流速和放网模式对金枪鱼围网网具形态的影响

网具形态是金枪鱼围网作业性能的一个重要指标，受网线材料、沉子配重、海流等诸多因素影响。为探究放网模式和流速对金枪鱼围网网具形态的影响，本研究依照上海开创远洋渔业有限公司金枪鱼原型围网，根据田内准则制作模型网，在日本下关西日本日网公司专业动水槽进行模型实验。实验设置3种放网模式（顺流放网、侧流放网、背流放网），3种流速（0 cm/s、5 cm/s、8 cm/s），比较各放网模式下，流速对金枪鱼围网网具沉子纲沉降深度、纵向网衣轮廓、浮沉子纲水平包围面积和浮沉子纲水平包围形状的影响。结果显示：（1）0 cm/s流速下放网，网具沉子纲沉降深度最大（1.21 m），浮沉子纲水平包围面积最大（8.44 m²，9.89 m²），纵向网衣轮廓最佳；（2）顺流5 cm/s条件下放网，网具浮沉子纲水平包围形状最佳；（3）顺流、背流放网，网具最大沉降深度随着流速增加逐渐减小1.21 m（0 cm/s） > 1.17 m（5 cm/s） > 1.13 m（8 cm/s），1.21 m（0 cm/s） > 1.16 m（5 cm/s） > 1.10 m（8 cm/s）]，网具最大沉降深度与流速显著相关（>0.05）；（5）3种放网模式下，流速与网具浮沉子纲水平初始包围面积不相关（<0.05）。综上建议，有流时为确保网具形态最佳及网具沉降深度最大，应首先采用侧流放网。

Effects of current speed and shooting pattern on the shape of tuna purse seine

Net shape is an important indicator of the operative performance of tuna purse seine, and can be affected by many factors, such as twine material, leadline weight, fishing operation, and currents. In order to understand the effect of shooting pattern and current speed on the shape of tuna purse seine, a model net was manufactured from the prototype net used by Chinese tuna purse seiners, based on the Tauti law. The experiment was carried out in the circulating tank at Nichimo Co., Ltd. of the Shimonoseki Research Institute. The effects of three shooting patterns (front set, cross set, and back set) and three current speeds (0 cm/s, 5 cm/s, and 8 cm/s) on the shape of the model net (the sinking depth of the leadline, the profile of the net, the opening surrounding the areas of the floatline and leadline, and the shape of the floatline and leadline) were investigated in this study. The results showed that:(1) when the current speed was 0 cm/s, the sinking depth of the leadline, and the opening area surrounded by the floatline and leadline reached the maximum of 1.21 m, 8.44 m², and 9.89 m², while the net maintained a better shape; (2) when the current speed was 5 cm/s at the front set, the shapes of floatline and leadline were better compared with the other experimental conditions; (3) at the front set and back set, the sinking depth of the leadline decreased with increasing current speed (1.21 m for the front set and 1.21 m for the back set at 0 cm/s > 1.17 m for the front set and 1.16 m for the back set at 5 cm/s > 1.13 m for the front set and 1.10 m for the back set at 8 cm/s), and the sinking depth of the leadline significantly differed with current speed (<0.05); (4) at the cross set, there was no significant difference in the sinking depth of the leadline for different current speeds (>0.05); (5) for each shooting pattern, current speed did not significantly affect the initial opening areas surrounding the floatline and leadline (>0.05); (6) the opening areas surrounding the floatline and leadline had a linear relationship with the square of time (<0.05). Based on the above results, we recommend cross set in practice, because it ensures a better shape of the net and a greater sinking depth of the leadline.