Abundance of Bottlenose Dolphins (Tursiops truncatus) in Estuarine and Near-Shore Waters of North Carolina, USA

Abstract

Abstract A capture-recapture survey of bottlenose dolphins ( Tursiops truncatus ) was conducted in the sounds, estuaries and near-shore waters of North Carolina during July 2006, using photographic identification techniques; 291 dolphins were identified from distinctive nicks and notches on their dorsal fins. The results of our photographic analyses were applied to several capture-recapture models. The best estimate of the number of bottlenose dolphins present in estuarine waters of North Carolina during July 2006 was 813 with a 95% Confidence Interval of 483–1,142. Previously in July 2000, 1,033 (95% CI: 860-1,266) dolphins were estimated to be present in the estuaries of North Carolina. When the analysis from the 2006 surveys was expanded to include adjacent coastal waters, then the estimate of abundance increased to 1,138. Therefore, the abundance of dolphins in this area remained relatively stable between the two studies. Most dolphins were found in the northern part of the study area and there was very little exchange between the northern and southern areas of the state. The recapture data was also used to identify a spatial boundary between two putative management units that may be useful for future stock delineations. Additionally, an unexpected potential bias was introduced with the transition from slide film to digital media in the evaluation of the distinctiveness scoring.