Spatial and temporal variations of biological sound in a shallow marine environment
Tzu-Hao Lin, Lien-Siang Chou
Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei, Republic of China (Taiwan)
Office of Protected Resources, National Marine Fisheries Service, Silver Spring, MD, USA
Department of Mechanical Engineering, The Catholic University of America, Washington, DC, USA
The shallow marine environment exhibits different soundscape characteristics compared to that from the deep ocean. In the shallow waters, biological sound plays an important role in local soundscape. Biological sounds such as fish calls and cetacean whistles are used for communication and finding mates. In addition, odontocetes also use high-frequency biosonars to search their prey. Thus, study the spatial and temporal variations of biological sounds can help us examine the behavior and habitat use of soniferous marine animals. In shallow waters of western Taiwan, most of the biological sounds are produced by snapping shrimps, croakers, and Indo-Pacific humpback dolphins. Shallow and coastal waters are highly influenced by tidal currents, seasonal change of river runoff, and temperature. Due to the difficulty of marine ecological research using visual-based surveys in turbid waters, the temporal and spatial variations of biological activities remain unclear. In this study, underwater sound recorders, SM2M and SM2+, were used to collect long-term acoustic data. Among biological sounds, croaker chorus was identified according to the daily change of sound pressure levels within the 0.5-2.5 kHz frequency band, and whistles and echolocation clicks of humpback dolphins were detected using the local-max detector and high frequency click detector, respectively. Croaker choruses and dolphin vocalizations were frequently detected at inshore and estuarine stations during wet seasons (from April to September). Croaker choruses were evident during the nighttime, especially after sunset. Humpback dolphins were primary detected after the midnight until the next morning. During dry seasons (from October to March), the durations of croaker chorus were reduced. There were no evident differences among inshore and offshore stations. The detection rates of humpback dolphins in the estuarine station were lower compared the detection rates in wet seasons. The temporal and spatial variations of croaker chorus and dolphin vocalizations indicate that the distribution and behavior of croakers and humpback dolphins changed between wet and dry seasons. Several offshore wind farms have been planned to be built in western Taiwan waters. The construction and operation noise of these wind farms may alter the acoustic environment and influence the behavior and habitat use of marine animals. Current results can be used to evaluate the potential impacts of offshore wind farms on the local ecosystem.