Status Of Fish Resources In The Lower Reaches Of Qililongba Of Qiantang River

The lower section of the Qililong Dam of the Qiantang River belongs to the lower reaches of the Qiantang River.It has always been an important place for fishery production.There are many indigenous economic fishes and migratory fishes in this water area.The construction of wading projects,sand mining,and overfishing since the last century have caused the decline of Qiantang River fish resources,but the research on Qiantang River fish is relatively lagging and not thorough and comprehensive.There are even fewer investigations on the lower section of the Qililong Dam.This study used custom multi-mesh gillnets and custom tandem cage pots to survey fish in the lower reaches of the Qililong Dam of the Qiantang River from 2015 to 2018.Based on the results of the 4th anniversary of the survey,the fishes in this section were analyzed and researched..The main research content includes fish species composition,dominant species,ecological types,diversity and community structure characteristics.A total of 8202 fish samples were obtained,belonging to 83 species of 59 genera,24 families and 13 orders.Among them,there are 48 species of Cypriniformes,accounting for57.83% of the total number of fish species investigated.The ecological types are dominated by freshwater settlement,bottom,and omnivorous,and show certain characteristics of temporal and spatial distribution.Compared with the record in 1990,fish resources in this section of the river have declined significantly.The number of species has decreased by 35.The reasons for the decline of fish resources mainly include wading projects,sand mining,and sewage discharge.During the investigation,two species of escaped fishes from culture were found,and it is necessary to be vigilant about possible invasion of alien species.The dominant fish species in the lower section of the Qililong Dam of the Qiantang River are six species of Hypophthalmichthys molitrix,Pseudobrama simoni,Hypophthalmichthys nobilis,Squalidus argentatus 、 Coilia nasus and Pelteobaggrus nitidus.There are differences in the dominant species in different sections of the river,and there is no same dominant species in the 4 sampling points.The results of biodiversity analysis showed that the overall fish biodiversity of Tonglu and Fuyang was higher than that of Yiqiao and Liuqiao,and the difference in Margalef richness index and species number between sampling points reached extremely significant levels(P<0.01).According to the abundance biomass curve,there are differences in the stability of the fish communities at each sampling point.Tonglu and Fuyang are moderately disturbed,while Yiqiao and Liuqiao are not disturbed.According to the results of Cluster analysis,each sampling point is divided into two groups.The average similarity of fish community composition between Tonglu and Fuyang is 45.41%,and the average similarity of fish community composition between Yiqiao and Liuqiao is 50.87%.There is a significant difference between the two groups(P=0.002),and the average difference is up to 80.88%.The reasons for the spatial differences in biodiversity,dominant species,and fish community structure are more consistent.They are all related to the hydrogeographic features of the lower reaches of the Qililong Dam of the Qiantang River: the Tonglu and Fuyang sampling points near the estuary have narrower rivers,The water flow is fast,and the Yiqiao and Liuqiao rivers in the estuary section are wide and the water flow is slow,and the fish habitat diversity in the estuary section is higher than that in the estuary section,and there are fish breeding and release areas near the estuary section.Compared with historical records,fishes in the lower section of the Qililong Dam of the Qiantang River have declined to a certain extent.Large fish and indigenous economic fish populations are small,and there are problems of simplification and miniaturization of fish species in this section.It is recommended to strengthen the water quality supervision of the river basin,improve the fishing ban system,establish germplasm resource protection areas,and carry out dynamic monitoring of fishery resources to protect fishery resources in the lower reaches of the Qiantang River.