THE IMPACT OF THE ECOHYDROLOGIC CONDITIONS OF THREE GORGES RESERVOIR ON THE SPAWNING ACTIVITY OF FOUR MAJOR CHINESE CARPS IN THE MIDDLE OF YANGTZE RIVER, CHINA
Wenyan Guo, Yg Jin, Ruixiang Zhao, H.X. WANG
Abstract
Black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) are the four major Chinese carps and are migratory fishes living in rivers and lakes in the Yangtze River of China. The flow regime alternation of rivers has an impact on the spawning and reproduction conditions of four major Chinese carps in the lower reaches of the Three Gorges Reservoir. To investigate the changes in hydrological conditions and spawning and reproduction performances of four major Chinese carps during their spawning period before and after impoundment of Three Gorges Reservoir, a quantitative analysis of the relevance between such hydrological parameters as flow, water level, sediment concentration and water temperature of Yichang Station and larva runoff of the four species during their spawning period was carried out. As suggested by the results, when four major Chinese carps are spawning, the proper hydrological parameters would be 11,000-15,000 m 3 /s for flow, 43.0-46.0 m for water level, 0.01-0.21 kg/m 3 for sediment concentration and 4-8 d for water rise, and 22-24 for water temperature. Among those values, water rise and sediment concentration appear to be in significant positive correlation with the larvae abundance of four major Chinese carps, and thus remain critical factors. After the impoundment of Three Gorges Reservoir, the declining trend in flow, water level and water temperature during the spawning period of four major Chinese carps is not significant when compared with that in sediment concentration (by over 98%). The spawning and reproduction time of four species also gets retarded due to the late-coming proper water temperature, so does the spawning scale. The proportions of four carps also change a lot, with silver carp ascending to be at the highest ratio among them. This study can provide a reference for the protection of important fishes in the lower reaches of Three Gorges Reservoir.