255. Pinnipeds use sound both in air and water for social and reproductive interactions (Southall et al. 2007) but not for finding prey. Therefore, Thompson et al. (2012) suggest damage to hearing in pinnipeds may not be as important as it could be in cetaceans. Pinnipeds also have the ability to hold their heads out of the water during exposure to loud noise, and potentially avoid PTS. As such, sensitivity to PTS in harbour and grey seal is considered to be low, with the individual showing some tolerance to avoid, adapt to or accommodate or recover from the anticipated impact.
12.6.1.1.1.3 Auditory injury (TTS onset) 256. As described for PTS above, harbour porpoise are assessed as having medium sensitivity to auditory injury, and grey and harbour seal low. The sensitivity of each receptor to TTS is considered the same as PTS.
12.6.1.1.1.4 Behavioural response
12.6.1.1.1.4.1 Flee response/likely avoidance 257. Southall et al. (2007) discuss a range of likely behavioural reactions that may occur as a result of exposure to noise. These include orientation or attraction to a noise source, increased alertness, modification of characteristics of their own sounds, cessation of feeding or social interaction, alteration of movement/diving behaviour, temporary or permanent habitat abandonment, and in severe cases panic, flight stampede or stranding, sometimes resulting in injury or death.
258. In the noise assessment (Appendix 9.1) the single pulse behavioural disturbance criterion is considered for the purpose of estimating ranges where a strong aversive response might occur (100% avoidance) as it is based on the onset of TTS. This type of response may be considered likely to affect vital rates based on the potential for a severe or sustained avoidance of an area.
259. The duration of any flee response can vary, and the time between individuals being displaced and returning to an area should be considered against the waiting time between piling events. It is likely that a behavioural disturbance from a single pile driving event would be sufficient to exclude harbour porpoise from the area around the noise source for several days (Thomsen et al. 2006; Brandt et al. 2009; 2011, Thompson et al. 2010a).
260. The duration of the exclusion could last up to three days following a single piling event if the animal is close to the source. Data presented by Brandt et al. (2009, 2011) indicated that harbour porpoise would completely leave the area (indicated by the duration of waiting time between porpoise detections after first piling) for a median time of 16.6 hours and a maximum of 74.2 hours within 0.5-6km of the noise
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 12 Marine Mammal Ecology Page 70
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