Document: Article
Abstract: Our understanding of the vocalizations of captive Indo-Pacific humpback dolphins (Sousa chinensis) is limited compared to our knowledge of these sounds in wild animals. Echolocation signals of wild Indo-Pacific humpback dolphins were recorded in the central-western Gulf of Thailand, and captive animals’ sounds were recorded in an ocean park in Trat Province, Thailand, using a cross array with five hydrophones. Both wild and captive animals produced broadband transient clicks of short duration (21 ± 4 ms in the wild and 36 ± 2 ms in captivity). The inter-click intervals (37 ± 13.5 ms) for wild animals were longer than for captive animals (25 ± 1.2 ms). Statistical analysis showed that mean peak-to-peak (p-p) source levels of on-axis echolocation clicks varied significantly between wild (185 ± 5.8 dB re 1 mPa) and captive (169 ± 2.8 dB re 1 mPa; p < 0.001) environments. The frequency domain parameters of echolocation clicks of wild humpback dolphins were similar to those of captive humpback dolphins, characterized by a mean centroid frequency of 106 ± 7.1 kHz and 105 ± 3.7 kHz, respectively. These results provide the first comparison of sound properties from both wild and captive humpback dolphins and could be valuable for the development of passive acoustic monitoring species classification tools to inform management and conservation efforts.
Key Words: echolocation clicks, source parameters, wild and captive, Gulf of Thailand, Indo-Pacific humpback dolphins, Sousa chinensis
DOI: https://doi.org/10.1578/AM.47.6.2021.574
Page Numbers: 574-584