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. 2026 Feb 11;16(2):e73095.
doi: 10.1002/ece3.73095. eCollection 2026 Feb.

Vocalization Characteristics of the Indo-Pacific Humpback Dolphins (Sousa chinensis) in Xiamen Bay With Insights on Regional Differences

Xuming Peng  1   2 , Zhiyuan Hua  1 , Fuxing Wu  3 , Fei Zhang  1 , Weijie Fu  1 , Yupeng Li  1 , Chuang Zhang  1 , Wenzhan Ou  1 , Wenjie Xiang  4 , Bing Zhou  3 , Zhongchang Song  1   2   5   6 , Yu Zhang  1
Affiliations

Vocalization Characteristics of the Indo-Pacific Humpback Dolphins (Sousa chinensis) in Xiamen Bay With Insights on Regional Differences

Xuming Peng et al. Ecol Evol. .

Abstract

Although whistles and high-frequency clicks of Indo-Pacific humpback dolphins (Sousa chinensis) had been documented in many wild populations, the small population inhabiting Xiamen Bay has received limited attention. Monthly surveys from 2021 to 2024 recorded a total of 107 whistles and 33,038 high-quality clicks. Whistles exhibited mean minimum and maximum frequencies of 5.2 ± 2.2 kHz and 7.5 ± 2.7 kHz, respectively, with a mean duration of 247.6 ± 174.2 ms. Clicks had a peak frequency of 86.4 ± 19.5 kHz, a -3 dB bandwidth of 53.3 ± 14.6 kHz, and a duration of 22.3 ± 6.4 μs. Statistically, clicks from dolphins in the West sub-region had a higher mean peak frequency, broader -3 dB bandwidth, and shorter duration than those from the East sub-region, suggesting adaptations to local environmental conditions and vessel noise. No significant difference was observed in whistles between the two communities. These findings indicated a potential risk of population subdivision for the Xiamen Bay population, underscoring the urgency of protective measures that sustain connectivity and reduce anthropogenic pressures.

Keywords: Indo‐Pacific humpback dolphins; acoustic characteristics; anthropogenic noise; vessel traffic; vocalizations.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
(a) An overall view of the location of the study site in a regional context. (b) Enlarged map of the study location. (c) Diagram of the on‐site survey recording. (d) Indo‐Pacific humpback dolphins encountered during a boat‐based survey.
FIGURE 2
FIGURE 2
(a) The spectrogram of an example click train. (b) The time series of a click extracted from the red box in (a) and (c) its corresponding spectra.
FIGURE 3
FIGURE 3
The spectrograms of examples of six types of whistles. (a) Constant‐frequency whistle. (b) Concave whistle. (c) Convex whistle. (d) Sinusoidal whistle. (e) Downsweep whistle. (f) Upsweep whistle.
FIGURE 4
FIGURE 4
The effective recording minutes for 45 surveys.
FIGURE 5
FIGURE 5
Pie chart of the proportion of different types of whistles for the total, East and West sub‐regions, respectively.
FIGURE 6
FIGURE 6
Comparison box plots of peak frequency, duration, −3 dB bandwidth and peak‐to‐peak sound pressure level for clicks between the East and West groups.
FIGURE 7
FIGURE 7
Comparison box plots of beginning frequency, ending frequency, duration, minimum frequency, maximum frequency, and frequency range for whistles recorded in the East and West sub‐regions.
FIGURE 8
FIGURE 8
Time series of the vessel density variation from June 2021 to September 2024 in the East and West sub‐regions. The vessel traffic data were obtained from Global Maritime Traffic.
See this image and copyright information in PMC

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