Listening to whales and earthquakes: on exploring hydrophone recordings and Distributed Acoustic Sensing

Sound plays a crucial role in marine environments. Biophony and geophony are key components of underwater soundscapes produced by marine fauna and natural sounds (Krause, 2008). The evolution of soniferous species depends on geophony, which has significant acoustic implications for their development and adaptation. Among biological sources, mysticetes are known for their vocal activity, produce complex acoustic repertoires, and have evolved specialised mechanisms for sound production and highly adapted auditory systems (Elemans et al., 2024). The analysis of earthquake signals, as a component of geophony, offers valuable insights into the Earth’s internal structure and dynamic behaviour (Marra et al., 2019). Passive Acoustic Monitoring (PAM) techniques enable the detection of animals through their acoustic presence and the tracking of changes in their acoustic behaviour in response to anthropogenic sound sources, and can also record the temporal and spatial distribution of earthquakes in oceanic regions (Howe et al., 2019). Although hydrophone networks are uniquely suited for continuous long-term monitoring, the recorded data are usually insufficiently sampled and expensive (Kowarski and Moors-Murphy, 2021). Distributed Acoustic Sensing (DAS) is showing progress in terms of data quality and spatial coverage. Also due to its ability to sample remote and inaccessible regions, DAS is increasingly used at sea to monitor whales and earthquakes (Landrø et al., 2022). In this pilot study, we build on Ragland et al. (2022) and Wilcock et al. (2023), and explore examples of acoustic recordings of fin whale (Balaenoptera physalus) calls and earthquakes recorded by hydrophones and fibre optics from the Ocean Observatories Initiative Regional Cabled Array (OOI-RCA) network in the NE Pacific Ocean. Further studies should move towards an indepth analysis and comparison of acoustic recordings gathered from multiple instrumentations