Radiographic assessment of pectoral fin bone maturation in bottlenose dolphins (Tursiops truncatus), as a novel technique to accurately estimate chronological age

The most frequently used 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, or worn teeth. A non invasive accurate method of aging free ranging dolphins would improve interpretation of biological health data. A database of 126 radiographs from 93 dolphins, in managed care, of known chronological age, was utilized to establish the stages of skeletal maturation 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. Ages could be estimated to within 3 months in animals < 5 years old, within 2 years between 5 and 30 years, and within 5 years in animals > 30 years old. This method can be applied to free ranging dolphins during health assessments to accurately estimate their age.