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.