Effect of connection methods on the mechanical characteristics of tuna longline fishing gear

Improving the efficiency of tuna longline fishing is highly dependent on the mechanical properties of the longline fishing gear, especially the choice of connection methods. This study aimed to explore the static characteristics of longline fishing gear by different connection methods under four stretching speeds using a tension machine. This study divides the branch line into three sections to pinpoint areas of mechanical vulnerability. This study addresses three issues: the static characteristics of the main line and the branch lines; the influence of connection methods in three sections of the branch lines on the static characteristics of the longline; and the impact of the entire branch lines on the static characteristics of the longline. To evaluate the performance of these connection methods, the breaking load was measured for each type. Four common connection methods were examined in this study, e.g. single-fixation, double-fixation, eye-splice, and sheet-bend. For comparison, the mechanical characteristics of twines without connections were also assessed. The results showed that the eye-splice and the sheet-bend connections of polypropylene twines are superior to the single-fixation and the double-fixation. Compared with the twines without connections, the breaking load of the connection twines is only reduced by 5 %. For nylon monofilament with a diameter exceeding 2 mm, the single-fixation connection is better than other forms, which reduces the load on the branch lines. The weakest mechanical performance of the entire longline fishing gear occurs in the third section, which requires special attention. This study is beneficial to understanding the static characteristics of the longline fishing gear and to the application of the longline fishing.