Catch per unit effort and bycatch composition of shrimp trawler boats in Bushehr province (Mond and Dayyer-Nakhiloo)

This study aimed to investigate the catch per unit effort of target and non-target species and to determine the bycatch composition in boat trawlers used in Mond and Dayyer-Nakhiloo coastal waters in Bushehr province. Field operations were carried out during the years 2020 (13 August to 15 February) and 2021 (11 April to 9 September). During the research, a 27-foot fishing boat with a 200 hp engine was used. The trawl net used was made of polyamide (PA). The sampling operation was performed in 32 steps. During this study, the amount of catch per unit effort, the ratio of by-catch to the target species, and the amount of by-catch were calculated. The highest frequency of Penaeus semisulcatus in July 2021 (96.67%), the highest frequency of Metapenaeus affinis in August 2021 (21.74%), and the highest frequency of Parapenaeopsis stylifera in July 2021 (63.75%) were recorded in Mond. 37 aquatic species were observed as a bycatch composition during fishing operations. Species including Saurida tumbil, Cynoglossus arel, Portunus segnis, Gerres filamentosus, Drepane punctata, Solea elongata, and Epinephelus coioides were permanently present in the catch composition. The highest rate of shrimp fishing effort was observed in the Mond region (58 kg/h) and the lowest rate was observed in the Dayyer-Nakhiloo (1 kg/h). Also, the ratio of by-catch to target (r) was 2.32 and the weight of by-catch during the fishing season was 1478.96 kg. The results indicate high fishing pressure on commercial and non-commercial species in this area and can be used to assess the damage caused by shrimp trawl nets on fish stocks in ecological risk assessment models. In addition, the findings showed that the deletion of some species can make the food chain longer due to their role in the food chain and reduce the resistance of the ecosystem food web, and ecological and habitat efficiency.