Sperm Whale Clicks Research Articles

Sperm whale click analysis using a recursive time-variant lattice filter

Sperm whale clicks, which are nonstationary broadband transients, are analyzed using the normalized recursive exact least-square time-variant lattice filter. The results are compared with those obtained using the classical techniques of energy detection and correlation. The algorithm presented in the paper, derived from an exact least-square formalism is well adapted to the nonstationary signal processing. At each time-step, the adaptive Schur filter calculates an optimal orthogonal signal representation using second-order statistics of the signal, resulting in a set of time-varying Schur coefficients. These coefficients are used to detect clicks and to estimate the click interpulse interval. The latter is commonly used to estimate individual body length and can thus be used for assessments of features of sperm whale populations. The results obtained using simulated and real-world signals demonstrate that a second-order signal description based on the time-varying Schur coefficients is efficient and robust i.e. resistant to the background noise. The adaptive Schur filter detects sperm whale clicks and estimates the interpulse intervals better than both classical waveform energy and correlation methods.

Passive acoustic detection and localization of sperm whales ( Physeter macrocephalus) in the tongue of the ocean

A set of algorithms for real-time detection and localization of vocalizing marine mammals has been developed as part of the Marine Mammal Monitoring on Navy Ranges (M3R) program. These algorithms work on a broad variety of vocalizations including sperm whale clicks. The detection algorithm is a two stage process utilizing a binary thresholded FFT as the first stage. The second stage examines the FFT output to determine whether a click is present in a given FFT window. Detected clicks are split out of the data stream and sent to a data association algorithm called a scanning sieve. Time differences of arrival (TDOAs) are calculated which are then fed into 2D and 3D hyperbolic localization algorithms. Software written to implement the algorithms was used to process a data set consisting of sperm whale vocalizations provided as part of the 2nd International Workshop on Detection and Localization of Marine Mammals using Passive Acoustics. Real-time detection and localization results from the data set are provided, along with a detailed description of the algorithms.

Detection of sperm whale clicks based on the Teager–Kaiser energy operator

The development of an algorithm for automatic detection of sperm whale clicks in large recordings is described. It is based on the Teager–Kaiser (TK) energy operator and it is able to detect efficiently creaks as well as regular clicks. A matching filter is first used as a pre-processor in order to overcome the difficulties caused by the multi-pulse structure of regular clicks. Next, the TK energy operator is applied to the output of the matching filter. A first selection of clicks is performed based on statistical measurements on the TK output, while the final selection is carried out by a forward–backward search algorithm. The proposed system has been tested on a total duration of 25 min of data containing regular clicks as well as creak clicks, where the location of clicks has been marked by hand. An average rate of 94.05% of correct detections was achieved by comparison with the hand-labeled data created from the tested files. Comparing to a standard method used for the same task, the proposed algorithm is more effective in detection rate by 30% and much more accurate and robust.

Measuring the off-axis angle and the rotational movements of phonating sperm whales using a single hydrophone

The common use of the bent-horn model of the sperm whale sound generator describes sperm whale clicks as the pulse series {p0, p1, p2, p3,...}. Clicks, however, deviate from this standard when recorded using off-axis hydrophones. The existence of additional pulses within the {p0, p1, p2, p3, ...} series can be explained still using the bent-horn model. Multiple reflections on the whale's frontal and distal sacs of the p0 pulse lead to additional sets of pulses detectable using a farfield, off-axis hydrophone. The travel times of some of these additional pulses depend on the whale's orientation. The authors propose a method to estimate the off-axis angle of sperm whale clicks. They also propose a method to determine the nature of the movement (if it is pitch, yaw, or roll) of phonating sperm whales. The application of both methods requires the measurement of the travel time differences between pulses composing a sperm whale click. They lead, using a simple apparatus consisting of a single hydrophone at an unknown depth, to new measurements of the underwater movements of sperm whales. Using these methods shows that sperm whales would methodically scan seawater while searching for prey, by making periodic pitch and yaw movements in sync with their acoustic activity.

Directionality of sperm whale sonar clicks and its relation to piston radiation theory

This paper investigates the applicability to sperm whales of the theory of sound radiating from a piston. The theory is applied to a physical model and to a series of sperm whale clicks. Results show that wave forms of off-axis signals can be reproduced by convolving an on-axis signal with the spatial impulse response of a piston. The angle of a recorded click can be estimated as the angle producing the spatial impulse response that gives the best match with the observation when convolved with the on-axis wave form. It is concluded that piston theory applies to sperm whale sonar click emission.

