Structure improvement design and performance experiment of Antarctic krill trawl net

Abstract: The Antarctic krill resource is very abundant in the area surrounding the Antarctic and the total production in China has reached nearly 60 000 t. At present, the existing problems are the lack of exclusive localization fishing gears for Antarctic krill fisheries and the low matching degree between the trawl net and the fishing vessels. Through collecting the production situation of fishery company at home and abroad, 6 kinds of different existing Antarctic krill trawl nets were selected as the experimental prototype. The model test was carried out in the flume of trawl fishing gear in East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences. The coefficient of energy consumption, net resistance and height of net opening of different trawl nets were measured under 3 test conditions. The model test results showed that the height of net opening of trawl net No.1-3 was higher than other types of trawl nets, but its mesh size was too large to stop the escape of Antarctic krill. The net resistance of trawl net No.4-6 was higher than others. Based on the analysis of the hydrodynamic performance of 6 kinds of existing Antarctic krill trawl nets imported from fishery developed countries, an improvement program of TN01 type four-panel Antarctic krill trawl net with small mesh was developed independently. In April 2015, a 9-day sea trial was carried out in the Antarctic krill fishing ground. The test fishing vessel was “Kaili” from Shanghai Kaichuang Ocean Fisheries Co., Ltd. The sea trial results showed that: 1) When the warp length was less than 230 m, the depth of cod-end was lower than body net, which meant the buoyancy force of cod-end was too large. When the warp length was longer than 230 m, the depth of cod-end and the working depth had a positive relationship. The best buoyancy-weight ratio was suggested to be 1:1.1; 2) No significant correlation was found between the length of the vertical net opening and the length of warp. When the trawl speed was 1.542 m/s, the height of the vertical net opening was 26-29 m and the vertical expansion ratio was 0.11-0.12. As releasing the warp length from 90 to 370 m, the height of the horizontal net opening increased from 14 to 20 m. The expansion ratio was 0.22-0.32. The expansion at vertical and horizontal direction had good effect, which has reached the requirement of design. 3) The comparative analysis of the catch showed no significant difference between the day and night. The average yield per net in the daytime was 33 t and the average yield per net at night was 28 t. The average yield per net in sea trial was 30 t, which increased by nearly 50% compared with other fishing vessels around the same fishing area (according to the statistical records, the average yield per net was about 20 t). The new type of Antarctic krill trawl net has the characteristics of high efficiency and is suitable for the fishing vessels, which can provide a theoretical basis for further independent research and development of the Antarctic krill trawl net.