Echolocation Clicks Research Articles

Assessing the effects of noise masking and transmission loss on dolphin occupancy rates reported by echolocation click loggers deployed on the eastern Scottish coast

C-PODs are commercially available echolocation click loggers used to monitor odontocete populations worldwide. Data from C-PODs have directly contributed to high-profile conservation efforts as well as provided major insights into cetacean behavior and habitat use. However, the “black-box” nature of the instruments poses a challenge to researchers seeking to validate data from these instruments. In this study, we simulate how changes in site-specific propagation conditions and ambient noise levels shift dolphin occupancy rates as reported by the C-POD. As part of the ECoMASS array, 10 calibrated continuous recorders (SM2Ms) were co-deployed with C-PODs in the North Sea. Transmission loss profiles, assumed dolphin source levels, and published C-POD performance metrics were combined to estimate the relationship between detection probability and ambient noise level at the 10 study sights. Bayesian models were then used to estimate dolphin occupancy rates with and without accounting for differences in detection probability. While absolute occupancy rates differed when detection probability was accounted for, relative trends in occupancy were generally consistent within the two models. These data suggest that, within the scope of the ECoMASS array, relative occupancy rates are somewhat robust to differences in transmission loss and ambient noise levels throughout the survey period and location.

Automatic detection method for monitoring odontocete echolocation clicks

Passive acoustic monitoring records large amounts of acoustic data, and thus an efficient detection method is essential to analyse these data. A novel approach is proposed to automatically detect odontocete echolocation clicks. A time–frequency filter detects echolocation clicks in the time–frequency domain, and then the Teager–Kaiser energy operator and Gabor curve-fitting method determine the start and end points of each echolocation click precisely. Detector performance is assessed by using synthetic data. The experimental results showed that the recall rates were higher than 90% when the signal-to-noise ratio was above 10 dB.

Spatio-temporal variation and seasonality of Odontocetes' foraging activity in the leeward side of the island of Hawaii

The Kona coast of the island of Hawaii hosts many species of odontocetes. These marine mammals are top predators and their foraging activity plays an important role in the ecosystem dynamics. Three passive acoustics recorders were used to study the temporal and spatial occurrence of the foraging activity of odontocetes (excluding beaked and sperm whales) at three locations along the Kona coast of Hawaii between 2012 and 2013. Echolocation clicks were detected using the M3R11M3R: Marine Mammal Monitoring on Navy Ranges; EAR: Ecological Acoustic Recorder; NK: North Kona; CK: Central Kona; SK: South Kona; CS-SVM: Class Specific Support Vector Machine; GLM: Generalized Linear Model; ANOVA: Analysis of variance. (Marine Mammal Monitoring on Navy Ranges) system, and custom-designed Matlab (MathWorks, Natick, MA, USA) programs were designed to analyze the detected data. A Generalized Linear Model was used to understand the influence of location and month on the foraging activity. Both location and month affected the foraging activity of Odontocetes in Hawaii. In general, the foraging activity was the highest in the north and the lowest in the south part of the study area. The model revealed that, at each location, the foraging activity tended to decrease over the time of the study. A seasonality seems to be seen for the two southernmost locations. At the northernmost location the foraging activity decreased from February 2012 till 11 months later (January 2013). Odontocetes daily foraging activity was higher at night-time at all locations sampled.

Bio Acoustic Sources Segmentation in a Noisy Underwater Environment Using Wavelet Denoising with Ica

An advanced type of Independent Component Analysis (ICA) algorithm is used in this paper for separation of biological sounds in underwater noisy environment. Underwater noisy environment are formed by echolocation clicks, snapping shrimps and dolphin whistles mixing. Different types of ICA algorithms like Infomax, Fast-ICA are used to apply on mixture of bio-signals. Depend upon separability performance, effectiveness of these algorithms has been compared. Using ICALAB and open source, signals are available and ICALAB simulation packages are based on this to compare the algorithms of ICA. Finally, graph for proposed technique is shown for comparisons using wavelet denoising.

