| Portunus trituberculatus,as one of the important economic species in the offshore areas of China,has been enjoying great popularity for its high productivity,short growth cycle and delicious meat.The east China sea is the high yield sea area of P.trituberculatus,and the yield is close to 40·104 t.In recent years,the yield of P.trituberculatus fluctuates greatly.There are many possible reasons,including unreasonable release and catch behavior.In order to maintain the sustainable development of P.trituberculatus resources,scientific resource assessment and fishing management are needed.In this paper,two typical sea areas in the east China sea area were selected:the Yangtze estuary fishing ground and adjacent sea areas,and the zhoushan fishing ground and adjacent sea areas.Based on the investigation data of fishery resources in the Yangtze estuary fishing ground and its adjacent waters from 2006 to 2014,the Ecopath model was constructed to preliminarily analyze the energy flow characteristics of the ecosystem in this sea area,and to estimate the proliferation capacity of P.trituberculatus in this sea area.Results showed that the area ecosystem mainly benthos,shrimp,Trichiurus leptures,P.trituberculatus foods utilization rate are higher.The Trachurus japonicus,Chelidonichthys kumu foods utilization rate is low;The fishery resources in this sea area can be divided into four trophic level,and the P.trituberculatus belongs to the middle trophic level.The total catch in this area was 1.614 t·km-2(the catch of P.trituberculatuswas 0.057 8 t·km-2),the total consumption was 280.744 t·km-2,the total export was 790.396 t·km-2,and the total production was 959.3 t·km-2.The biomass density of P.trituberculatus was 0.125 t·km-2,the ecological capacity was 1.125 t·km-2,and the proliferation capacity was 1 t·km-2.The results showed that the primary productivity of the sea area was high,Marine organisms were mostly distributed in the second and third trophic levels,and the ecosystem maturity was low.P.trituberculatus still has a certain release space in this sea area.Selecting the main area of the East China Sea District to catch the P.trituberculatus,and it is also the main work of Zhejiang province?26°00'N31°00'N,west of 128°00'E?.According to the catch statistics of P.trituberculatus from 2006 to 2015 in this sea area,and combined with the resource sampling data in this sea area for many times,the current situation of fishing mortality coefficient?F?and catch?C?of P.trituberculatus in this sea area was analyzed.Based on the biological reference points(F20%,F40%,FMSY and B20%,B40%,BMSY)related to F and biomass?B?.The reasonable catching,enhancement and releasing strategies were evaluated.The results showed that the maximum sustainable yield?MSY?in this sea area was 14.2·104t,corresponding to F=0.33-1·year.Based on the relationship between F-spawning biomass?SSB?and B-releasing?RW?,catching and releasing strategies were established.Catching strategy:when SSB drops to 20%,40%and MSY of the initial SSB?at this time,SSB is equal to 12.2·104t,24.4·104t and45.7·104t?,F is F20%=0.1,F40%=0.2,and FMSY=0.33.Although the current catch reaches to20·104t,F also reaches to 0.41-1·year,so it is not a sustainable development state.Based on this,the enhancement and releasing strategy in this paper:when the B drops to 20%and 40%and BMSY of the initial B(at this time,the density values of B are 0.274 t·km-2,0.548 t·km-2and 0.685 t·km-2),and the RW is 597 g·km-2,199 g·km-2 and 0 g·km-2.when B?BMSY,no release is allowed.The results of the study show that the release of P.trituberculatus is not as good as possible.It needs to rely on a reasonable fishing strategy to guide If the above two strategies are implemented,the values of F,B,SSB,C and RW are predicted to be stable in the 20 years after 2015,which are equal to 0.33,0.75 t·km-2,0.65 t·km-2,0.17 t·km-2 and0.At this time,P.trituberculatus resources are maintained in the state of sustainable development. |
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