| As the largest natural lake in Shanghai, Dianshan lake is the most concentratedShanghai fisheries production in inland watersas well as the top fishery production andoutput value area.Output value of Dianshan lake accounts for more than half of theentire Shanghai inland waters.On account of the influence of the environment pollutionand overfishing, the fishery resource diversity and resources in Dianshan lakeare boundto have been affected. In recent years, Dianshan lake fishery resources shows in a wholerecession trend and population structure become miniaturization and simplification.Inconsequence, this situation so urgently needs to be curbed by effective measures. Since2005, Shanghai fishery department began to carry out large-scale enhancementactivities in Dianshan lake and put in large number of economic species seedlings andsmall amounts of parents every year, so as to maintain the Dianshan lake of sustainableutilization of fishery resources effectively. The recovery of some traditional economicspecies resource has made important contribution to the Dianshan lake surroundingfishermen’s income. In recent years, according to research on the "indigenous" species,resources of Dianshan lake began to recover, especially shiny yellow catfish and shrimpspecies (including E.modestus and M.nipponense).This research carried out the biologicalstudy on the several kinds of economic types, so as to understand the resource dynamicof economic types in Dianshan lake. In addition, for commercial fisheries, statistics offishery production is always a difficult problem; the exact output statistics can providebasic support for the development of fishery resources development strategy. Accordingto2011~2012annual survey data, this study on "shanghai inland waters fishenhancement and effect assessment project" carry out biological preliminary research of shinyyellow catfish fish and shrimpin Dianshan lake and we estimated yield ofshinyyellow fish and shrimp in2012Dianshan lake. The purpose is that providing ascientific basis for the sustainable utilization of fisheries resources which aimed atDianshan lake.From August2011to July2012,780specimens of P.nitidus were sampled to studytheir biology.The results showed that:(1)The length distribution of shiny yellow catfishsamples was4.7~16.0cm, with a dominant group was8.0~12.0cm; The weightdistribution of those samples was1.3~28.4g, with a dominant group was5.0~15.0g.(2)The mean length of females and males were10.93cm and11.37cm, with a mean weightof15.10g and15.88g, respectively.(3)The length-weight relationships of females andmales were described asW♀0.041L2.533（r=0.8585，n=151）andW♂0.037L2.557（r=0.8597，n=87）, respectively, and with significant difference based on covarianceanalysis.(4) The length of minimum sexual maturity of female and male shiny yellowcatfishwere8.6cm and9.4cm respectively.(5) The mature individuals’ gonad somaticindex (GSI) of shiny yellow catfish was obviously higher than the immature individuals’and the female immature individuals’ GSI tended to increase with total length andconversely for the female mature individuals’.(6) The main prey of shiny yellow catfishwas shrimp and the feeding intensity was mostly in the class2and3which occupied57.66%of the total specimens.According to Dianshan Lakeshrimp trawl survey in2012, M.nipponense has beencollected5386with total weight8610.9g and E.modestus has been collected1843withtotal weight2056.2g. In Dianshan lake,weight range of M.nipponense were0.1~11.5gand the average weight was2.12g.Advantages of weight range are0.05~2.25g and theaverage length of upper frontal eminence is11.13mm. Advantages of length of upperfrontal eminence range are8.70~12.50mm. In Dianshan lake E.modestu weight rangeare0.3~2.9gand the average weight is1.10g.Advantages of weight range are0.75~1.0gand length of upper frontal eminence range are4.57~17.40mm.The average length ofupper frontal eminence is10.73mm and advantages of length of upper frontal eminencerange are9.00~12.00mm. The relationship of M.nipponense between body weight andbody length is as follows:1~7months of age:W0.016L3.115(r=0.9397, n=960);8~12months of age:W0.032L2.999(r=0.9192, n=650); E.modestus weight and length of the relationship between application model fitting get formula is as follows:1~7months ofage:W0.015L2.915(r=0.9214, n=550);8~12months of age:W0.035L2.670(r=0.9241, n=121). In2012, the largest CPUE of trawl shrimp in Dianshan lake is at the summerand autumn, which CPUEs of shrimp at every site of Dianshang Lake are different.CPUEs of shrimp in Dianshang Lake present significant downward trend from2011to2013, which rise as a whole at June, on the other hand show a peak at September, andthen began to decline until next May.According to the CPUE analysis of yellow catfish and shrimp and results show thatFrom2011to2013, yellow catfish CPUE began to gradually rise in March every yearand to reach the peak in July.Then began to decline to November and basically remainunchanged. Shrimp CPUEs in Dianshan lake present significant decline and CPUEs inJune are on the rise as a whole when come to the peak in September and then began todecline until the following year in May.In order to estimate2012yellow catfish and shrimp yieldin Dianshan lake, thisresearch adopts the annual survey sampling data and the sales records which areaccording to the market estimates and fishery production model methods evolution ofGomez-Munoz model respectively for yellow catfish and shrimp yield estimation andcomparative analysis in Dianshan lake. Market sales record estimated using simplemethod of estimating the overall sample average. Fisheries production model methodwas based on visiting, questionnaire, fishery market research and scientific investigationand then got the key data and parameters toestimatethrough statistical model. Finallyestimate results show that: In2012,production of yellow catfish and shrimp in Dianshanlake are32.73t and52.55t, compared with the results in2007and2008shows that thestatistics there is an obvious downward trend. The results of this study can help offishery resources in Dianshan lakefor better management, in order to achieve thedemand of sustainable utilization of fishery resources in Dianshan lake. |
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