Fish biophony in a Mediterranean submarine canyon: a preliminary investigation using Static Acoustic Monitoring and gliders

Submarine canyons are key structures for ecosystem functioning in the Mediterranean Sea. This study was conducted in the canyon of Calvi (North-West Corsica, France) by using a combination of Static Acoustic Monitoring (SAM) and hydrophone integrated gliders (Seaexplorer, Alseamar). During summer 2016 and 2017, three SAM campaigns (-125 m to -150 m, 3 kilometers from coastline) and one gliders mission (-900 m to -60 m, 6 kilometers to 3 kilometers from coastline) were here conducted. A total of 194 hours of recordings were analysed for fish sound diversity (i.e. number of sound types) and for fish sound abundance (number of sounds per sound type and per unit of time).

Biological sounds were detected in 37% of the recorded audio files. Besides for the presence of marine mammals clicks and whistles, at least 9 sound types (for a total of more than 8.000 sounds) with characteristics similar to those emitted by known vocal fish species were characterised; for one of these, emitter identity could be inferred at the genus level (Ophidion sp.). Furthermore, an increase in Sea Ambient Noise between 10 and 15 dB re 1 µPa was observed during daytime hours due to boat traffic.

The vastness of the deep-sea and, in particular, the heterogeneity of submarine canyons, their high biodiversity and level of fauna specificity, together with the very localized character of observations carried out to date fully justify the use of an holistic monitoring approach such as PAM, especially when a combination of methods is used (e.g. SAM and gliders). Our study demonstrate that PAM can provide novel information about the ecoacoustics and the distribution of vocal fish species in these pivotal Mediterranean environments and can assess the contribution of anthropogenic sound and their adverse effects (such as masking) on fishes.