Age-related changes to the speckle patterns on wild Indo-Pacific bottlenose dolphins

Age estimating wild dolphins using noninvasive methods will improve our understanding of their ontogeny. Speckles appear on the ventral through to the lateral areas of Indo-Pacific bottlenose dolphins (Tursiops aduncus) as they age. Age-related changes in the speckle density and shape were examined using type classification. Speckles first appeared on the ventral area of the genital area at approximately 6.5 years. They increased in two specific directions, from the genital area to the jaw and from the ventral side to the lateral side. The speckle shape changed with aging from a dot-shape to oblong. Individuals aged over 35 years possessed more speckles than those aged 24-26 years. The oldest age category of dolphins in this study was over 35 years. The speckling area similarly increased with age for all individuals. Therefore, the results suggest that speckle condition can be used to estimate age. The relationship between speckling area and age showed no significant sexual dimorphism except near the genital slit area. There was no speckle area around the genital slit which differed in shape between the sexes. Therefore, speckle patch shape may be a useful sex confirmation tool.

Automated summary

Studying the speckle patterns on Indo-Pacific bottlenose dolphins can help estimate their age. The speckles increase in density and change in shape as the dolphins age. The shape of the speckles may serve as a useful tool for determining the sex of the dolphins.