Examination of tori-pole configuration in middle-sized longline vessels
We examined the performance, practicality and effectiveness of tori-poles to explore the configuration suited to middle-sized Japanese longline vessels in the western North Pacific. Experiments on 2 types of poles, 3 types of bird lines and 3 classified lengths were conducted by a commercial longline vessel. Among 3 types of line, 2 heavy line types are characteristically strong type by wind whereas they appear to turn down aerial coverage of bird line. The behavior rates of catching the bait under long bird line were lower than that under short line. Although line length of tori-pole depends heavily on the situation in size of vessel and oceanic condition, use of bird line for as long as possible in consideration of safety and handling might be best practice to exert maximum effectiveness. To conclude from our preliminary examination of tori-poles, the appropriate tori-pole configuration for middle-sized longline vessels were the following specifications: approximately 100m of bird line length (approximately three times the total length of vessel), untwisted and lightweight bird line material, lightweight streamer such as polypropylene band.