Cetacean acoustic occurrence in the Southern Ocean from biologged southern elephant seals

The Southern Ocean is a crucial habitat for multiple species of cetaceans, from mysticete species to odontocetes such as sperm whales and delphinids. However, their presence at high latitudes is still poorly known due to the remoteness of the area, with little literature on delphinid presence and sparse sampling along mysticete migration routes. At the end of their breeding season, southern elephant seals leave their haul-out sites and set out on a foraging trip, covering vast expanses of the Southern Ocean during the austral spring. During these trips, elephant seals rest by entering drift phases, where their speed is minimal. These drift phases can act as listening points of opportunity to analyze sound sources across all frequency ranges. Between 2017 and 2020, nine female elephant seals (3 from the Península Valdés population and 6 from the Kerguelen population) equipped with DTAG4 (Digital Acoustic Recording Tag) devices recorded the underwater ambient soundscape continuously (samplerate of either 32000 Hz or 38400 Hz ). This study aimed at using drift phase recordings to assess cetacean acoustic occurrence, providing unique and complementary data to existing observations. Results show that multiple different cetacean species, both mysticetes and odontocetes, can be monitored, with high bioacoustic activity being found in some datasets. The annotation of the gathered recordings thereby offers a remarkable snapshot of cetacean acoustic presence in the Southern Ocean, giving new insights into their habitat use during spring. Results show acoustic presence of antarctic blue whales and humpack whales around the polar front and subantarctic front respectively in the Indian sector of the Southern Ocean and increased presence of sperm whales along important bathymetric gradients in the Atlantic sector of the Southern Ocean. These promising results emphasize the potential of biologged animals to monitor other species of interest, with the added benefit to sample across considerable areas and in harsh environments. This study paves the way for new research such as modeling cetacean acoustic presence using co-located environmental data collected by the tags.