The spatio-temporal distribution of fish larvae and juveniles in the surf zone of the Yangtze River estuary

To explore the spatio-temporal distribution of fish larvae and juveniles in the surf zone of the Yangtze River estuary,samples were collected monthly on the spring tide at 13 stations during May 2006 to June 2007.The species number and individual amount were the highest in summer especially in July and August and the lowest in late fall and winter especially in March.The investigation results indicated there were significant differences among the months.The freshwater fish were mainly distributed in the south branch of the estuary and the upper reaches of the north branch,the marine fish and estuary fish were mainly in the coastal areas,and the diadromous fish apeared in the estuary seasonally.The research on the length change of these four dominant fishes revealed that the selection of the surf zone by fish larvae and juveniles differed according to various species.The diadromous fish Coilia nasus and the estuary fish Liza haematocheila apeared seasonally in the surf zone.In addition,they made use of the surf zone as their nursery and feeding ground.Neosalanx taihuensis,the fresh water fish,lived in the surf zone all the year round while the marine fish including the Megalops cyprinoides were carried by the spring tide to the surf zone and lived there ephemerally.