Impacts of Belo Monte dam on fish co-occurrence and artisanal fishing

The operation of large hydroelectric dams, such as Belo Monte in the Brazilian Amazon, significantly disrupts local freshwater ecosystems, impacting the socio-economic fabric and food security of dependent communities. To investigate and simulate future dam-induced impacts on fish species crucial for subsistence and artisanal fishing, this study leveraged subsistence fishing data from four areas of the Xingu River: the reservoir, upstream, the de-watered reach, and downstream. Using network analysis and graph theory, we examined the temporal and spatial variations in fish species composition, focusing on species that co-occur in fishing catches and their ecological roles within the network. Results showed a 34 % reduction in total biomass, from 8442.51 kg (2012-2015) to 5537.42 kg (2016-2020). The analysis revealed marked changes in species diversity and catch composition, with substantial shifts in heavily altered regions. For instance, in the de-watered reach, traditional species such as curimatã (Prochilodontidae) were replaced by others like pacu (Serrasalmidae), reflecting ecological shifts and the replacement of a detritivorous species by an omnivorous one. Directed simulations projected the dynamics of species loss, revealing significant alterations in co-occurrence patterns and network centrality, particularly in the de-watered reach. These simulations demonstrated that species such as pacu, pescada (Sciaenidae), and tucunaré (Cichlidae) remained central to the network despite ongoing ecological transformations. While this study provides valuable insights into environmental shifts, the absence of direct socio-economic data highlights the need for future research to understand the broader impacts on artisanal fisheries better. These results underscore the profound transformations in fish diversity and emphasize the critical need for adaptive management strategies to mitigate these impacts, ensuring the resilience of local fishing communities. While our findings offer valuable ecological insights, the absence of direct socio-economic data highlights the need for future research to better understand the broader impacts of hydroelectric dams on artisanal fisheries.