Social structure and ‘situationships’ in Indo-Pacific humpback dolphin <i>Sousa chinensis</i> societies in north-western Peninsular Malaysia: conservation implications within an Important Marine Mammal Area

Abstract Indo-Pacific humpback dolphins Sousa chinensis face multiple anthropogenic threats in the coastal waters of Langkawi and the adjacent Perlis–Kedah mainland in north-west Peninsular Malaysia. The area is recognized by the IUCN as an Important Marine Mammal Area and harbours a significant population of humpback dolphins. Understanding their social structure is crucial for identifying conservation units to guide targeted management to preserve the species’ ecological processes, particularly for a species in the data-deficient Southeast Asia region. Association patterns and network analysis from a decade of photo-identification surveys (2010–2020) revealed a fission–fusion society defined by frequent changes in group membership and size, and characterized by loose associations between individuals. Association strength was generally low, although some non-random long-term associations persisted for 5 months to several years. Unusually large groups of humpback dolphins (81–204 individuals) were often observed, comprising travelling mother–calf pairs and functioning as nursery groups. The grouping plasticity and social dynamics reflect the species’ survival strategies in response to local environmental conditions, notably resource availability and predation pressure. Most importantly, our findings confirm that the humpback dolphin population in this region constitutes a stable and well-connected single conservation unit, necessitating coordinated protection by different governmental administrators across the extensive study area. The insights from our study should inform tailored management strategies for humpback dolphins and promote early detection of anthropogenic threats that may impact social-ecological processes and the overall survival of the population.