Fish community structure as an indicator of the long-term effects of the damming of an Amazonian river

In order to provide guidelines for the management of fish stocks in artificial reservoirs in the Amazon region, the present study analyzed the composition and structure of the fish communities of four sectors (upstream, lake, reservoir, and downstream) of the area affected by the Coaracy Nunes hydroelectric reservoir on the Araguari River in the Brazilian state of Amapa. Variation in ecological parameters was analyzed in the context of the impacts suffered since the damming of the river approximately 40 years ago. Standardized samples of fish were collected in gillnets during eight campaigns in 2009 and 2010. Abundance and biomass were initially evaluated by Analysis of Variance (ANOVA), and lognormal, log-series, geometric series, and broken stick models were then calculated. The K-dominance and Abundance-Biomass (ABC) curves were also analyzed, together with the size-spectrum of the specimens. The results indicated that the sector downstream from the dam had the highest species richness, and was most consistent with the broken stick model. The ABC and K-dominance analyses also confirmed that this sector was the most balanced, in ecological terms. The lake sector had the only community that fitted the geometric series model, and all the analyses indicated a predominance of small individuals, typical of impacted communities. The analyses of the reservoir sector indicated a disturbed environment, whereas the upstream sector was characterized by a more balanced community, reflecting its greater resilience to the impacts caused by the reservoir, and its potential of this area for the conservation of local fish communities. The results also confirmed the applicability of the analytical tools employed for the study of fish communities in reservoir environments.