Abstract
This paper reviews recent studies of infrasound detection in fish and the use if intense infrasound as a fish deter-rent. The possible use of intense infrasound in acoustic fish barriers is discussed. Fish are sensitive to infrasound (<20 Hz), even down to below I Hz, and the otolith organs are the sensory system responsible. Particle acceleration, and not sound pressure, is the relevant sound parameter for low frequency detection in fish, and the threshold values are in the range 10(-5)-10(-4) ms(-2). The hydrodynamic noise generated by swimming fish is mainly in the infrasound range, and may be important in prey-predator interactions. An infrasound source able to generate large near-field particle acceleration has been employed to divert downstream migrating Atlantic salmon (Salmo salar) smolts in a small river. At the observation site the river branched into a main course and a minor channel. The infrasound source was positioned in the channel, and at intensities above 10(-2) ms(-2) the 10 Hz sound effectively blocked passage of smolts through this alternative route. An improved version of the original infrasound source has been employed to test the effect of intense infrasound on downstream migrating European silver eels Anguilla anguilla. The tests were carried out in a river where 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 riverbank, infrasound increased the proportion of trapped eels to 144% of the control values. We conclude that intense infrasound has a great potential in acoustic fish barriers.