Variation of composition and structure of the fish fauna in three rivers with and without influence of dams in southern Brazil

Abstract

The Rio Ijuí basin has great energy generation potential, and is currently the target of implementations of hydroelectric dams. In this context, the main goal of this study was to characterize the fish assemblage structure and the composition in three rivers with and without influence of dams and to establish a prognosis for the fish fauna on rivers that still do not have dams installed. During the years 2009 and 2010, seasonal sampling was conducted using several methods in the three rivers, Palmeira, Alegre and Divisa, the last one without barrier. We recorded a total of 42 native and two exotic species of fishes. There is spatial variation in fish assemblage structure among sampled sites and no indication of seasonal variation. Steindachnerina biornata, Astyanax jacuhiensis, Oligosarcus jenynsii, Hoplias malabaricus, Crenicichla lepidota, Tilapia rendalli and Cyprinus carpio were associated with reservoirs. Due to the increased abundance in areas with dams, we can infer that implementation of hydroelectric dams might favor those species, while it might prejudice specialized riverine fishes, such as Pareiorhaphis cf. hystrix, Astyanax sp. and Bryconamericus iheringii.

Keywords: Fish assemblages, hydroelectric dams, Rio Ijuí basin, Uruguay River.