Understanding Hydropower Impacts on Amazonian Wildlife is Limited by a Lack of Robust Evidence: Results From a Systematic Review

Background and Research Aims: Although hydropower provides energy to fuel economic development across Amazonia, strategies to minimize or mitigate impacts in highly biodiverse Amazonian environments remain unclear. The growing number of operational and planned hydroelectrics requires robust scientific evidence to evaluate impacts of these projects on Amazonian vertebrates. Here, we investigated the existing scientific knowledge base documenting impacts of hydropower developments on vertebrates across Brazilian Amazonia. Methods: We reviewed the scientific literature from 1945 to 2020 published in English, Spanish, and Portuguese to assess the temporal and spatial patterns in publications and the types of study design adopted as well as scientific evidence presented. Results: A total of 25 published articles documented impacts on fish (n = 20), mammals (n = 3), and reptiles (n = 2). Most study designs (88%) lacked appropriate controls, and only three studies adopted more robust Before-After-Control-Impact designs. The published evidence did not generally support causal inference with only two studies (8%) including appropriate controls and/or confounding variables. Conclusion: Decades of published assessments (60% of which were funded by hydropower developers or their subsidiaries) do not appear to have established robust evidence of impacts of hydropower dams on Amazonian vertebrates. This lack of robust evidence could limit the development of effective minimization and mitigation actions for the conservation of diverse vertebrate groups impacted by hydropower dams across Brazilian Amazonia. Implications for Conservation: To avoid misleading inferences, there is a need to integrate more robust study designs into impact assessments of hydropower developments in the Brazilian Amazon.