Acoustic classification of dolphins in the California Current using whistles, echolocation clicks, and burst pulses

AbstractPassive acoustic monitoring of dolphins is limited by our ability to classify calls to species. Significant overlap in call characteristics among many species, combined with a wide range of call types and acoustic behavior, makes classification of calls to species challenging. Here, we introduce BANTER, a compound acoustic classification method for dolphins that utilizes information from all call types produced by dolphins rather than a single call type, as has been typical for acoustic classifiers. Output from the passive acoustic monitoring software, PAMGuard, was used to create independent classifiers for whistles, echolocation clicks, and burst pulses, which were then merged into a final, compound classifier for each species. Classifiers for five species found in the California Current ecosystem were trained and tested using 153 single‐species acoustic events recorded during a 4.5 mo combined visual and acoustic shipboard cetacean survey off the west coast of the United States. Correct classification scores for individual species ranged from 71% to 92%, with an overall correct classification score of 84% for all five species. The conceptual framework of this approach easily lends itself to other species and study areas as well as to noncetacean taxa.

Echolocation and burst clicks from franciscana dolphins (Pontoporia blainvillei) on the coast of Uruguay

Echolocation and burst clicks from franciscana dolphins (<i>Pontoporia blainvillei</i>) on the coast of Uruguay

Passive acoustic monitoring of the decline of Mexico's critically endangered vaquita.

The vaquita (Phocoena sinus) is the world's most endangered marine mammal with approximately 245 individuals remaining in 2008. This species of porpoise is endemic to the northern Gulf of California, Mexico, and historically the population has declined because of unsustainable bycatch in gillnets. An illegal gillnet fishery for an endangered fish, the totoaba (Totoaba macdonaldi), has recently resurged throughout the vaquita's range. The secretive but lucrative wildlife trade with China for totoaba swim bladders has probably increased vaquita bycatch mortality by an unknown amount. Precise population monitoring by visual surveys is difficult because vaquitas are inherently hard to see and have now become so rare that sighting rates are very low. However, their echolocation clicks can be identified readily on specialized acoustic detectors. Acoustic detections on an array of 46 moored detectors indicated vaquita acoustic activity declined by 80% between 2011 and 2015 in the central part of the species' range. Statistical models estimated an annual rate of decline of 34% (95% Bayesian credible interval -48% to -21%). Based on results from 2011 to 2014, the government of Mexico enacted and is enforcing an emergency 2-year ban on gillnets throughout the species' range to prevent extinction, at a cost of US$74 million to compensate fishers. Developing precise acoustic monitoring methods proved critical to exposing the severity of vaquitas' decline and emphasizes the need for continual monitoring to effectively manage critically endangered species.

Using line acceleration to measure false killer whale (Pseudorca crassidens) click and whistle source levels during pelagic longline depredation.

False killer whales (Pseudorca crassidens) depredate pelagic longlines in offshore Hawaiian waters. On January 28, 2015 a depredation event was recorded 14 m from an integrated GoPro camera, hydrophone, and accelerometer, revealing that false killer whales depredate bait and generate clicks and whistles under good visibility conditions. The act of plucking bait off a hook generated a distinctive 15 Hz line vibration. Two similar line vibrations detected at earlier times permitted the animal's range and thus signal source levels to be estimated over a 25-min window. Peak power spectral density source levels for whistles (4-8 kHz) were estimated to be between 115 and 130 dB re 1 μPa2/Hz @ 1 m. Echolocation click source levels over 17-32 kHz bandwidth reached 205 dB re 1 μPa @ 1 m pk-pk, or 190 dB re 1 μPa @ 1 m (root-mean-square). Predicted detection ranges of the most intense whistles are 10 to 25 km at respective sea states of 4 and 1, with click detection ranges being 5 times smaller than whistles. These detection range analyses provide insight into how passive acoustic monitoring might be used to both quantify and avoid depredation encounters.

