81. Although, as pointed out by McCauley et al. (2000a), it is not technically correct to convert RMS to peak SPL units (as defined in this report) an approximate conversion was provided by the authors resulting in peak SPL levels of around 168 to 173dB re 1 μPa. The review by Worcester (2006), which considered >10 studies of fish response to seismic air guns, reported only one where measured levels were lower than this. However, in that study, no statistical analysis was undertaken and the movements of the fish were reported to be difficult to distinguish from normal behaviour, occurring on only 8 out of 24 seismic shots (Bjarti 2002, cross-referenced from Worcester 2006). McCauley et al. (2000a) does point out that any potential seismic effects on fish may not necessarily translate to population scale effect or disruption to fisheries and show that caged fish experiments can lead to variable results. However, experimental studies by Engås et al. (1996) have shown catch rate reductions for cod and haddock both during and following a seismic survey, which could be caused by the fish leaving the immediate area or simply by the fish increasing their swim depth (water depth was >200m). Skalski et al. (1992) also experimentally demonstrated a reduction in rockfish catches during exposure to a seismic airgun where the peak pressure level or peak SPL was around 186dB re 1 μPa. Caged rockfish were also the subject of a study by Pearson et al. (1992) who observed an alarm response at a peak SPL of 180dB re 1 μPa (mean) where the alarm response is defined as a general increase in activity and changes in schooling or position in the water column. Although Pearson et al. (1992) did not expose the fish to lower peak SPL levels, regression analysis indicated that subtle behavioural response (defined as changes in swim depth) may occur a peak SPL of 161dB re 1 μPa, although this was not considered by the authors to indicate a likely response in an open environment, and more recent observations by McCauley et al. (2000a), indicate that such changes in behaviour may be expected to only occur at higher levels. Pearson et al. (1992) also observed a startle or C-turn response at peak SPLs beginning around 200dB re 1 μPa, although this was less common with the larger fish. This is higher than levels reported by McCauley et al. (2000a) where C-turn responses were observed at a peak SPL of 183 to 196dB re 1 μPa for small fish but it is consistent with the peak SPL of 203dB re 1 μPa reported by McCauley et al. (2000a) for larger fish. It should also be noted that in the studies by McCauley et al. (2000a and 2000b) and Pearson et al. (1992), the fish were observed returning to normal behaviour during the sound exposure at levels which caused the initial change in behaviour.


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 30


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