小型水坝梯级开发对永宁河流域鱼类多样性的影响

永宁河是长江上游右岸的一级支流,其干、支流上共建有20余座小型水坝。为探究梯级水电站对鱼类多样性的影响,在永宁河流域设置共42个采样点,覆盖干支流及各个水坝,分别于2018年7月、10月和2019年1月、4月进行了四次鱼类资源调查。调查期间通过刺网、地笼、电捕等方法共采集到鱼类69种7332尾,隶属于4目13科54属,其中有长江上游特有鱼类13种,列入《中国脊椎动物红色名录》濒危和易危鱼类3种,国家二级重点保护鱼类岩原鲤(Procypris rabaudi)1种。Pinkas相对重要性指数(IRI)值较大主要为宽鳍鱲(Zacco platypus)、鲫(Carassius auratus)乐山小鳔鮈(Microphysogobio kiatingensis)等小型鱼类,29种鱼类的IRI值小于10;平均全长＜10cm的鱼类有24种3620尾,平均体重＜50g的鱼类有47种6493尾,鱼类规格较小,小型化严重。永宁河干流下游种类最多,多样性最高,干流中游鱼类数量最多。受自然环境以及水坝等的影响,永宁河的鱼类分布具有明显的空间差异。水坝类型对鱼类多样性有显著影响;而季节对鱼类多样性影响不显著。无水坝阻隔河段鱼类多样性著高于低头坝和高头坝阻隔河段;夏季的短距离洄游鱼类种数显著高于冬季和春季,但由于数量较少对鱼类多样性的季节性变化影响不明显。各种结果表明水坝阻隔对永宁河鱼类多样性和时空分布存在明显影响,为保护受小型水电站影响河流的鱼类多样性,有必要修复重要鱼类栖息地,适当拆除部分小型水坝,并科学开展增殖放流。

Fish diversity in the Yongning River, a tributary with small cascade dams in the upper Yangtze River

The Yongning River is a tributary on right bank of the upper Yangtze River, and there are more than 20 small dams constructed along mainstream and tributaries of the river. In order to understand the effect of cascade dams on fish diversity, a total of 42 sampling sites were set up in the Yongning River basin, covering the mainstream and tributaries and dams. Four times of fish investigations were implemented in July and October 2018, January and April 2019. During the survey, 7332 fish of 69 species belonging to 4 orders, 13 families and 54 genera were collected by gill nets, ground cages and electronic fishing. Thirteen of which were endemic to the upper Yangtze River. Three fish speies were listed as endangered and vulnerable species in the Red List of China''s Vertebrates, and Procypris rabaudi was the second-class state protected wildlife in China. Fishes with higher index of relative importance(IRI) were small ones such as Zacco platypus, Carassius auratus and Microphysogobio kiatingensis, and there were 29 species with IRI<10. There were 3620 fish of 24 species with an average length of<10cm, and 6493 fish of 47 species with an average weight of<50g. The fish individuals collected were relatively small in size and in a trend of miniaturization. Species richness and diversity were the highest in downstream of the mainstream, and the most number of individuals were in midstream of the mainstream. Due to the influence of natural environment and dams, the fish distribution in the Yongning River represented obviously spatial difference. The type of dam had a significant impact on fish diversity, while season had no significant impact on fish diversity. Fish diversity in reaches without dam was significantly higher than that in the reaches with low-head dams and high-head dams. The number of short-distance migratory fish species in summer was significantly higher than that in winter and spring, but the seasonal change of fish diversity was not obvious due to the small population. To protect fish diversity in the river affected by small hydropower stations, it is necessary to restore crucial habitats, dismantle some small dams, and implement scientific artificial enhancement and release.