Dolphin Clicks Research Articles

Depredation mitigation of bottlenose dolphins on coastal and oceanic set net and line based fisheries by dolphin dissuasive device and dolphin interactive dissuasor pingers.

Depredation by marine mammals on coastal and oceanic net and line based fisheries is a major source of economic loss to fisheries where by‐catch levels are low. To further minimize possible habituation to DDD pingers that feature variable (frequency and amplitude) signals an interactive model, the DiD, was designed. The DiD reacts to broadband frequency clicks comparable to delphinid clicks. The detection sensitivity is about 130 dB re 1 μ Pa at 1 m at the minimum threshold. The sensitivity curve matched peak output of dolphin clicks, particularly those of larger toothed whales responsible for depredation, achieving minimization of snapping shrimp interference in shallow water fishery applications. The DDD and DiD output’s were changed to improve their effectiveness resulting in modulated tones and pseudo echolocation signals. Trials with dolphins in gillnet fisheries indicated DiD spacing could be 300 m. Spacing may change slightly with environment and fishery. DDD offers a reliable method for mitigating by‐catch. DiD offers a choice to address long term effectiveness of pingers for depredation mitigation with limitation of power requirements, restriction of sound exposure in sensitive environments, and with benefits to industry and the environment. [Work supported by CNR, SeaMed, IAMC, Trapani, Italy.]

Risso’s and Pacific white-sided dolphin habitat modeling from passive acoustic monitoring

Habitat characterization allows prediction of dolphin distributions in response to oceanographic processes and can be used to understand and predict effects of anthropogenic disturbances. Many habitat models focus on contemporary dolphin occurrence and environmental predictor data, but time-lagged oceanographic data may increase a model's predictive power due to ecological successional processes. Using hourly occurrence of Risso's dolphin Grampus griseus clicks and 2 types of Pacific white-sided dolphin Lagenorhynchus obliquidens clicks in autonomous passive acoustic recordings, we investigate the importance of time-lagged predictor variables with general- ized additive models. These models relate dolphin acoustic activity from recordings at 6 sites in the Southern California Bight between August 2005 and December 2007 to oceanographic variables including sea surface temperature (SST), SST coefficient of variation (CV), sea surface chlorophyll concentration (chl), chl CV, upwelling indices, and solar and lunar temporal indices. The most consis- tently selected variables among the trial models evaluated during cross-validation were SST (100% of models) and SST CV (80%) for Risso's dolphin clicks; solar indices (100%) and SST and SST CV (60% each) for Pacific white-sided type A (PWS A) clicks; and SST CV (100%), solar indices (100%) and SST (80%) for Pacific white-sided type B (PWS B) clicks. Best predictive models for Risso's dolphins and PWS A clicks included time-lagged variables, suggesting the importance of ecological succession between abiotic variables and dolphin occurrence, while best models of PWS B clicks were for current conditions, suggesting association with prey-aggregating features such as fronts and eddies.

The Application of Bioinspired Sonar to Cable Tracking on the Seafloor

Marine mammals have developed highly effective sonar systems for detecting, identifying, and following underwater objects. In this paper we demonstrate that bio-inspired wideband sonar offers great capability for tracking cables on the seafloor. The analysis of biological signals, including dolphin clicks, suggests two approaches. The first is to use a wideband signal, integrating the response of an object over many frequencies. For simple forms, this is known to give access to shape and material information. The second idea is to use intelligent signals designed to elicit information from specific target types. In this paper results are presented from sets of experiments using bio-inspired wideband sonar. The aim of these experiments is to determine the feasibility of tracking small diameter marine communications cables using the wideband responses. Echoes from four different cable types are analysed using a variety of signals. Experiments using bio-inspired pulses illustrate the benefits of using this type of wideband signal for detection and recognition. A strong correspondence between theoretical and experimental echoes is shown.