Unsupervised clustering of toothed whale species from echolocation clicks

Supervised learning of categories related to animal signals requires labeled data that are used to train a classifier. In areas where species assemblages are poorly understood, such labeled data are usually unavailable. We show that unsupervised learning techniques may be used to provide an initial assessment of an area. We demonstrate that clustering techniques can be used to group sets of echolocation clicks from different species into clusters that tend to contain a single species without any labeled examples. Results are presented on the 2015 Detection Classification Localization and Density Estimation (DCLDE) toothed-whale development dataset, which contains analyst labels for several species of odontocetes as well as an unknown category. Echolocation clicks were detected and grouped into acoustic encounters from which spectral and temporal features were extracted. We used a simplifying assumption of single species encounters and estimated distributions of features in each encounter. Dendrograms were constructed by average-linkage clustering using a symmetric Kullback-Leibler similarity metric. Different algorithms were used to partition the dendrogram, with partition quality estimated by the silhouette algorithm. Comparison of the best machine-generated partitioning with that produced by analysts yielded an adjusted Rand statistic of 0.66, demonstrating a good degree of concurrence.

Enhanced target detection and classification using two-pulse sonar methods

A number of two-pulse sonar techniques can be employed to separate linear and nonlinear scatterers. Twin Inverted Pulse Sonar (TWIPS) and Biased Pulse Summation Sonar (BiaPSS) are processes that exploit nonlinear bubble dynamics to perform such a classification, with clutter reduction. Consequently, these techniques can be used to enhance target detection in bubbly waters. TWIPS and BiaPSS rely upon bubbles being driven to large nonlinear pulsations, but this is dependent upon availability of a high-amplitude source. Previous studies could only access a narrow-band source and therefore used a low frequency so that, over the rarefaction cycle, most ocean bubbles would expand sufficiently (the size range of near-surface ocean bubbles under waves and wakes being large). However, recent access to a broadband high-power source has allowed exploitation of bubble resonances. This talk presents results of investigations using broadband linear sine sweeps, of which one is based upon the simulation of an Atlantic Bottlenose Dolphin (Tursiops truncatus) echolocation click from Capus et al. (2006). Insonifying a cloud of bubbles with a wide band of frequencies excites as many of those sizes at, or close to, their resonance. As such, the contrast between linear and nonlinear scatter is enhanced, improving the target detection capability.

Acoustic response of Indo-Pacific humpback dolphins to the variability of marine soundscape

Marine mammals can adjust their vocal behaviors when they encounter anthropogenic noise. The acoustic divergence among different populations has also been considered as the effect of ambient noise. The recent studies discover that the marine soundscape is highly dynamic; however, it remains unclear how marine mammals alter their vocal behaviors under various acoustic environments. In this study, autonomous sound recorders were deployed in western Taiwan waters between 2012 and 2015. Soundscape scenes were unsupervised classified according to acoustic features measured in each 5 min interval. Non-negative matrix factorization was used to separate different scenes and to inverse the temporal occurrence of each soundscape scene. Echolocation clicks and whistles of Indo-Pacific humpback dolphins, which represent the only marine mammal species occurred in the study area, were automatically detected and analyzed. The preliminary result indicates the soundscape scenes dominated by biological sounds are correlated with the acoustic detection rate of humpback dolphins. Besides, the dolphin whistles are much complex when the prey associated scene is prominent in the local soundscape. In the future, the soundscape information may be used to predict the occurrence and habitat use of marine mammals.

Automatic detection and classification of toothed whale echolocation clicks in diverse long term recordings

We present results of classification of toothed whale echolocation clicks to species for 4 TB of recordings in the development data of 7th Intl. DCLDE Workshop. The data span multiple seasons, years, locations, and instruments. Five species were acoustically identified by analysts, and a sixth category was assigned to echolocation clicks that could not be identified to species by analysts. Methods were developed to identify periods of echolocation activity taking into account sporadic false positives that occur throughout the data, and to reduce false positives from both anthropogenic and biologic sources. Dense echolocation activity presented particular challenges for noise removal and long term recordings permitted the targeting of regions for noise estimation outside of echolocation encounters. Extracted features consisted of noise normalized cepstral characterizations of spectra, inter-click interval, and -3 dB bandwidth. These features were classified with a Gaussian mixture model (GMM). A robust sco...

