长江中游鳜早期个体发生、摄食、生长与存活的时空格局——三峡大坝的影响与恢复过程

Dam operation modified the river flow regime, and hypolimnetic discharge of cold water from reservoir can lower water temperatures in downstream. Retention of sediments in the reservoir can induce a lowered nutrient state, and consequently lower primary productivity of downstream waters. Operation of dam influence the life history of fish, inducing the decline of fish abundance downstream. The impacts of river regulation on downstream river environment can be buffered with increased distance from the dam and the joining of tributaries, thus forming environmental gradients downstream from the dam. There are several major tributaries joining the middle reach of the Yangtze River, e.g., Dongting Lake watershed, the Hanjiang River, and the Poyang Lake watershed. With the addition of these major tributaries, environmental gradients likely form in the middle Yangtze River downstream from the dam. We hypothesized that temporal and spatial patterns of early life history resource of fish in the middle reach of the Yangtze River below the Three Gorge Dam (TGD) display patterns corresponding to these environmental gradients. In the present project, we test the above hypotheses by comparing characteristics in the early life history of fish among different sections downstream the dam in the middle reach of the Yangtze River. We select mandarin fish (Siniperca Chuatsi) as a model species, which is anti-potadromous species. In the project, temporal and spatial patterns in occurrence, feeding, growth and survival of early individual of mandarin fish will be investigated, and the relationship between larval patterns and environmental gradients will be established, influence of dam discharge on recruitment process during early life stage will be revealed. On the other hand, basing on the serial discontinuity concept (SDC), the recovery patterns of recruitment processes of the early life history stage downstream of the TGD will be obtained. The results will also provide valuable information for fishery resource conservation and management.

大坝运行改变坝下水文流态，低温水下泄导致坝下江段水温降低，水库悬浮物沉降和清水下泄使坝下江段水体生产力降低。大坝运行影响坝下鱼类生活史过程，导致坝下江段鱼类资源数量下降。坝下江段受到的影响会随着支流的加入而缓解，形成相应的环境梯度。三峡坝下长江中游江段依次有洞庭湖、汉江和鄱阳湖等主要的支流注入，中游的环境会随着离大坝距离的增加而形成环境梯度。我们假设鱼类早期资源的时空动态在长江中游会呈现与环境梯度相关联的格局。本项目通过比较不同江段早期个体的种群特征验证以上假说。本项目选取非洄游性鱼类鳜为研究对象，一方面研究长江中游鳜仔鱼发生、摄食、生长和存活的空间格局，建立与环境梯度的关系，确定影响三峡坝下鱼类种群补充的关键因素，揭示大坝运行对鱼类资源的影响机制。另一方面基于“河流非连续体理论”了解鱼类补充过程对环境梯度的响应及仔鱼的恢复过程，为长江中下游开展鱼类资源的管理和保护政策提供指导。

大坝运行后显著地改变了坝下江段的环境，将会影响鱼类的早期生活史过程，导致鱼类资源衰退。坝下江段受到的影响将随着距离的增加和支流的加入而减缓，形成相应的环境梯度。本项目提出坝下江段鱼类早期资源的时空格局将与环境梯度相耦合的假设。本项目通过比较不同江段鱼类早期生活史特征验证以上假说。项目以非洄游性鱼类鳜为研究对象，研究三峡坝下江段早期个体的发生、生长、摄食和存活及与环境因子的关系，研究结果揭示了三峡大坝对坝下鱼类资源的影响机制和恢复过程，对鱼类资源的保护和管理提供重要的依据。.鳜仔鱼的丰度、摄食、生长和死亡格局在长江中游监利、洪湖和武穴江段呈现明显的差异。在监利江段，鳜仔鱼的丰度最低，仔鱼高峰出现时间最晚，空胃率最高，生长最慢以及存活率最低。而在武穴江段呈相反的趋势，仔鱼的丰度最高，仔鱼高峰出现时间最早且持续时间长，空胃率最低，生长最快和存活率最高。三个江段环境因子（水温、透明度和流量）随着离三峡大坝距离的增加形成梯度格局，监利江段低水温和高透明度反映了坝下流量的影响；而洪湖江段相对升高的水温和低透明度，以及武穴江段最高的水温反映出支流的加入和距离增加缓解了大坝的影响。研究结果表明三峡大坝运行改变的环境梯度是决定长江中游鳜仔鱼发生、摄食、生长和存活空间格局的关键，离大坝距离越远江段越有利于早期阶段的补充。鳜早期补充过程（分布、摄食、生长和死亡）的空间格局与坝下不同江段的环境梯度相耦合，揭示了三峡大坝对坝下江段鱼类产生的影响差异以及仔鱼的恢复过程。

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