Avoidance responses to infrasound in downstream migrating European silver eels, Anguilla anguilla

• Published in: Environmental biology of fishes 2000-03, Vol.57 (3), p.327-336
• Main Authors: SAND, O, ENGER, P. S, KARLSEN, H. E, KNUDSEN, F, KVERNSTUEN, T
• Format: Article
• Language: English
• Subjects: Anguilla anguilla; Animal, plant and microbial ecology; Aquaculture; Biological and medical sciences; Field study; Field tests; Freshwater; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Marine; Methods and techniques (sampling, tagging, trapping, modelling...); River banks; River mouth; Rivers; Salmon
• ISSN: 0378-1909; 1573-5133
• DOI: 10.1023/A:1007575426155

In an attempt to develop an efficient acoustic fish fence, we have designed an infrasound source able to generate large nearfield particle acceleration. The source generates water movements by means of two symmetrical pistons in an air-filled cylinder with 21 cm bore. The pistons are driven by eccentric coupling to an electric motor, with 5 cm p.p. amplitude. The piston movements are 180 degree out of phase. The piston reaction forces are thus opposed, leading to vibration free operation. The submergible infrasound source is operated freely suspended in the water mass. The emitted sound frequency is 11.8 Hz. The particle acceleration is about 0.01 m s super(-2) at a distance of 3 m, corresponding to the threshold intensity for deterring effects of infrasound on Atlantic salmon smolts. The sound source was employed to test the effect of intense infrasound on migrating European silver eels. Fish confined in a tank displayed startle behaviour and prolonged stress reactions, telemetrically monitored as tachycardia, in response to intense infrasound. The field tests were carried out in the River Imsa. A trap that catches all the descending eels is installed near the river mouth. The trap was separated in four equal sections. During the periods with infrasound exposure, the proportion of silver eels entering the section closest to the sound source was reduced to 43% of the control value. In the section closest to the opposite river bank, infrasound increased the proportion of trapped eels to 144% of the control values. This shift of the migrating eels away from the infrasound source was highly significant.