Impacts on fisheries assessed by local ecological knowledge in a reservoir cascade in the lower São Francisco River, northeastern Brazil

Abstract Our study assessed the fishers’ perception (local ecological knowledge, LEK) concerning environmental impacts on fisheries and fish species in the final portion of Sub-Middle and Lower São Francisco. The river was divided into four areas where 107 fishers from 22 locations (4 states) were surveyed. The dam was the most significant impact on fisheries. The loss of connectivity, changing the environmental complexity, and its secondary effects (e.g., flow control, interruption of migratory routes) were determining factors. Other impacts were pointed out, such as pollution, macrophytes, overfishing, non-native species, and aquaculture. Among migratory species, Pseudoplatystoma corruscans and Salminus franciscanus have been absent from fishery catches for decades. Prochilodus argenteus records in fisheries are likely associated with migration routes to small tributaries. The environmental disturbance favored the establishment of non-native species such as Oreochromis niloticus, Cichla monoculus, and Metynnis lippincottianus along the studied section. Over the final portion of the São Francisco River, the more significant seawater intrusion changed the target species for fisheries activities. Thus, our data validate the importance of fishers’ LEK and reinforce the adverse effects of the reservoir cascade on fishing and migratory fishes.

摘要 本研究评估了圣弗朗西斯科河亚中游及下游末端河段渔民对环境影响水产捕捞及鱼类物种的认知（地方生态知识，Local Ecological Knowledge，LEK）。本研究将该河段划分为四个区域，对来自4个州22个地点的107名渔民开展了问卷调查。水坝是对水产捕捞影响最为显著的干扰因素，连通性丧失、环境复杂度改变及其次生效应（如水流调控、洄游通道阻断）为关键影响因子。此外，研究还指出了其他潜在影响，包括污染、大型水生植物滋生、过度捕捞、外来物种入侵及水产养殖活动。在洄游性鱼类类群中，Pseudoplatystoma corruscans与Salminus franciscanus已有数十年未出现在渔获物中；渔获记录中的Prochilodus argenteus，其出现大概率与小型支流的洄游通道相关。该河段的环境扰动助力了Oreochromis niloticus、Cichla monoculus及Metynnis lippincottianus等外来物种的定殖。在圣弗朗西斯科河末端河段，更为严重的海水入侵改变了捕捞作业的目标物种。综上，本研究数据证实了渔民地方生态知识的重要价值，并进一步佐证了梯级水库群对捕捞业及洄游性鱼类的负面影响。