The unexploited potential of listening to deep-sea fish

Covering more than 65% of the Earth surface, the deep sea (200-11,000 m depth) is the largest biotope on Earth, yet it remains largely unexplored. The biology of its communities is still poorly understood, and many species are still to be discovered. Despite this, deep-sea fish are already threatened by our exploitation and their conservation is hampered by a severe scarcity of data. Studies focusing on fish acoustic communication are receiving growing attention in coastal areas as they provide useful information to different fields, ranging from behaviour, ecology, wild population monitoring, biodiversity assessment, fisheries and aquaculture management. Modern non-invasive techniques such as passive acoustic monitoring (PAM) can provide high-resolution, long-term and large spatial scale information on populations and ecosystem dynamics in otherwise not accessible environments. Although acoustic communication of deep-sea fish is still poorly documented, many deep-sea species are likely to emit sounds as they possess the required anatomical structures. Here we suggest that monitoring deep-sea fish vocal communication might help to better understand their diversity, ecology and dynamics. Emerging technologies based on PAM have the potential to provide a holistic view of the importance of acoustic communication for deep-sea fish and, ultimately, to inform us about essential aspects for their management and protection.