Diurnal Variation Of Larval And Juvenile Fish Species Composition In Surf Zone Of Sandy Beach In Tian’ao, Si Jiao

In order to clarify the variation of larval and juvenile fish species compositionand the mobile mechanism in shallow water of surf zone. The sampling whichfocused on diurnal and tidal variation of larval and juvenile fish species number andCPUE were taken place in surf zone of sandy beach in Tian’ao. This work can behelpful in the research of the Ethology of early life history of the fish, and supplysome essential information for the operation of the fishery resources.This work was set up during the spring tide period from October2010toSeptember2011, using a seine net（1×4m,1mm mesh-aperture）. The sampling wastaken place every2hours from16:00to14:00the next day. Two seine hauls wasmade each time along the shore for about50m. The specimens were fixed in theformalin of5%concentration. The water temperature and salinity were measured andthe tidal circle (flood tide, slack tide and ebb tide）was identified at the sampling spot.A total of33species,22families,484individuals were collected which could bedivided into4ecological patterns (marine fish14; estuarine fish11; migration fish6;freshwater fish2). The most abundant species Liza haematocheila was29.5%of totalindividuals, followed with Stolephorus chinensis（17.1%）, Lateolabrax maculatus（12.2%）, Terapon jarbua（9.5%）Acentrogobius pflaumi（i4.1%）, Sardinella zunasi（3.5%）, Acanthogobius elongate(3.1%), Oplegnathus fasciatus（2.7%）, Mugilcephalus（2.5%）, Terapon theraps（2.0%）. These10species got86.2%of the totalabundance.The abundance of larval and juvenile fish from April to September wassignificantly higher than the rest months of the sampling period, which proved that theabundance of larval and juvenile fishes in the surf zone of sandy beach in Tian’ao wasmuch higher in spring and summer, and was very low in autumn and winter. Theflexional stage larval fishes were fund in Salanx acuticeps, Oryzias latipes, Lizahaematocheila, Lateolabrax maculates and Acanthogobius elongate. The total number of post-flexional stage, juvenile and young fishes was95.7%of the total individuals.And there is no pro-flexional stage fish collected in the sampling.During the year round sampling the CPUE（Catch Per Unit Effort）and speciesnumber in the daytime is significantly higher than that in the night (P<0.01). Thevariations of CPUE and species number during the24h were similar. The CPUE oflarval and juvenile fishes during6:00to8:00and14:00to18:00were higher than therest time of the day. The species numbers during6:00to8:00and12:00to18:00werehigher than that during20:00to4:00. These phenomenon proved that the larval andjuvenile fishes prefer live in the shallow water in the surf zone of sandy beach duringthe daytime, then they leave the shallow water to other place which is more suitablefor them to stay during the night.Generally, the species numbers of larval and juvenile fishes in the flood tide fromApril to September were highest, followed with the slack tide. And the speciesnumbers of larval and juvenile fishes in the ebb tide were the lowest compared withthat of flood tide and slack tide. The CPUE of larval and juvenile fishes in spring andsummer during the flood tide is highest, the slack tide second, the ebb tide lowest.Moreover, the CPUE of larval and juvenile fishes during the flood tide in the day timeis much higher than that during the flood tide in the night. The CPUE of Lizahaematocheila and Stolephorus chinensis in the day time were higher than that in thenight, and the CPUE during the flood tide were highest, the slack tide second, the ebbtide lowest. The CPUE of Lateolabrax maculates and Terapon jarbua during the slacktide is a little higher than that during the flood tide, the ebb tide was the lowest. Theseproved that there must be some selective tidal transport patterns（STST）of the larvaland juvenile fishes, and the STST are different from species to species.