Abstract
Accurate age estimation in wildlife conservation is an important diagnostic tool in the interpretation of biological data, necropsy examination, reproductive status and population demographics. The most frequently utilized methods to age bottlenose dolphins (Tursiops truncatus) include tooth extraction; counting dental growth layer groups and dental radiography. These methods are inaccurate in dolphins > 13 years old, due to overlapping of the growth layer groups in dolphins and worn teeth. Establishing a non-invasive method of accurately aging bottlenose dolphins across the entire age range is important to long term conservation efforts to understand health status, lifespan, reproduction and survivability. A database of 126 radiographs from 94 dolphins of known chronological age was utilized to establish the stages of skeletal ossification over time. A numerical score from -1 to 8 was assigned to 16 anatomic locations on the pectoral radiograph, to create a formula to estimate age. The most informative areas to evaluate morphologically were the metaphyseal regions of the radius and ulna, and the proximal and distal epiphysis of metacarpals II and III. Third order polynomial regression calculated separate age predictor formulas for male and female dolphins, with females reaching sexual maturity earlier than males. Completion of epiphyseal closure of the long bones correlated with average sexual maturity. Managed care dolphin ages could be properly estimated with decreasing precision from within 3 months in animals < 5 years old, to within 5 years in animals > 30 years old. This diagnostic tool could also be applied to diagnose atypical ossification patterns consistent with nutritional, developmental or growth abnormalities, and identifying subclinical health issues. In conclusion, knowledge of the lifespan and the onset of sexual maturity for each species will allow this model to be applied to other cetaceans, facilitating age estimation via pectoral radiography in future research.
Highlights
Estimating the age of cetaceans can have large implications in interpreting scientific data of individual health assessments, reproductive status and population demographics
A combination of physical exam, dental exam and radiographs are recommended to diagnose abnormal advanced or delayed maturation in children, as well as for the medico-legal age assessment of individuals
To establish the methodology to estimate the age of bottlenose dolphins via radiography three anatomic areas of interest were initially studied in 2005
Summary
Estimating the age of cetaceans can have large implications in interpreting scientific data of individual health assessments, reproductive status and population demographics. Determining the age of stranded individuals with limited pathology on post mortem examination can provide a reliable insight into the cause of death. In addition GLGs have been shown to be difficult to interpret in older cetaceans [4], giving misleading age estimations [5, 6]. Overlapping of dentine layers in bottlenose dolphins (Tursiops truncatus) at ages > 13 years has caused inaccuracy in estimating the ages of adult animals [1]. GLG methodology is challenging with variation in assessment, expertise and in tooth preparation techniques shown to reduce age estimate accuracy [1]. Tooth wear prevents this method from being utilized to accurately age adult dolphins
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