Spatial and temporal patterns of Risso’s dolphin echolocation in the Southern California Bight

Geographical and temporal trends in echolocation clicking activity can lead to insights into the foraging and migratory behaviors of pelagic dolphins. Using autonomous acoustic recording packages, the geographical, diel, and seasonal patterns of Risso's dolphin (Grampus griseus) echolocation click activity are described for six locations in the Southern California Bight between 2005 and 2007. Risso's dolphin echolocation click bouts are identified based on their unique spectral characteristics. Click bouts were identified on 739 of 1959 recording days at all 6 sites, with the majority occurring at nearshore sites. A significant diel pattern is evident in which both hourly occurrences of click bouts and click rates are higher at night than during the day. At all nearshore sites, Risso's dolphin clicks were identified year-round, with the highest daily occurrence at the southern end of Santa Catalina Island. Seasonal and interannual variabilities in occurrence were high across sites with peak occurrence in autumn of most years at most sites. These results suggest that Risso's dolphins forage at night and that the southern end of Santa Catalina Island represents an important habitat for Risso's dolphins throughout the year.

From mysticete song to odontocete echolocation: Monitoring cetacean sounds with high-frequency acoustic recording packages (HARPs).

Marine mammals produce a wide range of sounds from 10s of Hz to 100s of kHz. To remotely monitor these various sounds with autonomous systems, instruments with wide bandwidths are required. A general purpose, autonomous, high-frequency acoustic recording package (HARP) is described that can record sounds ranging from low-frequency blue whale (Balaenoptera musculus) song to mid-frequency dolphin whistles and beaked whale sweeps to high-frequency dolphin clicks. In addition to monitoring marine mammals, sounds from fish, contributions from wind and rain, and anthropogenic sources such as ships and sonar also are recorded potentially allowing for the study of cetacean behavioral response to these sounds. HARPs have been deployed for periods of up to one year, in various configurations such as standard moorings, seafloor packages, and arrays, and in remote locations including the Arctic, Bering Sea, Gulf of California, around Hawaii, and offshore of Washington State and southern California. The various configurations of these deployments and the wide range of marine mammal monitoring data they have provided are discussed in addition to lessons learned from these studies. [Work supported by the U.S. Navy CNO-N45.]

Classification of Risso’s and Pacific white-sided dolphins using spectral properties of echolocation clicks

The spectral and temporal properties of echolocation clicks and the use of clicks for species classification are investigated for five species of free-ranging dolphins found offshore of southern California: short-beaked common (Delphinus delphis), long-beaked common (D. capensis), Risso's (Grampus griseus), Pacific white-sided (Lagenorhynchus obliquidens), and bottlenose (Tursiops truncatus) dolphins. Spectral properties are compared among the five species and unique spectral peak and notch patterns are described for two species. The spectral peak mean values from Pacific white-sided dolphin clicks are 22.2, 26.6, 33.7, and 37.3 kHz and from Risso's dolphins are 22.4, 25.5, 30.5, and 38.8 kHz. The spectral notch mean values from Pacific white-sided dolphin clicks are 19.0, 24.5, and 29.7 kHz and from Risso's dolphins are 19.6, 27.7, and 35.9 kHz. Analysis of variance analyses indicate that spectral peaks and notches within the frequency band 24-35 kHz are distinct between the two species and exhibit low variation within each species. Post hoc tests divide Pacific white-sided dolphin recordings into two distinct subsets containing different click types, which are hypothesized to represent the different populations that occur within the region. Bottlenose and common dolphin clicks do not show consistent patterns of spectral peaks or notches within the frequency band examined (1-100 kHz).

The Experimental Pathology of Stress: Hans Selye to Paris Hilton

The Experimental Pathology of Stress: Hans Selye to Paris Hilton

Bio-inspired wideband sonar signals based on observations of the bottlenose dolphin (Tursiops truncatus)

This paper uses advanced time-frequency signal analysis techniques to generate new models for bio-inspired sonar signals. The inspiration comes from the analysis of bottlenose dolphin clicks. These pulses are very short duration, between 50 and 80 micros, but for certain examples we can delineate a double down-chirp structure using fractional Fourier methods. The majority of clicks have energy distributed between two main frequency bands with the higher frequencies delayed in time by 5-20 micros. Signal syntheses using a multiple chirp model based on these observations are able to reproduce much of the spectral variation seen in earlier studies on natural dolphin echolocation pulses. Six synthetic signals are generated and used to drive the dolphin based sonar (DBS) developed through the Biosonar Program office at the SPAWAR Systems Center, San Diego, CA. Analyses of the detailed echo structure for these pulses ensonifying two solid copper spherical targets indicate differences in discriminatory potential between the signals. It is suggested that target discrimination could be improved through the transmission of a signal packet in which the chirp structure is varied between pulses. Evidence that dolphins may use such a strategy themselves comes from observations of variations in the transmissions of dolphins carrying out target detection and identification tasks.

