Possible age-related hearing loss (presbycusis) and corresponding change in echolocation parameters in a stranded Indo-Pacific humpback dolphin

Abstract

The hearing and echolocation clicks of a stranded Indo-Pacific humpback dolphin (Sousa chinensis) in Zhuhai, China, were studied. This animal had been repeatedly observed in the wild before it was stranded and its age was estimated to be ∼40years. The animal's hearing was measured using a non-invasive auditory evoked potential (AEP) method. Echolocation clicks produced by the dolphin were recorded when the animal was freely swimming in a 7.5m (width)×22m (length)×4.8m (structural depth) pool with a water depth of ∼2.5m. The hearing and echolocation clicks of the studied dolphin were compared with those of a conspecific younger individual, ∼13years of age. The results suggested that the cut-off frequency of the high-frequency hearing of the studied dolphin was ∼30-40kHz lower than that of the younger individual. The peak and centre frequencies of the clicks produced by the older dolphin were ∼16kHz lower than those of the clicks produced by the younger animal. Considering that the older dolphin was ∼40years old, its lower high-frequency hearing range with lower click peak and centre frequencies could probably be explained by age-related hearing loss (presbycusis). © 2013. Published by The Company of Biologists Ltd.