基于局部附网法的南极磷虾拖网网身大网目选择性

了解南极磷虾(Euphausia superba)拖网网身大网目的选择性,对于提升应用渔业数据进行磷虾资源评估的准确性具有实际意义。为此,作者在FAO 48.1亚区执行项目调查期间,利用小网目(2a=5 mm)附网绑缚在“龙腾轮”所用拖网的第一段网身(400 mm网目,无内衬网)后端和第二段网身(200 mm网目,内衬网16 mm)前端,收集穿过网目的磷虾。根据附网内取样磷虾的体长分布,结合网囊内取样磷虾的体长分布等数据,选用logistic曲线方程,分析磷虾拖网大网目的选择性。结果表明：（1）“龙腾”轮拖网的磷虾逃逸主要发生在第一段网身大网目处,装配内衬网(2a=16 mm)的第二段网身近乎无逃逸发生。（2）磷虾接触网身第一段大网目的概率(Pc)范围为5.85~69.52%,平均为(23.17±14.80)%。昼夜间接触概率相似,统计学上无显著差异(P>0.05)。50%选择体长(L50)为25.05~47.74 (32.68±4.92) mm;L50在白天(30.06±2.23) mm显著(P<0.05)低于夜间(35.81±5.48) mm。选择范围(SR)为2.07~19.08 (7.65±4.02) mm;SR在白天(7.11±4.41) mm略低于夜间(8.30±3.53) mm,但是在统计学上无显著差异(P>0.05)。本研究结果弥补了拖网整体选择性中网身部位选择性研究的空白,并考虑了昼夜间磷虾选择性的差异,可为科学评估磷虾资源量和开发生态友好型磷虾拖网提供科学依据。

Selectivity of Antarctic krill trawl body with large mesh using local-attached fine mesh net method

Antarctic krill (Euphausia superba) is a key species in the Southern Ocean ecosystem, and the main target specie of the Southern Ocean trawl fishery. The size of Antarctic krill is small, the body of a krill trawl is usually lined with a small mesh netting to prevent krill from escaping. The length and assembly position of the liner netting vary from country to country, depending on operation habits and captain''s preferences, and some make up more than two-thirds of the body net length. The catch data are often used in the assessment of krill resources, so it is of practical significance to understand the selectivity and influencing factors of large mesh body net of Antarctic krill trawl net for the accuracy of krill resource assessment using fishery data. To this end, the authors attached a 0.2 m×0.2 m small mesh net to the first section (2a=400 mm, without liner netting) and the second section (2a=200 mm, lined with 16mm mesh size liner netting) of body net of the krill trawl used by krill factory trawler "LONG TENG" of the China National Fishery Corporation Ltd, to collect the krill that passed through the large mesh during conducting the survey at the northern waters (FAO statistical area 48.1) of the Antarctic Peninsula. We employed the logistic curve equation to study the selectivity index 50% selection body length (L₅₀) and selection range (SR) based on the body length composition of krill from the above attached fine-mesh net and codend. The results showed that the selectivity of the trawl used by "LONG TENG" trawler mainly occurs-red at the first section of the trawl body with large mesh, but there was almost none-selectivity in the second section of the trawl body due to the inner netting with small mesh size. The probability (P_c) of Antarctic krill contacting the first section of the trawl body ranged 5.85%~69.52%, the average was 23.17%±14.80%, and there was no significant difference between daytime and night (P>0.05). The L₅₀ range was 25.05~47.74 mm, the average was (32.68±4.92) mm, but L₅₀ was (30.06±2.23) mm at daytime, significantly (P<0.05) lower than was (35.81±5.48) mm at night. The SR range was 2.07~19.08 mm, the average was (7.65±4.02) mm, and the SR was (7.11±4.41) mm at daytime, slightly lower than (8.30±3.53) mm at night. This study focused on the selectivity of net body parts, and considered the difference in krill selectivity between day and night, which could provide scientific basis for scientific evaluation of krill resources and development of ecologically friendly krill trawl.