Vocalization Characteristics of the Indo‐Pacific Humpback Dolphins ( <scp> <i>Sousa chinensis</i> </scp> ) in Xiamen Bay With Insights on Regional Differences

Although whistles and high-frequency clicks of Indo-Pacific humpback dolphins (<i>Sousa chinensis</i>) 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.