Sperm whale acoustic ecology around two sub-Antarctic islands

Abstract

Sperm whales are cosmopolitan in nature, but very little is known about their occurrence in the sub-Antarctic region. This study aimed to investigate the acoustic occurrence of sperm whales relative to environmental conditions and underwater noise around two sub-Antarctic Prince Edward Islands (PEIs) using passive acoustic monitoring data collected between early 2021 and early 2023. Sperm whale clicks were detected continuously throughout the study period with high presence of calls in February through August, highlighting the PEIs as an essential habitat with sufficient year-round prey for this species. Moreover, the February through August peak occurrence corresponds to the migration period of males from Antarctica to the low latitudes for mating. Diel vocalizing pattern revealed high nighttime vocalization that varied slightly between seasons. Wind speed was classified by the random forest model as the most important predictor of sperm whale acoustic occurrence, indicating possible masking and attenuation of whale signals by wind-induced noise and wind-induced air bubbles respectively. Generalized additive model showed that the probability of detecting sperm whale clicks decreased with increasing high frequency band (25001–48000 Hz) noise, reflecting a significant influence of the high frequency noise on this species’ ecology. This is the first study to document the acoustic presence of sperm whales around the sub-Antarctic PEIs, showcasing the capability of bioacoustics method to effectively study marine mammals that are rarely sighted. Sperm whales should be considered in the spatial management and conservation plans of the PEIs given their year-round presence in this region.