Size selection of three commercial fish using sorting grids in the Persian Gulf shrimp trawl fishery

Abstract

Two bycatch reduction devices (BRDs); a Nordmore grid and a Nafted in combination with fisheye, were tested in the Persian Gulf shrimp fishery from an industrial shrimp trawler. Double rig trawls were used, one of them as an experimental net and the other as the control net. Three species of valuable fish—Scomberomorus commerson, Otolithes ruber, and Pampus argenteus were selected for selectivity analysis. For each of the three commercial fish studied, less individuals smaller than the minimum landing size (MLS) were retained in the experimental codends of both BRDs. The average exclusion rate of individuals smaller than MLS was calculated to be 47% and 32% for Nafted plus fisheye and Nordmore grid respectively. A two-sample Kolmogorov–Smirnov test detected a significant difference (P<0.05) in the length frequency of S. commerson, O. ruber and P. argenteus caught in the control and experimental codend of both BRDs. For S. commerson, O. ruber and P. argenteus fish length at 50% retention (L50) and selection range (SR) differs little between Nordmore grid and Nafted plus fisheye. Selectivity curves of both BRDs for three commercial fish indicated that the recorded L50 values were smaller than MLS values. The results have shown that Nordmore grid and Nafted in combination with fisheye have a reductional effect on bycatch of the juveniles of commercial fish species. This study has shown that by using BRDs in the Persian Gulf shrimp fishery decreased fishing impacts on bycatch species, helps to maintain ecological biodiversity and resilience of these demersal communities.