Planejamento energético e a conservação da fauna de peixe na bacia Tocantins - Araguaia: estudo de caso na sub-bacia do Rio do Sono

Abstract

This study addresses the fragmentation of water systems resulting from the construction of hydroelectric dams and its implications for the conservation of fish fauna, with a focus on migratory species. Dams restrict the movement of fish along rivers, preventing access to essential areas for the survival of species. This study is divided into two parts, the first dealing with changes to the entire Tocantins-Araguaia river basin, and the second specifically to the Rio do Sono river basin. The hydroelectric projects in operation and planned for the Tocantins-Araguaia basin were analyzed, taking into account the occurrence of species with a restricted distribution and migratory species. For the Rio do Sono river basin, a tributary of the right bank of the Tocantins River, whose mouth is in the lotic stretch between the Lajeado and Estreito hydroelectric plants, data provided by the National Electric Energy Agency was used on the hydroelectric plants in operation and planned, and the Fragmentation Index of the longest stretch was calculated based on the length of the drainage network, considering the natural, current (2023) and future (2050) scenarios. The results show that there are 75 hydroelectric plants in operation in the Tocantins-Araguaia basin, with a further 119 planned by 2050, which will intensify fragmentation in the lower stretches of the Araguaia River and the lower and middle stretches of the Tocantins River, especially the Rio do Sono basin. The stretches most affected in the future will be the upper Tocantins River and the upper Araguaia River. In the Tocantins-Araguaia ecoregion, the stretch upstream of the Tucuruí dam, 701 species of fish have been recorded, 218 of which have a distribution restricted to the basin, and 43 species are threatened with extinction, most of them with a restricted distribution. In addition, 66 migratory species were identified. In relation to the Rio do Sono, the results indicate that, in the natural scenario, the Rio do Sono watershed is 12.96% fragmented due to the presence of natural waterfalls. In the current situation, with three hydroelectric plants in operation, fragmentation reaches 29.03%, while in the future, considering the implementation of all the planned hydroelectric plants, fragmentation will reach 93.22% of the basin. Impact studies and Basic Environmental Plans are carried out late, after the works have been defined, making it difficult to plan conservation in advance. Therefore, comprehensive data collection and the involvement of communities in conservation is needed, taking into account biological, socio-environmental and cultural diversity to inform discussions in the basin. With regard to the Rio do Sono, it is essential to carefully select the locations of hydroelectric plants, or to stop building them, preserving free stretches for the maintenance of river ecosystems and ichthyofauna.