Research of development on midwater trawl for sampling larval and juvenile fish

为了持续有效地利用渔业资源，有必要对目标鱼种的资源丰度进行准确的估算。并指出仔稚鱼的定量采集是其手段之一。本研究开发了一种新型的中层拖网（MOHT），它具有方形固定框架，可以在不改变拖速的情况下拖行恒定深度，以定量采集中上层幼鱼。结果如下所示。(1)第一年设计了弧面比为15%、展弦比为6.0、上反角为20°的V型压气机。在循环水池中进行了1/5缩尺模型试验。在攻角为20°时，下沉力系数最大，为1.57。它比扁平形降压器的值大约两倍。其次，将该抑制器用四根长缰绳连接到网框的下侧，通过改变网的深度 ...更多信息 的流速进行测量。结果表明，在30-100cm/s的流速范围内，净水深的波动幅度仅为4.4cm，基本保持恒定。(2)在本财政年度，首先在东京湾使用东京水产大学的训练船“Hiyodori”进行了1/5比例模型的现场实验。对于MOHT模型，将网的水中重量调整为零，证实了在拖速为1.0-2.0 m/s的范围内，在经纱长度为20、30、40和50 m时，几乎能够拖至恒定深度。(3)根据模型试验结果，制作了全长12.5m、网口2.25m × 2.25m的足尺模型。在骏河湾和夏威夷外海，分别搭载国立水产科学研究所的“Soyo-maru”号和东京水产大学的T/RV“Umitaka-maru”号进行了现场试验。结果表明，在网具长度为100 m，网重为30 kg的情况下，拖速从1.0m/s提高到2.3m/s时，网深波动范围仅为2.7m。特别是，抑制器始终保持设定攻角是本研究开发的网络的特征之一。因此，无论拖航速度如何，只要在不同的作业中经纱长度相等，就可以始终将网的位置控制在目标深度。如上所述，在本研究中，实现了这一目标，并已与国立水产科学研究所等一些研究实验室一起使用所开发的网来收集幼鱼。作为资源调查的标准渔具，有望在今后推广。少

In order to continuously utilize the fisheries resource effectively, it is necessary to estimate the stock abundance of the target fish species accurately. The quantitative collection of the larval and juvenile is pointed out as one of the means. In this research, the new midwater trawl (MOHT) was developed with a square fixed frame and constant depth can be towed irrespective of the change in towing speed to collect pelagic larval and juvenile fish quantitatively. The results are shown as follows.(1) In the first year, the cambered V-type depressor was designed with the camber ratio of 15%, aspect ratio of 6.0 and dihedral angle of 20°. An experiment was carried out using 1/5 scale model in a circulating water tank. The maximum sinking force coefficient of 1.57 was obtained at the attack angle of 20°. It is larger about twice than the value of the flat shaped depressor. Next, this depressor was attached to the lower side of the net frame with four long bridles, the net depth by change … More of the flow velocity was measured. As the result, the fluctuating range of the net depth was slight 4.4 cm, and it was possible to maintain the constant depth almost in 30-100cm/s wide range of flow velocity. (2) In this fiscal year, first of all field experiment was carried out with the 1/5 scale model using training ship "Hiyodori" of Tokyo University of Fisheries in the Tokyo bay. As for the MOHT model that weight in the water of the net is adjusted to zero, it was confirmed to be able almost to towing constant depth within the range of towing speed of 1.0-2.0 m/s at warp length 20, 30, 40, and 50m. (3) The full scale of 12.5m in total length was made with net-mouth 2.25m x 2.25m based on the results of the model testing. The field experiments were carried out by the boarding to "Soyo-maru" of National Research Institute of Fisheries Science and T/RV "Umitaka-maru" of Tokyo University of Fisheries in Suruga Bay and the off Hawaii. As the results, the fluctuating range of the net depth was only 2.7m when the towing speed was accelerated from 1.0 m/s to 2.3 m/s in the case of warp length 100m and weight in water of the net was 30kg. Especially, it is possible that depressor always keeps setting angle of attack as one of the features of the net developed by this study. Therefore, the net position can be always controlled to the target depth regardless of the towing speed, if the warp length is equal even in the different operation.As mentioned above, in this research, the propose was achieved and the developed net has already been used to collect the juvenile fish with some research laboratories including National Research Institute of Fisheries Science. The spread as the standard fishing gear for resource investigation will be expected in the future. Less