The Temporal And Spatial Variation Of The Fish Recruitment Resource In Yangtze River Estuary

The integrative surveys were conducted in the Yangtze River Estuary (YRE) and its adjacent area from 1998 to 2010. Based on the survey data the ichthyoplankton species composition, community structures, spatial and temporal variations of diversities were analysed during spring and autumn, and the dynamic characteristics of the dominant species were discussed during spring in the YRE.Seven surveys were conducted in 1998, 2000, 2002, 2003, 2004, 2007 and 2009 during November, respectively, and ichthyoplankton was sampled from 40 stations. A total of 969 ichthyoplankton, representing 19 families and 33 species, were collected. Ichthyoplankton species was dominated by order Perciformes (7 families and 9 species). Ichthyoplankton species had three ecological types: brackish (12 species), coastal (10 species) and offshore (4 species) types. The dominant species had shown significant annual succession. Brackish species, Salanx prognathus and Chaeturichthys stigmatias, coastal species, Stolephorus commersonnii, and offshore species, Engraulis japonicus and Trichiurus lepturus, had the greatest contribution to the total ichthyoplankton abundance. Species richness, abundance and diversity of ichthyoplankton had shown a distinct increase since 2004. ANOSIM analysis indicated that the annual variations of ichthyoplankton stucture were significant in the YRE, and the dissimilarities of ichthyoplankton community structure were highest between the surveys before and after 2004 and other surveys. Ichthyoplankton species composition presented distinct annual variation in the YRE during autumn. Since 2004 ichthyoplankton structures had dedicated the greatest variance, ichthyoplankton diversity had shown increasing trend.Ichthyoplankton during autumn could be divided into three different assemblage in the YRE: 1) the estuary assemblage dominated by Chaeturichthys stigmatias; 2) the coastal assemblage dominated by Stolephorus commersonnii and Engraulis japonicus; 3) the nearshore assemblage dominated by Trichiurus lepturus. In the environment factors of the YRE, suspended matter and salinity were the main factors which had influenced the distributions of different assemblages , while chlorophyll a and sediment of the Yangtze River into the sea during rainy season were the factors which had drived annual variances of ichthyoplankton assemblage distributions.A total of 2281 ichthyoplankton were sampled in the two surveys in the YRE in 2009 and 2010, which represented 8 orders, 14 families and 19 species. There were three ecology types: coastal (8 species), semi-brackish (6 species), offshore (6 species ), and no fresh water species were catched. The predominant degree of Engraulis japonicus was greatly improved in 2010, but Coilia mystus and Trachidermis fasciatus which were dominat species before 2009, had lost their predominant status. The ichthyoplankton abundance during spring had gradually improved since 2009, and the abundance in 2009 and 2010 was much more than that in 2004-2007. There were great differences in the ichthyoplankton structures between 2009 and 2010, and the abundances of Engraulis japonicus and Larimichthys polyactisa had had maximum contribution dissimilarity..Spring dominant species, Engraulis japonicus, was mainly distributed in the east region to 122°20′E and its abundance had significant interannual variance. The distribution of Engraulis japonicus eggs was influented by surface chlorophyll-a content, and the distribution of the larvae was influented by temperature, salinity and dissolved oxygen of the surface water. The eggs and larvae of Coilia mystus occurred in the mouth of the YRE, and its abundance decreased. Salinity and dissolved oxygen were mainly factors which influenced the distribution of Coilia mystus. Trachidermis fasciatus and Hypoatherina valenciennei were located in the coastal area 122°—122°40′E,30°30′—31°30′N, and their abundance decreased since 2004. Significant correlation relationship was found between the distribution of Trachidermis fasciatus and total suspension matters. The distribution of Hypoatherina valenciennei significantly correlated to surface temperature, salinity and depth.