Resource Status And Variation In Critical Habitat Suitability Of Larimichthys Crocea In The East China Sea

In China’s coastal waters,the large economic fish represented by Larimichthys crocea are in serious decline and difficult to restore,which is the result of the combined effect of global climate change and human activities,however,the mechanism of these factors restricting the recovery of fishery resources is still unclear.Therefore,this study analyzed the status quo of L.crocea resources in the East China Sea and and decadal variation trend of the suitability of key habitats and explored the main reasons why the resources of L.crocea are difficult to recover,so as to provide a theoretical basis for the resource recovery of large economic fishes such as L.crocea.The main results are as follows:First of all,we carried out fishery surveys from 2018 to 2019 and found that:(1)The average abundance of L.crocea in four seasons in Sansha Bay(Traditional spawning grounds for L.crocea)was only 305±548 ind.km-2 and the average body length of L.crocea was 113±44 mm,which is much lower than the first sexual maturity length(226mm),so we speculated that there was few L.crocea propagation population.(2)We conducted vertical tows from April to September in 2019 to investigate spatiotemporal distribution of eggs in Sansha Bay,however,L.crocea eggs were only collected from two sites in May,indicating that the natural recruitment of L.crocea is low at present.(3)In Sansha Bay,abundance and body length of L.crocea was both lower in Spring than in Autumn.In the mid-southern East China Sea(ECS),abundance of L.crocea was significantly lower in spring than that in autumn and winter(P<0.05),and the maximum body length in spring was also lower than that in autumn and winter,it can be seen that fishing intensity during wintering phase is too large.Secondly,we established habitat suitability index models of L.crocea spawning ground and nursery ground according to the literature,then the models were used to analyze the decadal variation in habitat suitability of spawning ground and nursery ground in Sansha Bay,respectively.Our result shows that:(1)From 1990s to the present(May every year),the suitability of spawning ground in Sansha Bay has decreased,but the suitability of nursery ground had no obvious change.This is mainly because aquaculture changes the hydrodynamic conditions in the bay.(2)There was no apparent change in habitat suitability of nursery grounds.Finally,we established and validated habitat suitability index models of L.crocea wintering ground using historical catch data and corresponding environmental data,then the model was used to analyze the decadal variation of L.crocea wintering ground in the mid-southern ECS.Our result shows that the temperature variation in the midsouthern ECS have caused:(1)significantly decreased(P<0.05)optimal habitat in 2000s and 2010s compared with the previous decades(from 1970s to 1990s)(2)spatial distribution shift of habitat suitability with the distance between the optimal habitat and the land became longer.The above results show that the recruitment bottleneck still exist,wild populations have not recoverred and overfishing is the major impediment to L.crocea resource recovery.Climate change and aquaculture caused habitat bottleneck will directly affect the recovery of L.crocea population and will aggravate the impact of the overfishing on the recovery of L.crocea population.