was interpreted as a reduction in harbour porpoise density in the area. It should also be noted that acoustic mitigation devices (AMDs) were used at the foundation location prior to piling activity. A more detailed study by Tougaard et al. (2005) for the Nysted windfarm reported partial recovery in harbour porpoise abundance, based on T-POD detections, two years into the operational cycle of the windfarm.
108.
In a Danish offshore windfarm Horns Rev in the North Sea Tougaard et al. (2009) studied the echolocation presence of harbour porpoise. Pile driving was used to install 4m diameter monopiles in water depths of around 6m to 12m using a 600kJ hammer, generating an estimated effective peak pressure level source level of 229dB re 1 μPa. T-PODs were deployed out to a distance of 21km from the foundation and foundation installation entailed deployment of acoustic pinger deterrents prior to piling. All T-PODs recorded a noticeable change in vocalisation patterns during and after piling, but did not show any correlation with distance from the foundation as expected (i.e., the observed effect was the same at 21km as it was at less than 4km). Also, there was no indication of habituation for the subsequent piling events.
109. Thompson et al. (2010) used a combination of T-PODs and visual sightings to study the effects of impact piling of 1.8m diameter quad jacket foundations in more than 40m of water for the Beatrice Demonstrator project in the Moray Firth on harbour porpoise and bottlenose dolphin populations. T-PODs were positioned both near the foundation site and 40km away at a control site. The findings of Thompson et al. (2010) suggest there was some short-term response to the installation activities within 1km to 2km around the foundation location, although Bailey et al. (2010) measured piling noise beyond 50km at levels which were deemed sufficient to influence behaviour in harbour porpoise and dolphins. Monitoring vocalisation activity at greater distances was not undertaken or reported.
110. Brandt et al. (2011) studied the response of harbour porpoise to the installation of the Danish Horns Rev II offshore windfarm in the North Sea using a number of T- PODs out to a distance of 22km from the foundation. The 3.9m diameter monopile foundations were installed in water depths of around 4m to 14m using a 1,200kJ hammer. The work by Brandt et al. (2011) is perhaps the most informative, stating that harbour porpoise T-POD click detections reduced by 100% during the first hour after piling and stayed below normal levels for 24 to 72 hours at a distance of 2.6km from the foundation. The noise level at a similar range (2.3km) was measured to be 184dB re 1 μPa peak pressure level (164dB re 1 μPa2·s SEL) for an 850kJ hammer blow energy, albeit in a different direction from the source. Significantly, the period following piling activity during which reduced harbour porpoise echolocation click
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 48
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