Sperm Whale Clicks Research Articles

Heard off Heard: Acoustic detections of sperm whales (Physeter macrocephalus) and other cetaceans off Heard Island.

An underwater acoustic recorder was moored off Heard Island from September 2017 through March 2018 to listen for marine mammals. Analysis of data was initially conducted by visual inspection of long-term spectral averages to reveal sounds from sperm whales, Antarctic and pygmy blue whales, fin whales, minke whales, odontocete whistles, and noise from nearby ships. Automated detection of sperm whale clicks revealed they were seldom detected from September through January (n = 35 h) but were detected nearly every day of February and March (n = 684 h). Additional analysis of these detections revealed further diel and demographic patterns.

Sperm whale clicks are closest thing to human language yet found

Sperm whale clicks are closest thing to human language yet found

Generating Synthetic Sperm Whale Voice Data Using StyleGAN2-ADA

The application of deep learning neural networks enables the processing of extensive volumes of data and often requires dense datasets. In certain domains, researchers encounter challenges related to the scarcity of training data, particularly in marine biology. In addition, many sounds produced by sea mammals are of interest in technical applications, e.g., underwater communication or sonar construction. Thus, generating synthetic biological sounds is an important task for understanding and studying the behavior of various animal species, especially large sea mammals, which demonstrate complex social behavior and can use hydrolocation to navigate underwater. This study is devoted to generating sperm whale vocalizations using a limited sperm whale click dataset. Our approach utilizes an augmentation technique predicated on the transformation of audio sample spectrograms, followed by the employment of the generative adversarial network StyleGAN2-ADA to generate new audio data. The results show that using the chosen augmentation method, namely mixing along the time axis, makes it possible to create fairly similar clicks of sperm whales with a maximum deviation of 2%. The generation of new clicks was reproduced on datasets using selected augmentation approaches with two neural networks: StyleGAN2-ADA and WaveGan. StyleGAN2-ADA, trained on an augmented dataset using the axis mixing approach, showed better results compared to WaveGAN.

Click detection rate variability of central North Pacific sperm whales from passive acoustic towed arrays.

Passive acoustic monitoring (PAM) is an optimal method for detecting and monitoring cetaceans as they frequently produce sound while underwater. Cue counting, counting acoustic cues of deep-diving cetaceans instead of animals, is an alternative method for density estimation, but requires an average cue production rate to convert cue density to animal density. Limited information about click rates exists for sperm whales in the central North Pacific Ocean. In the absence of acoustic tag data, we used towed hydrophone array data to calculate the first sperm whale click rates from this region and examined their variability based on click type, location, distance of whales from the array, and group size estimated by visual observers. Our findings show click type to be the most important variable, with groups that include codas yielding the highest click rates. We also found a positive relationship between group size and click detection rates that may be useful for acoustic predictions of group size in future studies. Echolocation clicks detected using PAM methods are often the only indicator of deep-diving cetacean presence. Understanding the factors affecting their click rates provides important information for acoustic density estimation.

Assessing Northern Gulf of Mexico Sperm Whale’s (Physeter macrocephalus) time budget using passive acoustic monitoring

A time budget empirically measures species-specific behavior regarding the time periods spent engaging in a certain behavior. Sperm whales emit phonations categorized as either foraging or socializing, making it straightforward when creating their time budget based on acoustic observations alone. Understanding regional time budgets can help assessing habitat uses, prey availability, as well as identifying short and long-term trends across the population. Furthermore, sperm whales exhibit both high sexual dimorphism as well as sexually regulated group structures. Individualized multi-pulse echolocation click structure allows total body length as well as sex to be estimated. Apart from a case study conducted by McDonald et al., 2017, a long-term time budgets for sperm whales have not been investigated in the Northern Gulf of Mexico (NGoM). The analysis of multi-year archival acoustic data from the NGoM using a sperm whale click detector as well as CABLE software [Beslin et al., JASA (2018)] is presented to infer sperm whale’s time budget and group structures. [Data acquisition for this research was made possible in part by grants from The Gulf of Mexico Research Initiative and BOEM.]

