Assessments of modified codends that reduce the by-catch of fish in two estuarine prawn-trawl fisheries in New South Wales, Australia

Four experiments, comparing catches and by-catches from a conventional codend with several modified codends, were done in two estuarine prawn-trawl fisheries in New South Wales, Australia, The modified codends were designed to reduce by-catch and included panels of square-mesh, soft mesh separating panels and a Nordmore-grid. Compared to a conventional codend, the codends with square-mesh panels showed no significant differences in catches of school prawns (Metapenaeus macleayi) nor by-catches. The codends with soft mesh separating panels showed different results between locations. In the Clarence River estuary, these designs significantly reduced by-catch (up to 70%) with no reduction in catches of school prawns, while similar designs tested in Botany Bay showed significant reductions in by-catches and catches of king prawns (Penaeus plebejus) (up to 58% and 34% respectively). In the Clarence River the codend with the Nordmore-grid, showed a significant reduction in by-catch (77%) with no reduction in catches of school prawns compared to a conventional codend. The results are discussed in terms of the probable behaviour of fish and prawns in the modified trawls, the need for fishery-specific designs of by-catch reducing trawl modifications and the implications of introducing such designs into normal commercial practice.