Selectivity of conventional diamond- and novel square-mesh codends in an Australian estuarine penaeid-trawl fishery

The selectivities and relative efficiencies of (i) two conventional diamond-mesh codends with posterior sections 100 and 200 meshes in circumference and (ii) two novel square-mesh codends with different circumferences throughout and comprising panels of square-shaped mesh instead of drawn-strings were investigated in a New South Wales estuarine penaeid-trawl fishery. Paired simultaneous comparisons (using twin trawls) of each of these four treatment codends with their respective small-meshed controls showed that the conventional diamond-mesh codend with a 200 mesh posterior circumference had no detectable selectivity for all sizes of the school prawns, Metapenaeus macleayi and eastern king prawns, Penaeus plebejus encountered. While reducing the posterior circumference to 100 meshes marginally improved selectivity, both of the novel square-mesh codends were the most effective designs in selecting significantly larger prawns across a smaller range of sizes and releasing up to 99% more fish than the conventional diamond-mesh codend with the 200 mesh posterior circumference. The results are discussed in terms of the influences of the geometry of the various codends on their performances and the importance of examining simple changes to codend meshes as a means for augmenting bycatch reduction from penaeid prawn trawls