A Real-Time Acoustic Observatory for Sperm-Whale Localization in the Eastern Mediterranean Sea

A deep-water acoustic observatory for real-time detection and localization of vocalizing sperm whales was developed, deployed and operated for two 3-month periods in summer 2020 and 2021, off south-west Crete in the Eastern Mediterranean Sea, in the framework of the SAvEWhales project. Regular clicks, pulsed sounds produced by the diving animals, were detected and localized using a large-aperture array of three hydrophones suspended from surface buoys at depths of about 100 m and 1-2 km apart. Travel times of significant arrivals, arrivals with magnitude above a certain threshold, were extractedin situand transmitted, together with other supporting data,viamobile broadband to a land-based analysis center. Upon reception, the data from all buoys were combined to enable detection and 3D localization of vocalizing animals exploiting direct and surface-reflected arrivals and using a Bayesian approach. The large separations between hydrophones resulted in small localization uncertainties for ranges up to 7 km; on the other hand, they posed significant challenges related to synchronization and peak association between the buoys, as well as because of the directionality of sperm whale clicks. The integrated observing system which has been successfully tested in detecting and localizing sperm whales can have a significant effect in mitigating ship strikes on whales, the prominent threat for sperm whales in the Eastern Mediterranean Sea, by providing information about the presence and location of the animals in real time. The design and implementation, as well as results from the operation and validation of the acoustic observatory are presented.

Bio-Inspired Covert Active Sonar Detection Method Based on the Encoding of Sperm Whale Clicks

The covertness of an active sonar is a very important issue and the sonar signal waveform design was studied to improve covertness of the system. Click is one of the most common cetacean sounds, and has excellent detection performance. Meanwhile, existing interception systems normally classify cetacean sounds as ocean noise and filter them out. Based on this, a bio-inspired covert active sonar detection method is proposed by encoding the clicks produced by sperm whales. First, based on the frequency distribution characteristic of sperm whale clicks and frequency-hopping sequence, a set of bionic sub-pulses are constructed by encoding the centroid frequency of the real clicks. Based on the inter-click interval characteristic of the clicks and time-hopping sequence, the bionic sonar signal is constructed by combining the constructed bionic sub-pulses and encoding the inter-pulse interval between two adjacent pulses. Then, a single bionic sonar signal is utilized to estimate the speed and range of the target. Based on the characteristics of sperm whale click trains, a camouflage application method is designed to improve the camouflage ability of the bionic sonar signal. Finally, experiment results show that when the target speed is 5m/s and 10m/s and the signal to noise ratio varies from −20dB to 20dB, the root-mean-square error of estimated speed and range are lower than 0.1m/s and 0.1m, respectively. In addition, the constructed bionic sub-pulses have a 99% probability of being classified into sperm whale clicks. Experimental results demonstrate the effectiveness and covertness of the proposed method.

Seasonal and diel changes in cetacean vocalizations monitored by passive acoustic methods in Nemuro Strait adjacent to the Shiretoko World Natural Heritage Site

AbstractUNESCO World Natural Heritage sites are established to ensure the long‐term conservation of natural areas. Nemuro Strait in northern Japan is adjacent to the Shiretoko World Natural Heritage Site, and attracts various trophic levels of marine species, including marine mammals. Although the coexistence of humans and marine mammals is an important issue in this area, the temporal habitat use of cetaceans in this area is unknown. Here, we document seasonal and diel changes in cetacean vocalizations collected using passive acoustic recording devices during November 2012–March 2014. Killer whale calls occurred in spring and summer, and sperm whale clicks were detected in summer. Pacific white‐sided dolphin calls were recorded in summer and late fall. No cetaceans were recorded during the sea ice period in February and March. The dolphin calls and unknown click trains were significantly more frequent at night. In contrast, marginal diel changes in killer whale calls were detected. Our results suggest that the majority of cetaceans utilize Nemuro Strait at night during the ice‐free period, and we provide new insights into the habitat use and diversity of marine mammals in the Strait.

