Optimizing tori line performance through terminal towing configurations in tuna longline fisheries

This study examined the effects of different tail-section towing configurations on tori line aerial-extent performance using at-sea trials on Chinese tuna-fishing vessels. Three tori line configurations were evaluated at representative operational vessel speeds of 4.5, 6.0, and 8.2 kt. These included the baseline streamer configuration, a plastic-cone configuration (20 m long drag section with four 45 cm plastic cones installed at intervals of 2 m), and a drogue configuration (20 m long drag section with 50 cm drogue at terminal end, followed by 10 m of resin rope and a 200 mm float). A sensitivity analysis was also conducted using low-, moderate-, and high-drag scenarios, and the drag force generated by each configuration was estimated. The results showed that tail-section towing configuration clearly affected the aerial deployment of the tori line. The drogue configuration achieved the best aerial-extent performance at all tested vessel speeds, and met or exceeded the 100 m benchmark under all test conditions. The baseline streamer configuration ranked second. These findings indicate that both the magnitude and stability of the drag generated by the tail-section towing configuration are important factors influencing tori line aerial-extent performance.