Sensitivity to airborne sounds in ice-dependent bearded seals.

Abstract

As the Arctic warms and becomes more accessible to human activities and associated noise sources, it is important to understand the auditory capabilities of ice-associated marine mammals that rely on sound. In this study, the in-air hearing of one adult bearded seal (Erignathus barbatus) was measured in ambient outdoor conditions using psychophysical methods. 50% detection thresholds were measured for 10 frequencies (0.04-51.2 kHz) that extend across the subject's hearing range. For low to mid frequencies (0.04-12.8 kHz), thresholds were constrained, or masked, by ambient noise. Thresholds obtained at higher frequencies (25.6-51.2 kHz) were sufficiently elevated above background noise to provide absolute measures of hearing sensitivity. These measurements reveal that the high-frequency roll-off for bearded seals is in alignment with available auditory data for related species despite more than 11 million years of evolutionary isolation. Further, the data collected at low and mid frequencies enable an unconventional estimation of critical ratios, which can be applied in masking models. Collectively, these findings for bearded seals listening for airborne sounds highlight auditory similarities within the northern clade of phocid Carnivores and improve predictions of potential noise effects for seals in changing Arctic soundscapes.