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Mark-recapture abundance estimate of California coastal stock bottlenose dolphins : November 2009 to April 2011
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    The occurrence, distribution, group size and abundance of California coastal stock bottlenose dolphins (Tursiops truncatus) were assessed during a boat-based photo-identification study between November 2009 and April 2011 off San Diego, California. A total of 31 photographic surveys were completed and dolphin groups were encountered on 30 (97%) of them. A total of 115 dolphin groups were observed and 346 individuals photographically identified. All groups were sighted within approximately 1-2 km of shore. The mean group size was 8.2 (SE = 0.6) and the average number of dolphins and groups encountered per survey was 31.5 (SE = 4.2) and 3.9 (SE = 0.5), respectively. Low resighting rates (mean = 2.2; SE = 0.8) and an ever-increasing rate of discovery for previously unidentified dolphins were observed. Strikingly, 258 of the 346 identified dolphins during this study were not represented in the prior 1981-2005 photo-identification catalog for San Diego. Dolphins were considered “marked” if they had two or more dorsal fin nicks. Mark-recapture analysis using POPAN as well as closed models in RMark produced abundance estimates of 515 marked dolphins (95% CI = 470-564, SE = 24.0) and 453 marked dolphins (95% CI = 411-524, SE = 28.1), respectively. Differences in encounter rates, group size and number of groups encountered per survey during the 2009-2011 study were apparent when compared to earlier studies in the same area between 1984 and 2005. [doi:10.7289/V5/TM-SWFSC-563(http://dx.doi.org/10.7289/V5/TM-SWFSC-563)]
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