Efficiency of wear and decalcification technique for estimating the age of estuarine dolphin <Emphasis Type="Italic">Sotalia guianensis</Emphasis> |
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Authors: | Nicolle V Sydney Emygdio LA Monteiro-Filho |
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Institution: | 1.Instituto de Biociências,Universidade de S?o Paulo,S?o Paulo,Brasil;2.Departamento de Zoologia,Setor de Ciências Biológicas,Curitiba,Brasil;3.Instituto de Pesquisa em Cananéia,Cananéia,Brasil |
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Abstract: | Most techniques used for estimating the age of Sotalia guianensis (van Bénéden, 1864) (Cetacea; Delphinidae) are very expensive, and require sophisticated equipment for preparing histological
sections of teeth. The objective of this study was to test a more affordable and much simpler method, involving of the manual
wear of teeth followed by decalcification and observation under a stereomicroscope. This technique has been employed successfully
with larger species of Odontoceti. Twenty-six specimens were selected, and one tooth of each specimen was worn and demineralized
for growth layers reading. Growth layers were evidenced in all specimens; however, in 4 of the 26 teeth, not all the layers
could be clearly observed. In these teeth, there was a significant decrease of growth layer group thickness, thus hindering
the layers count. The juxtaposition of layers hindered the reading of larger numbers of layers by the wear and decalcification
technique. Analysis of more than 17 layers in a single tooth proved inconclusive. The method applied here proved to be efficient
in estimating the age of Sotalia guianensis individuals younger than 18 years. This method could simplify the study of the age structure of the overall population, and
allows the use of the more expensive methodologies to be confined to more specific studies of older specimens. It also enables
the classification of the calf, young and adult classes, which is important for general population studies. |
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