Model-based passive acoustic tracking of sperm whale foraging behavior in the Gulf of Alaska

In 2004, the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) introduced the use of passive acoustics to help monitor the behavior of sperm whales depredating longline fishing operations. Acoustic data from autonomous recorders mounted on longlines provide the opportunity to demonstrate a tracking algorithm based on acoustic propagation modeling while providing insight into whales’ foraging behavior. With knowledge of azimuthally dependent bathymetry, a 3D track of whale motion can be obtained using data from just one hydrophone by exploiting multipath arrival information from recorded sperm whale clicks. The evolution of multipath arrival patterns is matched to range-, depth-, and azimuth-dependent modeled arrival patterns to generate an estimate of whale motion. This technique does not require acoustic ray identification (i.e., direct path, surface reflected, etc.) while still utilizing individual ray arrival information, and it can also account for all waveguide propagation physics such as interaction with range-dependent bathymetry and ray refraction.

Diving and Feeding Behaviour of Sperm Whales (<I>Physeter macrocephalus</I>) in the Northwestern Mediterranean Sea

Sperm whale (Physeter macrocephalus) is one of the common cetacean species inhabiting the western Mediterranean Sea. The aim of this study was to describe the dive cycle of sperm whales in this region and gain insight into their foraging activity. Dedicated summer field seasons were conducted from 2001-2003. Visual and acoustic measures were undertaken and their relationships analyzed. The measures included surface/dive periods, blow rate, distance traveled, timing of clicks & creak activity, and inter-pulse interval measurements of sperm whale clicks. The whales exhibited dive cycle parameters consistent with those measured in other parts of the world: approximately 45 min dive duration, 9 min surface period (i.e., inter-dive interval), with 5 blows/min, and 1.3 nmi horizontal displacement between dives. An average of 25 creaks per dive were registered. Whale body size appeared to be significantly related with both the number of creaks per dive and the dive time at which the first creak occurred, suggesting that larger whales may increase their prey intake and use deeper water layers than smaller whales. The timing of the first creak and the last click of the dive (around 6 min after fluke-up, and just before the surfacing, respectively) suggest a foraging depth of between 500 and 800 m, based on known descent and ascent rates.

Detecting sperm whale clicks in the presence of ambient and shipping noise using higher order moments

The single-receiver detection of various sources using higher order moments is demonstrated. The data for this study come from the Littoral Acoustic Demonstration Center experiment in the northern Gulf of Mexico in the summer of 2001. Results show that in a time-varying environment it may be more meaningful to use non-normalized statistics (e.g., using the fourth central moment rather than the kurtosis). A whale click is detected over a 35-ms window, i.e., with a sampling rate of 11<th>718 samples per second, 40 samples are used to produce a statistic. In the past, energy and related detectors have been used for the single receiver detection of broadband signals produced by whale clicks. The presence of loud shipping noise, which is also broadband, tends to mask the clicks and make their detection difficult. Using short-time statistics may help mitigate this problem. Analysis with fractal exponents will be shown as well. [Research supported by ONR.]

Spectrogram analysis of low to mid frequency marine mammal clicks

Previous investigators have proposed explanations for some sperm whale click structure and pointed out that the separation of individual pulses within the click might be used to determine approximately the size of the sperm whales. Recently, Mohl et al. [J. Acoust. Soc. Am. 114, 1124–1154 (2003)] have shown that echo-location click structure is highly dependent on the received angle. In data measured by the Littoral Acoustic Demonstration Center using bottom-moored hydrophones in the northern Gulf of Mexico in the summers of 2001 and 2002, rich click structures were observed in the spectrograms of many click trains, some of which exhibit strikingly consistent spectral nulls across the train. Although this structure in the spectra could be due to propagation effects, investigations to date suggest this possibility is highly unlikely, as discussed in the next abstract. Therefore it is at least plausible that the structure could be used to identify individual animals. This is known to be a difficult problem in the case of sperm whales because of the angle dependence of at least some of their clicks. These difficulties are discussed, as is the possible use of the spectrograms of the clicks to identify individuals. [Research supported by ONR.]

