Comparative analysis of /kwa/ fish sounds recorded during an early ecoacoustics experiment in a Posidonia oceanica seagrass meadow (Ustica Island, 1999)

Passive acoustics enables studying marine habitats thanks to the sound production of their inhabitants. A key question is: “Can fish sounds be used as environmental proxies?” Posidonia oceanica (L.) Delile 1813 seagrass meadows constitute an important ecosystem of the Mediterranean Sea which protects many species of invertebrates and fishes, some of which producing sounds with distinctive features. An arched frequency modulation centred at 747 Hz which aurally sounds like /kwa/ is being investigated as an environmental proxy (Raick et al. 2017). Remarkably, these sounds were already noted as a distinctive feature of the soundscape recorded during an early acoustic ecology experiment, USTICA 99, which measured simultaneously photosynthetic gaseous exchange and fish migration at the scale of a Posidonia meadow (Hermand 2003). We revisit that dataset to describe the specific characteristics and variability of the early recorded /kwa/ sounds and make a comparison with our recent study carried out in France about 500 km north of the Sicilian Island and 15 years later. The sounds have been analysed both individually and all together, i.e., considering the entire choruses. Our comparative analysis based on a dictionary confirms a high homogeneity of the /kwa/’s but with little variations which are examined in detail.