source. Waiting times did not return to ‘normal’ until 22.7 hours after piling. At distances of greater than approximately 9km from the noise source the there was a much shorter duration of effect; with waiting times retuning to ‘normal between 1 and 2.6 hours after piling ceased. However, at 18-25km there was still a marked effect. Porpoise activity (measured by the number of minutes per hour in which porpoise were detected expressed as porpoise positive minutes) was significantly lower within approximately 3km of the noise source for 40 hours after piling.
261. Harbour porpoise have relatively high daily energy demands and need to consume between 4% and 9.5% of their body weight in food per day (Kastelein et al. 1997). If a harbour porpoise does not capture enough prey to meet its daily energy requirements it can rely on stored energy (primarily blubber) for three to five days, depending on body condition (Kastelein et al. 1997). Thermoregulation, especially in cold water, has high energy costs in marine mammals. Kastelein et al. (1997) estimate that a harbour porpoise may have a life expectancy of as little as three days in waters of 20°C under starvation conditions. Should harbour porpoise be excluded from an area of key prey resource, and be unable to find alternative food sources, there could be serious impacts from behavioural disturbance.
262. In a precautionary approach to the assessment, in dealing with uncertainty, harbour porpoise are assessed as having a medium sensitivity to likely avoidance.
263. Harbour seal and grey seal exhibit alternate periods of foraging and resting at haul out sites (during which limited or no feeding occurs). Prolonged fasting also occurs in these species during annual breeding and moult, when there are marked seasonal changes in body condition (Rosen & Renouf 1997; Bäcklin et al. 2011). Although adult seals may be relatively robust to short term (weeks rather than days compared to harbour porpoise) changes in prey availability, young and small individuals have a more sensitive energy balance. This is exhibited through effects of mass dependant survival (Harding et al. 2005). Although a fleeing response in harbour or grey seal may lead to a severe or sustained avoidance of an area, these species can be considered less sensitive to such an impact than harbour porpoise. Harbour and grey seal are assessed as having low sensitivity to likely avoidance.
12.6.1.1.1.4.2 Possible avoidance 264. This impact is not assessed in harbour or grey seal. As stated previously, only likely avoidance is considered in these species.
265. The behavioural response severity scaling for multiple pulses is used as an indicator of ranges where behavioural changes and some level of reduction in animal abundance may be expected (possible avoidance) in cetaceans. While no data are
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 12 Marine Mammal Ecology Page 71
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