SEASONAL OCCURRENCE OF SPERM WHALE (PHYSETER MACROCEPHALUS) SOUNDS IN THE GULF OF ALASKA, 1999–2001

AbstractAn acoustic survey for sperm whales was conducted in the Gulf of Alaska. Six autonomous hydrophones continuously recorded sound signals below 500 Hz from October 1999 to May 2001. After recovery, recordings were processed using an automatic process to detect usual clicks of sperm whales. The detection algorithm equalized background noise, summed the data in a frequency band, and then used autocorrelation to detect the whales' highly regular clicks. Detections were checked manually, revealing that 98% of detections did contain clicks. Results indicate that sperm whales are present in the Gulf of Alaska year‐round; this result extends what is known from whaling data, which were gathered principally in summer. Sperm whales were more common in summer than winter by a factor of roughly two, and occurred less often at the westernmost site surveyed (52°N, 157°W) than elsewhere in the Gulf. This is the first study of sperm whales based exclusively on remote acoustic sensing. This methodology is feasible because sperm whale clicks extend to frequencies (∼100 Hz) low enough to be recorded by low‐sample‐rate instruments that operate continuously, and because the detection algorithm has a low false‐detection rate. The methodology may be replicated to facilitate comparisons between different time periods and geographic regions.

The monopulsed nature of sperm whale clicks.

Traditionally, sperm whale clicks have been described as multipulsed, long duration, nondirectional signals of moderate intensity and with a spectrum peaking below 10 kHz. Such properties are counterindicative of a sonar function, and quite different from the properties of dolphin sonar clicks. Here, data are presented suggesting that the traditional view of sperm whale clicks is incomplete and derived from off-axis recordings of a highly directional source. A limited number of assumed on-axis clicks were recorded and found to be essentially monopulsed clicks, with durations of 100 micros, with a composite directionality index of 27 dB, with source levels up to 236 dB re: 1 microPa (rms), and with centroid frequencies of 15 kHz. Such clicks meet the requirements for long-range biosonar purposes. Data were obtained with a large-aperture, GPS-synchronized array in July 2000 in the Bleik Canyon off Vesterålen, Norway (69 degrees 28' N, 15 degrees 40' E). A total of 14 h of sound recordings was collected from five to ten independent, simultaneously operating recording units. The sound levels measured make sperm whale clicks by far the loudest of sounds recorded from any biological source. On-axis click properties support previous work proposing the nose of sperm whales to operate as a generator of sound.

Automated detection of sperm whale sounds as a function of abrupt changes in sound intensity

An algorithm designed to detect abrupt changes in sound intensity was developed and used to identify and count sperm whale vocalizations and to measure boat noise. The algorithm is a Matlab routine that counts the number of occurrences for which the change in intensity level exceeds a threshold. The algorithm also permits the setting of a ‘‘dead time’’ interval to prevent the counting of multiple pulses within a single sperm whale click. This algorithm was used to analyze digitally sampled recordings of ambient noise obtained from the Gulf of Mexico using near bottom mounted EARS buoys deployed as part of the Littoral Acoustic Demonstration Center experiment. Because the background in these data varied slowly, the result of the application of the algorithm was automated detection of sperm whale clicks and creaks with results that agreed well with those obtained by trained human listeners. [Research supported by ONR.]

Sperm whale sound production studied with ultrasound time/depth-recording tags.

Delphinoids (Delphinidae, Odontoceti) produce tonal sounds and clicks by forcing pressurized air past phonic lips in the nasal complex. It has been proposed that homologous, hypertrophied nasal structures in the deep-diving sperm whale (Physeter macrocephalus) (Physeteridae, Odontoceti) are dedicated to the production of clicks. However, air volumes in diving mammals are reduced with increasing ambient pressure, which seems likely to influence pneumatic sound production at depth. To study sperm whale sound production at depth, we attached ultrasound time/depth-recording tags to sperm whales by means of a pole and suction cup. We demonstrate that sperm whale click production in terms of output and frequency content is unaffected by hydrostatic reduction in available air volume down to less than 2% of the initial air volume in the nasal complex. We present evidence suggesting that the sound-generating mechanism has a bimodal function, allowing for the production of clicks suited for biosonar and clicks more suited for communication. Shared click features suggest that sound production in sperm whales is based on the same fundamental biomechanics as in smaller odontocetes and that the nasal complexes are therefore not only anatomically but also functionally homologous in generating the initial sound pulse.

