The soundscape in shallow marine environment displays a high level of spatial variation due to the regional change of geophysical environment, biological community, and human activity. Many marine animals rely on sounds for orientation; therefore the soundscape has been hypothesized as one of the environmental indicators. Indo-Pacific humpback dolphins in western Taiwan waters are critically endangered. The sound perception is essential for humpback dolphins, which communicate through 3-15 kHz whistles and echolocate through ultrasonic clicks. However, the importance of soundscape for their habitat selection remains unclear. In this study, SM2+ recorders were deployed in Miaoli waters to collect long-duration underwater recordings. Echolocation clicks were automatically detected to identify the core habitat of humpback dolphins. The long-term spectral average reveals that the soundscape in Miaoli waters evidently changed among the diurnal cycle. The spectral characteristic varied between the core habitat and non-core habitat. The soundscape at the core habitat was characterized by the higher standard deviations and lower means of SPL in mid- and high-frequency range. It indicates that the nighttime chorus of croakers and the low-level of ambient sound in the daytime represent the classical soundscape at the core habitat. On the contrary, the croaker chorus was less prominent at the non-core habitat. Instead, snapping shrimp sounds dominated the local soundscape. The current results can help understand the soundscape change of humpback dolphin habitat during the future development and operation of offshore wind farms.
Keywords：Sousa chinensis, marine soundscape, biological sound, temporal and spatial variations, sound detector