Comparing and modifying penaeid beam and otter trawls to improve ecological efficiencies

In an attempt to improve the selectivity and engineering performances of generic penaeid trawls, three established and one novel spreading-mechanism configurations were assessed: otter boards attached (1) with and (2) without 3.15-m sweeps to a 7.35-m headline trawl, and a beam rigged directly to a 9.19-m trawl (3) with and (4) without a horizontal wire and plastic streamers. Despite more surface area (7.5 vs 6.0 m2), both beam-trawl configurations had significantly lower drag than the otter trawls (≤30%). When catches were standardised to per ha, the otter trawl with sweeps retained significantly more (1.3–2.4 times) school prawns, Metapenaeus macleayi (Haswell), than the other three configurations. Within systems, removing sweeps or adding a horizontal wire significantly reduced the unwanted catches of a key teleost (southern herring, Herklotsichthys castelnaui Ogilby) by 41 and 48%. The results illustrate the utility of simple anterior modifications for independently addressing penaeid-trawling environmental issues.