Acoustic Characteristics of the Leopard Seal Underwater Vocalizations Measured in Inexpressible Island, Antarctica

Passive acoustic monitoring for marine mammals was conducted in the Seaview Bay off Inexpressible Island, Ross Sea, Antarctica, for 54 hours in austral early summer. In this period, leopard seal vocalizations were the predominant underwater sound source as their broadcast call became vociferous for mating. We manually detected calls and classified them into 6 types based on the previous study (high double trill, medium single trill, low double trill, hoot with single trill, descending trill and ascending trill ascending trill). Acoustic characteristics such as maximum, minimum, peak frequencies as well as pulse duration, of each call types were estimated from random samples of at least 100 signals. Among the call types of classified in this study, the ascending trill only showed a different form compared to previous studies which consisted of three trills in series. We identified this call as triple ascending trill and suggested that ascending trill is fundamentally composed of three parts. Our results can serve as fundamental data for studies related to the vocalization and behavior of leopard seals.