The Analytical Research Of Spatial Distribution Of Fish Larvae And Juveniles In Summer And Autumn In The Eastern Chongming,Yangtze River Estuary

Based on the data collected from the horizontal trawl(mesh size 0.5 mm,towing speed ca 2 knots)survey in the water area of Eastern Chongming,Yangtze River Estuary,in the summer(June)and autumn(September)season 2018,the environmental data were also synchronized.The ecological type and species composition,dominant species and species diversity were investigated in this paper.Cluster analysis and non-metric multidimensional scaling were used to study the spatial pattern of fish community,and its relationship corresponded with the environmental factors was discussed,using canonical correspondence analysis.A total of 10,925 fish larvae and juveniles,results showing,belonging to 52 species,were collected.The larval fish were in the class of Clupeiformes,Cypriniformes,Salmoniformes,Beloniformes,Mugiliformes,Myctophiformes,Perciformes and Tetraodotiformes.The Perciformes class was the most dominant,consisting 18 species.However,the Clupeiformes had the most share of the catches,42.92%.The most dominant species was Coilia mystus(21.51%),followed by C.nastus(18.11%),Hemiculter bleekeri(16.33%),Pseudolaubuca sinensis(10.82%)and Acanthogobius ommaturus(9.38%)respectively.The data shows that the pre-flexion stage of fish larvae was the most dominant within the whole sampling,consisting 76.49%,which was mostly contributed by summer surveying.Flexion-stage fish larvae were 11.94%,and post-flexion stage were 8.01 percentage of the sampling.Juveniles only consist of 3.43% of the whole surveying.Study found the yolk-sac stage fish larvae only showed in the summer season,small in quantity,only 0.13% of the sampling.The species,bio-diversity and the density of fish larvae were higher in the summer season than in the autumn season.The Margelef’s index experienced a drastically change in the northern branch of Yangtze River,and the Pielou evenness index had a few alter,the Shannon–Wiener index showed.C.nastus and C.mystus are both important economic fishes in the Yangtze River Estuary,but their resources have declined significantly.In this study,the density of Z4,5,7,13 and 15 C.mystus was significantly higher than that of C.nastus.The highest density was 0.38 ind./ 1000m3 in summer,and that of C.nastus was 0.74 ind./ m3 in Z1.C.nastus is a migratory fish,which propagates in the mouth of the Yangtze River from May to June,and then the spawning ground moves up gradually.Therefore,the breeding seasons of C.nastus and C.mystus overlap in the estuary.The canonical correspondence analysis(CCA)showed that the were the most important environmental variables affecting the spatial pattern of fish community in the water area of eastern Chongming,Yantze River Estuary,and adjacent waters,while the temperature also had some influence on spatial distribution of the fish community.