Habitat Evaluation Of Yangtze Finless Porpoise Provincial Nature Reserve In Nanjing

Nanjing Yangtze finless porpoise(Neophocaena asiaeorientalis asiaeorientalis)Provincial Nature Reserve is one of the important habitats of Yangtze River finless porpoise.In order to understand the natural population characteristics and habitat quality of the Yangtze finless porpoise in the reserve,from March to December 2019,the present situation of the Yangtze River finless porpoise population in this area was investigated by the method of transect sampling,and the survey of aquatic biological resources was carried out simultaneously.This paper analyzes the population quantity and distribution characteristics of Yangtze finless porpoise,as well as the status of aquatic biological resources,and explores the key influencing factors of Yangtze River finless porpoise distribution in Nanjing nature reserve,and finally the Ecopath model was used to evaluate the habitat status of the Yangtze finless porpoise in Nanjing nature reserve.The purpose was to provide theoretical basis and scientific basis for the relocation and local conservation of Yangtze finless porpoise in the future.The research results are as follows:1.A total of 186 groups and 424 times of Yangtze finless porpoises were found in Nanjing nature reserve.The estimated population number of Yangtze finless porpoise is the highest in winter(about 66),and the lowest in spring(about 36).It is mainly distributed in the waters near Meizizhou and there are scattered distributed in other waters of the reserve.In addition,it is mainly distributed in clusters(≥2),accounting for 67.7%of the total number of Yangtze finless porpoise population found;In terms of offshore distance,the nearshore distance(≤500 m)is the main distribution,accounting for 52.8%of the total number of Yangtze finless porpoises found.2.(1)A total of 85 species,48 genera,8 phyla of phytoplankton were collected and identified.Among them,there are 40 species of Chlorophyta,accounting for 47.1%of phytoplankton species;Then there are 27 species of Diatom,accounting for 31.8%;The least species is Xanthophyta,accounting for 1.2%.There are 9 dominant species of phytoplankton,and the greatest dominant species is Chroomonas acuta.(2)A total of 40 species of zooplankton were collected and identified.Among them,there are 13 species of copepods,accounting for 32.5%of zooplankton;The number of rotifer species is the least,6 species,accounting for 15.0%.There are 5 dominant species of zooplankton,and the greatest dominant species is Leprotintinnus fluviatile.(3)A total of 35 species,30 genera,3 phyla of benthos were collected and identified.Among them,arthropod species are the most,21 species,accounting for 60.0%of benthos species;The number of Mollusca species is the least,5 species,accounting for 14.3%.There are 5 dominant species of benthos,and the greatest dominant species is Nephtys sp.3.A total of 44 fish species were collected and identified,belonging to 7 orders,11 families,34 genera.Among them,Cyprinidae is the absolute dominant group,with 24 species,accounting for 59.1%of the total.The dominant species in the community are Pelteobaggrus nitidus,Parabramis pekinensis,Coilia nasus,Leiocassis crassilabris,Hemiculter bleekeri and Hemibagrus macropterus,accounting for 62.3%of the total catch and 62.0%of the total weight.In terms of feeding types,the proportion of fish species with omnivorous(50.0%)and carnivorous(36.4%)is relatively high;In terms of migration habits,freshwater fish are dominant(81.2%);From the perspective of perching water layer,the proportion of bottom fish is relatively high(47.8%).The diversity characteristics values based on the catches of the whole year are:Margalef index(R)is 5.92,Shannon-wiener index(H’)is 2.67,Dominance index(D)is 0.12,and Pielou index(E)is 0.70.One-way ANOVA showed that there is no significant difference in fish diversity index in time and space(P>0.05).4.The study on the factors influencing the distribution of Yangtze finless porpoise in Nanjing nature reserve shows that fish resources,shoreline and water depth are the main factors affecting the distribution characteristics of Yangtze finless porpoise in Nanjing nature reserve,while water quality,plankton and other water environment factors have no obvious influence on the distribution of Yangtze finless porpoise.5.Based on Ecopath model,the habitat quality of Yangtze finless porpoise in Nanjing Nature Reserve was analyzed and evaluated.The model consists of 16 functional groups including primary producers,primary consumers,main fishes,Yangtze finless porpoise and debris,and basically covering the whole process of energy flow in the ecosystem.There are two energy flow paths for the ecosystem in the Nanjing nature reserve,namely the grazing food chain and the clastic food chain,in which elastic food chain accounts for a relatively large proportion.The fractional trophic level(FTL)of each functional group ranged from 1.00 to 3.70,The total flow of ecosystem is 2308.376 t/(km2.a),and the energy flow mainly occurs in I-VI trophic level.The total transformation efficiency of ecosystem(TPP/TR)is 9.227%;The ratio of total primary production to total respiration was 4.703;System connection index(CI)is 0.335;System omnivory index(SOI)is 0.151;Finn’s cycling index(FCI)is 11.82%;Finn’s mean path length(FCL)is 2.893.It shows that the ecosystem of Nanjing nature reserve is still in an immature state,the complexity of food web is low,the nutrition structure is simple,the ability of material circulation is weak,the maturity and stability of system is low,and the ability of resisting external interference is low.