Echolocation signals of free-ranging pantropical spotted dolphins (Stenella attenuata) in the South China Sea.

Echolocation signals of free-ranging pantropical spotted dolphins (Stenella attenuata) in the western Pacific Ocean have not been studied much. This paper aims to describe the characteristics of echolocation signals of S. attenuata in the northern South China Sea. A six-arm star array with 13 hydrophones was used and a total of 131 on-axis clicks were identified to analyze the acoustic features of the echolocation signals of dolphins. The mean center frequency was 89 +/- 13 kHz, with mean peak-to-peak sound source levels of 190 +/- 6dB re: 1 mu Pa @ 1m. The mean -3dB bandwidth and root-mean-square bandwidth were 62 +/- 15kHz and 26 +/- 3kHz, respectively, with mean -10dB duration of 18 +/- 4 mu s and root-mean-square duration of 6 +/- 2 mu s. The results showed that click parameters of S. attenuata in the northern South China Sea are different from those of clicks of the species in Hawaii waters. The differences in click parameters may be due to both behavioral context and/or environmental adaptation of S. attenuata in different habitats.