Diving pattern and behavioral response to vessel traffic of Indo-Pacific humpback dolphins (Sousa chinensis) in Xiamen, China: implications for conservation

Marine mammals have evolved sophisticated diving strategies to balance foraging efficiency with the avoidance of disturbances, a challenge that is particularly acute in coastal environments heavily influenced by human activities. The Indo-Pacific humpback dolphin ( Sousa chinensis ), inhabiting Xiamen Bay, China, is among the species most vulnerable to such pressure. Despite this, knowledge of its diving behavior and sensitivity to vessel traffic remains limited. In this study, a total of 4,408 dives of Indo-Pacific humpback dolphins were recorded, with a mean duration of 20.41 ± 1.77 s. Within the same age group, no significant differences in dive duration were found between traveling and foraging behaviors. However, comparisons across age classes revealed that subadults and adults consistently executed longer dives than juveniles, reflecting an ontogenetic progression in diving capacity. Furthermore, the dolphins demonstrated pronounced negative behavioral responses to speedboats and vessels operating at distances less than 100 m, underscoring marine traffic as a substantial source of disturbance. Based on these findings, it is recommended that vessels maintain a minimum buffer zone of 100 m, comply with a strict 10-knot speed limit, and adopt proactive avoidance practices when transiting through dolphin habitats.