Studies on mitigation measures and gear optimization for reduction of incidental catch of seabirds and sea turtles in tuna longline fisheries

为了制定减少金枪鱼延绳钓渔业中海鸟意外捕捞的缓解措施，对日本金枪鱼延绳钓渔船所用支线的鱼钩下沉速度进行了调查，并试验制作了水下下沉装置。此外，为了避免海龟误捕，发明了一种新的方法，即将所有支线设置在几乎相同的深度，并将中水提升浮子安装到主线上。研究结果如下：(1)第一年，对日本金枪鱼延绳钓渔船使用的支线进行了调查，明确了支线的组成和特点。测试了10种支线的吊钩下沉速度。此外，为了提高吊钩的下沉速度，还试验了两项新技术：将吊钩附近10m线的材料由尼龙单丝改为氟碳纤维，并在吊钩上增加了10-60GW的重量。吊钩的平均下沉速度从0到1…10种支线埋深在0.161~0.228 m/S之间。然而，10种类型的鱼钩，在船速为10节时，没有一种鱼钩不能下沉到10米以上的深度，此时离抛缆点150米，即鸟吓拖缆(环杆)的有效区域。氟碳线吊钩的下沉速度是尼龙单丝吊钩的1.6倍，附加重量为45GW的吊钩下沉速度几乎是常规吊钩的两倍。(2)在本财政年度，首先制造了水下定位器，以防止意外捕获海鸟。通过海试，证实了鱼钩总是放入1.3m水深。另一方面，通过海试和理论分析，明确了金枪鱼延绳钓在有水流的海面上的摆放形状。(3)为避免海龟误捕，提出了一种利用中水提升浮子进行金枪鱼延绳钓作业的新方法。实验结果表明，通过给主线上的某些点以足够的浮力，可以将所有的鱼钩设置在几乎相同的深度。如上所述，本研究通过使用改进的支线和所开发的水下设置装置，达到了这一目的，并可以预期减少海鸟的附带捕获量。此外，通过在作业中引入中水提升浮子的新方法，也有可能避免海龟的误捕。较少

In order to develop mitigation measures for reduction in incidental catch of seabirds in tuna longline fisheries, the hook sinking speed of branch lines used by Japanese tuna longline vessels was investigated, and an underwater setting device was experimentally manufactured. Also, to avoid sea turtle by-catch, a new method in which all the branch lines are set at almost the same depth with instaling the midwater lifting-up floats to the main line was invented. The results are shown as follows.(1)In the first year, the branch lines used by Japanese tuna longline vessels was investigated, and the composition and the feature of branch lines were clarified. The hook sinking speed in ten types of branch lines was examined. In addition, to improve sinking speed of the hook, two new techniques were tested : material of 10m line close to the hook was altered from nylon monofilament to fluorocarbon ; and weight of 10-60gw was added to the hook. The average sinking speed of the hooks from 0 to 1 … More 0 m in depth varied from 0.161 to 0.228 m/s in the ten types of branch lines. However, no hook in the ten types was not able to sink in depth of over 10m before the fishing vessel at vessel speed of 10 knots for casting was 150 m away from the point of casting line, that is, effective area of bird scaring streamer (Tori-pole). The sinking speed of the hook with fluorocarbon line was 1.6 times larger than that with nylon monofilament, and the hook with additional weight of 45gw sank almost two times faster than conventional one. (2)In this fiscal year, First of all an underwater setting device was manufactured for preventing incidental catch of seabirds. By the sea trial, it was confirmed that the fishhooks were always released into the water depth of 1.3 m. On the other hand, the setting shape of the tuna longline in the sea with flow was clarified through the sea trial and theoretical analysis. (3)To avoid sea turtle by-catch, a new method using the midwater lifting-up floats for tuna longline was invented. From the experimental results, it was possible to set all the hooks at almost the same depth by giving adequate buoyancy to some points in the main line.As mentioned above, in this research, the purpose was achieved and the reduction in incidental catch of seabirds can be expected by using the improved branch line and by using the developed underwater setting device. Moreover, by introducing a new method using the midwater lifting-up floats in operation, it is also possible to avoid sea turtle by-catch. Less