Relationships between social structure, environmental conditions and whistle characteristics in common bottlenose dolphins (Tursiops truncatus) in the eastern Aegean Sea

Introduction Bottlenose dolphins ( Tursiops truncatus ) rely on whistle vocalisations for group cohesion and coordination. Although whistle characteristics are shaped by a wide range of factors, the combined effects of social structure, habitat characteristics and marine traffic remain poorly understood in the eastern Mediterranean. Methods This study investigated the acoustic ecology of bottlenose dolphins in the eastern Aegean Sea by integrating passive acoustic monitoring, photo-identification-based social network analysis, marine traffic ratio and environmental data collected between 2017 and 2025. A total of 986 whistles from 30 recordings were analysed. Results Individuals showed preferred associations, but modularity indicated that the nine detected clusters were not stronger than expected by chance, so clusters were considered tentative social units. Only the two largest clusters had enough independent recordings for acoustic comparison. When environmental variables were taken into account, whistle structure differed between the two clusters (PERMANOVA, R 2 = 0.29, p = 0.002). This result remained significant when accounting for group size and research vessel, and when excluding recordings shared by both clusters. Whistles of one cluster had more inflection points and a higher proportion of sinusoidal contours. Sea surface temperature was also associated with whistle structure, but this effect was not consistent across the robustness analyses and could not be fully separated from season. Marine traffic ratio, which was low throughout the study, showed no consistent effect on whistle structure, and depth had no effect. Social and environmental effects were only detected when considered together, suggesting that they may partly mask each other when examined separately. Discussion Whistle variation in bottlenose dolphins in the eastern Aegean Sea appears to be mainly related to social structure and, to a lesser extent, to environmental conditions, whereas no consistent effect of marine traffic was detected at the low traffic levels recorded. This study provides initial information on whistle variation in this population and its relationship with social and environmental factors, which can support future conservation and management strategies.