Listening for signals in seismic noise: A case study of masking in Arctic seals

Abstract

When considering the effects of noise on hearing in marine mammals, standard audiometric data are commonly applied to predict how a noise source will influence an individual or species. With regard to auditory masking, critical ratio measurements and average noise spectral density levels can be used to obtain masked threshold predictions. However, the extent to which this method is appropriate varies based on the features of the noise source in question. Temporally varying noise, such as that generated by seismic surveys, presents a significant challenge. To address this, we trained captive spotted and ringed seals to detect 100 Hz narrowband signals embedded within a background of seismic noise recorded from an operational air gun array. The masking data demonstrated that conventional masked threshold predictions were least accurate when the noise exhibited the greatest amplitude fluctuation in time. This study addresses the important issue of masking outside of the laboratory, and provides much needed information about when it is appropriate to use average noise levels and critical ratio data to predict masking in real environments. Our results can inform best management practices for evaluating the effects of noise on Arctic seals and other marine mammals.