Different resighting rates of bottlenose dolphins were obtained by the authors in separate photo-identification studies carried out in the coastal water of north San Diego County, California. Specifically, a subset of one data set (1981-83) showed strong site fidelity to the area while the other (1984-86) contained no such evidence. In an attempt to integrate the data set, possible methodological differences were evaluated, and the following conclusions were reached: (1) photo-identification procedures differed but both were judged equally effective in detecting resights: (2) survey effort did not contribute to resighting differences: (3) photographic efficiency was comparable for both studies. Thus, it appears that there was a real shift in the site fidelity patterns displayed by some dolphins within the study area. The El Nino event of 1982-83 occurred between the studies and probably precipitated or contributed to the apparent shift in site fidelity.
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