Acoustic study of diving sperm whales during a week of continuous monitoring in the western Ionian Sea

Endangered Mediterranean sperm whales (Physeter macrocephalus) have been monitored in the Ionian Sea via acoustic observatories since the early 2000s. SMO-OνDE acoustic antenna, deployed in the Gulf of Catania at 2100 m depth (2013-2021), consisted of a tetrahedron of synchronized hydrophones sampling at 192 kHz. Real-time acoustic data analysis saved a 5-minute subset every hour. We report sperm whale detection analysis from February to April 2017 and one additional week of continuous raw data. Sperm whale clicks were detected and tracked in a range of 15 km around the observatory. The species was detected almost daily during all months. Different sound types, including regular clicks, 3+1codas, and creaks were found throughout the continuous week. Diving whales’ movements were reconstructed by acoustic tracking. 47 dives were studied, and multiple whale movements were reconstructed. Our results confirm the presence of the species about ten years after the previous study in the area and demonstrate the first simultaneous underwater tracking of communicating sperm whales, even in the presence of large vessels and high noise levels. This study reveals essential information on sperm whale behavior and responses to noise, as required for conservation purposes.