水坝拆除对黑水河鱼类群落结构和空间分布的影响

水坝拆除引起河流连通性、水动力、河流地貌等一系列变化，直接影响了鱼类群落结构和空间分布。黑水河为金沙江左岸一级支流，其上共建四级电站，出于支流生境恢复需求，第四级水坝老木河水坝于2018年12月实行拆除。为探明低水头坝拆除对鱼类群落的影响，结合2018年6月和2019年6月黑水河下游60.4km河段10个点位的渔获物调查，对拆坝前后鱼类群落结构和生态类型变化、优势物种与单位捕捞努力量以及不同河段间的群落相似性进行了分析。结果表明，水坝拆除半年后优势物种仍以鲤科和鳅科为主，但物种数和丰度整体上增加；生态类型上以杂食、喜急流和产微粘性卵鱼为主；拆坝后鱼类群落空间分布变化明显，靠近河口的自然河段鱼类上溯洄游到原坝址的上下游，部分长江上游特有鱼类在原坝址附近发生定殖行为，且拆坝后各河段的鱼类组成结构有同质化趋势。总体上，老木河水坝的拆除对黑水河下游的鱼类群落结构和空间分布产生了积极的影响。

Effects of dam removal on fish community structure and spatial distribution in Heishui River

Dam removal causes a series of changes in river connectivity, hydrodynamics and river landforms, which directly affects the structure and spatial distribution of fish community. The Heishui River is a first-level tributary on the left bank of the Jinsha River with four power stations built on it totally. Due to the necessity of tributary habitat restoration, the fourth-level dam Laomuhe Dam was demolished in December 2019. In order to ascertain the effects of the low-head dam removal on the fish community, the changes in fish community structure and ecological type, dominant species and catch per unit effort and community similarity between different river sections were analyzed in combining with the fish survey at 10 points in the lower reaches of the 60.4 km Heishui River in June 2018 and June 2019. The results showed that the dominant species were still mainly Cyprinidae and Cobitidae after the dam was demolished six months ago, but the species and abundance increased overall. The ecological type was dominated by omnivorous, preferring to running water and spawning slightly viscous fish. The spatial distribution of fish community changes obviously after dam removal. Fish in natural river sections near the estuary migrated to the upstream and downstream of the original dam site. Some native fish in the upper reaches of the Yangtze River colonized near the original dam site, and the fish community structures in each section after dam removal tended to be homogeneous. In general, removing the Laomu River Dam has positive effect on the fish community structure and spatial distribution in the lower Heishui River.