Biosonar radiation field on the forehead of a Risso’s dolphin during prey capture

On-animal suction cups with embedded hydrophones allow examination of how signals on the forehead of echolocating odontocetes relate to the internal anatomical structure and the transmission beampattern. Risso’s dolphin (Grampus griseus) is an interesting species for this investigation due to the presence of a unique vertical groove in the middle of their forehead. In this study, a linear array of six broadband suction cup hydrophones were attached along the forehead groove of an adult female Risso’s dolphin trained to catch freshly thawed dead squid in front of an eight-element far-field hydrophone array. The animal’s movement was simultaneously observed using an underwater video camera. A total of nine successful prey captures were recorded. During each catch, the animal first emitted regular echolocation clicks, which quickly transitioned into buzzes (clicks with distinctively high repetition rate) until prey capture. The amplitude and relative time of arrival of these signals across all channels were analyzed. For a subset of trials, the relative amplitude distribution across channels vary significantly between regular clicks and buzzes in a manner that may be explained by beampattern changes. These observations were investigated jointly with data from the hydrophone array and interpreted in light of anatomical structure of the melon.

Recent bioacoustics researches on biosonar, hearing, and noise effect on the Indo-Pacific humpback dolphins (Sousa chinensis)

The Indo-Pacific humpback dolphins (Sousa chinensis) are widely distributed in the coastal waters of the tropical and sub-tropical ocean in Asia, including southeast China. Conservation of the humpback dolphins in Chinese waters has been on the agenda of local scientific and conservation communities since the 1980s, despite little research including bioacoustics research has been conducted. Our recent bioacoustics studies indicated that the biosonar clicks of the wild humpback dolphins were short-duration, broadband, ultrasonic pulses, similar to those produced by other whistling dolphins of similar body size. However, their click source levels with an average of around 190 dB re: 1μ Pa in peak-to-peak, appear to be much lower than those of other whistling dolphins. Hearing sensitive frequency range of the humpback dolphins is generally higher than 5 kHz and lower than 120 kHz with possible age-related hearing loss for old dolphins. The humpback dolphin could therefore be characterized as a mid-frequency cetacean, which operates sounds in mid- to high-frequency range. Any sufficiently intense sounds with mid- to high-frequency components could have deleterious effects on the humpback dolphins through interference on animals’ behavior and with the animals’ ability to detect signals from conspecifics, and echoes of echolocation clicks.

Spatiotemporal variation in habitat utilization of humpback dolphins (Sousa chinensis) potentially affected by freshwater discharge

Dynamics of habitat utilization of marine mammals are important for the conservation management of coastal ecosystems. Previous studies have shown that seasonal changes of humpback dolphin distribution are associated with seasonal changes of upstream rainfall. However, temporal variations of dolphin behavior at an estuarine habitat remain unclear. In this study, echolocation clicks of humpback dolphins were recorded at the Xinhuwei River Estuary, western Taiwan, between July 2009 and November 2015. Sound source bearing angles to identify different sound sources, intensity, and inter-click intervals (ICIs) as an index of the sensing distance were measured to investigate the sensing and movement of dolphin groups. Humpback dolphins searched for shorter sensing distances and moved back and forth near the estuary during spring and summer, which suggests foraging-related behaviors were much frequently observed during wet seasons. However, humpback dolphins changed to focus on longer detection ranges (ICIs changed from 40 to 50 ms to 50 to 70 ms) and move in straight forward when upstream rainfall increased during this period. The present result indicated the dynamics of habitat utilization of humpback dolphins at an estuary is likely driven by the distribution and abundance of prey resource which is influenced by the temporal change of river runoff.

The characteristics of dolphin clicks compared across recording depths and instruments

The identification of delphinid species on the basis of the characteristics of their acoustic signals is an important aspect of many passive acoustic monitoring efforts. The development of species classifiers relies on the assumption that species-specific signal characteristics will be consistent across different recording scenarios, including depth and instrumentation. However, this assumption has largely remained untested. Here, we report on an effort to examine whether and how the properties of echolocation clicks obtained from different delphinid species vary as a function of recording depth and the instrument employed. Field recordings of seven species of dolphins were obtained off Kona, Hawaii, and San Diego, CA, using a 250 m vessel-based vertical array composed of five microMARS recorders, two SoundTrap recorders, and four C75 broadband dipping hydrophones (Cetacean Research Technology). The clicks obtained were characterized on the basis of their spectral properties and duration for each recording depth and also compared among different instruments deployed at the same depth. Both depth and recording instrumentation influenced the click characteristics observed. However, the click properties of some species varied to a greater degree than others. These results suggest that developing species-specific classifiers based on dolphin clicks should be approached with caution and carefully validated.

