| Based on the survey data of fish resources and environment factors in the near-shore of Yangtze estuary in 2014, the community structure of fish and spatial and temporal distribution of juvenile fish were analyzed using multi-statistical analysis such as cluster, non-matric Multi-Dimensional Ccaling(n MDS), Principle Correspondence Analysis(PCA). Besides, the influences of environment factors on spatial and temporal distribution of fish community were explored by Canonical Correspondence Analysis(CCA). Furthermore, resource status and utilization of Collichthys lucidus in coastal waters of Yangtze estuary was assessed using Length-based Cohort Analysis(LCA) and Beverton-Holt dynamic model. 1. The temporal and spatial pattern of fish assemblage in the near-shore of YangtzeestuaryTo study the composition and temporal and spatial pattern of fish assemblage in the near-shore of Yangtze estuary, a beam trawl investigation was conducted at 14 stations in February(Winter), May(Spring), August(Summer) and November(Autumn), 2014. Results showed that a total of 29 species belonging to 7 orders and 11 families were collected, among which Perciformes was the order with the highest number. Fish community was classified into 4 ecological guilds including fresh water fish, migratory fish, estuary settled fish and coastal water fish. Estuary settled and coastal water fish had the highest diversity and the latter had the highest abundance. Peltebagrus nitidus, Cynoglossus joyneri, Collichthys lucidus, and Miichthys miiuy were dominant species. The biomass and abundance changed significantly in different seasons along with the occurrence of the maximal biomass and abundance in summer. The results of cluster analysis showed that 14 stations could be divided into 2 groups affected by the distribution of salinity. The discrepancy existing in the seasonal and spatial distribution of fish community were mainly caused by several species including Cynoglossus joyneri, Peltebagrus nitidus, Collichthys lucidus, and Miichthys miiuy. Due to the large percentage of juveniles in above species, it could be speculated that juvenile fish constitute a reasonable amount of fish community. 2. The temporal and spatial variation of juvenile fish in nearshore area of Yangtze estuaryTo investigate the temporal and spatial variation of juvenile fish in nearshore area of Yangtze estuary, a beam trawl survey was conducted at 14 stations in February(Winter), May(Spring), August(Summer) and November(Autumn) 2014. Results showed that 24 species belonging to 7 orders and 10 families were caught, of which Perciformes got the highest abundance and its number of species was also the most. The dominant species were Peltebagrus nitidus, Miichthys miiuy and Coilia nasus. The percentage of number and weight of juvenile fish were 88.85% and 53.41%, separately. Compared with adult fish, the juveniles were dominant in different stations and seasons. Furthermore, there were significant differences in temporal and spatial distribution of juvenile fish. Demonstrated by results of CCA, it can be attributed to the influence of environmental factors on dominant species of different ecological guilds. For this reason, it can be speculated that the varied needs of environmental factors for different life stages of juvenile fish of different ecological guilds lead to the diversity in temporal and spatial distribution of juvenile fish. 3. Preliminary assessment of resource situation of Collichthys lucidus in coastal waters of the Yangtze estuaryIn order to assess the resource status of Collichthys lucidus in coastal waters of Yangtze estuary, growth and population parameters were studied based on the length frequency distribution method and the bottom trawl investigation data from 2012 to 2013. Von Bertalanffy growth parameters were calculated by using the ELEFAN module in Fi SAT Ⅱ software while the natural mortality rate(M) was estimated via Pauly’s empirical equation. Besides, the Beverton-Holt dynamic model was developed to predict the variation trend of C.lucidus resource in coastal waters of Yangtze estuary. The results showed that in 2012~2013, a total of 4201 samples of C.lucidus with body length ranging from 18 to 155 mm were collected from the coastal waters of Yangtze Estuary. The growth parameter(K) and limit length(L∞) were 1.1 and 162.75 mm while the total mortality rate(Z), the natural mortality rate(M) and the fishing mortality rate(F) were 4.040, 1.683 and 2.357, respectively. Moreover, the current exploitation(E) of C.lucidus in coastal waters of Yangtze estuary was 0.583 per year, which was larger than Fopt(0.5). Corresponding to the average stock of 576.02 t, the resource amount of C.lucidus reached up to 1.33*108 individuals. These indicated that C.lucidus has been overfished in Yangtze estuary area. |
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