Large Fish Movement Patterns in Upper Sao Francisco River, Brazil: The Importance of Abaete River for Conservation

The Sao Francisco River is dammed in its upper part by the Tres Marias Hydropower plant. Downstream of the dam (34 km) there is a free-flowing tributary, the Abaete River. Understanding the upper Sao Francisco River´s migratory fish movements directions, as well as the role of the Abaete River as a reproductive area, is crucial for defining  conservation strategies. We evaluated through hydroacoustics the large fish (most of them migratory) movement pattern (ascending or descending) in Sao Francisco and Abaete River. Between August 2012 and July 2013 we sampled monthly the fish fauna using a stationary echo sounder with the transducer placed horizontally. We detected a total of 42,196 target fish. During the dry season, most of the large fish detected did not show a preferential direction of movement. However, during the wet season, the large fish showed preferential movement towards the Abaete River. After this period, downstream movements were dominant. We concluded that the Abaete River is the main large fish route indicating that it constitutes the most important breeding site for the migratory species in upper Sao Francisco River Basin.