Temporal And Spatial Changes Of Fish Community Structure And Diversity In The Three Gorges Reservoir Area

The Three Gorges is one of the world’s most high-profile large-scale water conservancy projects.The completion of the dam has created a 600km long reservoir with a water area of1,027km~2 from Chongqing to Yichang.The construction of the Three Gorges Dam has hindered the migration of fish and caused changes in the habitat of fish.The impact on the structure and diversity of fish community has attracted much attention.In the past,most studies on fish community assessed community composition and changes based on the species level,focusing on the number and quantity of species.Taxonomic diversity and functional diversity are important aspects of biodiversity measurement and have attracted more and more attention.In this study,the spatial pattern,seasonal variation and variation trend of fish communities in the Three Gorges Reservoir area were discussed from the aspects of species,classification and function,in order to provide scientific basis for the conservation of fish resources in the Three Gorges Reservoir area and provide background data for the assessment of the effect of"ten-year fishing ban"in the Yangtze River.The main research results are as follows:(1)Analysis of fish species composition and diversity in Three Gorges Reservoir Area.78 fish species belonging to 6 orders,15 families and 56 genera were collected from the Three Gorges Reservoir area and its main tributaries using composite gill nets and ground cages from2019 to 2020.Eurytopic and limnophilic fish species dominated the reservoir.The limnophilic species,such as Coilia brachygnathus and Hemiculter bleekeri,had higher relative abundance in the Zigui,Xiakou and Gaoyang sections.In Yunyang,Banan and Hechuan river sections,the relative abundances of eurytopic species such as Saurogobio dabryi and Pelteobagrus nitidus were high.Non-metric multidimensional scales(NMDS)and Bray-Curtis dissimilarity index analyses indicated that differences in fish community structure were greatest between Hechuan and Zigui,and most similar between Xiakou and Gaoyang.Margalef richness index(D),Shannon diversity index(H’)and Pielou evenness index(E)gradually increased from Zigui,through Yunyang to Banan in the main stream of the reservoir.In the tributaries,species diversity was highest in Xiakou,with lower diversity in Gaoyang and lowest in Hechuan.The spatial variation of functional diversity related to fish food acquisition,locomotion and reproduction were relatively consistent throughout the study area.The highest value was observed in Zigui and lowest in Hechuan.The total functional diversity had a consistent spatial variation with community species diversity in the Three Gorges Reservoir.The diversity indices gradually increased in the main stream from Zigui to Banan.In the tributaries,diversity indices were the highest in Xiakou,followed by Gaoyang and Hechuan.(2)The temporal variation of fish diversity in Yunyang River section was analyzed.A total of 42 species belonging to 7 orders,10 families and 30 genera were collected from Yunyangjiang River in the Three Gorges Reservoir in August and November 2020 and January and April 2021.Overall,the different months Yunyang section dominant species are Hemiculter bleekeri,Pseudobrama simony and C.alburnus.The results of non-metric multidimensional scale(NMDS)analysis and Cluster analysis were consistent,and the fish communities in Yunyang Section were divided into two groups in each month,group 1 in January and August,group 2 in April and November.Margalef richness index(D)was the highest in January and the lowest in November,Shannon-Wiener diversity Index(H’)and Pielou evenness index(E)showed the the highest in October and the lowest in November.On the whole,species diversity was higher in winter.The food acquisition functional diversity was higher in spring,and locomotion functional diversity was higher in winter.(3)Comparison of fish composition in the Three Gorges Reservoir Area before and after impoundment.152 fish species belonging to 10 orders,25 families and 90 genera were investigated in the Three Gorges Reservoir area before and after impounding.Among them,110 species belonged to 8 orders,15 families and 68 genera before impounding(before 2003).110 species belonging to 6 orders,17 families and 69 genera during the water storage period(2003-2010);After impounding(2019-2021),there were 101 fish species belonging to 7 orders,18 families and 66 genera.In terms of feeding habits,piscivore and omnivorous fish dominated before,during and after impoundment,accounting for 40.7%±8.5%of fish species.From the perspective of velocity preference,the species percentages of eurytopic fish domainsted before,during impoundment,accounting for 40.8%±5.8%;after impoundment,the main species were eurysitic and hydrostatic fish,accounting for 39.3%±3.6%.From the perspective of spawning types,the fish that produced Sticky eggs and drifting eggs accounted for 35.1%±9.1%of fish species in the Three Gorges Reservoir area before,during and after impoundment.Jaccard similarity analysis showed that the fish communities were moderately similar before and after impoundment,and the Jaccard index was 0.51.The similarity of fish communities was low during,before and after impoundment,and the Jaccard index was 0.39and 0.32,respectively.On the whole,the taxonomic diversity of the fish community before impounding was higher,and the average taxonomic distinctness index was the highest before impoundment and the lowest during impoundment.The variation in taxonomic distinctness index was the highest before impoundment and the lowest after impoundment.Functional richness related to food acquisition,locomotion and reproduction was the highest before impoundment and the lowest after impoundment.However,the functional evenness and functional divergence related to food acquisition,locomotion and reproduction function had little difference in the three time periods.