Clicking throughout the year: sperm whale clicks in relation to environmental conditions off the west coast of South Africa

Knowledge of cetacean occurrence and behaviour in southern African waters is limited, and passive acoustic monitoring has the potential to address this gap efficiently. Seasonal acoustic occurrence and diel-vocalizing patterns of sperm whales in relation to environmental conditions are described here using passive acoustic monitoring data collected off the west coast of South Africa. Four autonomous acoustic recorders (AARs) were deployed on 3 oceanographic moorings from July 2014 to January 2017. Sperm whale clicks were detected year round in most recording sites, with peaks in acoustic occurrence in summer and late winter through spring. Diel-vocalizing patterns were detected in winter, spring and summer. Higher percentages of sperm whale clicks were recorded by AARs deployed at 1100 m water depth compared to those concurrently deployed at 850 and 4500 m, likely inferring that the whales exhibited some preference to water depths around 1100 m. Acoustic propagation modelling suggested a maximum detection range of 83 km in winter for sperm whale clicks produced at 1100 m. Random forest models classified daylight regime, sea surface height anomaly and month of the year as the most important predictors of sperm whale acoustic occurrence. The continuous acoustic occurrence of sperm whales suggests that the study area supports large biomasses of prey to sustain this species’ food requirements year round. This is the first study to describe the seasonal acoustic occurrence and diel-vocalizing patterns of sperm whales off the west coast of South Africa, extending knowledge of the species previously available only through whaling records.

Covert underwater communication based on combined encoding of diverse time-frequency characteristics of sperm whale clicks

Bio-inspired camouflage covert underwater acoustic communication has been studied widely recently. In order to improve the camouflage ability and communication rate, a bio-inspired covert underwater acoustic communication method based on combined encoding of diverse time–frequency characteristics of sperm whale clicks is proposed. The characteristics of time–frequency contour shapes and frequency-band distributions are classified and counted, and the communication codes are constructed based on the two characteristics. According to the inter-click interval characteristic of sperm whale click pulse trains, the bionic communication sequences are constructed through differential time delay difference encoding between different communication codes. Based on the proposed combined encoding method of diverse time–frequency characteristics, the constructed communication sequence contains a large number of different modulated clicks. It conforms to the characteristic that there exists a large number of and a variety of clicks in the true click pulse train, which improves the camouflage ability. The true sperm whale click pulses are inserted into the communication sequences as camouflage pulses to further improve the camouflage ability. Furthermore, the communication rate is improved due to using multiple characteristics to represent different encoding information in the proposed method. Simulations are implemented to demonstrate the effectiveness, reliability and covertness of the proposed covert communication method.

Cetaceans and seismic surveys in the Southern Adriatic Sea

The first long-term, broadband, passive acoustic monitoring effort was conducted in the south Adriatic Sea from October 2018 to December 2019 using a High-frequency Acoustic Recording Package (HARP). The recording effort coincided with seismic surveys that took place off Montenegro in the fall and winter 2018–2019. These surveys occurred at distances 70 to 125 km from the recording site, at water depths between 70 and 800 m. Recordings were manually reviewed with start and end times of air-gun encounters and ship passages marked. A generic energy detector and unsupervised clustering procedure were used to extract odontocete echolocation clicks. During the surveys, sound pressure levels (SPL) in the 15 to 200 Hz band increased by up to 20 dB during fall and up to 10 dB during winter survey, with an average increase of 7.5 dB. Cuvier's beaked whale echolocation clicks were very commonly detected in the recordings, but sperm whale clicks were only sporadically present. At least three additional echolocation click types were also detected and their attribution to particular species is underway. Although mortality related to seismic surveys has not been recorded, high levels of noise have the potential to cause long term disruption to cetaceans in this region.

Deteclic: A multi-method detector of sperm whale's click

In the French EEZ of Crozet and Kerguelen Islands, longline fishing is heavily impacted by the depredation of sperm whale, with significant socio-economic implication and ecological impact. Until now, only visual observations of the surface have been used to monitor this phenomenon. Their limitations have raised the need to extend the methods of investigation. Thus, an autonomous acoustic recorder was attached directly to the longline and several hours of recording were collected, disqualifying de facto manual annotation of the data. To overcome this difficulty, we developed an automatic detector, based on five simple methods from the literature: intercorrelation with a reference signal, a Teager-Kaiser energy operator convolved with a Gabor function, spectrogram analysis, kurtosis-based statistical detection and analysis of the Daubechies 15 wavelet-transform. The different methods runs independently with a click-length analysis window allowing a click-by-click detection, and then performs a vote to limit the false alarm rate. Our tool performance is assessed on a dataset where 2450 clicks have been identified by an expert. The clicks detected give valuable indication of the presence/absence of cetacean around the longline, the level of click detection allows us to dissociate the different acoustic behaviours leading to the detection of the depredation event.

