Reducing the by-catch of juvenile fish (mulloway Argyrosomus hololepidotus) using square-mesh panels in codends in the Hawkesbury River prawn-trawl fishery, Australia

The numbers of prawns and small fish (mulloway) caught by two designs of prawn-trawl codends with square-mesh panels were compared in a manipulative field experiment in the Hawkesbury River prawn-trawl fishery. Compared with a conventional codend, catches from a codend made entirely of square meshes showed a 52% reduction in the mean weight of prawns caught and a 95% reduction in the numbers of mulloway caught. A codend with the posterior half made of diamond-shaped meshes and the anterior half made of square-shaped meshes showed no significant difference in the catches of prawns compared with the control, but reduced to 46% the mean numbers of mulloway caught. There were no differences in the sizes of prawns and mulloway caught by the half-square and the control codends. The codend made of all square meshes did not catch the smallest prawns and mulloway available. The results are discussed in terms of the probable behaviour of prawns and mulloway in trawls and the possibilities for future developments of these fishing gears. It was concluded that there is a great potential for square-mesh panels in codends to reduce the by-catch of fish such as juvenile mulloway in the Hawkesbury River prawn-trawl fishery while maintaining catches of prawns