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Accuracy and precision in estimation of age of Norwegian Arctic polar bears (Ursus maritimus) using dental cementum layers from known-age individuals

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Abstract

Validation of age estimation from tooth cementum growth layers was conducted for 32 polar bears (Ursus maritimus) of known age, by two readers. Both readers correctly estimated age for 24% of the bears, and 50–53% were within the year of correct age. The age of young animals (age 1–8) was overestimated, while ages for bears over 8 years were underestimated. Comparison between the readings of the two readers indicated that the precision was low. Further, one of the readers reread tooth slides earlier prepared and read by another age estimation laboratory. There was a large discrepancy between these readings indicating a bias in the ages estimated. We conclude that age estimation of polar bears can be difficult, particularly in populations where individuals may forage throughout the year. As tooth growth layers may deposit differently for bears from different areas, and as different laboratories may read the same slides according to different criteria, an evaluation of the methods should be conducted for all populations, based on a significant number of tooth slides, with a broad age range, from animals of known age.

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Acknowledgments

Thanks to Jon Swenson for very constructive and helpful comments on the master thesis of Signe Christensen-Dalsgaard (2006) that led to this publication. Thanks also to all persons that have been involved in fieldwork that has acquired the set of tooth samples and individual data used and to the laboratory technicians that helped prepare and read the tooth slides. Also thanks to the referees Aleta Hohn, Øystein Wiig and Sarah Medill for constructive and valuable comments which greatly improved the final manuscript.

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Author notes

  1. Signe N. Christensen-Dalsgaard

    Present address: Norwegian Institute for Nature Research, 7485, Trondheim, Norway

Authors and Affiliations

  1. Department of Biology, University of Tromsø, 9037, Tromsø, Norway

    Signe N. Christensen-Dalsgaard & Nigel G. Yoccoz

  2. Norwegian Polar Institute, Polarmiljøsenteret, 9296, Tromsø, Norway

    Jon Aars & Magnus Andersen

  3. Age Dynamics, Huldbergs Allé 42, 2800, Lyngby, Denmark

    Christina Lockyer

Authors
  1. Signe N. Christensen-Dalsgaard
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  2. Jon Aars
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  3. Magnus Andersen
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  4. Christina Lockyer
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  5. Nigel G. Yoccoz
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Correspondence to Signe N. Christensen-Dalsgaard.

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Christensen-Dalsgaard, S.N., Aars, J., Andersen, M. et al. Accuracy and precision in estimation of age of Norwegian Arctic polar bears (Ursus maritimus) using dental cementum layers from known-age individuals. Polar Biol 33, 589–597 (2010). https://doi.org/10.1007/s00300-009-0734-y

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  • DOI: https://doi.org/10.1007/s00300-009-0734-y

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