Distribution and relative abundance of sperm whales in the Mediterranean Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 243:281-293 (2002) - doi:10.3354/meps243281 Distribution and relative abundance of sperm whales in the Mediterranean Sea Alexandre Gannier1, Violaine Drouot2,*, John C. Goold3 1Centre de Recherche sur les Cétacés, Marineland, 306 avenue Mozart, 06600 Antibes Cedex, France 2Groupe de Recherche sur les Cétacés, 741 chemin des Moyennes Bréguières, Aurelia 13, BP 715, 06600 Antibes Cedex, France 3Institute of Environmental Science, University of Wales, Bangor, Robinson Building, Deiniol Road, Bangor, Gwynedd LL57 2UW, Wales, UK *Corresponding author. Email: violainedr@hotmail.com ABSTRACT: The distribution of sperm whales in the Mediterranean Sea was investigated over 4 consecutive years. Field surveys took place in 1997, 1998, 1999 and 2000 between June and August from a 12 m survey boat equipped with towed hydrophones. The boat cruised at a mean speed of 6 knots on zig-zag lines. The total transect length was 12709 km, and 3903 acoustic stations were assigned along the transects to monitor the underwater acoustic environment for sperm whale clicks. The Mediterranean Sea was divided into 6 regions for data analysis: the Ligurian Sea, the Gulf of Lions, the southwestern basin, the Alboran Sea, the Tyrrhenian Sea and the Ionian Sea. Relative frequencies and relative abundances of sperm whales were calculated from both visual and acoustic data. Acoustically, the Gulf of Lions yielded the highest relative abundance, with an average of 2.15 x 10-2 whales heard km-1 effort. High abundance was also seen in the southwestern basin and the Ionian Sea (1.90 x 10-2 and 1.21 x 10-2 whales heard km-1 respectively). Visual results indicated high relative abundance in the southwestern basin, with 4.88 x 10-2 sperm whales sighted km-1 effort. Intermediate values were obtained in the Ligurian Sea, and there were few sightings in the Alboran and Tyrrhenian Seas. Most of the sightings south of the 41° parallel consisted of sperm whale groups, of 5 to 7 individuals. Analysis of sperm whale distribution with respect to bathymetry did not establish a significant preference for either continental-slope waters or the open sea. High biological productivity in the northwestern basin might explain high sperm whale relative abundance, noticeably in the Gulf of Lions. KEY WORDS: Sperm whale · Distribution · Mediterranean · Survey · Acoustics · Sightings Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 243. Online publication date: November 13, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Vocal behavior of male sperm whales: why do they click?

Off Kaikoura, New Zealand, we recorded individually identified male sperm whales (Physeter macrocephalus) for entire dive cycles in order to investigate vocal behavior of individual whales and to examine possible functions of sperm whale clicks. In our study, sperm whales were almost always silent at the surface. They consistently started clicking within 25 s after fluking-up and diving. During the first 10 s of clicking, interclick intervals were significantly correlated with water depths at the location of fluke-up. The first "creak" was produced on average 7.5 min into a dive. Interclick intervals usually decreased substantially before clicks turned into "creaks." The highest click rate recorded in this study was 90.9 click/s, and clicks-within-creaks were much shorter than "usual clicks" (mean of 3.6 ms versus 17 to 30 ms). The number of creaks per minute of dive and the length of a dive were significantly correlated. On average, sperm whales were silent for the last 3.6 min before surfacing. Short sequences of "surface clicks" (3 to 8 metallic clicks with mean interclick interval of 5.5 s) were often produced at the end of a dive (in 57% of the dives), but their function remains puzzling. The results of this study suggest that usual clicks and creaks are both used for echolocation purposes, the former to gather information about acoustically reflective features and the latter to detect prey.

Three-dimensional localization of diving sperm whales using a short-aperture towed horizontal array

Three-dimensional sperm whale localizations are typically obtained via recording their ‘‘clicks’’ on widely distributed hydrophones. Here, an alternative 3D localization method is investigated, using data collected by an 8-m aperture, five-element horizontal towed array deployed from the NOAA ship Gordon Gunter in the Gulf of Mexico, as part of a recent sperm whale pilot study. During the night of 3 July 2000, the Gunter towed the array at a steady 1-kn speed and 60-m depth through a pod of sperm whales, in 1000-m-deep water. During that time, surface and bottom reflections from a single sperm whale click were often recorded. By measuring the bearings and relative arrival times of the direct arrival and reflections, the whale location, array depth, and array tilt could be computed. The latter results were checked against measurements obtained from a time-depth recorder attached to the array. Assuming that the speed of the ship remained fixed and the prevailing currents did not change, subsequent positions could then be obtained using only a surface reflection. This method may provide a convenient way for observing dive profiles of animals within a few kilometers of a survey ship. [Work supported by Minerals Management Service, National Marine Fisheries Service, and ONR.]

