Abstract
The ages of three species of cetaceans were estimated by counting the growth layer groups (GLG) and measuring the aspartic acid racemization rate (kAsp) by what is referred to as the Aspartic Acid Racemization (AAR) technique. Data on kAsp and the D/L ratio of aspartic acid at birth [(D/L)0] in North Atlantic common minke whales (Balaenoptera acutorostrata) are presented along with data on fin whales (B. physalus) and harbour porpoises (Phocoena phocoena) already published by Nielsen et al. (2012). The kAsp specific for minke whales was 1.40 x 10-3 yr-1 (SE ± 0.00005) and the (D/L)0 was 0.0194 (SE ± 0.0012). The correlation of GLG age and D/L ratio for all three species was highly significant; however, the correlation coefficient varied greatly (fin whales: R2 = 0.59, p <0.0001; minke whales: R2=0.96, P <0.0001; harbour porpoises: R2=0.36, P <0.0001). Asymptotic body length for all three species was estimated by a von Bertalanffy growth model on both the GLG and AAR techniques, and showed no difference.
Highlights
When it comes to management of wildlife populations, estimation of age is crucial in order to gain knowledge of their life history and population structure, and when managing harvested populations, knowledge of age composition is especially important for assessing sustainable quotas
Chronological age estimation in cetaceans has traditionally been done by counting the growth layer groups (GLGs) deposited within a persistent tissue, primarily in earplugs, teeth, bulla tympanica
The aim of this paper is to discuss the usefulness of Aspartic Acid Racemization (AAR) as a tool for age estimation of fin whales, harbour porpoises and North Atlantic minke whales
Summary
When it comes to management of wildlife populations, estimation of age is crucial in order to gain knowledge of their life history and population structure, and when managing harvested populations, knowledge of age composition is especially important for assessing sustainable quotas. Contrary to many terrestrial mammals, no obvious visual sign of age is present and up until today, a variety of different techniques have been used to estimate age in marine mammals, with variable success (Lockyer 1974, Watts and Gaskin 1989, Dietz et al 1991, George et al 1999, Olsen and Sunde 2002, Würsig and Jefferson 2004, Garde et al 2010, Nielsen et al 2012). Chronological age estimation in cetaceans has traditionally been done by counting the growth layer groups (GLGs) deposited within a persistent tissue, primarily in earplugs, teeth, bulla tympanica.
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