Age determination methods in harbour seals (Phoca vitulina) with a review of methods applicable to carnivores


  • Christina Lockyer NAMMCO, P.O.Box 6453, 21-23 Sykehusveien, N-9294 Tromsø, Norway
  • Beth Mackey University of Aberdeen Lighthouse Field Station, George Street, Cromarty, Ross-Shire, IV11 8YR, United Kingdom and Sea Mammal Research Unit, Gatty Marine Laboratory, University of St Andrews, St Andrews, Fife KY16 8LB, United Kingdom
  • Fiona Read Instituto Español de Oceanografía, Centro Oceanográfico de Vigo, PO Box 1552, E-36200, Vigo, Spain
  • Tero Härkönen Swedish Museum of Natural History, Box 5007, S-10405 Stockholm, Sweden
  • Ilk Hasselmeier Forschungs - und Technologiezentrum Westküste, Christian-Albrechts-Universität zu Kiel, Werftstr. 6, D-25761 Büsum, Germany



harbour seals, age determination, ageing, Growth Layer Groups, GLGs, dentine, cement


The development of age determination methods in marine mammals is reviewed with particular reference to the use of teeth Growth Layer Groups (GLGs) formed in the dentine and cement of carnivores. Using this background, practices for sampling, tooth extraction and collection, storage and different methods of preparation of teeth as well as reading and counting GLGs are discussed and evaluated for the harbour seal (Phoca vitulina). The paper includes comments on best practices for counting GLGs with new examples from known-age seals, and also a detailed examination of confounding factors in interpreting GLGs such as mineralization anomalies and the phenomena of accessory lines, “false annuli” and “paired laminae” which have not been discussed previously. The paper concludes with recommendations for undertaking age estimation in harbour seals from sampling through final GLG interpretation with special emphasis on standardization of methods with other researchers.




How to Cite

Lockyer, C., Mackey, B., Read, F., Härkönen, T., & Hasselmeier, I. (2010). Age determination methods in harbour seals (<i>Phoca vitulina</i>) with a review of methods applicable to carnivores. NAMMCO Scientific Publications, 8, 245–263.

Most read articles by the same author(s)

1 2 > >>