Sperm whale clicks: Directionality and source level revisited

In sperm whales (Physeter catodon L. 1758) the nose is vastly hypertrophied, accounting for about one-third of the length or weight of an adult male. Norris and Harvey [in Animal Orientation and Navigation, NASA SP-262 (1972), pp. 397-417] ascribed a sound-generating function to this organ complex. A sound generator weighing upward of 10 tons and with a cross-section of 1 m is expected to generate high-intensity, directional sounds. This prediction from the Norris and Harvey theory is not supported by published data for sperm whale clicks (source levels of 180 dB re 1 microPa and little, if any, directionality). Either the theory is not borne out or the data is not representative for the capabilities of the sound-generating mechanism. To increase the amount of relevant data, a five-hydrophone array, suspended from three platforms separated by 1 km and linked by radio, was deployed at the slope of the continental shelf off Andenes, Norway, in the summers of 1997 and 1998. With this system, source levels up to 223 dB re 1 microPa peRMS were recorded. Also, source level differences of 35 dB for the same click at different directions were seen, which are interpreted as evidence for high directionality. This implicates sonar as a possible function of the clicks. Thus, previously published properties of sperm whale clicks underestimate the capabilities of the sound generator and therefore cannot falsify the Norris and Harvey theory.

Improved signal processing techniques for measurement of the inter-pulse interval (IPI) of sperm whale clicks

Improved signal processing techniques are described for estimating the inter-pulse interval (IPI) associated with the multiple pulses in a sperm whale click. These pulses are believed to result from repeated reflections of the original pulse within the spermaceti organ in the whale’s head. Previous estimates of the IPI have been based on time series correlation or on computation of the cepstrum of the received waveform [J. Goold, J. Acoust. Soc. Am. 100, 3431–3441 (1997)]. The present work describes real-time computation and display of the spectrogram and cepstrogram (time-cepstral distribution) [G. Pavan, Proc. IoA 19 (1997)] and examines the benefits of the simultaneous display of this information for field analysis and for browsing long recordings to identify sperm whale clicks. In addition, a detailed model of the spectral modulation associated with the multiple pulses is developed and leads to improved estimation of the IPI. Examples are presented that indicate the method may be more robust with respect to additive noise and the effects of surface reflection than the cepstrum-based approaches. [Work of the first author supported by ONR. Work of the second author supported by the University of Pavia, Italy, the Italian Ministry of the Environment, and by the Italian Navy.]

Sperm whale clicks and the Norris/Harvey theory of click generation

In Odontocetes, sounds are generated within the melon, a structure homologous with the nose of terrestrial mammals. In sperm whales this nose is hypertrophied, accounting for about 1/3 of the length or weight of adults. A sound-generating function has been ascribed to this organ complex [K. S. Norris and G. W. Harvey, in NASA Spec. Publ. 262, edited by S. R. Galler et al. (1972), pp. 397–417]. A sound generator weighing upward of 10 tonnes and with a cross section of 2 m is expected to generate high level, directional sounds. This prediction is not supported by the published data for sperm whale clicks (SL’s of 180 dB re: 1 μPa; little, if any, directionality). Such data, if truly characterizing sperm whale clicks, does not support the Norris/Harvey theory. To increase the amount of data, a hydrophone array, suspended from three platforms separated by 1 km and linked by radio, was deployed at the slope of the continental shelf off Andenes, Norway, in the summers of 1997 and 1998. The SL’s above 210 dB re: 1 μPa were recorded. Also, SL differences exceeding 20 dB for the same click at different directions were seen. Thus, previously published properties of sperm whale clicks underestimate maximum capabilities of the sound generator and therefore cannot falsify the Norris/Harvey theory. [Work supported by the Danish National Research Foundation.]

Improved signal processing techniques for measurement of the interpulse interval (IPI) of sperm whale clicks

Improved signal processing techniques are described for estimating the interpulse interval (IPI) associated with the multiple pulses in a sperm whale click. These pulses are believed to result from repeated reflections of the original pulse within the spermaceti organ in the whale’s head. Previous estimates of the IPI have been based on time series correlation or on computation of the cepstrum of the received waveform [J. Goold, J. Acoust. Soc. Am. 100, 3431–3441 (1997)]. The present work describes real-time computation and display of the spectrogram and cepstrogram (time-cepstral distribution) [G. Pavan, Proc. IOA 19(9) (1997)] and examines the benefits of the simultaneous display of this information for field analysis and for browsing long recordings to identify sperm whale clicks. In addition, a detailed model of the spectral modulation associated with the multiple pulses is developed and leads to improved estimation of the IPI. Examples are presented that indicate the method may be more robust with respect to additive noise and the effects of surface reflection than the cepstrum-based approaches. [Work of the first author supported by ONR. Work of the second author supported by the University of Pavia, Italy, the Italian Ministry of the Environment, and by the Italian Navy.]