Echolocation signals of wild Atlantic spotted dolphin (Stenella frontalis)

Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida, United States
The Journal of the Acoustical Society of America (Impact Factor: 1.5). 02/2003; 113(1):598-604. DOI: 10.1121/1.1518980
Source: PubMed


An array of four hydrophones arranged in a symmetrical star configuration was used to measure the echolocation signals of the Atlantic spotted dolphin (Stenella frontalis) in the Bahamas. The spacing between the center hydrophone and the other hydrophones was 45.7 cm. A video camera was attached to the array and a video tape recorder was time synchronized with the computer used to digitize the acoustic signals. The echolocation signals had bi-modal frequency spectra with a low-frequency peak between 40 and 50 kHz and a high-frequency peak between 110 and 130 kHz. The low-frequency peak was dominant when the signal the source level was low and the high-frequency peak dominated when the source level was high. Peak-to-peak source levels as high as 210 dB re 1 microPa were measured. The source level varied in amplitude approximately as a function of the one-way transmission loss for signals traveling from the animals to the array. The characteristics of the signals were similar to those of captive Tursiops truncatus, Delphinapterus leucas and Pseudorca crassidens measured in open waters under controlled conditions.

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    • "Many studies on echolocation behaviour of captive odontocetes especially the bottlenose dolphins are summarised in Au (1993) and Au et al. (2000). There are also studies describing the echolocation of wild dolphins using hydrophone-arrays (Au and Herzing, 2003; Rasmussen et al., 2002; Wahlberg et al., 2011). But, no studies exist describing the echolocation behaviour of free-ranging dolphins using acoustic tags. "
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    • "Underwater acoustic tracking has become a common technology for studying and monitoring the movement and behavior of aquatic animals [15,16]. Usually the absolute time required for the acoustic signal to travel from the source location to the hydrophone is unknown, so time of arrival differences (TOADs) are computed. "
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    • "axis clicks as signals of highest amplitude as compared to adjacent receivers (Au et al., 2004) or within a certain amplitude difference, such as 3dB, compared to the same click on other receivers (Au and Herzing, 2003). This criteria is only useful for clicks recorded within a distance where there will be a measurable reduction in received level due to directionality on adjacent hydrophones. "
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