First evidence of underwater vocalizations in green sea turtles Chelonia mydas

Marine turtles have long been considered to be silent, but few investigations have been performed to confirm such muteness. However, recent studies on the aerial and underwater hearing abilities of marine turtles have shown they have an ability to perceive sounds, suggesting the potential existence of acoustic communication among them. In the present study, audio-video recorders were deployed on 11 free-ranging juvenile green sea turtles Chelonia mydas at Grande Anse d'Arlet in Martinique. The recordings revealed that the turtles produced 10 different sound types that were classified into 4 main categories: pulses, low-amplitude calls (LAC), frequency-modulated sounds, and squeaks. Although other turtles were not observed in close proximity to tagged turtles during the recordings, some of the described sounds were found in most recorded individuals and their frequency characteristics ranged within the underwater hearing range of green sea turtles, suggesting that the sounds could be used for intra-specific communication. While control recordings in the study area without the presence of green sea turtles contained sounds with similar general structure (pulses, LAC), the acoustic characteristics were significantly different to those recorded for green sea turtles. The 2 types of squeaks identified for the turtles were found to be individual-specific, also suggesting they could be used for intra-species communication. Further research on sea turtles is needed to better understand the behavioral and social context of these acoustic productions, especially during the developmental period and breeding season. Thus, the vocal repertoire of green sea turtles is likely to be more diverse than that currently described.