STUDIES ON THE ECOLOGICAL EFFECT ON SPAWNING OF THE BLACK CARP, THE GRASS CARP, THE SILVER CARP AND THE BIGHEAD CARP IN THE CHANGJIANG RIVER AFTER THE CONSTRUCTIONSOF THE GEZHOUBA HYDROELECTRIC PROJECT

In order to assess the ecological effect on the spawning of the four Chinese farm fishes——Mylopharyngodon piceus (black carp), Ctenopharyngodon idellus, (grass carp), Hypophthalmichthys molitrix (silver carp) and Aristichthys nobilis (bighead carp)——owing to the construction of the Gezhouba Dam, an investigation was made from 1981 to 1984. The results are summarized as follows:1. After the damming of the river, the natural environment and spawning condition of most spawning grounds can still meet the needs of the spawning of the four farm fishes except those at the upstream section, from Sandoupin to Nanjinguan of the Yichang spawning ground. 2. With the exception of three newly-discovered spawning grounds along the Jinsha River and part of the original Yichang spawning ground having been displaced upwards, the distribution of the spawning grounds remains generally the same as that recorded two decades ago.3. The total number of eggs laid annually by the four farm fishes in the upper reaches of the river is estimated to be 11-31 hundred millions in recent years, being less than 10% of that in the 1960s.4. Around the original Yichang spawning ground, the proportion of the spawners in the reaches above the dam was found to have been diminishing while the proportion below the dam has been increasing year by year.5. The composition of eggs and fry of these fishes in the upper and lower courses of the Gezhouba Dam varies to a relatively large extent. At the section of Gulaobei below the dam, eggs of grass carp, black carp and silver carp are predominant. Fry are chiefly grass carp, and contrary to the case of black carp, silver carp and bighead carp, they increased from year to year. Along the Wuling section above the darn, both eggs and fry were chiefly of the grass carp, neither silver carp nor bighead carp was found spawning there. In the Baixi section of the Jinsha River, eggs of grass carp were found, but fry have not been observed yet.6. During the breeding season, the spawners constituted about 70% of the shoal of the farm fishes in the mainstream of Changjiang. At the Gulaobei section, the spawners of the grass carp constituted 44.05%, those of the black carp, silver carp, and bighead carp constituted 26.19%, 17.86% and 11.9%, respectively. In the Wuling area, spawners were chiefly the grass carp, comprising 93.74% of the shoal. In general, the proportion of the spawners of the silver carp and bighead carp are declining, but that of the grass carp and black carp are relatively stable as compared with the data obtained in the 1960s.From the afore-mentioned results, we believe that the effect of the Gezhouba Dam on the spawning of the farm fishes is not so serious as it was once supposed. The presence of local populations of grass carp at the upper reaches above the dam shows that it is unnecessary to build a fish path at the site of the dam.In view of the fact that the fish resource in the Changjiang River has been diminishing extensively, it is essential to take intensive measures for the protection of the natural spawning populations of the four farm fishes in this river.