Short communication: Determining gill-net selectivity for longtail tuna (Thunnus tonggol Bleeker, ۱۸۵۱) using artisanal fishery data in the Iranian waters of the Oman Sea

Using the catch data obtained from local fisheries fleet, length frequency, length-weight relationship and multifilament drift gillnet selectivity of longtail tuna were determined in Iranian waters of the Oman Sea (Chabahar), Iran. Multifilament drift gillnets with ۱۰۰, ۱۱۰, ۱۳۰ and ۱۶۵ mm stretched mesh size were utilized in fishing operations. For each species, fork length, total weight, head girth and maximum girth were measured. A total of ۴۷۷ specimen were collected ranging from ۳۲ to ۹۰ cm fork length and mean length was recorded to be ۵۵.۱۵±۰.۶۱ cm. Head girth-fork length and maximum girth-length relationship were obtained as: Gh = ۰.۵۳۷۹ FL + ۰.۴۹۵۵ and Gmax = ۰.۵۸۷۹ FL + ۰.۵۰۹۵, respectively. All girth-length regressions were found to be linear. Using Sechin method, optimal catch size of ۱۰۰, ۱۱۰, ۱۳۰ and ۱۶۵ gillnet mesh sizes were determined as: ۳۵, ۳۸, ۴۶ and ۵۷ cm, respectively. Moreover, selection coefficient (K) was calculated ۰.۲۸۵ (۱۰۰ mm mesh size), ۰.۲۸۹ (۱۱۰ mm mesh size), ۰.۲۸۲ (۱۳۰ mm mesh size) and ۰.۲۸۹ (۱۶۵ mm mesh size) for longtail tuna gillnets. In this study, the selectivity curves were the shape of normal distribution and narrow.  

کلیدواژه ها:

Gillnet selectivity ، Longtail tuna ، Thunnus tonggol ، Chabahar ، Oman Sea