Examination of a short-term underwater soundscape in a southeast Chinese Bay

Passive acoustic monitoring (PAM) constitutes an effective means to monitor the status of coastal marine environments. Here, acoustic data were collected over a three-month period using an autonomous underwater recorder deployed in Xiamen Bay, Southeast China, during the construction of a new airport. Customized scripts based on power spectral density (PSD) and band-integrated sound pressure levels (SPLs) analysis were used to examine the local underwater ambient noise, which was found to be dominated by sounds below 10 kHz. SPLs were positively correlated with wind speed across the Bands I-III (1/3-octave bands centered between 50 Hz and 20 kHz). Clear diel patterns were observed mainly below 2.5 kHz, whereas variations at higher frequencies were less than 2.4 dB re 1 μPa throughout the day. Shrimp snaps and vessel noise were determined as likely primary contributors to the low-frequency acoustic energy. Clicks of Indo-Pacific humpback dolphins (Sousa chinensis) constituted the key factor to impact acoustic energy above 50 kHz but were infrequent and short in duration, contributing little to the overall acoustic baseline. This study provides a short-term construction-phase acoustic baseline, serving as an initial reference for future long-term monitoring networks and comparisons with the operational phase of the airport.