response and the level at which this response occurs is difficult to quantify. One study by Slotte et al. (2004) used sonar to observe the fish movement during a seismic survey, showing that the fish appeared to go to greater depths after exposure to a seismic airgun source and a study by Hassel et al. (2004) showed behavioural changes in sandeels Ammodytes marinus when exposed to a seismic airgun.
77.
Experiments using confined fish offer a more controlled way of studying the behavioural response of fish when exposed to sound and can provide better understanding of the sound field in the test volume. However, whilst confined fish experiments offer a convenient way to observe behavioural reactions, the confined nature of the experiment and the likelihood of increased stress in the fish should be considered carefully when assessing the implications on potential impact. This has been stressed by Popper and Hastings (2009) who have reviewed a number of studies exposing caged fish to sound. The level of background noise should also be carefully considered, particularly when measurements are performed in caged areas of low ambient noise or in test tanks where ambient noise would generally be expected to be very low relative to the open sea. When extrapolating these findings to impact on a species, population scale effect or disruption to fisheries, the context or other factors which might influence fish behaviour should be considered.
78. A study in the UK by Nedwell et al. (2006) showed an increase in activity of caged salmonids (brown trout and salmon) around 50m from a pile driving activity, although responses in other cages were not consistent. Another study in the UK analysed the effectiveness of an acoustic fish deterrent used to discourage fish from entering intakes for a nuclear power plant cooling system (Maes et al. 2004). This work showed a clear avoidance of some fish species to the deterrent which had a reported generated swept sinusoid from 20 to 600Hz with a measured SPL (RMS) of 174dB re 1 μPa. A more recent COWRIE funded project led by Cefas in the UK (Mueller-Blenkle et al. 2010) measured the behavioural response of both cod and sole to a play back of a measured piling sound. The temporal characteristics of the sound were reported to be similar to those to which fish might be exposed to at a distance of around 400m from a piling event but with a range of received level typical for much greater distances, although it should be noted that the fish were in some cases less than a wavelength away from the source. The report stated that there was considerable variation across subjects and that it was not possible to find an obvious relationship between the level of exposure and the extent of the behavioural response. Behavioural responses were observed at peak pressure levels of 140 to 161dB re 1 μPa for cod and 144 to 156dB re 1 μPa for sole. Low-frequency sound exposure studies in test tanks by Blaxter et al. (1981), Schwartz and Greer
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 28
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