Simulation models of click production in dolphins

The simulation model (SM) of dolphin click source originally presented by [Dubrovskiy and Giro, ‘‘Echolocation in Bats & Dolphins,’’ Chap. 10, 59–63 (2003)] was further developed by Gladilin, Dubrovskiy, Mohl, and Walberg, Acoust. Phys. 50, 463‐468 (2004). The SM describes movements of a solid sphere frozen in a compliant ring. A jet of air in a duct connecting air cavities brings the sphere into self‐oscillations. The SM allows calculating the waveform and sound pressure of the generated clicks. Here the mathematical and simulation model (MSM) of click production in dolphins is further developed. The MSM describes radiation of clicks by bodies comprising of waterlike tissue with different shapes (a ring, a blunted cone) pulsating and (or) oscillating under action of muscles tension. Calculations are made for the energy efficient case when acting force is consecutively applied not to the entire body but to its thin layer, which resulted in action of the progressing wave array. Directivity patterns of such a waterlike compliant body in main directions are similar to that of a rigid body with the same shape and dimensions. Comparisons are made of MSM predictions with properties of an actual radiation field of dolphins (in clicks wave forms, sound pressure levels, and directivity patterns) and dimensions of biological structures supposedly responsible for click production in dolphins.

Sound Sources and Levels in the Ocean

The standard definitions found in the American National Standards on Acoustics are applied to common sound sources used in both underwater acoustics research and naval sonar system operation. Recommended metrics are quantified for both continuous and transient sources of sound. Standard definitions are reviewed with theoretical sound source models. Requisite metrics are derived and applied to examples of energy sources of sound, such as transients from a small omnidirectional explosive, an air gun, a light bulb, and a dolphin click. A generic quantitative model of surface ship sonar system emissions is developed. Active sonar transmissions are analyzed with the requisite quantitative metrics required to characterize these emissions. These results should be useful in environmental assessments, biological experiments, and the sonar system design

Estimated transmission beam pattern of clicks recorded from free-ranging white-beaked dolphins (Lagenorhynchus albirostris).

Recordings were made from white-beaked dolphins in Icelandic waters using a four-hydrophone array in a star configuration. The acoustic signals were amplified and sampled to a hard disk at a rate of 800 kHz per channel. The 3 and 10 dB beamwidths were calculated to be 8 degrees and 10 degrees, respectively, indicating a narrower transmission beam for white-beaked dolphins than that reported for bottlenose dolphins (Tursiops truncatus). The beamwidth was more similar to that found for belugas (Delphinapterus lucas). The measured beam pattern included large side lobes, perhaps due to the inclusion of off-axis clicks, even after applying several criteria to select only on-axis clicks. The directivity index was calculated to be 18 dB when using all data for angles from 0 degrees-50 degrees. The calculated sound radiation from a circular piston with a radius of 6 cm driven by a white-beaked dolphin click had a beam pattern very similar to the measured beam pattern for the main transmission lobe of the white-beaked dolphin. The directivity index was 29 dB. This is the first attempt to estimate the directionality index of dolphins in the field.

A Note on Clicks Recorded from Free-Ranging Indo-Pacific Humpback Dolphins, <I> Sousa chinensis</I>

Opportunistic recordings of Indo-Pacific humpback dolphin clicks were made from a group of approximately ten humpback dolphins in the waters off Lantau Island, Hong Kong. Clicks were typically delphinid in waveshape, especially the click onsets, with spectral energy extending up to at least 200 kHz. Pulse durations were a few tens of microseconds. There appeared to be bimodality in the click spectra, an observation consistent with the hypothesis of asymmetric phonating lips. Due to the opportunistic nature of the recordings and the uncontrolled recording conditions, click waveforms captured here are unlikely to be representative of on-axis signals, so the spectrum of the recorded signals may differ from those that would be recorded directly in front of the animals.