Echolocation behavior of the Icelandic white-beaked (Lagenorhyncus albirostris) dolphins: Now and then

First studies of the echolocation behaviour of free-ranging white-beaked dolphins (Lagenorhyncus albirostris) were conducted in Faxafloi Bay in the Southwestern part of Iceland in the years 1997 to 1999. However, the sighting rate of white-beaked dolphins has decreased in that area since then and the current studies were conducted in the Northeastern part of Iceland. The aim of this study was to investigate the difference between normal clicks compared to clicks from buzz sequences. The recordings of the Icelandic white-beaked dolphins were conducted using a vertical linear 16-hydrophone array in Skjalfandi Bay, Northeastern Iceland during August 2015 and June 2016. The hydrophones were connected to NI-Boards and to a laptop computer on board using a sample rate of 1 MHz per channel. The group size of the dolphins varied from three individuals up to 30 animals in the area during the recordings. The dolphin echolocation clicks were recorded and it was possible to track individuals and to estimate beam-patt...

Intra-click time-frequency patterns across the echolocation beam of a beluga whale

The echolocation beam of toothed whales has been studied ever since it was first discovered in 1960. Recent studies have focused on the frequency distributions across the cross sections of the beams. Other studies have focussed on describing the entire acoustic field around the animal. However, no one has yet described the timing of each frequency component in the main lobe beam in relation to the other frequency components. Even though the echolocation clicks of broadband click species like the beluga whales (Delphinapterus leucas) are short in time (around 70 μs), previous results have shown indications on a frequency dependence with time, within each click. Little is known about the details of how the signal is generated and transmitted into the water. Investigations of when in time the frequency components occur within each click would give us further knowledge to how the signals are generated. This study takes a closer look at these intra-click time-frequency patterns across the echolocation beam of ...

Delphinid echolocation click detection probability on near-seafloor sensors.

The probability of detecting echolocating delphinids on a near-seafloor sensor was estimated using two Monte Carlo simulation methods. One method estimated the probability of detecting a single click (cue counting); the other estimated the probability of detecting a group of delphinids (group counting). Echolocation click beam pattern and source level assumptions strongly influenced detectability predictions by the cue counting model. Group detectability was also influenced by assumptions about group behaviors. Model results were compared to in situ recordings of encounters with Risso's dolphin (Grampus griseus) and presumed pantropical spotted dolphin (Stenella attenuata) from a near-seafloor four-channel tracking sensor deployed in the Gulf of Mexico (25.537°N 84.632°W, depth 1220 m). Horizontal detection range, received level and estimated source level distributions from localized encounters were compared with the model predictions. Agreement between in situ results and model predictions suggests that simulations can be used to estimate detection probabilities when direct distance estimation is not available.

Single-sensor, cue-counting population density estimation: Average probability of detection of broadband clicks.

Odontocete echolocation clicks have been used as a preferred cue for density estimation using single-sensor data sets, requiring estimation of detection probability as a function of range. Many such clicks can be very broadband in nature, with 10-dB bandwidths of 20-40 kHz or more. Detection distances are not readily obtained from single-sensor data. Here, the average detection probability is estimated in a Monte Carlo simulation using the passive sonar equation along with transmission loss calculations to estimate the signal-to-noise ratio (SNR) of tens of thousands of click realizations. Continuous-wave (CW) analysis, i.e., single-frequency analysis, is inherent to basic forms of the passive sonar equation. Using CW analysis with the click's center frequency while disregarding its bandwidth has been shown to introduce bias into detection probabilities and hence to density estimates. In this study, the effects of highly broadband clicks on density estimates are further examined. The usage of transmission loss as an appropriate measure for calculating click SNR is also discussed. The main contributions from this research are (1) an alternative approach to estimate the average probability of detection of broadband clicks, and (2) understanding the effects of multipath clicks on population density estimates.