Investigating species composition, length frequency composition and by-catch amount of longtail tuna drift gillnets in northeastern waters of the Oman Sea (Sistan and Baluchestan)

The present study was conducted to investigate the species composition, length frequency composition and by-catch amount in longtail tuna pelagic gillnets in northeast of Oman Sea and fishing grounds of Chabahar, Konarak and Ramin (Sistan and Balouchestan Province). Sampling operation was carried out using the fiberglass boat and wooden vessel from October 2016 to June 2017. Fishing gear was included longtail tuna pelagic gillnets with 100 and 110 mm stretched mesh size in fishing boats and gillnets with 130 and 165 mm stretched mesh size in wooden fishing vessels. Totally, by-catch species composition were 15 species belonging to 8 family including Scombridae, Istiophoridae, Coryphaenidae, Alopiidae, Carcharhinidae, Carangidae, Sphyraenidae and Trichiuridae. The significantly variation of by-catch species composition observed in used nets by boats and wooden vessels. In the entire study period, in boats, minimum and maximum catch amount was related to Carcharhinus sorrah with 35 kg and Euthynnus affinis with 1622 kg, respectively. Maximum catch was obtained for Euthynnus affinis as 260 kg per each netting and fishing operation. Maximum mean catch (±S.E) was obtained to Euthynnus affinis as 47.71±9.26 kg per each fishing operation. In wooden vessels, minimum and maximum catch amount was related to Alopias pelagicus with 93 kg and Thunnus albacares with 90013 kg, respectively. Maximum catch was observed for Thunnus albacares as 8219 kg per each netting and fishing operation. Maximum mean catch (±S.E) was related to Thunnus albacares as 1250.18±186.61 kg per each fishing operation.