The sea chordophones make the mysterious /Kwa/: emitter identification of the dominating fish sound in Mediterranean seagrass meadows

Abstract

The /Kwa/ vocalization dominates the soundscape of Posidonia oceanica meadows but the identity of the species emitting this peculiar fish sound remains a mystery. Information from sounds recorded in the wild indicates that the emitting candidates should be abundant, nocturnal and benthic. Scorpaena spp. combine all these characteristics. This study used an interdisciplinary approach to investigate the vocal abilities of Scorpaena spp.; morphological, histological and electrophysiological examinations were interpreted together with visual and acoustic recordings conducted in seminatural conditions. All observed Scorpaena spp. (S. porcus, S. scrofa and S. notata) share the same sonic apparatus at the level of the abdominal region. This apparatus, present in both males and females, consists of 3 bilaterally symmetrical muscular bundles, having 3-5 long tendons, which insert on ventral bony apophyses of the vertebral bodies. In all chordophones (stringed instruments), the frequency of the vibration is dependent on the string properties and not on the rate at which the strings are plucked. Similarly, we suggest that each of the 3-5 tendons found in the sonic mechanism of Scorpaena spp. acts as a frequency multiplier of the muscular bundle contractions, where the resonant properties of the tendons determine the peak frequency of the /Kwa/, its frequency spectra and pseudoharmonic profile. The variability in the length and number of tendons found between and within species could explain the high variability of /Kwa/ acoustic features recorded in the wild. Finally, acoustic and behavioural experiments confirmed that Scorpaena spp. can emit the /Kwa/ sound.

Characterization of the acoustic community of vocal fishes in the Azores

“…Sound sequence #12 (duration: 0.56 s, peak frequency: 1,175 Hz; Table 4) exhibits similarities with the /kwa/ recorded in Posidonia oceanica meadows in the Mediterranean Sea, recently attributed to Scorpaena spp. (0.27s duration and 747 Hz peak frequency; Di Iorio et al, 2018; Bolgan et al, 2019). This sound presents several acoustic features which are typical of the “kwa” sound.…”

“…This sound presents several acoustic features which are typical of the “kwa” sound. In particular, peak frequency is always higher than 600 Hz, the pulse envelop presents a highly stereotyped amplitude modulation where cycle period corresponds to peak frequency; finally, the sound presents a typical pseudo-harmonic structure where the pseudo-harmonic interval corresponds to the inverse of the pulse period (Di Iorio et al, 2018; Bolgan et al, 2019). Interestingly sound sequence #12 also shows some resemblance in frequency and duration with the chatter sound made by cusk-eels Ophidion marginatum (Ophidiidae) (Sprague & Luczkovich, 2001; Mann & Jarvis, 2004), although they do not seem similar to the human ear.…”

Redirection of ambient light improves predator detection in a diurnal fish

“…An additional, similar-sized area behind the latter was used to hide the alternative stimulus. All compartments had many slits and holes for water exchange to assure that the scorpionfish could be smelled and heard [27], even when only the stone was visible. Visual contact between fish and the outside was excluded by a 10 cm white side cover along the bottom edge.…”

The unexploited potential of listening to deep‐sea fish

“…For example, while upper and mid-slope Neobythitinae (Ophidiiformes) sonic system are well developed, several sonic muscles' adaptations occur in species inhabiting the lower slope (Fine et al, 2018). These adaptations, which include a reduced number of sonic muscles with long tendons, smaller and thinner swimbladders and larger muscle fibres, could facilitate rapid bladder movement while using less metabolic energy (Fine et al, 2018 (Amorim & Hawkins, 1994;Bolgan et al, 2019;Groison, Kjesbu, & Suquet, 2011;Hallacher, 1974;Hawkins & Picciulin, 2019;Myrberg, 1981;Onuki & Somiya, 2004;Parmentier, Gennotte, Focant, Goffinet, & Vandewalle, 2003;Parmentier, Lagardère, Braquegnier, Vandewalle, & Fine, 2006;Širović, Cutter, Butler, & Demer, 2009;Zhang, Guo, Zhang, & Song, 2015). Sounds or sonic mechanisms have never been reported in deep-sea resident counterpart species, simply reflecting a lack of investigations in this sense.…”

“…Besides these five families, at least nine other additional taxa include good candidates for sound production in the deep sea. In Gadidae (Gadiformes), Lotidae (Gadiformes), Merluccidae (Gadiformes), Carapidae (Ophidiiformes), Dactylopteridae (Scorpaeniformes), Scorpaenidae (Scorpaeniformes), Sebastidae (Scorpaeniformes), Triglidae (Scorpaeniformes) and Zeidae (Zeiformes) sound production and/ or sonic mechanisms have been reported in different shallow living species (Amorim & Hawkins, 1994; Bolgan et al, 2019; Groison, Kjesbu, & Suquet, 2011; Hallacher, 1974; Hawkins & Picciulin, 2019; Myrberg, 1981; Onuki & Somiya, 2004; Parmentier, Gennotte, Focant, Goffinet, & Vandewalle, 2003; Parmentier, Lagardère, Braquegnier, Vandewalle, & Fine, 2006; Širović, Cutter, Butler, & Demer, 2009; Širović & Demer, 2009; Zhang, Guo, Zhang, & Song, 2015). Sounds or sonic mechanisms have never been reported in deep‐sea resident counterpart species, simply reflecting a lack of investigations in this sense.…”