Balancing renewable energy and river conservation: effects of hydropeaking from small hydroelectric power plants on fish stranding in small Brazilian rivers

Small hydroelectric power plants (SHPPs) are often promoted as clean and renewable energy sources. However, SHPPs are often characterized by hydropeaking, which is a practice involving the sudden release of water from turbines. Hydropeaking may have multiple detrimental effects on downstream ecosystems, among which is fish stranding. This phenomenon involves trapping fish in isolated pools or dry riverbeds, which detrimental effects on fish populations and assemblages are often poorly quantified. Here, we investigated the implications that hydropeaking may have on fish populations in small Brazilian rivers. Specifically, we recorded fish stranding events (including the number of individual fish stranded) while monitoring the practice of hydropeaking by SHPPs in two watersheds. By combining observational and modeling approaches, we examined the relationships between fish stranding events and the operation of six SHPPs along a 5 km downstream stretch. For this analysis, we focused primarily on fish families which were dominant in the rivers. Our results indicate an exponential increase in fish stranding due to hydropeaking, which significantly affects fish populations as we move away from the SHPPs axes and towards downstream sections. The principal affected fish families were Characidae (23.7% of stranding), Heptaperidae (23.2%), Loricariidae (19.8%), and Pimelodidae (11.1%). In the monitored watersheds, our models predicts that if even one fish stranding event occurs annually, it could results in the stranding of nearly 500,000 individuals. This, in turn, could have severe adverse effects on the ability of these fish families to replenish themselves. We thereby emphasize the importance of adaptive management for flow regulation and incorporating lateral fish passage structures into the riverbed. This approach is essential for achieving sustainable hydroelectric power generation in Brazil while safeguarding the ecological integrity of small rivers and their fish populations.