Target reconstruction from broadband acoustic backscatter

Broadband acoustic backscatter data are examined for mine reconstruction using LFM and dolphin clicks. Broadband backscatter data from free-field and bottom mines were collected during tests conducted in ARL/UT’s sand tank and sponsored by ONR. The data set includes multi-aspect broadband LFM (50–200 kHz) acoustic backscatter returns from a collection of targets. Both free-field and bottom target data were collected. Bottom target data sets include returns from two different levels of bottom roughness. Each data file is sampled over an interval that is large relative to the echo duration with sufficient sampling both prior to the echo onset and post-echo return to enable meaningful target characterization. Data collected over 360 deg in 2-deg increments are processed to generate a descriptive target pattern. The data are pulse compressed and system artifacts are removed using adjacent channels over the entire frequency band and within subbands. The target pattern is generated by applying the new adaptive wavelet filters to the scattered signals. In particular, the multi-aspect data that have several targets are tested to determine the ability of this new adaptive wavelet transform to reconstruct the external and internal structures of mines. Comparisons are made to previous results generated from broadband dolphin clicks.

Dolphin hearing: Relative sensitivity as a function of point of application of a contact sound source in the jaw and head region

The auditory input area of the dolphin head was investigated in an unrestrained animal trained to beach itself and to accept noninvasive electroencephalograph (EEG) electrodes for the recording of the auditory brain-stem response (ABR). The stimulus was a synthetic dolphin click, transmitted from a piezo-electric transducer and coupled to the skin via a small volume of water. The results conform with earlier experiments on acute preparations that show best auditory sensitivity at the middle of the lower jaw. Minimum latency was found at the rear of the lower jaw. A shaded receiver configuration for the dolphin ear is proposed.

Real-time sonar classification of proud and buried targets using dolphinlike echolocation signals

A broadband active sonar system using dolphinlike echolocation signals and biologically inspired signal processing algorithms was developed to classify proud and buried targets in real time. A dolphin simulator transducer was attached to a bottom-crawling remotely operated vehicle and used to transmit a dolphin click (120-kHz center frequency, 39-kHz bandwidth, 50-μs duration) through seawater. Reflected target echoes were received and transmitted via cable to a shore-based computer system where the echoes were digitized at 1 MHz and subsequently processed. Two time-frequency representations of the echoes, one based on the short-time Fourier transform and the other on the Morlet wavelet, were processed in a hierarchical neural network system to derive target classifications. Echolocation returns were collected from six objects (cast iron pot, stainless steel sphere, glass jar, concrete tile, and coral rock) that were placed either on the ocean bottom or buried by bottom sediment. Echoes were separated into three target categories: (1) cast iron pot; (2) stainless steel sphere; and (3) a miscellaneous category consisting of the remaining four objects. Following supervised neural network training, the system was able to correctly identify 74%, 97%, and 88% of the category 1, 2, and 3 test echoes.

Aspect-independent classification of ‘‘dolphin’’ ensonified mines using Choi–Williams representations

Contemporary anti-invasion mines have aspect-dependent shapes, making discrimination of mines from nonthreat objects, and classification of mines, a difficult task for human mine countermeasures personnel. Shallow-water (SW) noise and bottom reverberation substantially degrade the acoustic structure of mine echoes. Traditional MCM target strength and FFT classifiers are not effective under these conditions. The testing of a novel neural network classifier to solve the task of classifying mines in the SW acoustic environment was begun. Three mine types were ensonified at 1 deg rotations using synthetic dolphin clicks. A learning vector quantization network was trained to classify the mines using the Choi–Williams joint time-frequency distributions of echoes. A training set of 36 echoes per mine (5, 15, 25,..., 355 deg) was created, with the remaining echoes (0, 10, 20,..., 350 deg) reserved for generalization testing. The network correctly classified the mines at novel orientations with 85% accuracy. Performance using CWD will be contrasted with biomimetic sonar target classifiers under varying signal-to-noise ratios. [Research funded by ONR Underseas Active Signal Processing Program.]

