Summary

During the past three years, the NSW DPI Fisheries Conservation Technology Unit has been working with industry to reduce unwanted bycatches of small prawns and fish from the various prawn-catching gears used throughout NSW. This work has mostly involved designing and testing codends made from square-shaped mesh in seines, hauls, pocket nets and trawls.

In March 2002, we did our first experiment with estuarine prawn trawlers in Lake Woolooweyah. This work involved comparing existing 40-mm diamond-mesh and new square-mesh (made from 20-mm mesh hung on the bar) codends. The results showed that the conventional diamond-mesh codends retained nearly all sizes of prawns. In contrast, the square-mesh designs excluded small unwanted prawns and fish while maintaining commercial catches. These results led to many fishers in Lake Woolooweyah and the Clarence, Hawkesbury and Hunter Rivers voluntarily using square-mesh codends (mostly made from 20-, 25- or 27-mm mesh hung on the bar) as part of their normal fishing operations. All fishers reported the best results with the 27-mm mesh codend and so, during the last season, we tested this design throughout nearly all of the estuarine prawn-trawl fisheries.

For this work, we secured a fine-meshed cover (designed to collect all of the escaping organisms) to a 27-mm square mesh codend. Between March and May 2004, this codend/cover configuration was attached to trawl nets on randomly-selected commercial prawn trawlers working in Lake Woolooweyah (1 trawler) and the Clarence (5 trawlers), Hunter (2 trawlers) and Hawkesbury Rivers (2 trawlers). We completed between 4 and 6 tows with the covered codend on each trawler. After each tow, the catches of prawns in the codend and the cover were separately weighed, counted and measured.

In each of the estuarine trawl fisheries, between approx. 5 and 17% of prawns (by weight) per tow escaped through the meshes of the 27-mm square-mesh codend. However, the majority of these escaping prawns were very small, unwanted individuals. For all estuaries, catches of commercial-sized prawns were maintained.

The results from this work confirm the utility of square-mesh codends for improving the size selection of prawns in NSW estuarine prawn trawls. Additional voluntary testing of modified codends by industry will facilitate the refinement of appropriate modifications to conventional fishing gears that maximize the reduction of unwanted prawns while maintaining commercial catches.