The Expansion Performance Of Antarctic Krill Mid-water Trawl Used By Chinese Fishing Fleets-examination By Modeling Experiments

The Euphausia superba, also known as Antarctic krill is a species of krillfound in the Antarctic waters of the Southern Ocean. Antarctic krill is probably themost important species of the Antarctic ecosystem, if we only consider them frombiomass they are the most successful species in the creaturely world. Antarctic krillcontains medicinal value, nutritional value, scientific value, and economic value,which lead the interest of the public. People used to praise Antarctic Ocean as “Thefood bank of human”, from1960s, human being starting development of krill. As tonow, there are around20counties and regions all over the world attempt to catch andcommercial develop the Antarctic krill successively. China first starts investigation andtrial production in2009, the vessels are Chinese trawler fishing vessels of productingjack mackerel. So far we are still in the stage of groping. Before2013, the gears Chinaused are mainly on the basis of the original jack mackerel and modified big meshmid-water nets. Because of the lack of experiences of fishing gears for Antarctic krill,the gears we used are big mesh mid-water trawls with poor productivity, low net portexpansion. In2013, we have introduced the Japanese professional krill ship whichusing professional operational network fishing gears with efficient productivity. But inthe actual production the expansion performance have very important influence onAntarctic krill fishery and the production. In paper will analyze the trawl through amodel test of small mesh Antarctic krill trawl, and considering the comprehensiveperformance and optimize the productivity of trawl, will become the gist of futuredevelopment of Antarctic krill fishing gears in China.Liaoning pelagic fisheries co., LTD is the main enterprise of production ofAntarctic krill, now own three vessels. In this paper, we will be selected two differentkind of middle small mesh Antarctic krill trawls as prototype,#1trawl Japaneseprofessional trawl imported by Dalian Ocean fishery Group and#2trawl designed byKorea for Dalian Ocean fishery group respectively, convert them and design the modeltrawl that taking the model test in the static water tank. The experiment contains theanalysis of the expansion of trawls, optimization of orthogonal experiment, andreduction of the trawl inner net area of3series experiment.(1) Comprehensive analysis of model trawl’s expansion and performance The experiment indicate that in the different towing speed, horizontalexpansion ratio, net port vertical expansion, resistance force, and energy consumption#1trawl under the circumstance of different towing speed, the resistance force willincrease exponentially as the speed increased. When the towing speed keep the same,as the horizontal expansion ration L/S increased, resistance force will increase as well.Additionally, when the towing speed increased, net port vertical expansion willdecrease exponentially. As the towing speed is3kn, the cover area at max will beL/S=0.5will equal to294.46m2. However, for#2trawl, the resistance force didn’tincrease too much when the level expansion ratio L/S increase, and after speed reach3kn, the ratio of L/S will have few effect on the resistance force. Moreover, when#2trawl experience the same towing speed, the cover area will increase as the ratio L/Sincreased. Under the same horizontal expansion ratio L/S, net port vertical expansionfor#1trawl will higher than that of#2trawl, and the cover area is also bigger than#2trawl. When the horizontal expansion ratio L/S between0.4and0.45, the coefficient ofenergy consumption for#1trawl will decrease as L/S increased. And when L/S>0.45,the coefficient of energy consumption will decrease as L/S increase. For#2trawl thecoefficient of energy consumption will decrease when the ratio L/S increase,meanwhile the cover area will increase as well. Therefore we can conclude that theperformance of#1trawl will be better than#2trawl.(2) Orthogonal optimization test for#1trawl model trawlThe orthogonal optimization experiment will be running by adjusting thebuoyancy/sinking force ratio, bridles and empty outline three factor; buoyancy/sinkingforce ratio will be factor A (0.9,1.2,1.5), bridle will be factor B (1.8,2.1,2.4), andempty outline will be factor C (2.0,2.1,2.2). This experiment are taking place under thecircumstance of three different types of L/S with level3speed indicated that whenL/S=0.4, the coefficient of energy consumption will be affected by following orderbridle>empty outline>buoyancy/sinking force ratio; when L/S=0.4the optimalcombination is A3B2C2, when L/S=0.5, the optimal combination is A3B2C3, andwhen L/S=0.55, the optimal combination is A2B3C3.(3) Diminishing the inner net area of trawl and its performanceBy analyzing the model trawl that has6th,7thand8thtotally three partsremoved and the towing speed reach3kn, the resistance of the trawl will decreasewhen the inner net area decreased. When L/S=0.45, net original port vertical expansionwill be higher than that of the removed6thand7thinner net; when L/S=0.5, the original net port vertical expansion will be higher than that of the removed6thinner net; andwhen L/S=0.55, the minimum energy consumption for net original port verticalexpansion will decrease since the inner net area is decreasing.