金沙江梯级大坝运行和三峡水库运行水位增高对长江上游干流寡鳞飘鱼仔鱼丰度和分布的影响

2009年、2012年和2015年在长江上游干流宜宾江段、朱杨江段和木洞江段采集鱼类早期资源, 确定寡鳞飘鱼(Pseudolaubuca engraulis (Nichols))仔鱼的发生动态和丰度。金沙江梯级大坝运行前的2009年和2012年, 寡鳞飘鱼仔鱼出现高峰开始于5月中旬; 运行后的2015年, 6月下旬之前很少有仔鱼出现, 高峰开始于7月中旬。梯级大坝低温清水下泄是导致坝下江段寡鳞飘鱼仔鱼发生高峰期推迟的主要原因。与2009年和2012年相比, 2015年寡鳞飘鱼仔鱼丰度在宜宾江段有明显的增加, 在朱杨江段略有增加; 这表明寡鳞飘鱼种群能够适应大坝运行导致的生境条件的变化。木洞江段2009年至2015年间寡鳞飘鱼仔鱼丰度持续显著升高, 可能与该江段位于三峡水库变动回水区相关; 调查期间三峡水库运行水位由156 m增至175 m, 变动回水区缓流生境为寡鳞飘鱼仔鱼等提供了优良的育幼环境。基于研究结果, 我们认为寡鳞飘鱼仔鱼丰度和分布的时空差异是上游梯级大坝和下游三峡水库运行共同作用的结果, 反映出广适应性鱼类对建坝水域环境变化的更高的适应能力; 同时, 我们提出水库上游河流与水库库尾(甚至整个水库)形成的 “河-库”复合生态系统可能具有与“河流-泛滥平原”复合生态系统相似的结构和功能, 对产漂流性卵鱼类的种群补充具有十分重要的价值。

EFFECT OF THE IMPOUNDMENT OF DAM CASCADE IN JINSHA RIVER AND INCREASED WATER LEVEL OF THE THREE GORGES RESERVOIR ON THE DISTRIBUTION AND ABUNDANCE OF PSEUDOLAUBUCA ENGRAULIS (NICHOLS) LARVAE IN THE UPPER MAINSTEM OF THE YANGTZE RIVER

Ichthyoplankton were collected in the upper mainstem of the Yangtze River at Yibin, Zhuyang and Mudong in 2009, 2012 and 2015 to determine the occurrence dynamic and abundance of Pseudolaubuca engraulis (Nichols) larvae. The abundance of P. engraulis larval peaked from mid-May in 2009 and 2012 (pre-impoundment of dam cascade in the Jinsha River), while few larvae occurred before late-June and the abundance peaked from mid-July in 2015 (post-impoundment of the dam cascade). Hypolimnetic and clean water discharge from the dam cascade are critical factors on delaying spawning seasons and peak occurrence of the larval fish. The abundance of P. engraulis larvae showed an apparent increase at Yibin and a slight increase at Zhuyang in 2015 comparing to that in 2012 and 2013, indicating that the fish may adapt to the altered habitat environments by the dam cascade. Abundance of P. engraulis larvae at Mudong showed a significant increase during 2009 to 2015. The increase of the fish is probably related to the increasing operational water level (from 156 m to 175 m) of the Three Gorges Reservoir (TGR), which created slow flow habitats at Mudong section and then offered a favorable nursery for the larvae. Based on the results of this study, it is suggested that the temporal-spatial variation of P. engraulis larvae was jointly controlled by the upstream dam cascade and downstream TGR. Meanwhile, we suggest that the " River-Reservoir” ecosystem, constrained by the tail of reservoir (even all the reservoir) and its upstream river section, may have similar functions as the river-floodplain ecosystem in natural systems, and is valuable to the successful recruitment of fishes which produce drifting-egg.