It is a difficult task to trace the historical events leading to the application of acoustics in fisheries research. The first echo-sounders giving successful results were constructed just before World War I in order to measure ocean depths. But it took some years until the echo-sounding technique was applied in fisheries. According to Fridriksson and Hodgson (1955), fish shoals were probably first observed by the French navigator, R. Rallier du Baty who in 1926 noted, when on a trip to Newfoundland, that the sounder in his ship was giving abnormal signals which he attributed to a shoal of cod. In Japan Kimura (1929) made experiments of fish detection with acoustics in small ponds. Several other reports from around 1930 show that fish shoals were detected in the open sea with echo-sounders (Balls 1945; Fridriksson and Hodgson 1955.)