The acoustic repertoire of wild common bottlenose dolphins (Tursiops truncatus) in Walvis Bay, Namibia

Abstract

Describing the repertoire of sounds produced by wild cetaceans is necessary for understanding their function, for acoustic population monitoring and for measuring the potential influence of anthropogenic impact. Geographic variation in the types and parameters of sounds makes regional assessment of vocal behaviour necessary. We describe the acoustic repertoire of a small population of common bottlenose dolphins (Tursiops truncatus) inhabiting Walvis Bay, Namibia from recordings made over 59 encounters (72 h) between 2009 and 2012. The characteristics of burst pulse (BP) sounds, low-frequency narrow-band (LFN) sounds, brays, whistles and chirps are described. The BP sounds identified were generated at 150-1050 pulses per second, and most were short, lasting less than 1 s in duration. Bottlenose dolphins from Walvis Bay produce the lowest frequency LFN sounds described for the species. Whistles ranged in frequency from 1.58 to 23.24 kHz, and the mean acoustic parameters were within the range of those described from other geographic regions. Chirps were identified infrequently and usually as single occurrences. Although several sound types were often produced in close temporal succession, we found little evidence of stereotyped bray production, even during recordings of animals feeding. Our results demonstrate geographic variation in both the characteristics and sound types used by bottlenose dolphins and highlight the importance of regional data collection as a pre-curser to passive acoustic monitoring programmes.

Review of Underwater and In-Air Sounds Emitted by Australian and Antarctic Marine Mammals

“…Much of the literature focuses on whistles and geographic differences [151,152,156,163,174,253,270,276,286,[289][290][291][292][293][295][296][297][298]300,302]. Biphonic whistles have been reported [299].…”

“…Together, CW and FM sounds range from 300 Hz to 39 kHz in fundamental frequency and from 40 ms to 4 s in duration (Fig. 27), with source levels of 114-163 dB re 1 µPa rms @ 1 m. FM sounds at lower frequency have sometimes been described separately and called "low-frequency narrow-band" sounds with a 30 Hz-1 kHz fundamental frequency and 10-ms-8.7-s duration [284,287,292,303].…”

“…Common bottlenose dolphins inhabit tropical to temperate waters globally and occur around Australia in coastal as well as offshore waters [147,272]. Bottlenose dolphins have been acousti- [501] cally recorded in QLD, Australia [284], New Zealand [285], the Eastern Tropical Pacific [151,152], Hawaii [230], California [276,286], the Gulf of Mexico [163,253,276,287], the Caribbean [288], Central America [286,289], Brazil [270,290], Uruguay [291], Argentina [276], Namibia [292], the Northwest Atlantic [163,174], the Northeast Atlantic [282,293,294], Scotland and the UK [282,295,296], Mediterranean [156,293,[297][298][299], and Portugal [300]. Many recordings have also been taken of bottlenose dolphins in captivity (e.g.…”

Changes in bottlenose dolphin whistle parameters related to vessel presence, surface behaviour and group composition

“…The duration of behavioural bout length (measured as the average length of time dolphins are continuously engaged in one of a predetermined number of key behavioural states, as defined below) also decreases when tour boats are present, indicating agitation during tour boat presence (Indurkhya, 2012). The frequency of engine noise produced by these tour boats has the potential to overlap the frequency of whistles produced by bottlenose dolphins in Walvis Bay (Gridley, Nastasi, Kriesell, & Elwen, 2015). Short-term changes in the acoustic behaviour of this population relative to tour boat presence could indicate a human impact which should be properly managed to mitigate any potential long-term, negative effects on this small population of dolphins.…”

Vocal activities reflect the temporal distribution of bottlenose dolphin social and non‐social activity in a zoological park

“…Whistles are the most studied category and are often associated with social affiliative functions (Janik & Sayigh, ; Mello & Amundin, ; Tyack, ), although there are controversies (e.g., Acevedo‐Gutiérrez & Stienessen, ). Chirps present strong acoustic similarities with whistles, but it is not clear whether chirps and whistles should be classified together or not (Gridley, Nastasi, Kriesell, & Elwen, ). In captivity, positively reinforced dolphins produce chirps more frequently than non‐reinforced individuals (Caldwell, Caldwell, & Tyack, ).…”