南极磷虾四片式小网目中层拖网作业性能分析

为了促进南极磷虾(Euphausia superba Dana)渔业发展,提出2种四片式小网目中层拖网网型设计(型号分别为dh256-1和dh256-2),2种网型网口拉直周长相同,背(腹)网与侧网拉直宽度比(以下简称"WRBS")分别为1和1.11。通过模型实验对2种WRBS小网目南极磷虾拖网的作业性能进行比较,并进行浮沉力(SBSW)、手纲长度和水平扩张系数(以下简称"L/S")的匹配优化实验,结果表明:实验条件下,当L/S介于0.5~0.6时或者L/S为0.45和0.65且拖曳速度≤1.5 m/s时,2种网型网口垂直扩张差异显著(P0.05),dh256-2型拖网网口垂直扩张明显高于dh256-1;为了保持侧网衣受力均匀,dh256-1型拖网浮沉力配备要求显著高于dh256-2型拖网,dh256-1型拖网浮沉力配备应≥4.59 tf,dh256-2型拖网浮沉力配备应≥1.98 tf;2种网型的能耗系数(C_e)差异不明显(P0.05);L/S与能耗系数(C_e)呈反相关;手纲长度≥50 m,手纲长度对2种网型作业性能的影响不明显;综上所述dh256-2型拖网网口垂直扩张性能较好,浮沉力配备要求较低,较适合拖速较低的南极磷虾捕捞,适宜的手纲长度为50 m。以上结论可为小网目南极磷虾拖网网具设计提供参考。

Performance analysis of the four-panel mid-water trawl for Antarctic krill fishery

To promote the development of Antarctic krill (Euphausia superba Dana) fishery, we proposed two de-signs of the 4-panel trawl (dh256-1 and dh256-2). The net mouth perimeter of the two trawls was the same, and the width ratio of belly panel to side panel (WRBS) was different: 1.00 for dh256-1 and 1.10 for dh256-2. Model ex-periments were used to study trawl performance, and to determine the optimized nets and accessories, which in-clude the sum of buoyance and sinker weight (SBSW), bridle length, and horizontal opening coefficient (L/S). The results showed that, under the test condition, when the L/S was between 0.5 and 0.6 or when the trawl speed was under 1.5 m/s and the L/S was 0.45 or 0.65, significant difference (P<0.05) was noted in the vertical net opening between the two trawls: the vertical net opening of dh256-2 was remarkably faster than that for dh256-1. For im-proving the trawl performance, the SBSW should be larger for dh256-1: the minimum SBSW for dh256-1 was 4.59 tf and that for dh256-2 was 1.98 tf. These differences might be related to the flow attack angle of the nets. The WRBS of dh256-2 was larger than that of dh256-1; the flow attack angle and head surface of belly panels in-creased and improved the vertical net opening. Conversely, when the WRBS was smaller, the flow attack angle and head surface of side panels increased, and the pull of side line to bridle was strengthened, thereby limiting the vertical net opening. Therefore, when the WRBS is smaller, the SBSW should be larger. No significant difference in coefficient of the energy consumption (Ce) was found between dh256-1 and dh256-2. The L/S was inversely related to the Ce. No relationship was found between bridle length and Ce; when the bridle length was ≥50 m, the effect of bridle length to both the trawls was not obvious. Therefore, 50 m bridle needs to be used for the two trawls. The effect of SBSW on the Ce of dh256-1 was related to the trawl speed: when the speed was ≤1.5 m/s, the effect of SBSW on Ce was not obvious; however, when the speed was >1.5 m/s, Ce declined remarkably with an increase in SBSW. Since the trawl speed of the Antarctic krill is usually around 1.5 m/s, the dh256-2 was rec-ommended for Antarctic krill fishery. These results can provide a basis for designing Antarctic krill trawls.