Anthropogenic noise is a dominant component of the shallow-water soundscape of the eastern Ionian Sea

The eastern Ionian Sea is an important area for marine fauna, but it is also a region of substantial overlap between human activities and natural ecosystem components. Using data from a fixed passive acoustic monitoring station deployed over a 7-month period (July 2022 – January 2023), this study describes the near-shore marine soundscape of northern Kefalonia Island and documents elevated noise levels associated with coastal and offshore anthropogenic activities. Underwater noise from recreational speedboats exhibited a prominent diel pattern during the summer months that was absent in winter. In contrast, diffuse low-frequency noise from offshore shipping traffic was persistent throughout the monitoring period. Additionally, offshore oil and gas seismic surveys conducted at the end of 2022 had a major acoustic footprint on the coastal soundscape. During the first two weeks of December 2022, sustained seismic airgun activity resulted in broadband (10–2000 Hz) received sound pressure levels of 114.4 dB re 1 μPa (Root-Mean-Square), with maximum daily zero-peak levels ranging from 140 to 147 dB re 1 μPa. Continuous soundscape monitoring in these waters is essential for informing underwater noise management and mitigation measures under the European Union Marine Strategy Framework Directive, particularly in light of ongoing hydrocarbon exploration efforts in the eastern Ionian Sea and the establishment of the Ionian National Marine Park, which is primarily aimed at the conservation of marine mammals.