Impact Of Three Gorges Project On The Population Dynamics Of Chinese Sturgeon (Acipenser Sinensis) In The Yangtze River

Chinese sturgeon(Acipenser sinensis),a wild animal with first-class protection in China,is receiving more and more attention recently.In 2003,the Three Gorges Project,the world's largest hydropower station,was built and put into operation,which changed the water temperature and hydrological regimes of the spawning ground and posed a profound impact on the population of Chinese sturgeon.Although researches on Chinese sturgeon have been widely carried out in China since 1980s,there is still a lack of systematic and long-term studies on the effect of Three Gorges Project on the survival and reproduction of Chinese sturgeon.In order to find out the reasons for the decline of Chinese sturgeon population resources,this study analyzed the dominant factors of Chinese sturgeon population decline and the response of Chinese sturgeon population to the changes of habitat,combined with the time variation of Chinese sturgeon population dynamics.The influence of Three Gorges Project on the habitat suitability change and the reproduction of Chinese sturgeon were also studied based on two-dimensional hydrodynamics model.The population dynamics of Chinese sturgeon under the environment change was also predicted using vortex and population matrix model.The results of this study could provide theoretical basis and scientific support for further protecting the population resources of Chinese sturgeon.The main results were as follows:(1)The study on population variation of Chinese sturgeon shows that the influence of human activities on population was increasing year by year.However,under the influence of intensified human activities,the population resources of Chinese sturgeon further decreased which decreased to less than 50 from 2011 and still decreased year by year.According to the 50/500 theory,the population will not survive for a long time.(2)The study on habitat of Chinese sturgeon shows that the dam operation needs a water flow of at least 10000 m3/s to provide a suitable spawning environment for Chinese sturgeon,and when it reached 17000 m3/s,it could provide the best spawning site conditions for Chinese sturgeon.The impoundment of the Three Gorges Project resulted in a significant decrease in the flow of Chinese sturgeon spawning grounds during the breeding season,resulting in a continuous decrease in the habitat suitability area of Chinese sturgeon and restricting the natural breeding scale of Chinese sturgeon.The change of habitat suitability was the main factor affecting the reproduction of Chinese sturgeon after 2002.Therefore,restoring the habitat suitability of Chinese sturgeon population through ecological regulation will be an important method to promote the restoration of Chinese sturgeon population.(3)The study on the population viability of Chinese sturgeon shows that,with the increasing proportion of female and the ratio of male to female,the growth rate of population has increased after 2010.Therefore,the gender bias of the ratio of male to female might be the survival strategy for Chinese sturgeon population to cope with the environmental change.The most important factor affecting the population growth rate is the proportion of females participating in reproductive activities,followed by fishing,and finally the ratio of males to females.Therefore,the most feasible way to promote the natural recovery of Chinese sturgeon population will be to provide the suitable spawning ground environment through ecological regulation,reaching the maximum number of females to participate in breeding activities.(4)The study on the population transient dynamics of Chinese sturgeon shows that the population dynamics of Chinese sturgeon fluctuates in a certain period after being disturbed,and finally returns to a stable level.In terms of population transient dynamics,the superimposed uncertainties prolonged the time for the population to return to a stable level,and the increasing human activities after 2003 led to the increase of the population fluctuation of Chinese sturgeon.Therefore,the main reason for the further decline of the population dynamics of Chinese sturgeon is the flow change of spawning ground during the breeding period caused by the impoundment of the Three Gorges Project.The interference analysis also showed that increasing number of female sturgeon individuals aged 20-30 or promoting the growth of female sturgeon individuals at this stage was the most effective way to promote the recovery of Chinese sturgeon,while increasing the female sturgeon individuals aged 1-5 would further promote the population decline.In brief,the operation of the Three Gorges Project makes the suitability of the spawning ground of Chinese sturgeon decline,affecting the breeding activities of Chinese sturgeon.The influence of the Three Gorges Project,combined with other human activities and the influence of Gezhouba Dam,prolonged the time for the Chinese sturgeon population to return to a stable state,and increased the decline of population dynamics,which was the main factor for the further decline of the Chinese sturgeon population in recent years.Therefore,the most effective and feasible way to maintain the survival of Chinese sturgeon population will be to eliminate the impact of Three Gorges Project operation through ecological regulation.