Improvement Of Fishing Method And Experiment Of Net-Building Fishing Gear In Zhoushan

With the improvement of people's living standard in our country,the requirement for the quality of high-quality animal protein-aquatic products is also increasing day by day.From the past salted,chilled and frozen catches to fresh catches,we enjoy organic,pollution-free and delicious wild fresh aquatic products.For this reason,we need to keep alive all aspects of fishing,transportation,distribution and sales.Zhoushan fishing ground is rich in fishery resources,with abundant reef fishery resources such as Epinephelus,Sparus macrocephlus,Dentex tumifrons,Miichthys miiuy,Nibea albiflora,Lateolabrax japonicus,Pseudosciaena crocea,Pseudosciaena polyatis,Pagrus major,Microcanthus strigatus,Hapalogenys nitens,Harpadon nehereus,Scomberomorus niphonius,Setipinna taty,Ynoglossus semilaevis Gunther and crabs.There are many fishing operations such as trawl,gill net,purse net,lamplight net,truss rod shrimp dragging,net stretching,lamplight net,net inserting,crab cage,net matching,harrowing and fishing.As a fixed fishing gear,bag set-net has the advantages of less fuel consumption,no damage to bottom materials,clear main fishing objects and the like,and is an environment-friendly living fishing gear.This paper intends to investigate the structure,materials,specifications,sizes,manufacturing techniques,laying techniques,operation procedures,fishing seasons,fishing grounds,main catch species,economic benefits and existing problems of the existing bag set-nets.It is believed that the existing bag set-nets have good effects on catching the living bodies of large and valuable economic fishes,but there is still some room for optimization and improvement:(1)The length of the net wall is not enough to effectively intercept fish schools,so the net wall is extended from 50m to 75m;(2)The net area is not enough to induce fish to leisurely enter the net bag,increasing the net area from 78m~2 to 176m~2;(3)The angle of raising the net was reduced from 14.5°to 10.5°,increasing the swimming space of the catch in the bag set-net.;(4)The angle of the curtain still needs to be studied.There is a phenomenon of catch escaping.The angle between the curtain and the side net of the net ring is changed from 90°to 60°.After improvement,a test net and a contrast net are made,and a suitable test site is selected for comparison.The results are as follows:(1)The test net will operate for 47 days in total;The total weight of the catch was986kg,with 260 catches.A total of 46 days were spent on the contrast net.The total weight of the catch was 697kg,totaling 193.The catch increased by 289kg and the number of catches increased by 67.(2)Analysis on the Variation of Dominant Body Length of Main Catch VarietiesIn the operation of the contrast net,a total of 6 kinds of catches were found,including:Lateolabrax japonicus accounting for 0.52%of the mantissa of the contrast net,Nibea albiflora accounted for 21.24%,Miichthys miiuy accounted for 74.61%,Microcanthus strigatus 1.55%,Pagrosomus major 1.55%and Pseudosciaena polyatis(0.52%).The optimized bag set-net has a total of 7 kinds of catches,including:Lateolabrax japonicus accounts for 0.77%of the tail number of the test net,Nibea albiflora accounts for 19.62%,Miichthys miiuy accounted for 77.31%,Sciaenops ocellatus 1.15%,Pagrosomus major0.38%,Pseudosciaena crocea 0.38%,and Ynoglossus semilaevis Gunther 0.38%.A total of4 kinds of catches are the same between the two set-nets.There are 3 kinds of different catches,of which 1 kind is unique to the contrast net and 2 kinds are only found in the operation of the test net.Compared with the original nets,the test net has 1 more kinds of catches.With Miichthys miiuy as an example.in the body length group of 240mm~300mm,300mm~360mm and 360mm~420mm,compare what the net caught Miichthys miiuy is higher than that of test net.But in the body length group above 420mm,what was captured by the test net Miichthys miiuy is higher than that of contrast net.This means that for Miichthys miiuy,although the dominant body length groups of the catches caught by the test net and the contrast net are the same,the test net is not suitable for catching large individuals Miichthys miiuy has more advantages.As far as Nibea albiflora is concerned,there is no catch in the test net and the contrast net from the 120mm~160mm body length group.In the 160mm~200mm and200mm~240mm long groups,the output of the contrast net was slightly higher than that of the test net.However,in the body length group of more than 240mm,the test net is dominant.This shows that the test net has the same advantages to capture large individuals of Nibea albiflora.From the above analysis,it can be seen that compared with the contrast net,the test net has greatly improved the variety,quantity and specifications of catches.However,due to limited resources such as funds and time,there is still some room for improvement:(1)Means of releasing juvenile fish.The existing bag set-net still lacks special juvenile fish releasing means,which can increase the Y-type juvenile fish releasing device and reduce the fishing of juvenile fish by bag set-net.(2)The influence of the color change of the mesh on the catch.The color of the mesh can have certain influence on the behavior of fish.In order to achieve the goal of accurate fishing,it is necessary to fully study the rules and make reasonable use of them.The above ideas need to be further tested in the future.