Study On The Selectivity Of The Codend Mesh Of Double Stake Stow Net In Shandong

Stow net is a traditional fishing gear in Shandong province. Because of its low cost, low energy consumption and stable output, stow net has already become an important fishing method. As a kind of passive filter fishing gear, mesh size of codend of stow net is relative small, and a lot of young fish or shrimp are often bycatched. It brings out seriously negative influence on the offing fish resource. So it is necessary to carry out study on the selectivity of stow net. It is the basal work of the study on the minimal mesh size of stow net in Shandong and it will provide some theoretical basis for the management of stow net fishery.This paper describes the general situation and basal knowledge of stow net in the first part, and points out that there are many problems along with the development of stow net. So carrying out study on the selectivity of stow net is imperative under this situation.The second part introduces the experiment methods and selectivity model of study on the selectivity of fishing gear. Many scholars have studied the selectivity of trail net, gill net, stow net, and have obtained some fruits. It provides some referrence for the study on the experiment in Shandong.So under covered net method, the selectivity of the codend mesh of stake net was experimented in Shandong. Three codends were designed in the experiment and the mesh size was 30mm,33mm,40mm. Each codend net was carried out thirty times in the experiment. Then the fishing target was sorted and identified in the laboratory. Trachypenaeus curvirostris was the main fishing target in stow net, and many Argyrosomus argentatus were bycatched in the experiment sea area. So their body length distribution was analysed in the different codends and covered nets. The result indicated that:the selection effect of the codend was better for Trachypenaeus curvirostris, but it was not obvious for Argyrosomus argentatus. For the catch data of Trachypenaeus curvirostris and Argyrosomus argentatus, different mesh sizes selectivity curves of Trachypenaeus curvirostris and Argyrosomus argentatus were drawn by using Logistic curves as a selectivity model. Parameters of selectivity were estimated according to the maximum likelihood method. The result of the experiment indicates that:when the mesh size for the Trachypenaeus curvirostris is 30mm,33mm, 40mm, its L0.5 is 5.309cm,5.778cm,6.972cm, its SR is 1.091,1.290,1.571 respectively; when the mesh size for the Argyrosomus argentatus is 30mm,33mm, 40mm, its L0.5 is 6.581cm,6.908cm,7.441cm; its SR is 1.934,2.144,2.322 respectively. The relation between L50 and codend mesh size are showed as follows.Trachypenaeus curvirostris L0.5=1.6706m+2.8404,R=0.9998Argyrosomus argentatus L0.5=0.8425 m+40.84, R=0.9960If the mesh size of stake stow net increases, the L50 of Trachypenaeus curvirostris and Argyrosomus argentatus will enlarge, and the SR will enlarge too. According to the results, the authors suggested that codend net with 33mm mesh size has better selectivity,so it was more suitable than 30mm and 40mm mesh sizes in the experiment sea area.The last part of this paper discusses the minimum mesh size of stow net, and describes the future study. For protecting fishery resource, maintaining its continuable development farther and providing basis for the innovation of stow net in Shandong, the experiment on fish/shrimp separating device and the livability after being released will be studied.