Influence of top-panel orientation (lead-ahead) on targeted and incidental catches in a penaeid trawl

Abstract

Various, low-cost modifications to the anterior sections of penaeid trawls have been shown to realise significant improvements in species selectivity. This study expands the existing options by quantifying the importance of top-panel orientation relative to the bottom panel (dictated by relative headline and footrope lengths; termed ‘lead-ahead' or ‘lead’) on targeted and incidental catches in an Australian penaeid-trawl fishery. Three trawls were compared in a double rig: (1) the conventional configuration with identical footrope and headline lengths (7.53 m) and a 200-mm diameter buoy attached to the latter (termed the ‘buoyed no-lead trawl’); (2) the same trawl, but with the buoy removed (‘no-lead trawl’); and (3) a trawl with the same headline length as above, but the footrope 1.14× longer, creating lead-ahead (‘lead trawl’). Between 11 and 26 deployments of each configuration were done over six fishing days. Compared to the buoyed no-lead trawl, both the no-lead and lead trawls had greater wing-end spreads and both caught less total bycatch (absolute and standardized weights ha–1 trawled reduced by up to 64 and 48 %, respectively) and fewer individual unwanted species, including jellyfish, Catostylus mosaicus (by up to 61 and 58 %) and southern herring, Herklotsichthys castelnaui (by up to 59 and 43 %). However, only the lead trawl maintained catches of the targeted school prawns, Metapenaeus macleayi. These target catches were reduced by 37 % in the no-lead trawl (without the buoy). The results imply a trawl without lead-ahead requires sufficient headline height to maximise catches of school prawns, but simply introducing lead-ahead and removing the buoy (lowering the headline) can maintain target catches while dramatically reducing bycatch. Similar subtle refinements may have application in other penaeid-trawl fisheries.