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First Results of an Underwater 360° HD Audio-Video Device for Etho-Acoustical Studies on Bottlenose Dolphins (Tursiops truncatus)
Abstract: Bottlenose dolphins (Tursiops truncatus) are highly social odontocetes that live in a fission-fusion society and demonstrate production of a varied sound repertoire, including clicks, whistles, and burst-pulsed sounds, as well as a diverse behavioral repertoire. To better understand the species’ behavior, it is necessary to compare visual and acoustic observations and link vocalizations to individuals and their specific actions. However, the task of linking sounds to individual dolphins is challenging for human observers because dolphins do not always display specific visual cues when producing a sound, and also because human hearing is not naturally adapted to locate underwater sound sources. To respond to these challenges, a new underwater 360° HD audio-video device, the BaBeL, was designed and built. This device consists of a five-hydrophone array attached to two wide-angle video cameras that together cover a 360° field of vision. Acoustic recordings were analyzed with a customized program to detect and localize sound sources and to identify individual vocalizing dolphins. Data from a population of bottlenose dolphins were collected during 14 boat surveys along the northwest coast of Reunion Island (France) by following a strict pre-established protocol to standardize data collection. A total of 21 min of audio-video were recorded when dolphins were present, and 42 click trains and 42 whistles were detected from these data. Dolphins identified as vocalizers were also present for 17% (n = 7) of emitted click trains and 33% (n = 14) of emitted whistles on the videos. Therefore, an analysis of three video sequences as examples of the scope of this methodology is presented. The results show that when the observers stayed ahead and avoided the direct path of groups of five to nine dolphins, only one animal emitted click trains while swimming towards the observers or after turning its rostrum in the humans’ direction, and this dolphin was never the one leading the group. The benefits of using this audio-video device for underwater observations of dolphins in clear water with good visibility are discussed.
Key Words: behavior, acoustics, hydrophone array, acoustic localization, bottlenose dolphin, Tursiops truncatus
Document Type: Research Article
Page Numbers: 162-176