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

Abstract:

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.