Estimating age of harbor seals (Phoca vitulina) with incisor teeth and morphometrics

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Abstract

We compared annuli counts from sets of canine, postcanine, and incisor teeth from 450 subsistence-harvested harbor seals, submitted blind to a laboratory. Postcanine and incisor ages were highly correlated with canine age estimates (r= 0.985 and r= 0.984, respectively), as were postcanine and incisor teeth (r= 0.984). Age estimates from teeth of 23 known-aged seals were highly correlated; canine teeth r= 0.987; postcanine r= 0.996; incisor r= 0.992, although age for all tooth-types was underestimated for a 29-yr-old seal. Incisor estimates were variable; comparison of age estimates from two incisors/individual (n= 42) was r= 0.992 if only high-quality age estimates were used and r= 0.705 if lower-quality estimates were used. Morphometrics and incisor-based ages of 164 live-captured seals were explored to derive a method of estimating ages of harbor seals when age estimates are needed immediately; 39 seals were of known age. Curvilinear length, mass, and axial girth were most predictive of age for females, and curvilinear length and mass for males (equations for morphometrically calculating ages are given). Morphometric-based age estimates were highly correlated with known ages (r= 0.896) and incisor-based estimates (r= 0.904) and discrepancies between known and morphometric-based ages were small for younger seals. Morphometric-based age estimates also accurately distinguished between young and mature individuals.

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