Study On Temporal And Spatial Variation Of Fish Larvae And Juvenile Assemblages In The North Of Hangzhou Bay

To clarify the characteristics of the community of fish larvae andjuveniles in the north of Hangzhou Bay, species composition,spatial-temporal distribution and diversity index were analyzed, as well asrelevant environmental factors. Monthly collections were hold horizontallyon surface waters by a larvae net (1.3m mouth-diameter,0.5mmmesh-aperture), which fastened by a flowmeter on the mouth, fixed in afishing-boat (trawling speed=2sea mile/hour) for10minutes among10sampling stations each during January to December2013. Specimen wasfixed in5％formalin seawater solution, and water temperature and salinitywas measured at the same time.A total of81eggs belonging to6species from4families and a total of143,782individuals of more than69species from23families werecollected. The number of estuarine species and marine species was34and24respectively, bigger than that of diadromous species (4species) andfresh water species (7species). Collichthys lucidus is in the majorityamong eggs. The most dominant species of larvae and juveniles was Tridentiger barbatus, accounting for62.88%of this total abundance,followed by Collichthys lucidus for13.02%, Coilia mystus for9.22%,Acanthogobius flavimanus for2.56%and Acanthogobius ommaturus for2.32%. The most dominant species in March was Platycephalus indicus,Acanthogobius ommaturus for April and May, Tridentiger barbatus forJune, Coilia mystus for July and August, Stolephorus chinensis forSeptember and October and Salanx ariakensis for November and December.Tridentiger barbatus contributed a large cumulative frequency percentageof the sampling stations for more than40%each except for St.6, and St.2was the most for92.22%.Fish larvae in preflexion stage accounted for89.12%of totalabundance and were most in June, followed by fish larvae in postflexionstage (4.21%), fish juveniles (2.61%), fish larvae in flexion stage (2.57%),fish larvae in yolk-sac stage (1.43%) and egg (0.06%). Tridentiger barbatus,Coilia mystus, Collichthys lucidus, Larimichthys polyactis used offshorewaters as important nursery area. Moreover, Acanthogobius ommaturus,Platycephalus indicus, Stolephorus chinensis, Larimichthys crocea andEupleurogrammus muticus occurred in specific body length, whileSyngnathus acus, Harpadon nehereus and Salanx ariakensis used offshorewaters as feeding ground.The community of fish larvae and juveniles presented distinct seasonal variation. The individual number of fish larvae and juveniles in summerand spring was significantly higher than that in autumn and winter. Thespecies number was most in summer by48, followed by autumn (23),spring (17) and winter (5). The density in June had a sharp increase(13.50ind./m3) and species numbers in July (species number=18) were mostof all months. Result of the Person Correlation analysis showed that therewas no significant correlation between density and water temperature,together with salinity (p>0.05). Species number had significant positivecorrelation with water temperature (p<0.01). However, there was nocorrelation between species number and salinity (p>0.05).Based on the individual number of main species clustering analysisand MDS analysis were conducted by months and stations.10samplingstations could be divided into4groups: The individuals of main dominantspecies were close between St.2and St.5, so they came to one group; St.6and St.8possessed much more abundance of Collichthys lucidus andTridentiger barbatus than other stations separately, making these twostations one group respectively; St.1, St.3, St.4, St.7, St.9and St.10ownedsimilar species composition and individuals, making them one group.12sampling months could be divided into5groups: January and Februarycame to one group; March, April and May were in one group; June madeone group alone; it was a big group from July to October, and November met December in one group.There was a similar trend between the α-diversity index H’and J’,while the α-diversity index D changed sharply between months. Themaximum of H’and J’was the highest in St.4, but one of D was in St.10.According to the β-diversity analysis, βwsof St.10located in peak positionoverall showing that there were significant difference between St.10andthe others.The offshore waters in the north of Hangzhou Bay provided importanthabitat for fish larvae and juveniles, especially for marine and estuary fish.There were many kinds of important commercial fishes in the north ofHangzhou Bay, such as Mugil cephalus, Liza haematocheila, Lateolabraxmaculatus, Larimichthys crocea, Larimichthys polyactis, Trichiurusjaponicus and Eupleurogrammus muticus. In order to ensure the sustainableutilization of the fishery resources, it was necessary to lay great emphasison the protection of fish habitat and environmental management when thefish resources were overdeveloped.