南海区虾拖网网囊对刀额新对虾的选择性研究

Size selectivity of codend mesh size of shrimp beam trawl for Metapenaeus ensis in South China Sea

为了研究虾拖网网囊对刀额新对虾(Metapenaeus ensis)的选择性,2014—2017年于南海海域使用套网法和裤网法对2组菱目网囊(D25和D30)和6组混目网囊(S35+D18、S25+D25、S30+D25、S35+D25、S35+D30和S35+D35)进行选择性试验。以SELECT模型为基础框架,以logsitic曲线为模型,使用极大似然估算法估算单网次和联合网次下网囊对刀额新对虾的选择性。结果表明,菱目网囊D25和D30对刀额新对虾的选择性很差,逃逸数量很少;套网法试验中,混目网囊S35+D18、S25+D25、S30+D25和S35+D25对刀额新对虾的平均50%选择体长(L50)分别为51.52 mm、60.84 mm、63.21 mm和64.53 mm,平均选择范围(SR)分别为16.48 mm、14.31 mm、12.84 mm和9.75 mm;裤网法试验中,混目网囊S35+D25、S35+D30和S35+D35对刀额新对虾的平均L50分别为75.43 mm、82.38 mm和95.39 mm,平均SR分别为6.93 mm、6.39 mm和20.44 mm,平均相对作业强度(p)分别为0.51、0.52和0.64。综合南海区刀额新对虾的首次性成熟体长(80 mm)和网囊选择性等多方面因素,认为S35+D30网囊的选择性较好,研究结果可为南海海域虾拖网的渔具管理和刀额新对虾资源的合理利用提供参考。

In order to investigate the size selectivity of codend of shrimp beam trawl for Metapenaeus ensis,with covered codend method and trouser trawl method,we carried out fishing experiments on two traditional diamond-mesh codends(D25 and D30),and six novel combined square-mesh and diamond-mesh codends(S35+D18,S25+D25,S30+D25,S35+D25,S35+D30 and S35+D35)in the South China Sea during 2014.2017.We used maximum likelihood method to estimate the selective parameters at haul by haul level and combined haul level with the logistic equation.The results indicate that the D25 and D30 codend were nearly nonselective for M.ensis.In experiments of covered codend method,the mean 50% retention lengths(L50)of M.ensis for the S35+D18,S25+D25,S30+D25 and S35+D25 codends were 51.52 mm,60.84 mm,63.21 mm and 64.53 mm,respectively,and the mean selection ranges(SR)were 16.48 mm,14.31 mm,12.84 mm and 9.75 mm,respectively.In the experiments of trouser trawl method,the mean L50s for the S35+D25,S35+D30 and S35+D35 were 75.43 mm,82.38 mm and 95.39 mm,respectively,and the mean SRs were 6.93 mm,6.39 mm and 20.44 mm,respectively,and the mean relative fishing intensities(p)were 0.51,0.52 and 0.64,respectively.Considering the first mature length of M.ensis(80 mm)in the South China Sea as well as economical efficiency of fishing and selective properties of codends,it is suggested that the S35+D30 has the best selectivity.The results are benefit for the management of shrimp beam trawl and sustainable harvest of the fishery resources of M.ensis in the South China Sea.