Real-time passive acoustic monitoring results of the 2018 Pacific Region International Survey of Marine Megafauna off Western Canada

Real-time passive acoustic monitoring (PAM) was conducted as part of the first large-scale systematic survey of marine mammal distribution and abundance in territorial outer-coastal waters off western Canada. The survey was conducted for approximately five weeks, from early July to mid-August, 2018 using a 69-m Canadian Coast Guard and Fisheries Vessel. A four-element, towed hydrophone array and sonobuoys (type AN/SSQ-53F and AN/SSQ-53G) were deployed and monitored in real-time 24/7 by experienced bio-acousticians. The towed array was deployed for approximately 640 h (78% of the time underway). Approximately 145 independent detections of marine mammals were made. Sperm whales (n = 53) and porpoises (n= 49) represented just over two-thirds of all detections. Ten near real-time localizations of sperm whales and 31 localization of porpoises were made, representing just over 60% of all (n = 67) all high-quality localizations. Sonobuoy effort consisted of semi-systematic deployments day and night and when sightings of large baleen whales occurred. A total of 112 sonobuoys were deployed successfully and monitored in directional (DIFAR) mode. Marine mammal calls were recorded on 32% (36) of sonobuoys. Sonobuoy detections included killer whales calls and clicks, sperm whale clicks, dolphin clicks, fin whale calls, and blue whale calls (both B and D type calls).

Sperm whale (Physeter macrocephalus) acoustic ecology at Ocean Station PAPA in the Gulf of Alaska – Part 1: Detectability and seasonality

Sperm whales Physeter macrocephalus produce loud, stereotypical click sequences and are an ideal species to be studied with passive acoustic techniques. To increase our limited knowledge of sperm whale occurrence patterns in remote and inaccessible locations of the North Pacific, we analyzed a five-year-long (June 2007–April 2012) acoustic data set recorded at Ocean Station PAPA (OSP; 50°N, 145°W) in the Gulf of Alaska (GOA). Firstly, we assessed the sperm whale detection performance of the Passive Aquatic Listener (PAL), and secondly, we investigated temporal patterns of sperm whale presence at OSP. The PAL proved highly efficient, with above 50% probability of detecting more than two sperm whales, a condition met for over 50% of the recordings. Results indicated that sperm whale clicks were recorded year-round, with a clear seasonal pattern. The number of detections during the summer months was approximately 70% higher compared to winter. An ambient noise analysis showed that differences in detection rates were likely not driven by seasonal changes in ambient noise levels. The average propagation range of sperm whale clicks ranged between 7 and 8 km between summer and winter, with slightly decreased detection distances observed in winter. Seasonal shifts in the intensity of the Alaska Current and the latitudinal oscillations of the North Pacific Transition Zone results in changes in water mixing, transport of nutrients and the concentration of prey such as squid, which likely drives sperm whale distribution.

A sonar-embedded disguised communication strategy by combining sonar waveforms and whale call pulses for underwater sensor platforms

The security and covertness are very important for underwater sensor platforms, especially for underwater military sensor platforms. In this paper, different from the conventional low probability of intercept detection and communication methods which generally relies on the low signal-noise-ratio (SNR) or changed-parameters, a sonar-embedded disguised communication strategy for underwater sensor platforms is explored by combining the chirp sonar waveforms and sperm whale call pulses. In the presented strategy, to achieve the target detection, the conventional sonar waveforms (e.g. chirp) are selected. To accomplish covert communication, the original sperm whale clicks are nicely utilized. Then the selected sonar waveform and the utilized original clicks are superimposed together to form a combination waveform to synchronously complete underwater target detection and covert communication functions. Because the clicks of whales are almost always classified into ocean noises and filtered out, the covert communication is achieved depending on this disguised strategy. Simulations demonstrate the feasibility of sonar-embedded covert communication.

