| Surveys for resources of fish in early life stages during 2008 to 2010 and the annual characteristics of plankton communities in 2010 were carried out in the Jianli section in the middle reach of the Yangtze River. The main findings were as follows.1. A total of 54 of fish species belonging to 8 orders,15 families and 46 genera were identified. Cypriniformes, Perciformes Siluriformes, Cyprinodontiformes, Salmoniformes, Clupeiformes, Beloniformes and Mastacembeliformes, accounted for 66.7%,13.0%, 7.4%,3.7%,1.9%,1.9% andl.9% of the observed species were the dominant species from May to July in 2008-2010.2. A total of 17,974 eggs and 1,392,005 larvae and juveniles were collected between May and July in 2008,2009 and 2010. The monitoring data showed that small fish occupied the main advantage including Hemiculter(94.54%), Gobiidae (1.06%), Salangidae (0.67%), Gobioninae(0.48%) and Cobitidae(0.42%), but economic fishes were less proportion including the four famous Chinese carps(1.49%), Pelteobagrus(0.18%), Siniperca(0.12%), Cyprinus carpio Linnaeus and Carassius auratus Linnaeus (0.02%) and Silurus(<0.01%). Eggs, larvae and juveniles density variation of the four famous Chinese carps were 0.18 billion in 2008 (June 0.154 billion, JulyO.028 billion),0.04 billion in 2009 (June 0.032 billion, July 0.01 billion),0.18 billion in 2008 (May 0.004 billion, June 0.014 billion, July 0.41 billion).3. In 2010, we also evaluated spatial and temporal distribution patterns of eggs, larvae and juveniles were carried out at Jianli section in the middle reach of the Yangtze River from May to July. The results showed that the average density for eggs, larvae and juveniles were 13.3 ind./100m3 and 61.8 ind./100m3respectively. The density of eggs was higher in May, with a maximum observed density of 87.8 ind./100m3. Larvae and juveniles achieved a maximum density of 489.0 ind./100m3. There were significant difference in the distribution thalweg of eggs density vertically between surface and mid-depths and horizontally between the banks and middle area (P<0.05). Differences were found in the distribution at north bank and middle area (P<0.01), and there were no significant difference at south bank and north bank(P>0.05). No significant difference was found in the density of larvae and juveniles between surface and middle section in vertical distribution and at two banks and middle area (P>0.05). Our results indicated significant differences in density of eggs and larvae and juveniles between day and night (P<0.05), the density of eggs during the day was lower than that at night.4. Surveys on the phytoplankton communities were carried out at Yichang to Chenglingji section in the middle reach of the Yangtze River in January, April, July and October,2010. A total of 147 plankton species belonging to 8 phyla and 74 genus were identified. Bacillariphyta (40.1%), Chlorophyta (26.5%) and Cyanophyta (20.4%) were the dominant forms. As the seasons changed, the variation of phytoplankton was obvious. The quantity of species was greatest in autumn (110) and leastin spring (55). The mean density was 16.11×104cell/L, and the mean biomass was 2.26 mg/L. The biomass was greatest in summer(4.97mg/L), and lowest in autumn(0.44mg/L).The mean Shannon-Wiener diversity was 1.22, the mean Pielou diversity was 0.27, and the mean Margalef diversity was 1.54. The Shannon-Wiener diversity, Pielou diversity and Margalef diversity were highest in spring. Obtained by biological evaluation, the section fromYichang to Chenglingji in the middle reach of the Yangtze River wasβ-moderately polluted, and some sections were eutrophication of the water body in autumn.5. Surveys on the zooplankton communities were carried out at Yichang to Chenglingji section in the middle reach of the Yangtze River in 2010. A total of 81 zooplankton species were identified including Protozoa (18species,22.2%), Rotifera (32species, 39.5%), Cladocera (21 species,25.9%) and Copepoda (10species,12.3%). As the seasons changed, the variation of phytoplankton was obvious. Species richness was highest in autumn (49) and lowest in the winter (25). Spring had 31 species and summer had 29 species. Rotifera was the dominant species for all seasons with a mean density of 12.6 ind. /L. Biomass was highest in summer (23.30 ind./L), and lowest in spring(8.23 ind./L). The biomass of autumn and winter were 8.75 ind./L and 8.38 ind./L,... |
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