the Fisheries Hydroacoustic Working Group (FHWG) that has been adopted by several states in the USA (Popper et al. 2006; Carlson et al. 2007), whilst for assessment of behavioural impacts an indicative two-level behavioural influence criteria based on observational studies (McCauley et al. 2000; Pearson et al. 1992) has been used. As part of the study by McCauley et al. (2000), these levels were compared against other findings in the literature and found to be comparable. The threshold values were also confirmed in a more recent publication (Fewtrell and McCauley 2011). It should be noted that the criteria are based on a limited amount of information and do not account for variation between fish species, size, age and sex and life-history stage.


130. Due to the nature of sound propagation and the generally lower sound pressures near the sea bed, the behavioural impact from piling noise on fish has been modelled in terms of fish in mid-water column (pelagic) and fish that dwell near or on the sea bed (demersal). The impact ranges for demersal fish also extend to any fish which may temporarily move closer to the sea bed in response to the sound.


131. The threshold noise levels used for the assessment of impacts on fish are summarised below in Table 11.21 and Table 11.22. The use of the term ‘peak SPL’ follows the definition provided by Southall et al. (2007) i.e. peak SPL represents the zero-to-peak pressure level of the pulse, which for a symmetrical pulse can be assumed to be 6dB less than the peak-to-peak pressure level.


132. Underwater sound propagation modelling for East Anglia THREE was undertaken assuming a worst case 3,500kJ hammer strike energy, as well as, a number of smaller hammer strike energies including 1,400kJ, 2,000kJ, 2,300kJ and 3,000kJ. The lowest hammer energy is 40% of the full hammer energy, which may be considered sufficiently high to encompass the hammer strike energy at the onset of piling (assumed to be around 10 to 20% of the full hammer strike energy).


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Chapter 11 Fish and Shellfish Page 55


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