Community Structure Of Netkon And Its Relationship With Environmental Factors In The Conservation Zone Of Spawning Ground For Wen-tai Fishing Ground And Nearby Waters

Based on the bottom trawl survey data of fishery resources of nekton in the conservation zone of spawning ground for Wen-tai fishing ground and nearby waters and the effects of environmental factors on it.Based on the bottom trawl survey data of fishery resources in April(spring)and October(Autumn)of 2019,this thesis studies the species composition,dominant species,resource density,community similarity,species diversity and seasonal variation characteristics of nekton community,and reveals the relationship between taxonomic diversity and dominant species and environmental factors.The main results are as follows:(1)The species composition,dominant species,resource density,biodiversity and community similarity of nekton were analyzed.The results showed that 42 species of nekton were captured in the spring of 2019,belonging to 3 classes,12 orders,24 families and 35genus,a total of 54 species of nekton were captured by bottom trawl in autumn,belonging to 3 classes,11 orders,28 families and 43 genus,.The dominant species in spring are Harpodon nehereus and Portunus trituberculatus,and in autumn are H.nehereus,P.trituberculatus and Oratosquilla oratoria.In spring,the average biomass density of nekton at each station is 75.41 kg/km~2,and the average abundance density is 7481.40 ind./km~2;in autumn,the average biomass density of each station is 225.62 kg/km~2,and the average abundance density is 12992 ind./km~2.The nekton community was disturbed to a moderate extent in spring and autumn.The nekton community can be divided into three groups in spring and autumn.The main characteristic species between each group in spring are Engraulis japonicus,H.nehereus and Coilia nasus,etc,the main divergent species are Engraulis japonicus and H.nehereus,etc,in autumn,the main characteristic species among each group are H.nehereus and P.trituberculatus,etc,and the main divergent species are Miichthys niiuy,H.nehereus,Collichthys lucidus,etc.There is little difference between community characteristic species and divergent species,and the grouping of community may be caused by the different spatial distribution of these species.(2)A total of 66 species of nekton were caught in the spawning ground reserve of Wentai fishing ground and its adjacent waters in spring and autumn.The average numbers of Class(orders,families,genus,species),orders(families,genus,species),families(genus,species)and genus(species)owned by the constituent classes,orders,families and genus of nekton in spring are(4.00,8.00,11.67,14.00),(2.00,2.92,3.50),(1.45,1.75)and(1.20)respectively;The average numbers of(orders,families,genus,species),(families,genus,species),(genus,species)and(species)owned by the constituent classes,orders,families and genus of nekton in autumn are(3.67,9.33,14.33,18.00),(2.54,3.90,4.90),(1.54,1.93)and(1.25)respectively.The theoretical average value ofΔ~+is 80.53 in spring and 78.80 in autumn;The theoretical average value ofΛ~+is 664.56 in spring and 693.32 in autumn.Through GAM model,it is found that bottom temperature(BT),surface temperature(st),bottom salinity(BS)and surface salinity(SS)have significant effects onΔ,BS,ST and season have significant effects onΔ~*,and BT and ST are the key environmental factors affectingΔ+andΛ+respectively.(3)In spring,the average biomass density of H.nehereus at each station is 35.85kg/km~2,and the average abundance density is 4634.63ind./km~2,the average biomass density in autumn is 67.81kg/km~2,and the average abundance density is 3722.70 ind./km~2;The average biomass density of P.trituberculatus in spring is 10.67kg/km~2,and the average abundance density is 359.97ind./Km~2,the average biomass density in autumn is43.96kg/km~2,and the average abundance density is 1867.35ind./km~2。BT and BS significantly affected the spatial distribution of H.nehereus,while BT and water depth significantly affected the spatial distribution of P.trituberculatus.The average value of HSI of H.nehereus in spring is 0.37 and 0.50 in autumn.The average value of HSI of P.trituberculatus in spring is 0.36 and 0.47 in autumn.To sum up,the species number of nekton community in the conservation zone of spawning ground for Wen-tai fishing ground and nearby waters is less than that of historical research.The community is in a moderately disturbed state.The nekton community has the trend of resource decline and miniaturization.The occurrence frequency of special protected objects is low,and most of them are juveniles.It is suggested to extend the special protection period to the end of the“summer fishing moratorium”,and carry out proliferation and release of the specially protected objects,and track and evaluate their reimbursement.