Analysis Of Annual Variations For The Fish Community Structure And Estimation Of Fisheries Manage Parameters For The Dominant Species Indianshan Lake

As the biggest freshwater lake, Dianshan Lake is conveniently located in the junctionof Shanghai Municipality, Zhejiang Province andJiangsu Provincewith the total area of67.3km2. The ArticleXXI of “Rules of Shanghai environmental protection (revisedvision)”definites Dianshan Lake as the water conservation district.Dianshan Lake played avery important role in fishery, food supplying and conservation for aquatic livingresourcesin ShanghaiMunicipality.Since the1960s, because of pollution and overfishing, the fishery resourcesofDianshan Lake declined continuously. In this study, we firstly analyzedthe annualvariations on diversityof fish community structure andthe composition of dominantspeciesthen estimatedgrowth and mortality parameters, catch-per-unit-effort, sotck andoptimum catchable body-lengthbased on the survey data in Dianshan Lake from January2010to December2013, for the purpose of taking the scientific adivices tomaintain thereasonable andsustainable developmentfor thefishery resources of Dianshan Lake.According to data analysis, fish species composition was similar among2010-2013and the dominant species tended to be mini-type fish of fish composition. It dedicated thatthe Diversity Indices of fish community were not significantly different among2010-2013(P>0.05). Moreover,Abundance Biomass Comparison (ABC) Curves showed that fishcommunity structure was disturbed significantly in Dianshan Lake in these four years.Abundance of Coilia nasus and Culter erythropterus tended to be rising. For each ofthese two species,theaverage body-weight was with a decline trend and the dominantforth length was smaller than before. It showedthatthe sizes of both Coilia nasus andCulter erythropterusare all smaller than before.Through the analysis of the biological datacollected from trawlsurvey, growth and mortality parameters ofCoilia nasus and Cultererythropterus were estimated by the FiSAT II software, and current status of stock and fishery manage parameters were assessed by yield-per-recruit model. Optimum catchablebody-lengthwas determined by comparing the critical age/body-length and the maximumyield-per-recruit.The result showed:(1) The relationship between length and weight ofCoilia nasus and Culter erythropterus could be fitted asW aLb, bwas approach to3;(2)The critical age was1.94a and2.23a separately, corresponding to the body-lengthwas17.67cm and14.83cm separately;(3)Total mortalitywas1.93and1.80, naturemortality was0.58and0.40separately, meanwhileexploitation rate was0.70and0.78,respectively.The isopleth plot of yield-per-recruit was simulatedby fixing fishing mortalitycoefficient to tentively get theoptimum catchable body-lengthand yield-per-recruit.Underthe actual fishing mortality coefficient (Coilia nasuswas1.35and Culter erythropteruswas0.95), the maximum yield-per-recruitcould be estimated if increased first catch age(Coilia nasuswas0.74aand Culter erythropteruswas0.78a) to1.62a and2.10a (first catchlength was16.34cm and14.46cm). Considering thespecies’ spawning, growth, death andeconomic benefits of fishermen of Dianshan Lake, we should control thefirst catch ageas1.62a-1.94a and2.10a-2.23a, the first catch body-length was16.34cm-17.67cm and14.46cm-14.83cm.According to the exploitation and isopleth plot of yield-per-recruit of Coilia nasus andCulter erythropterus, the fisheries resources was in the status of over-fishing andover-exploited. The mesh size lookedtoo small.According to data analysis and overallconsideration, the following advices were made:(1) adjusting enhancement species, such asTakifugu obscurus, Anguilla japonica, Anguilla japonica, Mugil cephalus and Elopichthysbambusadeclining even disappearing recently, as well asCulter erythropteruswho was wildspecie, to enhancing the effect of enhancement and releasing, improving fish communitystructure of Dianshan Lake;(2)enlargingthe mesh size;and (3) changing the closureseasonsFebruary sixteenth to August fifteenth as March first to September first forgillnet,and February sixteenth as March first at least for trawlnet, to protenting thespawning of economic species and avoiding declingof fishery economic benefits ofDianshan Lake as much as possible.