Peixes a jusante da usina hidrelétrica Amador Aguiar II, rio Araguari, MG: diversidade, biologia e mitigação de mortes.

Abstract

From construction to operation, hydropower plants impact fish in a variety of ways. Fish near tailrace are at risk of death since several operational procedures of hydropower plants can affect them. During generator units dewaterings, fish can be trapped in the draft tube and suffer stress, hypoxia and physical injuries. The larger the amount of fish trapped, the more complex is the recovery and the greater is the risk of death. Such fish deaths may hurt the company’s image and lead to fines and stoppage of power generation. In the Amador Aguiar II Dam (Araguari River, Minas Gerais state), mandi (Pimelodus maculatus) represents 90% or more of the number of fish recovered in generator units dewaterings. The present work was conducted in the Amador Aguiar II Dam and aimed (i) to evaluate the fish community structure downstream of the dam and its relationship with abiotic factors of the habitat; (ii) to investigate the biology and ecology of the mandi downstream of the dam; (iii) to elaborate a prediction model of the amount of mandi trapped in the draft tube as a function of its abundance in the tailrace and (iv) to verify whether spillway discharge reduces the amount of fish trapped in the draft tube during generator units dewaterings. The fish community downstream of the dam was dominated by few species, mainly small and medium body size, and mandi was the most common species. The abiotic variables explained 53.13% of the abundance variance of the most captured fish species, but only the water temperature and the sampling month precipitation were significant. The presence of few mandi with higher gonadosomatic index indicated that this species probably does not spawn in the studied site. Mandi was omnivorous and its abundance presented marked seasonality, with more captures made during the rainy season when the water temperature and rainfall were higher. For this reason, the maintenance of generator units during the rainy season is not advisable since there is risk of death for more fishes in this period. The number of mandi trapped in the draft tube presented positive linear correlation with its abundance in the eve of dewatering. The prediction model was significant and the equation obtained was Y = 5.666 + 0.552 X (P = 0.01), where Y = ln of the number of mandi trapped and X = ln (catch per unit effort of mandi in the tailrace + 1). This equation can predict the risk associated with future dewaterings and therefore represents a significant advance for the mitigation of impacts caused by hydropower plant. Studies conducted to evaluate the spillway discharge previous to dewaterings suggested that it may not attract mandi from the tailrace to the spillway region, but it may reduce the number of mandi trapped in generator units dewaterings.