A primary study on characteristics of Chinese midwater trawls of Chilean jack mackerel(Trachurus murphyi)
XU Yong-jiu,ZHANG Min,ZOU Xiao-rong,ZOU Li-jin(College of Marine Science and Technology,Shanghai Fisheries University,Shanghai 200090,China)
The 1440m×472.25m(330.00m) and 1632m×496.25m(387.00m)mid-water trawls,widely used for Chilean jack mackerel fishing in the southeast Pacific,were selected for the target net in model test.Based on the performances of two mid-water trawl models with 1:55 and 1:70 scale tested in towing tank,following results were obtained: The formula of headline of these nets is H=0.076CV-0.559 4.The formula of drag of these nets is R=0.089 9(d/a)LCV1.738.According to the comparative analysis between the two nets and previously used mid-water nets for haddock,the results were as follows:(1) The vertical opening of net mouth was 79 m,77 m for the two nets,when L/S=0.4,and the speed was 0.255 m/s.The results were in accordance with the research on board.The hydrodynamic performance(vertical opening,drag,horizontal spreading etc.) of the net 1440 was better than the net 1 632.(2) The hydrodynamic performances of the currently used nets 1440,1632 were highly improved after assembling the soft canvas.