Estudo do comportamento de peixes no canal de fuga da usina hidrelétrica de Três Marias utilizando telemetria acústica

Abstract

In attempt to perform migrations toward to upstream areas, the fish can be trapped and killed in the draft tube during an operational maneuver (turbine stop/startup procedures) in a Hydropower plant. The comprehension of fish movement and distribution patterns in an area under hydropower plant operational conditions can be an important key to provide useful insights as to how to manage dam operations in order to minimize the impacts on the ichthyofauna. In this sense, the movements patterns of two migratory species were evaluated in the tail race of Três Marias Dam, located on the upper São Francisco River, Minas Gerais, Brazil. We tracked the movements of 90 fish, being 50 Prochilodus argenteus and 40 Pimelodus maculatus, using acoustic telemetry from October 31st 2011 to February 16th 2012. We evaluated the temporal variations of the inward and outward movements to the tail race and the spatial distribution immediately downstream from the dam (arbitrarily defined up to 30 meters downstream from the dam). Moreover, the influence of water transparency, time scale and hydropower operation (turbine and spill discharge) were evaluated on the found patterns. The majority of tagged fish left the tail race in a short period of time, however, visits to the tail race were performed by some fish (35 individuals) over the study period. Differences in the behavior between the two species were observed in this study. The rate of visits to the tail race was predominantly performed by P. argenteus during diurnal period, while P. maculatus showed nocturnal behavior (visits to the tail race and the permanence time in the area immediately downstream from the dam). Differences in depth preferences also were observed between the two species, in which P. argenteus remained closer to the surface and P. maculatus closer to the bottom. Besides, we were able to observe the influence of spillway and turbine discharge on the rate of visits to the tail race, with greater activity during the presence of spillway discharge and the turbine operation in maximum generation. Although the increase of turbine discharge can attract the fish to the tail race, the greater permanence of P. maculatus in area immediately downstream from the dam was during the minimum discharge. In this sense, the maximum generation followed by minimum generation can represent a risky situation to happen an event of fish mortality. Despite the attempt to conciliate operational maneuvers with a minimum impact on the ichthyofauna is still a big challenge, our results can provide useful information to elaborate action strategies in order to minimize the fish kill in the turbines.