When possible, the use of multiple sampling techniques is preferable to obtain an overview on the fish assemblage structure. Sampling strategies are essential and depend on the scientific objectives, on the study area, on the allotted time and on the spatio-temporal scales of the ecosystem. In this project, we relied on the results of the research project carried out in the Gironde estuary. Through methodological and ecological issues, this work has provided a glimpse into the interests of hydroacoustics in terms of estuarine monitoring but also in terms of analysis of ecological dynamics. A Simrad EK60 split-beam echosounder controlled by the Simrad ER60 (version 2.2.0) program was used for data acquisition at two frequencies, 70 kHz and 120 kHz. Two circular transducers were used, with beam angles of 7° at -3 dB. An elliptical transducer with a beam angle of 2.5° X 10° was added in horizontal position. All transducers were fixed to the side of the boat, 0.50 m below the surface and vertically or horizontally oriented.