Estimating the abundance of the northern North Carolina estuarine system stock of common bottlenose dolphins (Tursiops truncatus)

The Northern North Carolina Estuarine System (NNCES) stock of the common bottlenose dolphin (Tursiops truncatus) has a small population size and low Potential Biological Removal level (PBR). Levels of serious injury and mortality due to commercial fisheries interactions may exceed the PBR. In addition, the prior abundance estimate, from a survey in 2006, is no longer valid for computing the PBR for the stock after 2014. To obtain a new abundance estimate, we conducted a capture-mark-recapture survey of the NNCES stock in the Pamlico-Albemarle Estuarine Complex (PAEC) from 15 June to 27 July 2013. The PAEC is the primary summer habitat for the stock. We surveyed 4,779 km of trackline, encountering 128 dolphin groups. We took 30,991 photographs, from which 471 individual dolphins were identified from distinctive nicks and notches on dorsal fins. Because dolphins in the most southern portion of the summer habitat overlap with the Southern North Carolina Estuarine System (SNCES) stock in July, some photographed dolphins could have been members of the SNCES stock. We developed a decision tree to identify dolphins that may have belonged to the SNCES stock, thereby allowing us to estimate abundance using all dolphins and then excluding those that might belong to the SNCES stock. We then calculated lower (823; 95% posterior interval (PI) = 733-931) and upper (873; 95% PI = 775-989) bounds on the abundance estimate based on habitat-use assumptions from the decision tree. Both estimates were obtained using closed capture-mark-recapture models and a novel method to correct for dolphins with indistinctive fins. doi:10.7289/V5VH5KS8 (http://dx.doi.org/10.7289/V5VH5KS8) by Antoinette M. Gorgone, Tomoharu Eguchi, Barbie L. Byrd, Karen M. Altman, Aleta A. Hohn. "August 2014." doi:10.7289/V5VH5KS8 (http://dx.doi.org/10.7289/V5VH5KS8) System requirements: Adobe Acrobat Reader. Includes bibliographical references (pages 15-16). 2014 NMFS (National Marine Fisheries Service) SEFSC (Southeast Fisheries Science Center) Library http://doi.org/10.7289/V5VH5KS8 Public Domain 1864