| Antarctic Krill(Euphausia superba),a species with the largest biomass of a single community in the world,is not only a major food organism for seabirds,seals and whales but also a rich source of high-quality protein for humans.The current annual cathc is about3.0×10~5 tones,So far,South Korea,Norway,Ukraine,Chile and China are engaging in fishing Euphausia superba.The fishing method of Antarctic krill is middle level trawling,including single boat otter trawling and beam trawling,otter trawling is widely used in Chinese fishing boats.In recent years,the continuous pump beam trawl has attracted more and more attention because of its high fishing efficiency and good catch quality.Because of the great prospect of fishing in Antarctica krill,The fishing of Antarctic krill has become increasingly important in our country.For Antarctic krill fishing research on Antarctic krill beam trawl is still in the preliminary stage in our country,Therefore,while steadily improving the traditional trawling techniques and the catch yield,advanced fishing techniques should also be studied.The author has followed the Antarctic krill production fishing boats to the Antarctic to carry out the biological development and investigation of Antarctic krill in the fishing seasons of 2020/21 and 2021/22.The sea data of this study are derived from two investigations.The research contents of this study mainly include the following three points:to study the distribution characteristics of Antarctic krill resources;Based on the actual measurement on the sea,the characteristics of the traditional otter net trawling operation of the stern slide are studied and analyzed;The hydrodynamic performance of a new type of beam trawl is studied through a flume model test.The main conclusions of this study are as follows:(1)Most of the Antarctic krill concentrate in the water depth of more than 100 meters.The depth of the central cluster varies significantly between months.There is a phenomenon of sinking in the day and floating in the night.The krill begins to sink at 4a.m.and rises at 19 p.m;The fresh weight density of Antarctic krill varies significantly between months,and has a strong correlation with body length(density=0.72+0.30×L(body length)(R~2=0.72));The egg holding ratio and the female/male ratio have the same variation characteristics,reaching the maximum value of the fishing season from February to March,and the immature ratio reaching the maximum value of the fishing season from July to August;The inter-month variation of body length is characterized by gradually increasing body length from January to March,reaching the maximum average of 47.53 mm in March,and gradually decreasing body length from March to August;The closer the distribution of Antarctic krill is to the island,the larger the individual is,and the higher the CPUE is.(2)Otter trawl is still the mainstream operation mode in China’s Antarctic krill fishery,Taking"Longfa"as an example,analyzed.the operation performance of the net,compared with the continuous pump beam trawling net operation performance which used at the“Antarctic Sea”.The production test shows that(a)the change of trawling speed has no significant impact on the net position;(b)the length of trawling wire has a linear correlation with the net position,and the depth of net position(m)=-8.57+0.27×L(drag length,m)(R~2=0.73);(c)The change of drag speed has no significant impact on the resistance,while the net production has a significant impact on the resistance;(d)Continuous pump boom trawling is working longer and produces higher catches per fishing effort than traditional trawl.(3)The beam trawl is one of the important components of the continuous pumping truss trawl fishing system for Antarctic krill.In order to deeply understand the operational performance characteristics of the beam trawl in the system and promote the optimization of the operational performance of nets,this part carried out the exploratory study on the impact of the net structure and the weight of sinkers on the operational performance of nets through model tests.The net structure includes six types(three web widths,each of which adopts two suture methods),respectively A,B,C AA,BB and CC indicate that there are three types of sinker weights.Comprehensive comparison shows that the order of operation performance of different test net types is BB>CC>C>A>B>AA,but the difference is not significant.Narrowing the width of the web and oblique stitching can effectively improve the vertical expansion of the net,reduce the energy consumption coefficient,and improve the performance of the mesh,especially for the operation scenarios with low towing speed;The weight of sinker has a significant positive correlation with the resistance of net and the vertical expansion of height of net opening,but has no significant correlation with the energy consumption coefficient;In order to promote the vertical expansion of the net opening,the appropriate weight of the sinker will increase with the increase of the towing speed.Under the condition of 1.5 m/s,the weight of the sinker of each test mesh type should not be less than 3.05 t;Under the test conditions,the change trend of mesh resistance and energy consumption coefficient of each mesh type is relatively stable,and the gradual change of slope is small.The relationship between mesh resistance and towing speed is a power function,with an index between 1.49 and 1.64.Compared with“Shen Lan”in operational performance,The optimized self-designed beam trawl net has better network expansion performance and energy-saving effect.Under the same test conditions,the optimized net has a larger sweeping area and lower energy consumption coefficient,which is conducive to improving fishing efficiency and improving energy-saving efficiency of the trawl. |
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