长天井、大网目囊网的机帆渔船双拖网增产对虾和释放幼鱼的试验研究

为合理利用我国北方海区对虾资源，每年秋季在渤海使用机动渔船双拖网捕捞生产。由于渤海既是主要的对虾渔场，又是多种经济鱼类产卵繁殖和幼鱼生长的良好场所。在拖网捕虾的同时，大量捕到当年的幼鱼，损害渔业资源。因此，在1974—1977年研究一种能够多捕对虾、大量释放幼鱼的新型双拖网。新型网的主要特点如下：它的天井网比原型网长一倍左右，并增加侧网使网口的覆盖面积和网高相应扩大，防止对虾接触网具后弹跳逃逸；将囊网网目放大到50毫米，以释放网内的幼鱼。试验效果较为满意。在模型网水槽试验中，新型网的主要优点是阻力较小、网口较高和网口前方覆盖面积较大。捕捞生产试验证明可以增产对虾40％以上，少捕幼鱼不少于60％。

STUDIES ON A TWO--BOAT TRAWL OF LONG SQUARE AND LARGE MESHES COD--END TO INCREASE PRAWN CATCH AND FREE YOUNG FISHES

Two-boat trawl is generally in use for fishing prawn (Penaeus orientalis) at Po Haiarea in autumn. Po Hai is not only the main fishing ground for prawns, but is also thespawning and nursery ground of many commercial fishes. Unfortunately, a considerablenumber of young fishes have been destroyed in the prawn trawing every autumn. It is avery serious problem for the fish stock, so that, a new two-boat long square prawn trawlwas designed in 1974--1977, in order to increase catching efficiency and to reduce thedamage on young fishes. The characterstics of this newly designed trawl are: its square was twice as largeas that of the original one, the side panels were added to increase the covered net moutharea and the height of trawl, in order to prevent prawn in jumping over the headline ofthe net when they touc on the ground rope, and its cod-end mesh size was increased to50 mm. Consequently it saves a large quantity of young fishes from escape. The experimental results are satisfactory. In comparing with the old trawl model inwater tank, the principal advanges of new trawl model are the lower resistance, the higherheadline and the larger area of the covered mouth. The fishing operations have provedthat the eatching efficiency is increased over 40% and the damage to young fishes redu-ced over 60%.