Alternative Approach for Sectioning Beaked Whale Teeth for Ageing

Abstract

Beaked whales are one of the least known groups of cetaceans and very little information is available on age for most species in this family. The paucity of age data is due to the availability of specimens and also a reluctance to allow the destructive sampling required to age these rare teeth. We examined teeth from four species of ziphiids that inhabit subantarctic waters to evaluate whether sections taken on a plane that was not mid-longitudinal would produce counts of cemental growth layer groups (GLGs) comparable to sections taken on the traditional mid-longitudinal plane. We used teeth of Cuvier?s beaked whale Ziphius cavirostris (n=12), Layard?s beaked whale Mesoplodon layardii (n=8), Gray?s beaked whale M. grayi (n=6) and Shepherd?s beaked whale Tasmacetus shepherdi (n=2) of different ontogenetic classes from the R. Natalie P. Goodall collection, held at the Museo Acatushún de Aves y Mamiferos Marinos Australes, Tierra del Fuego, Argentina. Teeth were initially cut on a low-speed saw into sections using pre-defined planes, one mid-longitudinal and 1-2 at different tangents at the edge of the tooth. At all selected locations, a 2-3mm thick section was cut, decalcified, and stained. Teeth from most specimens showed a clear layering pattern. GLGs in dentine were generally visible and similar to delphinids, but dentine became irregular at a relatively young age precluding use for age estimation. GLGs in cement varied among species but generally were distinct. In at least two species, M. grayi and M. layardii, it does appear that, from cemental GLGs, sections taken tangential to the mid-longitudinal plane can produce age estimates similar to mid-longitudinal sections. Finding a less destructive approach to sectioning teeth may facilitate ageing for beaked whale species.