Sperm whale inter-pulse intervals and size: The anomaly called Yukusam

Yukusam is the name given to a male sperm whale who was first documented off northeastern Vancouver Island in February 2018. He spent several weeks in this area before traveling south to the inland waters of the Salish Sea in late March 2018. Sperm whale clicks have been used as a proxy to determine overall size by using the time difference of arrival between the initial noise pulse and its reflections within the spermaceti organ. Different equations have been derived in order to use this Inter-Pulse Interval (IPI) to estimate overall length. Here we use Yukusam’s usual clicks recorded from the Lime Kiln hydrophone on the west side of San Juan Island (WA State, USA) to compare IPI-based length estimates with visual observations. Photo and video documentation indicate that this whale is ~15 m in length. Our initial acoustic results indicate that equations in the literature underestimate his length by at least a few meters. The potential reasons behind these anomalies are explored in this presentation.

Littoral Acoustic Demonstration Center passive acoustic localization and tracking of marine mammals in the Northern Gulf of Mexico

The Littoral Acoustic Demonstration Center (LADC) consortium, founded in 2000, has collected underwater acoustic data in the northern Gulf of Mexico since 2001 using Environmental Acoustic Recording Systems (EARS) buoys. These hydrophone systems were developed by the U.S. Navy, and originally LADC could record underwater signals only up to 11.7 kHz. Since then the EARS have been upgraded several times and currently record up to 192 kHz, thus allowing recordings of not only sperm whale clicks and codas, but also signals of beaked whales and dolphins. One goal of LADC is to develop an acoustic method for identification of individual animals, with the goal of an “acoustic catalog” similar to the existing photographic catalog of individual whale flukes. Localization and tracking is an important component for acoustic identification. Some localization and tracking techniques and procedures developed and used by LADC will be presented and discussed.

The energy based characteristics of sperm whale clicks using the Hilbert Huang transform analysis method.

In this paper, a unique analysis method for sperm whale clicks based on Hilbert-Huang transform (HHT) is proposed. Four sperm whale click samples with durations of 10 ms (defined as click I), and four sperm whale click samples with durations of 5 ms (defined as click II) were illustrated. These click samples were recorded in the Mediterranean Sea by Centro Interdisciplinare di Bioacusticae Ricerche Ambientali, Università degli Studi di Pavia. The empirical mode decomposition method was used to decompose click I samples into seven intrinsic mode functions (IMFs) and one residue function (RF), and click II samples were decomposed into six IMFs and one RF. The average energy distributions of multiple IMFs and the single RF domain for click I and click II samples were explored using the HHT analysis method. The average energy-frequency representations were also investigated for the same click I and click II samples. The analysis results show that the energy-frequency characteristics of sperm whale clicks can be extracted and understood by applying several IMFs and one RF signal with a high-resolution analysis.

Using a coherent hydrophone array for observing sperm whale range, classification, and shallow-water dive profiles

Sperm whales in the New England continental shelf and slope were passively localized, in both range and bearing, and classified using a single low-frequency (<2500 Hz), densely sampled, towed horizontal coherent hydrophone array system. Whale bearings were estimated using time-domain beamforming that provided high coherent array gain in sperm whale click signal-to-noise ratio. Whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements. Multiple concurrently vocalizing sperm whales, in the far-field of the horizontal receiver array, were distinguished and classified based on their horizontal spatial locations and the inter-pulse intervals of their vocalized click signals. The dive profile was estimated for a sperm whale in the shallow waters of the Gulf of Maine with 160 m water-column depth located close to the array's near-field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the horizontal array. By accounting for transmission loss modeled using an ocean waveguide-acoustic propagation model, the sperm whale detection range was found to exceed 60 km in low to moderate sea state conditions after coherent array processing.

Using a coherent hydrophone array for observing sperm whale range, classification, and shallow-water dive profiles.

Sperm whales in the New England continental shelf and slope were passively localized, in both range and bearing, and classified using a single low-frequency (<2500 Hz), densely sampled, towed horizontal coherent hydrophone array system. Whale bearings were estimated using time-domain beamforming that provided high coherent array gain in sperm whale click signal-to-noise ratio. Whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements. Multiple concurrently vocalizing sperm whales, in the far-field of the horizontal receiver array, were distinguished and classified based on their horizontal spatial locations and the inter-pulse intervals of their vocalized click signals. The dive profile was estimated for a sperm whale in the shallow waters of the Gulf of Maine with 160 m water-column depth located close to the array's near-field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the horizontal array. By accounting for transmission loss modeled using an ocean waveguide-acoustic propagation model, the sperm whale detection range was found to exceed 60 km in low to moderate sea state conditions after coherent array processing.