Identification Of Keystone Species Of Fish And Evaluation Of Their Resource History(A Case Of Zhushan Bay,Taihu Lake)

Clarification of key fishery species with both ecological regulation and control functions and economic value is the basis for forming an effective model of large water surface aquaculture in synergy with the aquatic ecological environment.The evaluation of suitable models based on multi-source long series data is helpful for evaluating the resource status of key species and the formulation of utilization strategies.In this study,Zhushan Bay of Taihu Lake was taken as the research scope,combined with the survey literature of fish in the same water area and the measured data in 2019～2020,and identified keystone species in the structure of its food web based on network analysis.For the most important species,a suitable evaluation model was selected according to the data facts,and the assessment and judgment of resource utilization status and associated impact were carried out.The main results are as follows:（1）From November 2019 to October 2020,fish samples were collected monthly from the waters,a total of 48 species of fish were collected,and 39 functional groups were divided based on diet.Then,based on the feeding relationship,the topology map of food network in Zhushan Bay of Taihu Lake was constructed,and the keystone species of fish were identified by network analysis.The results showed that the Culter mongolicus and Culter alburnus,Protosalanx hyalocranius and Salangichthys tangkahkeii are keystone fish species in the food web of Zhushan Bay in Taihu Lake.Among them,the Culter mongolicus and Culter alburnus have the largest D,D_in,IC,CC,and H_in values,the large silverfish have the highest BC value,and the new whitebait of Chen’s has the highest D_out,H_out and K_bu.Culter mongolicus,Culter alburnus and large silverfish are key predators,Culter mongolicus and Culter alburnus have the greatest destructive effect on the food web after removal,and the large silverfish transmit information in the food web at the fastest speed.Chen’s new whitebait is a key food species and has the strongest ability to determine the species structure of the higher trophic strata of the food web.（2）After identifying the keystone species of fish,this study selected large Culter fish with long growth cycle（Culter mongolicus and Culter alburnus）as the research object,and used two resource assessment models（DLMs）with limited data,CMSY and LBB,to evaluate the resources over a long period of time（1973-2019）.The results of LBB showed that in 2016,the stock faced high fishing pressure and the problem of fishing juveniles,the Lc/Lc_opt and Lmean/L_opt of the stock were less than 1,and the Z/K,F/M and F/K were4.07,1.1 and 2.1,respectively,all higher than the ideal value,and the asymptotic body length was 69.1 cm,and the stock was overfished that year.CMSY results show an overall downward trend in large Culter fish resources over the past 50 years,with the maximum sustainable catch estimated by CMSY being 490 tonnes and the maximum sustainable catch estimated by BSM using CPUE data being 456 tonnes.The study found that 14 of the 47 years of catch exceeded the long-term MSY,the biomass was less than half of the environmental capacity for about 30 years,the highest development rate exceeded 5,the B/B_msy of the population was below 1 for a long time,the F/F_msy was greater than 1 for a long time,and the large Culter fish population of Taihu Lake in 2019,the last year before retiring,was still overfished.（3）The correlation analysis results of the model on the main influencing factors of large Culter fish resources preliminarily show that the improvement of fishery productivity,the upgrading of production tools,natural disasters,urbanization process and fishery production mode are the potential factors affecting the status of large Culter fish resources in the past 50 years.And based on simulations over the next decade,current large Culter fish populations struggle to support maximum sustainable catches without the help of human releases.The study preliminarily identified keystone species in the food web of Zhushan Bay in Taihu Lake.The historical dynamics and resource status of large Culter fish resources,as well as the main influencing factors associated with them,were analyzed.In the fishery management of Taihu Lake,it is a correct direction to adhere to the proliferation and release of large Culter fish and continue to increase their population size.