Fish Community Characteristics And Biological Integrity Evaluation In Waters Near Chongming Island

Chongming Island is located in the mouth of the Yangtze River.It is the largest estuarine alluvial island in the world.The waters around Chongming Island have excellent ecological environment conditions and rich aquatic biological resources.However,with the over-exploitation of water resources,the fishery resources in the waters near Chongming Island are facing serious threats,and the health of aquatic ecosystem is becoming more and more prominent.Based on the fish survey data in August and November 2018,2019 and 2020 in the waters around Chongming Island,this study analyzed the characteristics of fish community structure by using species diversity index,relative importance index,cluster analysis and other methods.Combined with the historical research data and ecosystem characteristics of the waters under study,a fish-index of biological integrity evaluation system was initially established.The ecosystem health status of waters near Chongming Island was evaluated,and the uncertainty of fish-index of biological integrity was quantitatively analyzed by computer simulation for the first time,and the influence of data uncertainty on the evaluation results of fish biological integrity in Chongming Island was explored.The results show that:(1)A total of 24 fish species belonging to 1 class,8 orders and 13 families were observed in the waters around Chongming Island during the survey in August and November of 2018,2019 and 2020.The mean Margelef richness index(D)in August and November of 2018,2019 and 2020 were 0.74,1.05 and 1.37,respectively.Pielou evenness index(J’)was 0.60,0.74 and 0.78,respectively.Shannon-Wiener diversity index(H’)was 0.74,0.98 and 1.28,respectively.The dominant fish species in August and November 2018,2019 and 2020 were coilia nasus,and IRI% were 13.60,17.96 and 52.34,respectively.According to the results of Cluster analysis and n MDS analysis,the fish community structure at each station in the waters around Chongming Island in August and November 2018 can be divided into 4 groups in space,5 groups in 2019,and 3 groups in 2020.The W values in August and November of 2018,2019 and 2020 were all lower than 0,which were-0.142,-0.075 and-0.028,respectively,indicating that the fish community structure was seriously disturbed during the survey.(2)The fish biological integrity scores of the waters near Chongming Island in August and November of 2018,2019 and 2020 were 30,28 and 28,respectively,all in the "poor" level.As can be seen from the score,the main reason for the low fish biological integrity score in the waters around Chongming Island is the low fish species composition,trophic structure and biomass attribute indexes,among which the total number of fish species,the percentage of number of omnivory species,the percentage of number of benthic feeding species and the catch per haul per hour score during 2018-2020 are lower.Is an important factor in bringing down the score.(3)The results of data uncertainty analysis showed that when the monitoring value of the index had 30% variation,the fish biological integrity evaluation conclusion did not change,but the fish biological integrity score changed to a certain extent.Moreover,with the increase of uncertainty of index monitoring value,the fluctuation degree of fish-index of biological integrity evaluation results in waters near Chongming Island gradually increased.The analysis results showed that the degree of influence of the uncertainty of the monitoring value on the evaluation results was related to the specific position of the monitoring value in each zone of fish-index of biological integrity.Data uncertainty can affect the assessment of aquatic biodiversity level and health status in the study area,so the uncertainty of monitoring data should be carefully considered in the construction of evaluation system and interpretation of results.In general,the fish community in the waters near Chongming Island was heavily disturbed,and the biodiversity level and health status were poor.This study analyzed the fish community structure and its change characteristics in the study waters,evaluated the ecosystem health status of the waters near Chongming Island based on the fish-index of biological integrity,and for the first time,the impact of data uncertainty on the evaluation results was simulated by computer.In order to provide data support for the rational development of fish conservation measures,provide suggestions for the practical application of fish-index of biological integrity under the background of Yangtze River conservation,and provide reference for the improvement of aquatic ecosystem protection measures in waters near Chongming Island.