Performance of Bycatch Reduction Devices in the Small-Scale Shrimp Trawl Fishery of the Persian Gulf

Abstract

High rates of discards have been noted for shrimp fisheries worldwide and especially for the small-scale shrimp trawl fisheries of the Persian Gulf. Bycatch reduction devices (BRDs) can significantly decrease discards in shrimp trawl fisheries. We tested the performance of a square mesh panel BRD (SMP) and a juvenile and trash fish excluder device (JTED) in the small-scale shrimp trawl fishery of the Persian Gulf. Efficiency of the BRDs was determined in terms of shrimp loss, by-product loss, the reduction in discards by weight and differences in size selectivity of commercial fishes. Where a JTED was used, reductions in catch, by weight, were (mean ± 95% CI) 12% ± 2.35 for shrimp, 31.9% ± 5.22 for by-product fish and 49% ± 7.52 for discards. Similar reductions were observed when a SMP was used: 16% ± 4.19, 38.3% ± 6.41 and 45% ± 6.15 for shrimp, by-product and discards, respectively. There was no significant difference in the exclusion rate of discards between the JTED and SMP. Significant difference was found for loss of shrimp between JTED and SMP. The mean escapement rate for by-product species in trawl net with JTED and SMP were 35% and 40%, respectively. Selectivity curves of both BRDs indicated, that for each species, the length of 50% retention probability (L50) were smaller than the length at maturity (LM) and an increase in bar spacing in JTED and mesh opening in SMP would be required to delay capture until fish had reached Lm. The results indicated that SMP allows a higher proportion of sub-legal by-product species to escape the trawl, compared to the JTED used in the study. Implementing BRD requirements for the Persian Gulf small-scale shrimp fisheries would contribute to meeting strict sustainability criteria, a good outcome for this small-scale fishery.