Age determination and morphological variation of Ontario otters

Annular layering of cementum was evident in hematoxylin-stained sections of canine teeth from otters (Lontra (Lutra) canadensis canadensis) collected throughout the year. A wide cementum layer was formed during the first summer and narrower layers were formed in subsequent summers. The winter deposition formed a darkly stained line which was observed in animals of known age up to 4½ years and in wild-caught animals up to 13 years. The number of annuli in known-age specimens over 1 year old showed complete agreement with age. Indistinct and extraneous lines were encountered in the cementum of a few specimens which required subjective interpretation. Ages were assigned to 99% of otters examined for cementum annuli. Males were larger (P < 0.05) than females as indicated by body weights and body and skull measurements. Juvenile otters could be distinguished by the size of the body, skull, and baculum and morphology of the skull. Extensive overlap in weights and measurements in older age classes prevented a reliable division into age groups. The cementum-layering technique was the only valid age criterion for animals older than 1 year.