Vocal repertoire and consistency of call features in the meagre Argyrosomous regius (Asso, 1801)

Passive Acoustic Monitoring (PAM) is a non-intrusive and cost-effective method capable of
providing high-resolution, long-term information on the status and health of vocal populations
and communities. To successfully monitor the same species over wide geographical
and temporal scales, it is necessary to characterise the range of sound variability, as well as
the consistency of sound features between populations. The meagre (Argyrosomus regius,
Asso 1801) is an interesting case study because recent investigations suggest a wider vocal
repertoire than previously described. In this study, meagre vocalizations were recorded and
analysed from a variety of settings, ranging from rearing facilities to wild populations to provide
a comprehensive characterisation of its vocal repertoire, while investigating the consistency
of spawning sound features between populations. All sounds presented a similar
acoustic structure in their basic unit (i.e. the pulse), while an important variability was found
in the number of pulses; the meagre can emit sounds made of one single pulse or many
pulses (up to more than 100). High level of overlap in the Principal Component Analysis
made difficult to differentiate sound type clusters. Despite this, two sound types were identifiable:
knocks (sounds from 1 to 3 pulses) and long grunts (sounds with more than 29
pulses). Discriminant Analysis carried out on PCA residuals showed that knock had the
highest proportion of correct placement (92% of the observations correctly placed) followed
by long grunts (80%). All other previously described sound types (intermediate grunt, short
grunt and disturbance sounds) could not be separated and presented low levels of correct
placement, suggesting that care should be taken when defining these as independent
sound types. Finally, acoustic features consistency was found in meagre grunts emitted by
different populations during spawning nights; statistical differences could be explained by
recording settings and fish conditions. The results of this study provide important information
for fostering PAM programs of wild meagre populations, while contributing to the discussion around the definition of fish sound types in vocal fish communities. Studies of this kind,
which evaluate both variability and consistency of sound features, are of fundamental importance
for maximising PAM efforts in the wild, at both the specific and the community level.