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Errors in identification using natural markings: rates, sources, and effects on capture-recapture estimates of abundance
Stevick, P.T.; Palsbøll, P.J.; Smith, T.D.; Bravington, M.V.; Hammond, P.S. (2001). Errors in identification using natural markings: rates, sources, and effects on capture-recapture estimates of abundance. Can. J. Fish. Aquat. Sci. 58(9): 1861-1870
In: Canadian Journal of Fisheries and Aquatic Sciences = Journal canadien des sciences halieutiques et aquatiques. National Research Council Canada: Ottawa. ISSN 0706-652X, more
Peer reviewed article  

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Keywords
    Patterns; Patterns; Populations; Populations; Phocidae Gray, 1821 [WoRMS]; Marine

Authors  Top 
  • Stevick, P.T.
  • Palsbøll, P.J.
  • Smith, T.D.
  • Bravington, M.V.
  • Hammond, P.S.

Abstract
    The results of a double-marking experiment using natural markings and microsatellite genetic markers to identify humpback whales (Megaptera novaeangliae) confirm that natural markings are a reliable means of identifying individuals on a large scale. Of 1410 instances of double tagging, there were 414 resightings. No false positive and 14 false negative errors were identified. The rate of error increased with decreasing photographic quality; no errors were observed among photographs of the highest quality rating, whereas an error rate of 0.125 was identified in sightings for which only part of the area used for identification was visible. There was also a weaker relationship between error rate and the distinctiveness of markings, which may result from non-independence in coding for image quality and distinctiveness. A correction is developed for the Petersen two-sample abundance estimator to account for false negative errors in identification, and a parametric bootstrap procedure for estimation of variance is also developed. In application to abundance estimates from the North Atlantic, the correction reduces the bias in estimates made using poorer quality photographs to a negligible level while maintaining comparable precision.

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