There are substantial gaps in our understanding of the effects of sounds upon fish. This paper describes experiments on the behaviour of wild, pelagic fish in response to sound playback, observed by means of sonar. Fish, including sprat (Sprattus sprattus) and mackerel (Scomber scombrus) were examined at a sheltered and quiet coastal location. Short bursts of repeated impulsive sounds were presented at different sound pressure levels, simulating the strikes from a pile driver. Behavioural responses included the break up of fish schools and changes in depth. The incidence of responses increased with increasing sound levels. The levels of sound to which the fish schools responded on 50% of presentations were estimated from dose response curves, in terms of the received sound pressure level and the single strike sound exposure level. Observations by means of sonar are especially valuable for examining the behaviour of unrestrained fish exposed to different sound sources. The technique allows testing of the relationship between responsiveness, sound level, and sound characteristics for different types of man-made sound. It is only by examining the responses of wild fish to sound, under natural conditions, that we can fully understand how marine renewable energy and other marine or coastal developments might interact with natural populations of fish.
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