The Selectivity Of The Big Mesh Gillnet For Scomberomorus Niphonius

Scomberomorus Niphonius is widely distributed in the yellow sea,the bohai and theeast china sea.It is an important pelagic fishes in China who has greater volume andhigh economic value.So it receives wide attention in recent years.With the developmentof fisheries and the increase of fishing intensity, the number of ScomberomorusNiphonius population is declining. So the resource conservation is urgently needed.Gillnet fishery is an important part of Scomberomorus Niphonius fishery. Research ofselectivity of fishing gear of gill net is very urgent and necessary.The research hasimportant theory meaning and realistic meaning for the protection and sustainableutilization of fishery resources.Finally, the research can promote the research ofselectivity of fishing gear.In order to study the selectivity of Scomberomorus niphonius gillnet meshsystematically, four different meshes of110mm、115mm、120mm and125mm weretested during fishing operation from April to May2013. Finishing the calendar year inScomberomorus niphonius resource monitoring biological data, Combined marinefishing information dynamic data acquisition system, The selectivity of Scomberomorusniphonius, distribution, changes in biological parameters and the state of fisheries werestudied systematically. Results showed:1、Test Scomberomorus niphonius catches fork length range of160~950mm,Advantage fork length group was230~450mm, Accounting for87.95%of the total,Average fork length408.36mm；Weight range of40~6200g, advantages bodyreorganization150~750g, accounting for78.59%of the total, the average weight of791.19g. the relationship between fork length and weight can be expressed asW=3×10-5xL2.81（n=2041， R2=0.98）. The growth equation isW3974[10.39t1.062.81W3974[1039t1.06te]and.2te].81.The spinodal ofgrowth appears at age of1.59.2、 Selectivity model curves and body shape coefficients were used to analyze the mesh selectivity. Results showed that①The gillnet tested had good selectivity, the dominantspecies were Scomberomorus niphonius and sebastes fuscescens with IRI Values of18626.8and2740, respectively.②Gamma model obtained the best goodness-of-fit withthe selectivity model curves among the common models tested.③The formulaedescribing the relationship between mesh size (α) and fork length (l) or body weight (W)were α=0.0927l and α=4.59W1/3, respectively.④The formula describing therelationship between mesh size and maximum perimeter of body section(S) was α=0.224S-5.37.⑤The optimum meshes for catching3-4ages of Scomberomorusniphonius were estimated to be120.4mm and121.5mm respectively by Gammaselective curve and the aforementioned formulae. The optimum meshes for differentages of Scomberomorus niphonius were also calculated based on the historical fishingdata.