两种底拖网渔业资源调查船捕捞效率标准化分析

渔业资源科学调查是开展渔业资源状况评价、物种保护和管理等分析的重要数据来源,当调查方式发生变化时,维持数据的时间一致性至关重要。因此,原位试验获取不同调查方式的捕捞效率校正因子（fishing power correction,FPC）成为资源状况评价的先决条件。本研究通过平行拖网对比试验分析了科学调查船“中渔科211”（试验船）和生产性渔船“浙嵊渔10201-10243”（标准船）在开展渔业资源调查时对不同种类或类群的渔获率差异。结果表明,标准船和试验船平均渔获率分别为（47.27~1836.72）kg/nmile²和（12.28~311.85）kg/nmile²。标准船主要种类为小黄鱼（）,渔获率范围分别为（1.17~1113.26）kg/nmile²和（0~565.39）kg/nmile²;试验船主要种类为鳀（）,渔获率范围分别为（0~277.59）kg/nmile²和（0~125.24）kg/nmile²。2种调查方式对不同种类/组的渔获率随深度变化趋势出现分化,其中总渔获率、鱼类、银鲳（Apogonichthys lineatus）、绿鳍鱼（）8个种类/组表现为相似的变化趋势;甲壳类、细点圆趾蟹（Erisphex pottii）5个种类/组变化趋势相反;头足类、小黄鱼、龙头鱼在各深度变化具有异质性特征。这种变化与网口垂直扩张和所在水层位置有关。均值比和Kappenman方法估计的总渔获率FPC分别为0.35（95%置信区间为0.24~0.61）和0.43（95%置信区间为0.27~0.70）,各种类渔获率均值比结果显示,FPC变化范围在0.03~2.61,其中总渔获率、鱼类、头足类、小黄鱼和绿鳍鱼达到显著水平,建议对上述种类的资源丰度指标年际变化趋势分析时进行数据校正。标准船以近底层种类为调查对象,尤其在捕获经济种类方面表现出优良性能,但对完整生态系统代表性较弱。试验船适合浅水区调查,在深水区由于网口垂直扩张不足,且网位存在上浮现象,难以反映近底层生态系统。

Assessment of fishing power correction factors between two types of bottom trawlers

Fisheries stock assessments often rely on time series of abundance indices obtained from annual surveys. Thus, it is important to maintain the temporal continuity of such series when vessels have changed. This can be achieved by estimating conversion coefficients between the two vessels through an intercalibration experiment. This paper describes such an experiment conducted between the commercial trawler "zheshengyu10201-10243" (standard vessel) and the research vessel "zhongyuke211" (experimental vessel). Two analytical techniques were applied to compare trawl data and obtain fishing power correction factors for twelve major species and four species-group combinations caught by the two trawlers. Fishing power correction techniques included ratios of catch per unit effort (CPUE) and the Kappenman method. The results showed that 74 and 84 species were identified from the standard trawler and the experimental vessel, with catch rates range of (47.27-1836.72) kg/nmile², and (12.28-311.85) kg/nmile², respectively. The standard vessel had high catch rates of , The catch rate range were (1.17-1113.26) kg/nmile² and (0-565.39) kg/nmile², respectively. However, were the top two species caught by the experimental vessel, with catch rates range of (0-277.59) kg/nmile² and (0-125.24) kg/nmile², respectively. The trends of capture rate varied with depth showed differentiation between the standard vessel and the experimental vessel. Eight species/groups showed similar changes in capture rate by depth, including species-group, fish-group, Apogonichthys lineatus, . Five species/group showed the opposite trend in capture rate by depth, including crustaceans, Amblychaeturichthys hexanema and Harpadon nehereus showed mixed changes in catch rate at different depth stratum, which was related to the vertical expansion and the position of the net mouth. The ratio of mean CPUE and the Kappenman method estimated the total catch fishing power correction factor (FPC) to be 0.35 (95% confidence interval 0.24-0.61) and 0.43 (95% confidence interval 0.27-0.70), respectively. FPC values based on the ratio of mean CPUE ranged from a low of 0.03 for . The FPC was significantly different for five species-groups (Larimichthys polyactis and . It was necessary to correct the CPUE data by applying the estimated correction factor. The harvest of the standard vessel was dominated by near-bottom species, which represented its excellent performance in capturing economically important commercial species. However, the composition of the standard vessel''s harvest was not strongly representative of the ecosystem. The experimental vessel was suitable for the investigation of shallow water areas. In deep water areas, due to insufficient vertical expansion and settlement of net mouth, it had difficulty capturing species reflecting the composition of the near-bottom ecosystem.