帆张网网囊网目尺寸对带鱼的选择性

为探索帆张网不同网目尺寸网囊对带鱼(Trichiurus lepturus)的选择性,作者于2018年10月在大沙渔场用传统选择性试验方法(套网法)对5种不同网目尺寸(35mm、45mm、55mm、60mm、65mm)网囊进行了选择性对比试验,应用Logistic选择性模型对带鱼选择性曲线进行拟合,采用极大似然法估算模型参数。结果表明：(1)试验期间测量带鱼4265尾,肛长范围76～305mm,平均肛长167±43mm；(2)网目尺寸为35mm时,带鱼基本无逃逸行为；网目尺寸为65mm时,套网和囊网中的带鱼肛长分布基本一致；随着网目尺寸的增加(45~60mm),网囊中带鱼优势肛长总体上大于套网；(3)网囊网目尺寸为45mm、55mm和60mm时,带鱼L50分别为171.839mm、180.562mm和215.905mm,SR分别为60.402mm、104.861mm和157.292mm,L50呈现逐渐增大的趋势；(4)带鱼网囊网目尺寸(m)与50%选择体长(L50)的关系为：L50=2.643m+48.491 (R²=0.748)；(5)以带鱼最小可捕肛长205mm(浙江省地方标准)计算,即当带鱼50%选择肛长为205mm时,帆张网对带鱼的网囊最小网目尺寸应为59.2mm。综合以往研究结果,帆张网最小网目尺寸应为57.47mm。综上分析可知,同时结合目前渔业资源状况,为保护当前带鱼幼鱼资源,目前实施的最小网目尺寸55mm是较为适宜的,能满足保护幼鱼资源的目的。

Selectivity of different mesh size codends of canvas spreader stow net for Trichiurus lepturus

In order to explore the selectivity of different mesh size codends for Trichiurus lepturus, the covered net method was adopted, and selection experiments were carried out with 5 different mesh sizes(35,45,55,60 and 65 mm) codends on canvas spreader stow net. The Logistic selection model was used to fit the selectivity curve of Trichiurus lepturus and the model parameters were estimated by the maximum likelihood method. The results showed that:(1) 4 265 ind. of Trichiurus lepturus were measured during the experiment, the anal length ranged from 76-305 mm with an average anal length of (167±43) mm; (2) When the mesh size was 35 mm, it was non-selective for Trichiurus lepturus. While the mesh size was 65 mm, the distribution of anal length of Trichiurus lepturus in covered and codend net was basically the same. With the increase of mesh size, the dominant body length of Trichiurus lepturus in the codends was larger than that of the covered nets; (3) When the mesh size for Trichiurus lepturus was 45,55 and 60 mm,its L₅₀ was 171.839,180.562 and 215.905 mm, its SR was 60.402,104.861 and 157.292 mm, respectively. L₅₀ showed a gradual increase trend; (4) The relationship between the codend mesh size(m) of Trichiurus lepturus and L₅₀:L₅₀=2.643m+48.491 (R²=0.748); (5) When the anal length of Trichiurus lepturus is 210 mm, the minimum mesh size of canvas spreader stow net should be 61.1 mm. In summary, combined with the current status of fishery resources, the current minimum mesh size of 55 mm is more appropriate to protect the juvenile Trichiurus lepturus resources, which can achieve the aim of protecting the juvenile Trichiurus lepturus resources.