East China Sea Fisheries Ecosystems And Protected Areas Scenario Simulation Analysis

Fishery is an important insurance for the global food safety and has provided 15%animal protein for the whole world consumption.The wide continental shelf waters of the East China Sea(ECS)provide high abundance of fishery resource in China.Marine fishing production of the ECS reached 625.4×10⁴t and 42.33%of the total marine fishing production of China Mainland.However,heavy fishing pressure has resulted in a significant change in fishery resources in the past few decades.The mean trophic level of the catch has decreased from 3.5 in 1965 to 2.8 in 1990 and the catches have become to be smaller,younger and premature individuals for some species.On the other hand,a large increase in jellyfish blooms in the ECS has occurred over the last 10 years.In response to this the Chinese government has introduced a range of fishery management measures including the introduction of fishery protected areas since 1970s.Previous studies indicated the modelling approach is a useful contribution to the overall knowledge needed to allow policy decisions to be explored in an ecosystem scale context.The purposes of this study are using the ecosystem modelling approach to analyze the status of ECS fishery ecosystem,and to examine the likely nature of trade-offs between fishery and conservation goals resulting from the marine protected areas(MPAs).Main results and conclusions are detailed as follows.1 Analysis on the ECS fishery ecosystem status and jellyfish bloomMean trophic level of the fishery catch was 2.71 while the mean trophic level for all groups was 2.87 in the ECS ecosystem.Network analysis results show the increase in fishing effort by trawl and stow net may aggravate the declining of hairtail stock in the ECS.Trophic interactions are 'web-like' where most flows occur in the lower part of the trophic web.Total throughput was 5 035.6 t km^-2year^-1and the geometric mean transfer efficiency was 14.6%.The ratio between total primary production and total system respiration P_p/R=3.4 estimated by the model indicates an immature and developing system.Analysis of the trophic interactions has identified a possible pelagic feedback loop allowing large jellyfish blooms to develop as a result of mutual competition and predation between large jellyfish,zooplankton and small pelagic fishes.The pelagic pathway of the ecosystem will be disrupted at the initial stage of a large jellyfish bloom.And fluctuation of zooplankton biomass might be one of the natural control mechanisms of large bloom.2 Spatial validation on the Ecospace modelSpatial validation work has been done using the North Sea Ecospace model. The results indicate:the validations of the model are different to different groups at the model start stage;the model prediction of the spatial biomass are more flat and smooth than the observation as model over-estimate the biomass in low abundance areas and under-estimate the biomass in high abundance areas;the degree of over-estimation on spatial biomass by the model was very slight;the model has lower ability on predicting the peak area of the spatial biomass;biases of the model predictions were stay in the same areas for each groups after dynamics compare with the start stage.So,the model would get a good prediction for a group if it gets a good start.3 Examine the fishery and conservation trade-offs resulting from marine protected areas(MPAs)in the ECSA spatial ecosystem model(Ecospace)of the ECS was developed to examine the likely nature of trade-offs between fishery and conservation goals resulting from the MPAs.The results suggest that the overall fishery has benefited from all of the simulated MPAs and those benefits come from the cost and benefit between fishing fleets.The simulations indicate that a win-win outcome for fisheries and conservation status is possible as a result of introduction of prohibited fishing line and implement of summer fishing closure while using the average longevity and BDI as the metrics of the ecosystem status,but not guaranteed. 4 Suggestions for the ECS fishery management(1)A win-win outcome for fisheries and ecosystem conservation status has resulted from the introduction of prohibited fishing line and implement of summer fishing closure.We suggest the enforcement of summer fishing closure be continued, and supervision and administration to the implement of prohibited fishing line be improved.(2)Shrimp trawl fishery benefit a lot from the implement of summer fishing closure whereas the benefit of trawl,stow net and pure seine fishery are small.We suggest shorten the fishing off season and fishing off region for the trawl,stow net and pure seine fleets.