Impact of Cascade Hydropower Station Operation at Lower Jinsha River on Fish Producing Pelagic Eggs with Emphasis to Their Mitigation Countermeasures

摘要

In present paper spawning seasons, water temperatures and incubation durations of 20 economically important fish species producing pelagic and slightly adhesive eggs were presented. The analysis of alternation of hydrological regime and water temperature after power station operation and their impacts on fish spawning and embryonic development showed that after operation of dams the natural 5-6 flow pulses during April to July would disappear, and spawning grounds of fishes producing pelagic eggs would be destroyed in this river section; the temperature of discharged water will be 1. 72^C lower than that of natural water in March, and 2. 7TC lower in April. As for the joint operation of the four cascade dams, the magnitude of changes of water temperature below Xiluodu dam is supposed to increase further due to cumulative effects. The spawning season will be postponed due to lower water temperature, and late spawning season shortens growth period of fingerlings that decreases nourishment accumulation, so survival rates of wintering fingerling will be seriously influenced. For mitigating these impacts three countermeasures were presented; Discharging reservoir water early to change discharged water temperature as higher as natural water, the dam operation should mimic the natural characteristics of water temperature features to the utmost extent as to reduce and avoid the impact of cold water on fish breeding; in order to create new spawning grounds in river section below Xiluodu dam operators of four cascade power stations should mimic 4-5 artificial flow pulses based on understanding historical records; promoting whole catchments of Chishui River being brought into NNRASF protected area, and turning this protected as a refuge of important fishes of upper stream of the Changjiang River.