Underwater soundscape indicates low anthropogenic influence around two sub-Antarctic islands

Contributions and effects of anthropogenic activities on the underwater
soundscape of the sub-Antarctic regions remain poorly studied. Over 21
months (April 2021 to December 2022), we recorded underwater noise levels
amid two sub-Antarctic Prince Edward Islands (PEIs) within an offshore
marine protected area (MPA) to quantitatively investigate the sources of
underwater noise and the impact of such noise on the detectability of
marine mammal vocalizations. We measured underwater noise levels within
the low (20–120 and 121–800 Hz), medium (801–25000 Hz), and high
(25001–48000 Hz) frequency bands. Wind speed was the primary predictor of
low and medium-frequency underwater noise levels, whereas iceberg volume
was the primary predictor at the high-frequency band. Probabilities of
detecting vocalizations of Antarctic blue, fin, humpback, Antarctic minke,
and killer whales decreased with increasing noise levels. On the contrary,
probabilities of detecting sei and Madagascan pygmy blue whales increased
with noise levels. Overall, these novel results indicate that geophonic
noise dominates the underwater soundscape of the PEIs in the absence of
intense anthropogenic activities such as marine traffic, and that
conservation efforts through this MPA might be protecting this remote
region from anthropogenic activities.