Annual Changes Of Fish Larvae And Juveniles Resource In The North Of Hangzhou Bay

To clarify the annual changes of fish larvae and juvenile s resource, monthly collections were held by a larva net( 1.3 m mouth- diameter,0.5 mm mesh-aperture) in the north of Hangzhou Bay from June in 2014 to May in 2015. There are 10 sample stations in this study. Monthly collections were hold horizontally on s urface waters by a larvae net(1.3m mouth-diameter, 0.5mm mesh-aperture), fixed in a fishing-boat(trawling speed=2 sea mile/hour) for 10 minutes among 10 sampling.The survey results show that a total of 143,782 individuals of more than 60 species from 23 families were collected in 2013, the average density was 1.17 ind./m3; 96,118 individuals were caught from June 2014 to May 2015, belonging to 23 families and 55 species and the average density was 0.73 ind./m3. There are 46 common species in two year. The dominant species were Tridentiger barbatus, Collichthys lucidus and Coilia mystus in both two years. The most dominant species was Tridentiger barbatus, Development stage showed a similar tendency and pre- flexion larvae were dominant in 2 years.According to different ecological types of fish larvae in the north of Hangzhou Bay, the species catches were divided into estuarine fish(Es), marine fish(Ma), migratory fish(Mi) and freshwater fish(Fr) four categories. There were 24 kinds species of estuarine fish in 2013, accounting for 72.38%, and 25 species of marine fish ratio at 16.90% of the total catches, and 4 species of migratory fish, accounting for 10.55%, and 7 species of freshwater fish, accounting 0.16%. While from June 2014 to May 2015 estuarine fish appears 21 species accounting for 65.82% of the catch, marine fish 24 species accounted for 24.20%, 5 kinds of migratory fish accounting for 9.80%, and 6 kinds of freshwater fish accounting for 0.18%. The analysis of density was significantly difference(P<0.05) between stations and no significant difference(P> 0.05) among months.Result of the Person Correlation analysis showed that species number had significant correlation with water temperature, however there was no significant correlation between denity with water temperature in two years. Species number and denisity had no significant correlation with salinity in 2013; In 2014 to 2015, density had no significant correlation with salinity; there was significant correlation between species number and salinityThe dominant species were Tridentiger barbatus,Collichthys lucidus,and Coilia mystus in both two years.The dominant body length group of Tridentiger barbatus arranged from 4.00 to 4.50 mm in 2013 and from 3.50 to 4.00 mm in 2014 to 2015; The dominant body length group of Collichthys lucidus arranged from 5.00 to 7.500 mm in 2013 and from 2.50 to 5.00 mm in 2014 to 2015; and the dominant body length group of Coilia mystus arranged from 10.00 to 15.00 mm in 2013 and from 5.00 to 10.00 mm in 2014-2015.The number of Margalef richness index(D) demonstrated distinct seasonal variations:they were higher in summer and lower in winter.The results of Margalef richness index(D), Shannon-Wiener diversity index(H’)and Pielou evenness index(J’) in summer 0f 2014 were higher than in 2013.Based on the density of clustering analysis and MDS analyses were conducted by months and stations. 10 sampling stations could be divided into 3 groups: St.6.St.8 and other group in 2013;10 sampling stations could be divided into4 groups: St.7.St.8, these two stations made one group respectively; St.9 and St.10 came to one group; the other groups were in one group.12 sampling months could be divided into 4 groups: March made one group respectively; April and May were in one group; it was a big group from June to October, and November met December in one group in 2013; In 2014 to 2015,12 sampling months could be divided into 5 groups: March made one group respectively; April and May were in one group; June and July came to one group;August and September came to one group;January,from October to November were divided in one group.