Studies on fishing mechanism of semi-trammel net

1988年10 - 11月和1989年在东京湾进行了半束缚网对沙棘鱼的选择性和捕捞效率试验。结果表明，计算出了小孔径网目尺寸的选择性，并绘制出了右侧的选择性曲线，分别为3.6、5.1和6.8cm网目尺寸的最佳长度为13.5、18.8和25.5 cm。垂直松弛的变化对选择性曲线的形状没有任何实质性的变化。利用松田刺网浮线高度近似预测公式，对束缚网和半束缚网的浮线高度进行了估算。将估算值与水槽试验的实际值进行了比较。所得的估计值与实际值非常吻合。以实验鱼（虹鳟鱼）为实验对象，在室外水箱中进行了半系网和刺网的捕捞实验，了解了虹鳟鱼的种群大小和叉长分布。光强对半束缚网渔获量的影响大于刺网渔获量，网目尺寸对刺网渔获量的影响大于半束缚网渔获量。在捕获的鱼与体长分布相适应的情况下，刺网的捕获效率高于半束缚网。这一现象与东京湾渔捞实验的结果十分吻合。

Fishing experiments were conducted in Tokyo Bay in October-November, 1988 and 1989 to determine the selectivity and catching efficiency of semi-trammel net to gizzard shad. Results were showed that the selectiveties of the mesh sizes of small-meshed net were calculated and the plotted selectivity curves were showed to the right with optimum lengths of 13.5,18.8 and 25.5 cm for 3.6,5.1 and 6.8cm mesh size, respectively. Variations in vertical slack did not show any substantial change on the shape of the selectivity curves.Matuda's approximate formula for predicting the floatline height of gillnet was utilized in estimating the floatline height of trammel and semi-trammel net. The estimated values were compared with the actual values obtained from a flume tank experiments. The resulting estimating values were found to be in close agreement with the actual values.The fishing experiments for semi-trammel net and gillnet were conducted in out door water tank by using experimental fish (rainbow trout), of which the population size and the fork length distribution were known. The effect of light intensity on catch by semi-trammel net was greater than that by gillnet, while the effect of mesh size on catch by gillnet was greater than that by semi- trammel net. On case where the fish caught were suited into the body length distribution, the catching efficiency of gillnet was higher than that of semi- trammel net. This phenomena was in close agreement with the results obtained in the fishing experiments in Tokyo Bay.