(Southall et al. 2007). No data exist for severity score 9. Specifically, a severity score of 5 indicates a change in swimming behaviour but not avoidance, and 6 indicates minor to moderate avoidance. A combination of both is used in absence of explicit data for either. Based on the limited behavioural observations collated as part of the US NMFS criteria (Southall et al. 2007), the following statements can be made which are appropriate for multiple pulses:
• Pinnipeds in water
o Based on limited data for ringed seals, received level of 190dB re 1 μPa (RMS over pulse duration) are likely to elicit responses with a possible severity scaling of 5.
• Low-frequency cetaceans
o For low-frequency cetaceans not engaged in migration, the onset of significant disturbance (severity scaling of 6 and above) may occur over a range of received level from 150 to 160dB re 1 μPa (RMS over pulse duration). Significant disturbance could occur at lower levels depending on the activity of the animal. It should be noted here that these are based on seismic airguns which can generate very low frequencies when compared to piling which might be significant for low-frequency cetaceans. They were also performed in deeper water than that in which piling is typically performed, allowing the lower frequencies to propagate.
• Mid-frequency cetaceans
o Very little information exists for mid-frequency cetaceans’ exposure to multiple pulse source types. There is some indication that a received level of 160 – 170dB re 1 μPa (RMS over pulse duration) would elicit a response of 6 on the severity scale (Southall et al. 2007). A recent study by Finneran et al. (2012), exposing a bottlenose dolphin Tursiops truncatus to a seismic airgun, indicates that this higher level threshold may not be unrealistic and small mid-frequency cetaceans may well be less sensitive to impulsive sounds than harbour porpoise.
• High-frequency cetaceans
o No data is reported in Southall et al. (2007) for high-frequency cetaceans (this category includes the harbour porpoise).
65.
It should be noted that the RMS over the pulse duration results in dB values that would likely be higher than the equivalent SEL dB value for a piling pulse. Robinson
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 23
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