Using composite square-mesh panels and the Nordmøre-grid to reduce bycatch in the Shark Bay prawn-trawl fishery, Western Australia

An industry-modified Nordmøre-grid was tested on its own and with a composite square-mesh panel as a secondary bycatch reduction device (BRD) at two different positions (aft and forward) in codends. Compared to the control codend (which had no BRDs), all three combinations (Nordmøre-grid only, Nordmøre-grid and aft composite square-mesh panel and Nordmøre-grid and forward composite square-mesh panel) reduced catches of prawns (mostly western king prawns, Penaeus latisulcatus). However, prawns were found to escape out of the Nordmøre-grid - not through the composite square-mesh panels. The Nordmøre-grid with the aft composite square-mesh panel significantly reduced the weight of bycatch (by 49%) and the numbers and weights of several commercially and non-commercially important bycatch species (by up to 75.7%). No other significant differences were detected. The results are discussed in terms of the likely factors influencing the performance of the various designs, including the behaviour of fish in codends, influences of hydrodynamics on their escape and the importance of the positioning of BRDs in codends