MEASUREMENT OF PHOTOGRAPHIC QUALITY AND INDIVIDUAL DISTINCTIVENESS FOR THE PHOTOGRAPHIC IDENTIFICATION OF HUMPBACK WHALES, MEGAPTERA NOVAEANGLIAE

Abstract

Accurate identification of humpback whales from photographic identification data depends on the quality of the photographs and the distinctiveness of the flukes. Criteria for evaluating photographic quality and individual distinctiveness were developed involving judgments about overall quality or distinctiveness and about specific aspects of each. These criteria were tested for the level of agreement among judges. The distinctiveness scheme was tested for the independence of distinctiveness judgments and photographic quality. Our results show that judges could agree when evaluating specific and overall aspects of photographic quality and individual distinctiveness. The level of agreement varied for different pairs of judges, and less adept judges were identified. Ability to agree on evaluations of photographic quality was independent of the experience of the judges. Overall photographic quality and overall distinctiveness were successfully predicted from more specific variables, but the agreement between judges for these was not significantly greater than the agreement for the overall measures judged directly. There was no correlation between individual distinctiveness and photographic quality for four of the five judges, but the power of this rest may be low. Analyses of photographic identification data frequently require evaluations of photographic quality and individual distinctiveness. To obtain reliable results from such analyses, evaluation schemes and judges should be tested to ensure reliable and consistent evaluations.

Organismal and 'gametic' capture-recapture using microsatellite genotyping confirm low abundance and reproductive autonomy of humpback whales on the wintering grounds of New Caledonia

“…In retrospect, these errors can be attributed to a lack of distinctiveness in the fluke coloration of these 2 individuals, non-optimum photographic quality or fluke angle, and changes in markings over time. These sources of error have been noted before (Carlson & Mayo 1990, Perry et al 1990, Friday et al 2000, Stevick et al 2001) but had not been detected in the New Caledonia catalogue prior to the genotyping, despite careful review. However, the small number of missed photo-identifications should help allay concerns (Anonymous 1998) that whales from the Group V stock are difficult to identify individually because of a high proportion of white flukes (Rosenbaum et al 1995).…”

“…focus and exposure, Mizroch et al 1990, Perry et al 1990). To assure accuracy of individual identification and avoid biases in estimates of abundance (Perry et al 1990, Friday et al 2000, all photographs of poor quality were deleted from the capture-recapture analyses presented here. To investigate the possibility that flukes with predominantly white coloration were difficult to individually identify (Anonymous 1998), flukes were ranked from all white (Type I) to all black (Type V) following Carlson & Mayo (1990).…”

First time series of estimated humpback whale (Megaptera novaeangliae) abundance in Prince William Sound

“…Typically, in the case of photo identification of humpback whales, it is unlikely to have false positive errors; namely, instances where photos are wrongly designated as re-sightings. However, the occurrence of false negative errors-instances where photos are wrongly designated as new sightings when they are actually resightings-increases with the inclusion of poor quality photos (Friday et al 2000(Friday et al , 2008Stevick et al 2001). Efforts were taken to reduce the occurrence of this type of error by removing the photographs determined to be of poor quality.…”

“…Fluke distinctiveness could also play a role in producing false negative errors, instances where photos are wrongly designated as new sightings, which would introduce positive bias in abundance in a mark-recapture analysis (Friday et al 2000(Friday et al , 2008Stevick et al 2001). Flukes bear wildly different patterns and markings, making some individuals more identifiable than others.…”

“…Values from each of the six categories were then summed to generate an overall index of quality for each photo; thus, index values could range from 6 to 18, with lower values indicating a better quality photo. Criteria used to rank these photos are a modified version of the protocols described by others 1 (Calambokidis et al 2008;Friday et al 2000). We deemed all photos with a total photo quality index greater than or equal to 9 to be "poor" and removed them from the analysis.…”