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Age Determination in Belugas (Delphinapterus leucas): A Quest for Validation of Dentinal Layering
Abstract: A workshop for experts in age determination of beluga whales was convened to (1) determine the number of dentinal Growth Layer Groups (GLGs) in beluga teeth and the variation therein among readers; (2) assess the deposition rate of dentinal GLGs in beluga teeth, specifically on the question of one or two GLGs per year; (3) define the appearance of dentinal GLGs in order to standardize reading methods among readers of beluga teeth; and (4) provide a consensus report with specific conclusions on deposition rate and GLG definition. Tooth specimens from ten belugas, all originally from Churchill, Manitoba, Canada, with captive histories ranging from 4 to 30 y, were the focus of the investigation. Three of these animals had medication histories of tetracycline antibiotics which “time-mark” hard tissues. Results from the inter-reader GLG comparisons, GLG counts compared with captive history, and tetracycline mark placement indicated that despite considerable problems with the inter-reader count variability, using certain assumptions, there was evidence that two GLGs per year was not possible in six of the ten specimens; however, there were some specimens for which it was clear that two GLGs per year could be feasible, and yet others where the derived estimate of age at first capture did not appear to be compatible with the most likely age for that size of animal. The conclusions were that one GLG annual deposition rate in dentine was clearly upheld in some instances but that the results were equivocal for several specimens for a variety of reasons. In light of the fact that tooth GLGs are likely to continue being the predominant method for aging in this species, the workshop members agreed on a list of seven recommendations that included, as a priority, experimental approaches that could help to standardize and validate GLG counting in age determination.
Key Words: BELUGA WHALES; DELPHINAPTERUS LEUCAS; AGE ESTIMATION; AGING; TEETH; DENTINE; GROWTH LAYER GROUPS; GLG; AGE VALIDATION; TETRACYCLINE
Document Type: Research article
Page Numbers: 293 – 304