Impacts of the Hydroelectric Power Generation Over the Fish Fauna of the Tocantins River, Brazil: Marabá Dam, the Final Blow

Abstract

As the eyes of environmentalists and researchers focused on the Madeira, Xingu and Tapajós rivers dams, one unknown project to bystanders will negatively affect an entire watershed, causing impacts far greater than any other megadam constructed in Brazil. Despite the environmental modifications, little is known about the UHE Marabá dam and its impacts over such a splendid cellar of species: the Araguaia-Tocantins basin. Historically the Tocantins River is the most impacted amazon tributary, with several already built dams, though the Araguaia River is free of dams. Building the UHE Marabá dam will affect both rivers, and probably extinguish many species increasing the already high number of Amazonian endangered fish species. Due to its unique evolutionary history among Amazonian tributaries, the endemicity found in the basin is probably higher than any other Amazon tributary, as some authors consider it as a different watershed, separated from the Amazon. Describing and foreseeing the impacts locally and globally are the main goals of the present study.

Geomorphology of fluvial deposits in the middle Tocantins River, eastern Amazon

“…Moreover, our results also have potential to support decision makers in conservation programs in a region under constant threat. The possibility of installing a large hydroelectric plant in the Tocantins River near the Marabá city (Brasil, 2012) reinforces the importance of this study because of predicted reduction of floodplains and unknown threats to the aquatic environments (Akama, 2017).…”

“…Part of the city of Marabá is located on the Proximal Floodplain (Main Map), which is seasonally flooded by the Tocantins and Itacaiúnas Rivers. This floodplain is the most extensive floodplain of the Tocantins River, and the place where recruitment occurs for migratory and non-migratory fishes (Akama, 2017). Therefore, it is an important habitat for conservation of aquatic ecosystems.…”

“…The geomorphological history of the Tocantins River, in turn, is mostly associated with the geological evolution of the Brazilian Shield (Lima & Caires, 2011;Lima & Ribeiro, 2011). The middle stretch of the Tocantins River consists of wide floodplains and fluvial terraces with numerous lakes and wetlands that provide diverse wildlife habitats and important ecological services (Merona et al, 2010) and due to its evolutionary history among Amazonian tributaries (Akama, 2017), has one of the highest endemicity and species richness rates (Dagosta & Pinna, 2019).…”

A new miniature cryptic species of the seasonal killifish genus Spectrolebias from the Tocantins River basin, central Brazil (Cyprinodontiformes, Aplocheilidae)

“…The same occurred in the das Mortes floodplains, where original vegetation was substituted by plantations and swampy areas were drained. In the Tocantins River basin, the dense forest previously present at the river floodplains was drastically removed in recent years, and large dams have inundated floodplain areas (Akama 2017). For example, in recent field studies we found that the Lajeado Dam, which shut off river flow in 2002, forming a reservoir that now occupies an area of 630 km 2 along 172 km of the middle section of the Tocantins River (Agostinho et al 2007).…”

“…As a result, the river has permanently inundated all seasonal killifish habitats around the dam, including the type locality of rare killifishes endemic to this region, such as Hypsolebias multiradiatus (Costa & Brasil, 1994), Maratecoara formosa Costa & Brasil in Costa, 1995, Plesiolebias xavantei (Costa, Lacerda & Tanizaki, 1988), and Trigonectes strigabundus Myers, 1925. The Tocantins River basin has been considered as the most impacted Amazon tributary, with a dense concentration of dams (Winemiller et al 2016;Akama 2017). The five presently operating dams in the middle section of the Tocantins River probably promote wide distribution gaps for fish living in temporary pools situated close to rivers, putting in risk their existence.…”