Use of passive acoustic monitoring to fill knowledge gaps of fish global conservation status

1. Knowledge of the ecology, spatial distribution and conservation status of fish populations is achieved by fishery-dependent techniques, and by more recently developed non-invasive fishery-independent techniques. Passive acoustic monitoring (PAM) is a fishery-independent method that provides remote sensing of soniferous species, populations, communities and ecosystems by recording soundscapes and their components. 2. A case study is presented to demonstrate how PAM can contribute to a dynamic understanding of fish distribution, ecological preferences and conservation status. This case study refers to the cusk-eel Ophidion rochei (Ophidiiformes), a nocturnal, behaviourally cryptic, soniferous fish species, described as uncommon and rare in the scientific literature, and listed as Data Deficient in the IUCN Red List. 3. A systematized literature review was carried out using Ophidion+rochei as the search term, and by grouping records into two main categories: (i) traditional techniques (including all fishery-dependent techniques and underwater visual census); and (ii) PAM. 4. This review highlights how PAM has provided new sightings of O. rochei at a rate three times higher than all other monitoring techniques combined. In contrast with the knowledge achieved to date by fishery-dependent techniques, the reported acoustic mass phenomena indicate that this species can be very abundant. Ophidion rochei was found to inhabit a wide range of depths and ecosystems, at least throughout the Mediterranean basin. 5. This paper supports the urgency and the importance of relying on the integration of different fishery-independent techniques for multidisciplinary monitoring, in line with the Goal 14 requirements of the UN Decade of Ocean Science forSustainable Development.