Underwater passive acoustic monitoring of leopard seals ( Hydrurga leptonyx ) off Inexpressible Island, Antarctica during 2021 Austral Summer

Underwater passive acoustic monitoring (PAM) of marine mammals, particularly seals, was conducted at seven sites around Jang Bogo Station in Terra Nova Bay, Antarctica, during the 2021 austral summer to investigate the interaction across trophic levels, from lower levels such as plankton and fish, through intermediate predators like penguins and skuas, to higher levels. Killer whales, mink whales, and three species of seals (Weddell seals, Leopard seals, Crabeater Seals) were visually observed. This study presents data focusing on the hydrophone data recorded for three days off Inexpressible Island. The recorded acoustic data revealed that vocalizations of leopard seals, which are relatively stereotyped, were the dominant sound source, and their acoustic characteristics were analyzed in comparison with previous studies. To overcome limitations of PAM which inherently requires prior identification data, two types of cameras were operated: one used underwater and the other on the sea ice, along with an unmanned aerial vehicle. A triple ascending trill, consisting of three trill parts, was newly identified, and the temporal variations of the identified call type were further analyzed and discussed.