Fish diversity in the cascade of reservoirs along the Paranapanema River, southeast Brazil

ABSTRACT The Paranapanema River is a major tributary of the upper Paraná river basin. Eleven hydropower dams regulate its main course, but no study has investigated fish diversity in these impoundments at the basin-scale. The present study investigated spatial patterns of richness, composition, and abundance of native (non-migratory and migratory) and non-native fishes in the cascade of reservoirs along the Paranapanema River. The study is based on data collected from 34 independent studies conducted in nine reservoirs (47 samples). The compilation recorded 161 species, being 111 native (14 migratory) and 50 non-native. Total richness ranged between 56 and 112 species/reservoir, with a mean of 72 (49.9 non-migratory, 8.1 migratory and 14 non-native). The number of non-migratory species showed no spatial trend along the cascade system, but migratory and non-native richness increased toward downstream reaches. We also observed spatial variation in species composition along the cascade system, but some non-native fishes were widely distributed. Migratory fishes showed low relative abundance (usually < 10%), while non-native species were common and more abundant, especially in reservoirs downstream. Our results revealed a high diversity of fishes in the cascade of impoundments, but indicated that migratory fishes are rare, while non-native species are common or dominant.

摘要 巴拉那帕内马河（Paranapanema River）是巴拉那河（Paraná River）上游流域的主要支流。该干流由11座水力发电大坝调控，但目前尚无研究在流域尺度下探究这些拦蓄水库（impoundments）中的鱼类多样性。本研究针对巴拉那帕内马河沿岸的梯级水库（cascade of reservoirs），探究了土著（含定居性与洄游性类群）与外来鱼类的物种丰富度（species richness）、群落组成（species composition）及丰度（abundance）的空间分布格局。本研究的数据来源于针对9座水库开展的34项独立研究，共计47份采样样本。本次数据汇编共记录到161种鱼类，其中111种为土著鱼类（包含14种洄游性鱼类），50种为外来鱼类。单座水库的物种丰富度介于56至112种之间，平均丰富度为72种，其中定居性鱼类平均49.9种、洄游性鱼类平均8.1种、外来鱼类平均14种。定居性鱼类的物种丰富度沿梯级系统未呈现显著空间趋势，但洄游性与外来鱼类的丰富度则随河流向下游方向逐渐升高。研究同时发现，梯级系统内的鱼类群落组成存在空间异质性，但部分外来鱼类的分布范围较为广泛。洄游性鱼类的相对丰度（relative abundance）普遍较低（通常低于10%），而外来鱼类则较为常见且丰度更高，尤其在下游水库中更为突出。本研究结果表明，该梯级拦蓄水库的鱼类多样性较高，但同时也显示洄游性鱼类种群较为稀少，而外来鱼类则占据优势或成为群落优势类群。