Echolocation signals of dusky dolphins (Lagenorhynchus obscurus) in Kaikora, New Zealand

Texas A&M University - Galveston, Galveston, Texas, United States
The Journal of the Acoustical Society of America (Impact Factor: 1.5). 06/2004; 115(5 Pt 1):2307-13. DOI: 10.1121/1.1690082
Source: PubMed


An array of four hydrophones arranged in a symmetrical star configuration was used to measure the echolocation signals of the dusky dolphin (Lagenorhynchus obscurus) near the Kaikoura Peninsula, New Zealand. Most of the echolocation signals had bi-modal frequency spectra with a low-frequency peak between 40 and 50 kHz and a high-frequency peak between 80 and 110 kHz. The low-frequency peak was dominant when the source level was low and the high frequency peak dominated when the source level was high. The center frequencies in the dusky broadband echolocation signals are among the highest of dolphins measured in the field. Peak-to-peak source levels as high as 210 dB re 1 microPa were measured, although the average was much lower in value. The levels of the echolocation signals are about 9-12 dB lower than for the larger white-beaked dolphin (Lagenorhynchus albirostris) which belongs to the same genus but is over twice as heavy as the dusky dolphins. 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 wave form and spectrum of the echolocation signals were similar to those of other dolphins measured in the field.

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    • "Consequently, the porpoises are attacked by Killer Whales during their social communications (Szymanski et al., 1999). However, if the depredator uses low frequency echolocation for detecting fishes, the porpoises can detect Killer Whales (Au et al., 2004). Finally, the third group with the high Doppler effect is formed by certain species of the Ziphidae family, particularly the genus Mesoplodon, Indopacetus pacificus and Ziphius cavirostris. "
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    ABSTRACT: Cetaceans are widely diversified in their sonometric characteristics but no comparative research has determined the general patterns that condition their bio-acoustic evolution across a large number of species. Echolocation calls of 69 cetaceans species has been obtained from different data sources. Through analysis by a Hierarchical Partitioning test, a non-parametric substitute of variance analysis, the absence of statistical differences between bioacoustic data sources has been demonstrated. Sounds were normalized and the fundamental frequency of each species was determined by autocorrelation. Also, the average swimming speed of each species was obtained from published papers. Finally, the intensity of the Doppler effect was calculated for each species using the mathematical equation of underwater sound physics. Doppler shifts lower than 160 Hz were found for the majority of species. This can be explained as a behavioral strategy to avoid depredation by Killer Whales. Only certain species of Ziphidae (genus Mesoplodon, Indopacetus pacificus and Ziphius cavirostris) and six species of Delphinidae (from Lagenorhynchus and Cephalorhynchus genus) present higher Doppler shifts. These species had found other strategies to avoid depredation such as the use of echolocation only in deep waters, very high average swimming speeds, large flocks or the use of very high frequencies. From these results it is possible to conclude that depredation conditions all the evolution of echolocation signals of cetaceans except in a reduced number of species that had developed different behavioral strategies to escape from Killer Whales.
    Full-text · Article · Jun 2014 · Journal of Experimental Marine Biology and Ecology
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    • "Most of the species ' echolocation signals have bimodal frequency spectra with a low-frequency peak between 40 and 50 kHz and a high-frequency peak between 80 and 110 kHz. The wave form and spectrum of the echolocation signals are similar to those of other dolphins measured in the fi eld ( Au and Würsig, 2004 ). "
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    • "The measurements of the scattering layer off Hawaii in the present study were also quite similar to those taken at the same locations in previous work ( Benoit - Bird & Au 2003a ) . Mean scattering , maximum scatter - ing , and variance in scattering were all similar in their distribution to those measured previously at various times of the year encompassing all ' seasons ' ( Benoit - Bird & Au 2003a , b , 2004a , 2006 ) . While migration tim - ing is similar relative to sunset and sunrise in all stud - ies ( as in the New Zealand data ) unlike off New Zealand , the duration of scattering layer presence also changed little throughout the year off Hawaii . "
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