lective and less damaging to the non-target communities. The approach was to incrementally improve the performance of BRDs after each stage: underwater observations in a flume tank and engineering trials at sea ; rigorous and controlled scientific trials on the RV Southern Surveyo r; testing under normal commercial fishing conditions. Bycatch Reducti on Devices were improved throughout these procedures; only the best-pe rforming devices were tested in the next stage. All four inclined grid s (Super Shooter, Nordmore grid, AusTED and NAFTED) were extremely eff ective at excluding large sharks, stingrays and sea turtles. They were also effective at excluding some of the unwanted small-fish catch, es pecially when used in combination with other BRDs, such as a fisheye o r square-mesh window. Fish exclusion ranged between 0 and 39%. Exclusi on of sea snakes was substantially increased by using BRDs, such as th e AusTED or square-mesh windows. The ability of BRDs to maintain the c atch of the target species was part of the assessment. The Super Shoot er had the best prawn retention rate, losing only between 2 and 12% of prawns in scientific trials and gaining 3.4% during the commercial tr ials. The Super Shooter also performs well in areas where the other in clined grids tend to clog with sponges or other large objects. The NAF TED, which was used only during the commercial trials, lost only 3.3% of the prawn catch of a standard trawl. There is evidence that the fis heye may increase prawn catches. Other devices lost substantial number s of prawns, but modifications could greatly improve their performance . Some of these devices could be used successfully in their present fo rm. The performance of most BRDs were also strongly affected by the we ather and fishing procedures, such as delay in haulback of the trawl. This study has shown that there are BRDs that can be of major benefit to prawn trawl fishers in the NPF by excluding much of the unwanted by catch while maintaining catches of commercially valuable prawns. The m ain benefits to the NPF fishery of using BRDs are: fewer or no sea tur tles caught or killed; fewer small fish to be sorted from catches; few er large animals (stingrays, sharks and sea turtles) that can damage v aluable prawns, resulting in a higher catch value; and decreased fishi ng impacts on bycatch species, which helps to maintain ecological biod iversity and resilience of these demersal communities. Failure of the NPF and other Australian prawn trawl fisheries to voluntarily adopt BR Ds may result in an involuntary adoption brought on by pressures from community, conservation and trade bodies. (C) 1998 Elsevier Science B. V. All rights reserved.