Community overlap of bottlenose dolphins (Tursiops truncatus) found in coastal waters near Charleston, South Carolina

Long-term photo-identification (photo-id) research into the identity, distribution and movements of dolphins in the estuarine waters near Charleston, South Carolina has been conducted since 1994. However, relatively little is known about dolphins in adjacent coastal waters. In our study, movements of dolphins between estuarine and coastal waters were investigated both to characterize short-term movements and determine the degree of mixing between putative coastal and estuarine dolphins. Bi-monthly photo-id surveys were conducted along a 33 km transect of the Charleston coastal area from January 2003 to December 2006. Using ArcGIS spatial analysis, dolphins sighted along the coast were separated into two communities: coastal dolphins (68%) and estuarine dolphins (22%); the remaining 10% showed no preference to either area. Over half (57%) of all coastal dolphins were only sighted a single time. The majority of dolphins (69%) were encountered in mixed groups composed of both coastal and estuarine dolphins. Only 17% of groups were composed exclusively of coastal individuals, while 14% of the groups were composed entirely of estuarine individuals. Findings from this study document at least two communities of dolphins and provide insight into the mixing of coastal and estuarine dolphins near Charleston and the movements of coastal dolphins. Newly identified dolphins from the coast were occasionally seen in estuarine waters, but more importantly known dolphins from estuarine waters were not only seen in the coastal waters but the majority of their sightings occurred with dolphins identified as coastal individuals. These results support management and conservation efforts of coastal bottlenose dolphins. [JMATE. 2011;4(2):10-18]