Marine mammal permanent threshold shift prediction from down-the-hole piling noise exposure using kurtosis

In assessing auditory effects on marine mammals from sound exposure, regulators currently estimate noise-induced threshold shifts (NITSs) based on classifying anthropogenic sound in two mutually exclusive categories: impulsive or non-impulsive. However, in real-world situations, marine mammals are often exposed to complex sound fields containing both impulsive and non-impulsive components, making it difficult or even impossible to accurately assess NITSs from sound exposure. One example of complex sound originates from down-the-hole (DTH) pile installation, which generates both impulsive sound from percussive drilling/striking and non-impulsive sound from simultaneous debris removal. This study employed a relatively simple approach of using kurtosis values to quantify the impulsiveness of two DTH pile installation datasets for six different marine mammal functional hearing groups. A kurtosis adjustment approach was then used—one that has been suggested to be able to predict human hearing loss from sound exposure—to calculate the correction factors for estimating NITSs of marine mammals exposed to DTH piling sound. Fur-ther research on marine mammal NITSs from complex sound exposure is needed to validate and improve this model.