An assessment of bycatch reduction devices in a tropical Australian prawn trawl fishery

Our study assessed 16 different Bycatch Reduction Devices (BRDs) for use in Australia's Northern Prawn Fishery (NPF), during three cruises in the Gulf of Carpentaria. The study was a response to pressure from conservation and community groups to make harvesting of the sea more selective 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 Surveyor; testing under normal commercial fishing conditions. Bycatch Reduction Devices were improved throughout these procedures; only the best-performing devices were tested in the next stage. All four inclined grids (Super Shooter, Nordmore grid, AusTED and NAFTED) were extremely effective at excluding large sharks, stingrays and sea turtles. They were also effective at excluding some of the unwanted small-fish catch, especially when used in combination with other BRDs, such as a fisheye or square-mesh window. Fish exclusion ranged between 0 and 39%. Exclusion of sea snakes was substantially increased by using BRDs, such as the AusTED or square-mesh windows. The ability of BRDs to maintain the catch of the target species was part of the assessment. The Super Shooter had the best prawn retention rate, losing only between 2 and 12% of prawns in scientific trials and gaining 3.4% during the commercial trials. The Super Shooter also performs well in areas where the other inclined grids tend to clog with sponges or other large objects. The NAFTED, 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 fisheye may increase prawn catches. Other devices lost substantial numbers of prawns, but modifications could greatly improve their performance. Some of these devices could be used successfully in their present form. The performance of most BRDs were also strongly affected by the weather 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 bycatch while maintaining catches of commercially valuable prawns. The main benefits to the NPF fishery of using BRDs are: fewer or no sea turtles caught or killed; fewer small fish to be sorted from catches; fewer large animals (stingrays, sharks and sea turtles) that can damage valuable prawns, resulting in a higher catch value; and decreased fishing impacts on bycatch species, which helps to maintain ecological biodiversity and resilience of these demersal communities. Failure of the NPF and other Australian prawn trawl fisheries to voluntarily adopt BRDs 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.