|Other Abstract||Baiji and Yangtze finless porpoise, two beautiful and cute mammals living in the middle and lower reaches of the Yangtze River, have been as human being’s neighbours for millions of years. In the past few decades, populations as well as habitats of these two animals have been decreasing and degrading significantly due to direct or indirect effect of human activities such as, water pollution, busy ship traffic, illegal fishing, hydro-project construction, sand dredging, and so on. During “Yangtze freshwater dolphin expedition 2006”, we failed to find any Baiji, and the population of the Yangtze finless porpoise in the main stream of Yangtze was estimated probably 1200 individuals. The drastic deterioration of the Yangtze ecological environment and the future of the cetaceans has become one of the hot topics in conservation community both at home and abroad.
Initial success of ex-situ conservation of Yangtze finless porpoise has been achieved, but we also encountered some difficulties. In order to enlarge conservation scale, and establish more ex-situ pupulations of the porpoise, we have been considering the Three Gorges Reservoir as potential ex-situ conservation site of the Yangtze finless porpoise, and have conducted initial feasibility study on the environment. The aim of this study is to evaluate if the environment of Three Gorges Reservoir is suitable for Yangtze finless porpoise’s living. The contents and results of this study are summarized as follows:
1) The overall water quality of the Three Gorges Reservoir was relatively good, and water quality of the main stream was better than that of the tributaries. All water temperature, flow velocity, transparency, pH value, and hardness met the survival demand of the Yangtze finless porpoise. Organic pollutants were at low levels. Total coliform counts were lower than the highest levels in artificial dolphin rearing pool, but were at Grade Ⅲ of the “Environmental quality standards for surface water”(GB 3838-2002). The concentrations of nitrogen and phosphor nutrients were relatively high, but would not harm the porpoises’ survival once they were introduced into the reservoir. The concentrations of heavy metals met Grade Ⅰof the “Environmental quality standards for surface water”, except for Hg and Pb, which were at high levels in both the reservoir and main streams of the Yangtze River from Yichang to Shanghai. The overall concentration of heavy metals in the reservoir was not apparently different from that in the middle and lower reaches of the Yangtze River.
2) Ship traffic intensity in the Three Gorges Reservoir was much lower than that in the middle and lower reaches of the Yangtze River, moreover, twisted shoreline and deepened water will help the finless porpoise avoid ships. Underwater noise level was below hearing threshold of the finless porpoise, if not take large ships into consideration. The status was even better in the tributaries, where there were almost no large vessels traveling and underwater noise level was far lower than that in the main stream. However, the "hydrofoil airship", which travels on main stream of the reservoir at a speed of 60 km/h and caused horrible underwater noise, would impose threat on the finless porpoise. Measures must be taken to overcome or mitigate the negative impacts.
3) Small-sized fishes and fish species used to living in low flow or still waters have been getting to be big populations in the reservoir after impounding, which would benefit the porpoise in food supply. Harmful fishing gears, which have been one of the reasons for porpoise’s death in the middle and lower reaches, were seldom found in the main stream of the reservoir. But, the nets deployed under the water and across the tributaries in numerous numbers would be threats to the Yangtze finless porpoise.
4) The selections of habitat of the Yangtze finless porpoise was influenced largely by food conditions. It’s hard to find habitats in the main stream of the reservoir that were similar with those in the middle and lower reaches of the Yangtze River, but some backwater areas in the tributaries seemed suitable for porpoise’s inhabiting
5) Based on the environmental conditions, the temporary rearing and releasing sites for the porpoises have been primarily selected; the safe transportation method and monitoring plan after releasing the animals were also designed.
In conclusion, the introduction of the Yangtze finless porpoise into the Three Gorges Reservoir would be a big potential and feasible measure to protect them from extinction in their nature habitats. However, fisheries as well as shipping activities in the reservoir must be regulated and controlled strictly. External pollution sources should also be kept away to ensure water quality of the Three Gorges Reservoir in good status.|