Y型幼鱼释放装置在张网渔具中的应用初探

近年来,张网渔具渔获中幼鱼比重大的问题突出,而使用放大网目等传统手段在一些场合下并不适用。本研究设计制作了一种新型刚性幼鱼释放装置,该装置由3个框架组合构成、框架使用铰链连接、外型呈Y型,并通过2014年冬季海上测试,分析这一装置对幼鱼的释放效果。海上对比试验结果显示,安装于张网囊头网部、不锈钢材料、栅栏间距2 cm、分隔框架与来流方向呈60°的装置能释放90%的幼鱼并同时保留大部分大个体渔获。该Y型幼鱼释放装置角度可调等特点使其功能得以扩展、适用性增大,可为今后开展过滤性渔具幼鱼释放研究提供参考。

Preliminary study on Y-shaped exclusion device for juvenile fish in Chinese stow net

In recent years,the issue of large proportion of juvenile fish in total catch in Chinese stow net fisheries has caught great concerns and the voices for improving the catch efficiency of stow nets are increasingly rising. The traditional measures, including enlarging the mesh size, have been proved inappropriate in some cases.In this paper,to analyze the feasibility of rigid grids in releasing the juvenile fish in offshore stow net fisheries,a novel exclusion device was designed and developed for releasing juvenile fish. The device was made of 3 hinged frames,including 2 upper frames for filtering and releasing the juvenile fish catch and 1 lower frame for guiding the marketable size fish catch to swim through the device and ultimately to enter the cod-end,and it was shaped like the letter "Y".The juvenile fish release efficiency of the device was assessed in the sea trial experiments carried out in the East China Sea offshore canvas stow net,in the winter of 2014,by comparing the catch weights between experimental stow net with the Y-shaped releasing device and the control net.Results showed that the juvenile fish exclusion device,made of stainless steel, with 2mm bar space and 60 degree angle between 2 upper frames,which was installed in the extension part and extended the net panel with a 0.33 hanging ratio of the stow net,released 90% of juvenile fish while retained most of marketable size fish catch (94.6%).Based on the results,the author concluded that the device achieved good effects in juvenile fish release.The angles between different frames of the releasing device could be adjusted to accommodate nets of different sizes,different installing locations or different net panel extension requirements,improving the applicability of the device.Additionally,the function of the device could be expanded by simple restructuring.In our opinion,the design of this device can provide a reference for future study on juvenile fish release in filter fishing gears.Finally,some technical problems encountered in the device design,installation and use were discussed.