EFFECTS OF THE CIRCUMFERENCE OF CODENDS AND A NEW DESIGN OF SQUARE-MESH PANEL IN REDUCING UNWANTED BY-CATCH IN THE NEW-SOUTH-WALES OCEANIC PRAWN-TRAWL FISHERY, AUSTRALIA

Effects on the escape of small fish from prawn-trawl codends due to (i ) codend circumference and (ii) a new design of square-mesh panel were investigated in the New South Wales oceanic prawn-trawl fishery, Simu ltaneous comparisons of two conventional diamond-mesh codends, constru cted with posterior sections of 100 and 200 meshes circumference, resp ectively, showed that halving this circumference significantly altered the selectivity of the codend and decreased the by-catch of small fis h, A new design of square-mesh panel incorporated composite panels of netting (60 mm and 40 mm mesh), sewn in such a way that the meshes wer e square-shaped and inserted into the top of the anterior section of t he codend. This panel was designed to allow larger fish to escape thro ugh the 60 mm mesh (at the poir.t where waterflow was thought to be th e greatest) and also increase the random escape of smaller individuals through the 40 mm mesh, To determine any influences of codend circumf erence on the performance of this panel, it was inserted into two code nds with posterior sections of 100 and 200 meshes circumference, respe ctively. Simultaneous comparisons with each other and with their contr ols showed that the two-panelled codends, with posterior sections of b oth 100 and 200 meshes, performed similarly and significantly reduced the weights of discarded by-catch without significantly reducing the c atch of prawns, There was evidence that more fish tended to escape thr ough the square-mesh panel in the codend with the posterior section of 200 meshes circumference, The results are discussed in terms of the e ffects that codend circumference (and therefore hydrodynamic pressure) may have on the escape of small fish through codends that do/do not h ave square-mesh panels.