Increasing lateral mesh openings in penaeid trawls to improve selection and reduce drag

Abstract

In an attempt to improve selection and engineering efficiency in an Australian penaeid fishery, the mesh size and side taper of a generic trawl design were reduced (from 41 to 35mm) and increased (from 1N3B to 1N5B), respectively and, within the revised design, the independent and combined utility of (i) increasing the frame-line hanging ratio, and (ii) replacing the diamond-orientated wing/side panel with square-orientated mesh were investigated. Compared to the 41-mm mesh conventional trawl, all of four smaller-meshed designs (comprising either loose or tight hanging ratios, and with diamond- or square-mesh wing/side panels) had lower drag (9–12%) and required less fuel (up to 4–12%). Some of the small-meshed trawls caught fewer unwanted fish—attributed to the steeper side panels allowing individuals to swim forward and escape. Within the small-mesh trawls, there were incremental improvements in size selectivity for the targeted school prawns, Metapenaeus macleayi associated with both modifications. But the square-mesh wing/side panels were by far the most effective, reducing the catches of sub-commercial school prawns by up to 72%. The results support simple, retrospectively fitted alterations to existing penaeid-trawl bodies to improve selection and efficiency.