Ecological distribution of fish larvae and juveniles in the Yangtze River estuary and its adjacent waters in spring

We investigated the distribution, abundance and species composition of fish larvae and juveniles in the Yangtze River estuary and its adjacent waters based on the data obtained from integrated multi-disciplinary survey in mid-May of 2008. The results show that spring witnessed high species richness and occurrence frequency of fish larvae and juveniles. A southward increasing trend in the species richness and an opposing trend in the number of dominant species were detected. The spatial trend in species richness was accord with the surface temperature, and the catch per unit effort (CPUE) and surface salinity showed a similar spatial trend. The high-density zone of fish larvae and juveniles was characterized by a narrow temperature range of about 2.5 ℃ and a wide salinity range of about 7. The spatial distribution was different among dominant species. Larimichthys polyactis and Chaeturichthys hexanema were mainly distributed in the Yangtze River estuary and Lusi Fishing Ground, while Engraulis japonicas was mainly inhabited off the Zhoushan Inlands. The high-density zones of fish larvae and juveniles were located in the confluence zone of cold and warm currents,which were the most productive areas in the coastline of the East China Sea. The abundant prey items were expected to satisfy the nutrient requirements for the early development of the ichthyoplankton in the survey area.