Optimal positioning and design of behavioural-type by-catch reduction devices involving square-mesh panels in penaeid prawn-trawl codends

Two experiments were done in the oceanic penaeid prawn-trawl fishery in New South Wales to investigate (i) the optimal positioning of behavioural-type by-catch reduction devices (BRDs) involving square-mesh panels; and (ii) the relative performances of two industry-developed square-mesh panels against a composite square-mesh panel developed by scientists. In the first experiment, three codends, each containing one square-mesh panel (located on the tops of the codend at distances of 0.7, 1.2 and 1.6 m anterior to the last row of meshes respectively) significantly reduced the catches of some small fish and total discards compared with a control codend that held no BRD. Rates of reduction significantly increased with proximity of the square-mesh panel to the end of the codend. There was, however, a significant reduction in catches of prawns from the codend containing the square-mesh panel at 0.7 m. Based on these results, the optimal position for these sorts of BRDs was determined to be at 1.2 m anterior to the last row of meshes. In the second experiment, at this position, two codends containing industry-developed plastic and metal square-mesh panels were less effective in excluding by-catch than a codend containing the composite square-mesh panel. The results are discussed in terms of species-specific differences in behavioural responses and swimming ability and the future development and testing of behavioural-type BRDs in penaeid prawn trawls.