Assessment of social mixing and spatial overlap as a pathway for disease transmission in a northeast Florida estuarine dolphin community

Common bottlenose dolphins (Tursiops truncatus) in estuarine systems are often subjected to natural and anthropogenic risks, which may impact their health and behaviors. Effective management for this species should incorporate continual, updated information on behavioral patterns of the individuals within populations. Currently, the Jacksonville Estuarine System stock assessment report, which includes dolphins in the St. Johns River (SJR) in northeast Florida, is based on data from the 1990s. Since then, dolphins’ use of the SJR has shifted, and the community has been impacted by two unusual mortality events (UME). This study analyzed site fidelity, space use and overlap, and social mixing with respect to the epizootic 2013–2015 UME, whose infectious agent was cetacean morbillivirus (CeMV). Examination of residency status determined that most dolphins sighted in the river were year-round residents (x¯ =45%, SD = 3.20). Space use and overlap of core areas occurred among residency categories but varied between cold and warm seasons and across time periods. There were key, highly connected individuals in the social network, which may have influenced disease transmission during the UME. Individuals infected by CeMV that stranded during the UME shared overlapping core areas with each other and with individuals from different residency categories. Altogether, this information on site fidelity, spatial overlap, and social mixing will help improve management plans for SJR dolphins, lead to better response efforts to future unusual mortality events, and increase the understanding of disease transmission in social species.