Influences of small hydroelectric power plants on homogenization of the ichthyofauna in a tropical river

The native fishes of the Neotropical region have been heavily impacted by the construction of reservoirs that block the rivers in different degrees. Small Hydroelectric Power Plants (SHPP) have been an alternative way to take advantage of small electricity production potential, with low cost. However, there is no basis in the belief that SHPP have less deleterious effects on river habitat than large hydropower plants. The aim of this study was to evaluate eventual changes in the ichthyofauna because of the influences of SHPP in the middle reaches of a tropical river in south-eastern Brazil. The raised hypothesis is that SHPP change the ichthyofauna composition and increase the taxonomic and functional similarities (homogenization). Fish collections were carried out quarterly at six locations along a 20 km stretch of the Paraíba do Sul River, before and after the construction of the SHPP. The fish community structure changed between the two periods, with a decrease in the fish numerical abundance, whereas the species richness did not change. Sensitive species with specialized feeding habits (namely, Hartia loricariformis, Steindachineridium parahybae, Hypomasticus mormirops, Characidium alipioi, Chyphocharax gilbert, Corydoras nattereri and Pogonopoma parahybae) occurred only before the SHPP, being replaced by several species of Characiformes, among them four of genus Astyanax (namely, A. giton, A. hastatus, A. taeniatus, and A. intemedium) that are tolerant and omnivores; however, most of functional traits were maintained. The taxonomic dissimilarity increased significantly, whereas the functional dissimilarity did not differ between the two periods. The hypothesis of ichthyofauna homogenization was not confirmed in this study, probably because of the short time period since the SHPP construction.