5. Conclusion and implications
Underwater passive acoustic monitoring was conducted at Inexpressible Island in the Ross Sea region marine protected area for 3 days during the austral summer season, and we found that leopard seal vocalizations were the dominant sound sources in this region. Leopard seal underwater vocalizations, known to be relatively stereotyped, can be categorized into six call types based on previous studies, and their acoustic characteristics are presented. Among the low-frequency vocalizations, we have termed a new call type, triple ascending trill, which consists of three trill parts in a frequency range of approximately 400 to 1,540 Hz. These observationss were supported by UAV and monitoring camera data collected together during the underwater acoustic measurements. Our research includes passive acoustic monitoring results that were conducted in a region, which has limited human access in the ASPA and no prior acoustic observations. We have applied state-of-the-art techniques, which can be effective for pinnipeds, to research Antarctic marine mammals, as vocalizations can be recorded both underwater and out of the water, unlike those of whales. Our results can be applied to studies that estimate the population and distribution of marine mammals by measuring their acoustic habitat and could contribute to understanding the Antarctic marine ecosystem from a soundscape ecology perspective.