Measurement of echolocation signals of the Atlantic bottlenose dolphin, Tursiops truncatus Montagu, in open waters

Abstract

The echlocation signals of two Atlantic bottlenose dolphins, Tursiops truncatus, were measured while the animals were involved in a target-detection experiment conducted in open waters. The time intervals between successive pulses in a pulse train were found to be highly variable, although the intervals were longer than the time needed for an acoustic signal to travel from the animals to the target and back. Sound pressure levels of the echoranging signals were measured for target ranges of 60, 70, 75, and 80 yds. The peak-to-peak click-source level at 1 yd showed little variation with the target range; the average level was 120.4 dB re 1 μbar for one animal and 122.3 dB for the other. These open-water sound pressure levels are at least 30 dB higher than any click-source levels reported in the literature. Oscilloscope photographs and their Fourier transforms of these high-amplitude clicks are presented. The typical clicks had average durations of 40 μsec, with peak energies between 120 and 130 kHz, much higher than the previously reported energy peaks centered at 35 to 60 kHz.

Amazon river dolphins (Inia geoffrensis) use a high-frequency short-range biosonar

“…Toothed whales generally do not produce a new click until relevant echoes from the previous click are received to avoid range ambiguity problems, so the two-way travel time (TWTT) corresponding to the ICI is expected to represent an upper estimate of range to targets of interest (Au et al, 1974;Au, 1993;Akamatsu et al, 1998). The ICI can be divided into TWTT to furthest target of interest plus a lag time, which may be species dependent (Madsen et al, 2013b) and also task dependent (Au, 1993;Wisniewska et al, 2012).…”

Echolocation clicks of free-ranging Cuvier’s beaked whales (Ziphius cavirostris)

“…Since the basic characterization of echolocation clicks of bottlenose dolphins by Au et al ͑1974͒, it has been known that toothed whales are capable of producing highly directional ultrasonic clicks with source levels of more than 220 dB pp re: 1 Pa at 1 m. During 30 years of studies on captive animals ͑Au, 1993͒, and increasingly during the last decade on free-ranging animals ͑Møhl et al ., 1990;Au and Herzing, 2003;Schotten et al, 2003;Au et al, 2004;Madsen et al, 2004͒, it has become apparent that toothed whale species produce a diverse range of biosonar signals ͑Au, 1997͒. Overall, toothed whale sonar signals can be divided into the low-output, monochromatic, high frequency pulses of Phocoena and Cephalorhynchus and the shorter more broadband and higher source level clicks of most dolphin species ͑Au, 1997͒.…”

Effects of Noise of Offshore Oil and Gas Operations on Marine Mammals - An Introductory Assessment. Volume 2

“…As noted by Myrberg (1968), it is possible that this may be done by animals, particularly if the noise is audible to the animal L.. producing the signals. Bottlenosed porpoise in noisy Kaneohe Bay, Hawaii, have been reported (Au et al, 1974) to exhibit an adaptive response by increasing both level and frequency of acholocation signals relative to those of the same species in a quiet environment.…”