Acoustical localization of dolphins in shallow water

Previous attempts at localization of cetaceans have generally used multiple hydrophone arrays and multichannel recording systems. In this paper a low-budget localization technique using only one hydrophone will be described. The time delays of the signals traveling on the surface and bottom reflection paths to the hydrophone, relative to the direct signal, are used to calculate the distance and the depth of a phonating animal. Only two additional measures, the depth of the bottom and hydrophone, have to be taken. The method requires relatively shallow waters and a flat ground surface. The received signals are digitized directly into a laptop computer via a PCMCIA A/D converter card with a sampling rate of 260 ksamples/s. Hawaiian spinner dolphins (Stenella langirostris) were localized by echolocation and burst pulse click trains over different bottom substrates. The method is most valuable for examining source levels of dolphin clicks in the wild and could lead to a better understanding of the nature and use of click trains by dolphins. [Work supported by Deutsche Forschungsgemeinschaft and Office of Naval Research.]

Broadband acoustic imaging of complex shaped targets

In some recent experiments conducted at the ARL:UT Lake Travis Testing Facility, acoustic images were created from scattering data of targets with complex geometries. The acoustic measurements were made in the volume in a monostatic scattering configuration at an approximate range of 40 m. The targets were constructed of either fiber-reinforced plastics and/or metals. A variety of large and small bandwidth product waveforms were chosen for the experiments including LFMs, simulated dolphin clicks, and short sinusoidal tone bursts. The frequencies of the waveforms span the range from 15 to 160 kHz. Data were taken by rotating the targets through 360 deg in finely spaced increments about several prechosen axes. The scattering data are processed in several ways. The processed data from different aspects are combined to reconstruct the shape of the object using image processing algorithms based on synthetic aperture and tomographic techniques. By varying the parameters of the incident waveforms, the resulting quality of the acoustic images is examined as a function of frequency and bandwidth. [Work supported by ONR.]

Sonar recognition of targets embedded in sediment

Dolphins have biological sonar abilities that exceed those of any man-made system in an aquatic environment. One problem of particular importance, and for which only limited capabilities exist, is the detection and recognition of targets buried under sediment. This paper reviews dolphin echolocation capabilities and describes a system that uses a dolphin-like signal and biomimetic signal processing mechanisms to emulate the performance of the dolpin on such targets. The system employed a digitized dolphin click with a center frequency of 120 kHz and a 3dB bandwidth of 39 kHz, 50 μs duration. This signal was transmitted through seawater into mud and the echoes reflected from the objects were recorded and digitized. Two spectral estimators were used to extract a time-frequency representation of the echo. One was based on short-time fast Fourier transforms, and the other was based on an autoregressive estimator. The time-frequency representation was then processed by a separate backpropagation neural network for each estimator, designed to derive independent identifications of the targets. These identifications were then combined in a modified probabilistic neural network that used a linear transfer function rather than a binary function for its output. Finally the output of the probabilistic network was processed symbolically by a simple expert system. Three experiments are described in which the system was used to discriminate a small stainless-steel cylinder from cyliners of the same size made of hollow aluminium, foam-filled aluminium, or coral rock embedded in resin. Each of the targets was presented buried in mud at a depth of several centimeters. The system proved highly effectively at recognizing these buried targets.

Clicks and Communication: The Behavioural and Social Contexts of Hector's Dolphin Vocalizations

AbstractHector's dolphins (Cephalorhynchus hectori) have a simple vocal repertoire, consisting almost entirely of ultrasonic clicks. They produce no whistles, and very few audible sounds. To examine acoustic communication in this species I analysed the relationship between click types and behaviour. The proportion of complex click types was greater in large groups, suggesting that these sounds have social significance. Clicks having 2 peaks in their time envelope and two frequency peaks were strongly associated with behaviours indicative of feeding. High pulse rate sounds, in which the repetition rate of ultrasonic clicks was audible as a “cry”, were most strongly associated with aerial behaviours. These data suggest that echo‐location is not the sole function of Hector's dolphin clicks, and that echo‐location and communication are likely to be closely linked. I hypothesize that dolphins may have the ability to gather information from the echoes of each other's sonar pulses. This may reduce the need for a large number of vocal signals, and may explain the apparent simplicity of the acoustic repertoires of some odontocetes.