Southall et al. (2007) for high-frequency cetaceans. Lucke et al. (2009) reported TTS- onset at 194dB re 1 μPa peak pressure level and 164dB re 1 μPa2·s SEL from a seismic airgun pulse, and aversive behavioural reactions observed at received level of 168dB re 1 μPa peak pressure level (reported at 174dBpk-pk re 1 μPa) or 145dB re 1 μPa2·s SEL. These findings also find support in acoustic detection studies in Denmark that reported a reduction in harbour porpoise vocalisations out to ranges of around 20km during impact pile driving of monopile foundations for a Danish windfarm (Tougaard et al. 2009; Brandt et al. 2011).
9.5.4 Review of Available Criteria Data for the Impact of Underwater Noise on Fish 69.
The hearing capabilities of fish species have previously been characterised as either a hearing specialist or generalist (it should be noted that this terminology is no longer advocated by its originators). In general, the term hearing specialist was used to refer to fish species that have a structure linking the swim bladder and ears, whereas hearing generalist was not normally considered to have this connection (Webb et al. 2008). Hearing generalists were described as generally hearing over relatively narrow frequency ranges from 50Hz or below to 1,000Hz or 1,500Hz with a hearing sensitivity which was often not very good, although it was acknowledged that there was considerable variation between species. The fish species which were categorised as hearing specialists were usually considered to have improved sensitivity over the same range and sensitivity to sound at higher frequencies extending above 3,000Hz. For marine piling, where most of the acoustic energy is radiated between around 100 to 400Hz, the high frequency capability of specialist species may be considered to be of minor importance. Given that many fish species have been described as having their highest sensitivity to sound in or around this 100 to 400Hz frequency range, they would perceive piling noise at relatively large distances (Thomsen et al. 2006). It should also be noted that many fish which might be affected by marine piling would have a hearing threshold which is either close to or below the level of ambient noise in the area. This means that they perceive the ambient noise and that their ability to hear a sound is limited not necessarily by their threshold of hearing but by the level of the ambient noise. When considering marine impact piling, the distinction between species by hearing specialisation or hearing threshold, as was done in the past, may not strictly be relevant.
70. One specific aspect of the sensitivity of fish species to sound is their sensitivity to acoustic particle velocity as opposed to sound pressure. This has been noted by a number of researchers (Hawkins 2006; Nedwell et al. 2007b; Popper and Hastings 2009; Sigray and Andersson 2011) and is acute at low frequencies where this particular sensitivity of their otoliths enables fish to discriminate sounds from different directions. The lateral line can also be sensitive to the particle velocity
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 25
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