Bycatch and discards in the shrimp trawl fishery off the Persian Gulf

The Persian Gulf waters, like other tropical regions, are rich in aquatic animal fauna and demersal trawling is one of the most common and practical methods to exploit aquatic resources. In the meantime, fishing vessels equipped with trawl nets can generate large amounts of bycatch and subsequent discards. This study aimed to identify fish species and estimate catch per unit area (CPUA) in the shrimp trawl bycatch off northwestern coasts of the Persian Gulf. The data were collected during trawl hauls for one year (September 2021– September 2022) between Delwar and Helle fishing grounds at three depth layers. The bycatch samples included 75 fish species with a total CPUA of 2392.4 kg/nm2. The largest amount of the discarded bycatch (77.8%) belongs to teleost and cartilaginous fishes, of which gilded goatfish and Japanese threadfin bream accounted for the first and second places with a total CPUA of 433.9 kg/nm2 and 202.8 kg/nm2, respectively. The abundance of the identified bycatch varied at different water layers, and the highest bycatch rate was obtained in the depth water (21-30 m; 44.1%) and the lowest value was recorded in the shallow water (up to 10 m; 21.7%). Fifteen fish species had percentage of occurrence (100%) at all studied depths. According to the distribution map provided by ArcGIS software, the density of discards was increased by moving toward the western part of the Persian Gulf. The assessment of the bycatch composition of traditional shrimp trawler fisheries is not only practical to take preventive actions regarding the marine ecosystem balance but also the results can be used as an ecological model to evaluate the risk of the trawlers in the study area.