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

## TL;DR

This study examines the vocalizations of Indo-Pacific humpback dolphins in Xiamen Bay, revealing regional differences in their clicks that suggest adaptation to local conditions and a risk of population subdivision.

## Contribution

The study provides new insights into vocal divergence between dolphin communities in Xiamen Bay linked to environmental factors.

## Key findings

- Dolphins in the West sub-region produced higher frequency, broader bandwidth, and shorter duration clicks compared to the East sub-region.
- Whistles showed no significant differences between the two sub-regions.
- The vocal divergence suggests a potential risk of population subdivision and highlights the need for conservation measures.

## 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.

The Indo‐Pacific humpback dolphin population in Xiamen Bay was divided into two geographically separated but socially associated communities inhabiting the West and East sub‐regions. Based on 3 years of boat‐based surveys, this study established baseline acoustic characteristics and investigated whether vocal patterns varied with habitat conditions between these two communities. Our findings reveal emerging inter‐community vocal divergence, highlighting the urgency of protective measures to mitigate anthropogenic pressures and reduce the risk of further fragmentation.