Conventional environmental assessments are inadequate for predicting and mitigating impacts of dams on migratory fish in Brazil: an integrative assessment approach for the Neotropics

The escalating pace of dam construction in Brazil poses a significant threat to migratory fish. This study uses data from previous research to predict the impacts of new dams on the life cycle of the migratory fish Prochilodus costatus. The species was studied for five reproductive seasons in a 500-km free-flowing stretch of the São Francisco River, where the construction of six hydroelectric dams is now planned. These studies investigated migratory periods, routes, critical habitats, and the genetic structure of the P. costatus population, assessing potential impacts of the planned dams and exploring various mitigation strategies. The assessment shows that maintaining this river stretch free of dams is crucial for the species’ survival. The comparison of this in-depth analysis with information generated by conventional environmental impact assessments (EIAs) conducted in Brazil revealed that conventional EIAs often fail to predict the actual impacts of dam construction as they rely on inadequate collection and analysis methods. Therefore, the proposed mitigating measures prove inefficient for migratory fish. Our comparison highlights the importance of obtaining essential information about the ecological requirements of migratory fish and integrating it with the characteristics of newly planned dams before determining their environmental feasibility. We thus propose an integrative approach to assess the impact of dams on Neotropical migratory fish (IANMF), aimed at providing researchers and environmental agencies with higher quality information on migratory fish ecology and the potential impacts of future dams on their life cycles.