Primeiras hidrelétricas em rio de águas brancas na Amazônia: resistência da ictiofauna bentônica

Abstract

River damming for hydropower generation is one of the most impact activities in river systems. The environmental consequences of large dams are numerous, including direct impacts on biological, chemical and physical properties of rivers environments. Recently the Amazon basin are experiencing an unprecedented boom in construction of hydropower dams. Studies were conducted at six years in the Madeira River, three years before and three years after two reservoirs built in cascade in the largest white-water tributary of the Amazon River (Jirau and Santo Antônio dams’). Fish assemblages depending on floodplains areas (pelagic) and bottom main channel (benthic) were sampled with gillnets and bottom trawl net respectively. To understand the effect of reservoirs in cascade my thesis was organized into three chapters. The first chapter present the length–weight relationships (LWR) for 112 freshwater fish species representing 23 families and five orders captured in the Madeira River. Eight new LWR records are presented for Amazonian species as information for Fish-Base database. LWRs provided historical data about a and b coefficients prior to the damming of the Madeira River, allowing comparison of estimates to predicted future population parameters influenced by human impacts. The second chapter brings an article about the temporal and spatial distribution of young giants’ catfish Brachyplatystoma spp. Larvae and juveniles were present in low abundances in all areas and during all hydrological periods. The presence of larvae and juveniles of Brachyplatystoma rousseauxii along the channel throughout the hydrological cycle suggests spawning regulated by asynchronous floods events in the headwaters of the Madeira River. Finally, we examined responses from fish assemblages depending on floodplains areas (pelagic) and bottom main channel (benthic) three years before and three years after the dams. Overall, there were major differences in species richness, biomass and density but no significant differences in fish diversity and evenness before and after dam construction. Differences in pelagic fish assemblage composition into both reservoirs were noticed immediately, and linked to the increasing in conductivity, deep, oxygen and temperature while channel bottom fish assemblage seems to not respond immediately to the dams’ closure. Our study is especially relevant considering responses from fish assemblages to bulb turbines face to burgeoning new hydroelectricity development plans for rivers across Amazonia.