Ecologia trófica das principais espécies de peixes do Rio Paraíba do Sul na área de influência do Aproveitamento Hidrelétrico Simplício durante o período pré-represamento

Abstract

We herein describe the feeding ecology of the main fish species of the Paraíba do Sul River, during the dry and rainy seasons, previously to its impoundment by the Simplício Hydroelectric Dam. A total of 13 species were selected. Although representing only 20.6% of species richness in the area, they correspond to 84.2% and 74,1% of all individuals in terms of biomass and abundance, respectively. Sampling was conducted between November 2009 and November 2011. Trophic guilds were assigned through a Correspondence Analysis. Pairwise feeding overlap was calculated. The feeding ecology of each species was described through the proportional importance of condumed items (volumetric method), niche width and feeding strategies. Seasonal variations were evaluated through comparisons between the dry (April to October) ad rainy (November to March) seasons. Species were grouped into five guilds in the diet space: detritivores, herbivores, invertivores, omnivores and piscivores; however, most groups did not differ significantly. Overall, fishes consumed more allochthonous material during the rainy season, but seasonal differences in diet were statistically significant only for Astyanax gr A. bimaculatus, O. hepsetus e P. fur. The consumption of large amounts of insects, also by species recognized as piscivores, (O. hepsetus e P. squamosissimus) might indicate high availability in the river. For species with more than 10 individuals collected at the same site and field trip (considered herein as a population), we calculated the degree of individual specialization (IS). Is achieved intermediate and high values, indicating intrapopulational variation. Most species showed opportunism. The River Paraíba do Sul is highly impacted in the studied area, mainly because of urbanization, which was reflected in the diet of several species through the consumption of materials of anthropic origin (e.g. plastic). The overall opportunism of fish species might favor their adjustment and permanence after reservoir formation. Nevertheless, the actual responses of these species as well as alterations in the trophic structure caused by the impoundment will only be detected through long-term projects for monitoring, as described in several studies in other impounded Brazilian basins.