Effects of square-mesh panels in codends and of haulback delay on bycatch reduction in the oceanic prawn-trawl fishery of New South Wales, Australia

Two experiments were conducted in the New South Wales oceanic prawn- trawl fishery, 1) by comparing catch from a conventional codend with that from two new codend designs with square-mesh panels and 2) by showing the effects on catches of a short delay in haulback of trawls with squaremesh panels. The two new codend designs incorporated panels of netting (85-mm mesh) sewn such that the meshes were square-shaped (measuring 7 x 11 bars) and inserted lengthwise and widthwise into the tops of the anterior sections. Simultaneous comparisons among these designs and a conventional codend showed that both designs performed similarly by significantly reducing the weights of bycatch that would be discarded (by 46% and 38%, respectively) without significantly reducing the catch of the prawn Penaeus plebejus. The second experiment showed that juvenile red spot whiting, Sillago flindersi, an important commercial finfish, escaped from the square- mesh panels in the trawl during a 10-15 second haulback delay. Trawls without any haulback delay showed no significant reduction in the bycatch of this species. The results are discussed in terms of the probable behavior of fish in the modified trawls and in terms of the implications that factors such as haulback delay may have on the survival of fish escaping through square-mesh panels in codends.