A comparison of variability and bias when ageing Northeastern Atlantic minke whales (Balaenoptera acutorostrata) by counting growth layer groups in the mandible and bulla tympanica

Abstract

The age of 43 minke whales (Balaenoptera acutorostrata) was estimated by counting growth layer groups (GLGs) GLGs in 500um thick haemotoxylin stained transverse sections of left and right mandible. The same whales were also aged by counting GLGs in 150um unstained sections of left and right bulla tympanica. The staining and preparation methods were also used to prepare and stain mandible sections of a sperm whale and the GLG count of this was the same as the GLG count of a longitudinal section of a tooth from the same animal. Minke whale mandible age estimates had higher CV (63% on average) than the bulla age estimates (36% on average). Comparing the age estimates with the number of ovulations revealed that both methods underestimated the true age of the whales.