Associations and ranging patterns of common bottlenose dolphins near Brunswick, Georgia, USA

Abstract

AbstractThe Southern Georgia Estuarine System (SGES) stock of common bottlenose dolphins (Tursiops truncatus) resides in estuarine waters near Brunswick, Georgia, USA. There are concerns for this population due to the presence of anthropogenic stressors, particularly in the Turtle‐Brunswick River Estuary (TBRE), where polychlorinated biphenyl (PCB) concentrations in dolphins are >10 times higher relative to dolphins elsewhere in the southeastern United States. The goal of this study was to evaluate the association patterns and distribution of the SGES stock based on long‐term photo‐identification data (2010–2021) using analyses of social dynamics and spatial movements. Social analyses identified 5 distinct clusters, 3 of which were substantially larger and more well‐defined than the other 2. Spatial analyses indicated geographic partitioning among the 3 large clusters, with little overlap in their core ranges (50% utilization distributions) but shared ranges in their 95% utilization distributions. Despite having variable ranging patterns, all 3 large clusters used the TBRE in proximity to the Linden Chemicals and Plastics (LCP) Superfund site to a degree, suggesting that they have likely been exposed to high levels of PCBs. Given the spatial distinction and low connectivity between clusters, loss in any of the identified clusters has potential to further segment the population and lead to a decline in the SGES stock as a whole. The fine‐scale population structure should be considered in identifying effective conservation efforts at the appropriate scale.