AVOIDANCE RESPONSES TO LOW-FREQUENCY SOUND IN DOWNSTREAM MIGRATING ATLANTIC SALMON SMOLT, SALMO-SALAR

The possibility of using intense sound as an acoustic barrier for down stream migrating smolt of the Atlantic salmon (Salmo salar) was studie d by observing the reactions of smolt to 10 and 150 Hz sounds in a sma ll river. At the observation site the river branched into a main cours e and a minor channel, the latter rejoining the main stream after 30 m . The sound sources were positioned at the lower end of the channel. T he number of smolt re-entering the main stream at the lower end of the channel was recorded during alternating periods with and without soun d. Intense 150 Hz sound had no observable effects on the smolt, even a t intensities 114 dB above the hearing threshold at this frequency. At intensities above 1.0 . 10(-2) ms-2 the 10 Hz sound was an effective deterrent for the smolt, which turned and left the channel at the upst ream branching point.