Listening to tuna: Acoustic characterization of captive juvenile yellowfin tuna ( <i>Thunnus albacares</i> )

The effectiveness of passive acoustic monitoring (PAM) for studying marine biodiversity highly relies on comprehensive libraries of species-specific sounds. While sound production is well-documented in reef and freshwater fishes, the acoustic behaviour of ecologically and economically vital pelagic species like tunas still remains largely unexplored. This study provides a detailed characterization of sounds produced by the yellowfin tuna (Thunnus albacares), a widely distributed species sustaining a global fishery. Acoustic recordings were conducted in a large concrete tank to minimize acoustic artefacts and ensure species-specific attribution, where 19 juveniles were maintained in captivity during 16 days. Over 6400 sounds were detected and categorized into two distinct types: short sounds (average duration 47 ms) and long sounds (534.4 ms) consisting of trains of pulses, both with a peak frequency of 263.1 ± 31.3 Hz. There was a clear diel difference in yellowfin tuna sound production: long sounds were more abundant during the day than at night, whereas short sounds varied more modestly, peaking in the evening and declining overnight, with intermediate levels during the day. This characterization is a critical first step towards using PAM for monitoring this tropical tuna species, thereby providing a novel, fisheries-independent method to study its distribution, behaviour and abundance.