Ageing beaked whales from southern SouthAmerica

ALETA A. HOHN; NATALIA A. DELLABIANCA

Valparaiso

Congreso; XVII Reunion de Trabajo de Especialistas en Mamiferos Acuaticos de America del Sur y 11° Congreso SOLAMAC; 2016

Beaked whale are one of least known groups of cetacean and very little information is available on age estimation of most species of this family. In this study, we examined teeth from four species of ziphiids that inhabit subantarctic waters to evaluate the viability of this technique for age estimation. We used teeth (mainly tusks, but also maxillary or vestigial teeth when available) 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 (RNP) collection, held at the Museo Acatushún de Aves y Mamiferos Marinos Australes, Tierra del Fuego, Argentina. In order to investigate the most reliable section for age estimation, sections of different thickness and/or planes of orientation were made for some specimens of each species. In addition, teeth were stained using Mayer?s hematoxylin and Ehlrich?s hematoxylin to test which one provided the best resolution of the tooth structure. In general, teeth of most specimens analyzed showed a clear layering pattern in both tissues. The growth layer groups (GLGs) in dentine were similar to delphinids, consisting of a thin unstainable layer and a thick stainable one. However, irregular dentine is deposited at early age, mainly in Mesoplodon species. Despite the structure of cement differed between species, GLGs were conspicuous and quite distinct. When more than one preparation was available for each tooth, sections 25 um thick and buccal-lingual orientation provided the highest definition of the GLGs in both tissues. Sections stained with Ehrlich?s hematoxylin showed the best contrast of the tooth material. Although still preliminary, our results suggest than counting GLGs in cement, using decalcified and stained section is highly suitable for estimating the age of all species studied. Dentinal GLGs were also well-defined in all species but it soon becomes irregular early in life, it would not be useful to estimate age for older animals.