Assessment of cumulative sound exposure levels for marine piling events

The installation of offshore wind farms in European waters and the scale of the planned activity have led to concern over the generation of noise and its potential impact on marine life. Much of this concern is centered around the noise generated by pile driving, which is used for the installation of the turbine foundations, and its potential impact on marine life (Thomsen et al. 2006). The noise generated by pile driving has the potential to cause injury, induce temporary or permanent hearing loss, and evoke avoidance reactions. One injury criterion for marine mammals is defined as the onset of auditory permanent threshold shift (PTS) (Southall et al. 2007), which is governed by either an instantaneous peak pressure or an integrated sound exposure level. The latter is the total noise energy to which the mammal is exposed during a given duration that, for a pile-driving source, would be either the duration of the piling or the time over which the mammal is in auditory range and is known as sound exposure level (SEL). In this case, cumulative exposure can be a useful parameter. This paper considers a summation of the SELs to which the animal is exposed during the entire piling sequence.