Whale Signals Research Articles

Echolocation parameters of toothed whales measured at sea

Historically, data on toothed whale echolocation parameters and abilities were collected from captive animals. Acoustic parameters under investigation were inter-click-interval, spectral content, source level, directionality, emission direction, including correlation and variation of those parameters. Technological advances over the past decade have allowed collecting data on those parameters from animals at sea using acoustic recording tags or hydrophone arrays. Using a vertical, linear array of 16 hydrophones, echolocation clicks from harbor porpoises, white-beaked dolphins, common dolphins, and bottlenose dolphins were recorded around Iceland and the Azores. The animal’s position at click production was computed for each click based on the time of arrival differences. Intensity and spectral differences at the array allowed measuring source levels, beam width, and spectral variation at different angles relative to on-axis. Advancing knowledge on the use and variation of echolocation signals of toothed whales in their natural habitat will allow widespread and effective use of acoustic monitoring.

Tracking whales in the Indian Ocean using the comprehensive test ban treaty hydrophone data

This paper will present preliminary results and status in development of an automated tracking algorithm for whale signals using the Comprehensive Test Ban Treaty (CTBT) sensor network. The data from the CTBT stations is being made available for academic work, and the stations are also detecting bioacoustics sounds as well as seismic activity. We present an approach used to process several channels of the acoustic data collected off Cape Leeuwin, Australia, and automatically search for biologic activity using cross-correlation and Time-Difference-of-Arrival methods. After developing a graph of locations for peak correlation amplitude, the locations are mapped and grouped using location and proximity, in order to develop motion tracks and compare coherence of the signals within a grouping and between groupings, thus identify individual whales based on the differences in location and coherence levels.

Long-term monitoring of Physeteroidea (sperm whales, dwarf, and pygmy sperm whales) in the Central and Western Pacific

The superfamily Physeteroidea includes three extant species: the sperm whale (Physeter macrocephalus), the dwarf sperm whale (Kogia sima), and the pygmy sperm whale (K. breviceps). Despite extreme difference in size between the Kogia spp. and their large Physeter relative, all three share ecological and acoustic traits relating to their deep-diving behavior and high rates of acoustic activity. All three species can be found across the Central and Western Pacific ocean, an area that has been monitored using passive acoustics (High-frequency Acoustic Recording Packages, HARPs) for more than 10 years. We identified sperm whale and Kogia spp. signals in the long-term HARP records from 13 locations across the Central and Western Pacific ocean. A combination of automated tools and human analysis were used to record detection events of both types of signals. While sperm whales were found at all 13 locations, the Kogia species (which cannot yet be distinguished acoustically) were detected at approximately half of the sites. Presence of sperm whale signals was modeled to determine if temporal parameters, such as lunar cycle and day of the year, could explain patterns of presence. Across the whole region the best model included the day of the year and the recording site, while sub-regions and site-specific models had slightly different combinations of parameters.

Killer whale (Orcinus orca) whistles from the western South Atlantic Ocean include high frequency signals.

Acoustic parameters of killer whale (Orcinus orca) whistles were described for the western South Atlantic Ocean and highlight the occurrence of high frequency whistles. Killer whale signals were recorded on December of 2012, when a pod of four individuals was observed harassing a group of sperm whales. The high frequency whistles were highly stereotyped and were modulated mostly at ultrasonic frequencies. Compared to other contour types, the high frequency whistles are characterized by higher bandwidths, shorter durations, fewer harmonics, and higher sweep rates. The results add to the knowledge of vocal behavior of this species.

Classification of beaked whale and dolphin clicks measured by environmental acoustic recording system buoys in the northern Gulf of Mexico

The Littoral Acoustic Demonstration Center (LADC) has used its Environmental Acoustic Recording System (EARS) buoys to record sperm and beaked whales and dolphins, with frequencies up to 96 kHz, in the northern Gulf of Mexico in 2007 and 2010. The 2007 experiment was the first to record beaked whales in the Gulf. It has been found that there is considerable overlap in the band of beaked whale signals from 20 to 60 kHz with deep-water dolphin clicks, so traditional energy-band detectors have a high occurrence of false positives. Although acoustic measurements in this frequency range validated by visual observations have been limited, for the Gulf of Mexico species, progress is being made in automatically delineating clicks that belong to beaked whale species observed in the Gulf and those originating from dolphins. Spectrograms of the classified clicks are shown and compared to known spectrograms for beaked whale and dolphin species. Many of the spectrograms show an upsweep in the observed spectrum but others do not. Improved classifiers can provide higher accuracy estimates of the regional abundance trends and effects of environmental changes on both beaked whale and dolphin groups. [Research supported by BP/GOMRI, SPAWAR, ONR, NSF, and Greenpeace.]

Temporal patterns in detections of sperm whales (Physeter macrocephalus) in the North Pacific Ocean based on long-term passive acoustic monitoring

Sperm whales (Physeter macrocephalus), a long-lived, cosmopolitan species, are well suited for long-term studies, and their high amplitude echolocation signals make them ideal for passive acoustic monitoring. NOAA’s Pacific Islands Fisheries Science Center has deployed High-frequency Acoustic Recording Packages (200 kHz sampling rate) at 13 deep-water locations across the central and western North Pacific Ocean since 2005. Recordings from all sites were manually analyzed for sperm whale signals, and temporal patterns were examined on multiple scales. There were sperm whale detections at all sites, although the rate of detection varied by location, with the highest rate at Wake Island (15% of samples), and the fewest detections at sites close to the equator (<1%). Only two locations (Saipan and Pearl and Hermes Reef) showed significant seasonal patterns, with more detections in the early spring and summer than in later summer or fall. There were no significant patterns relating to lunar cycles. Analysis of diel variation revealed that sperm whales were detected more during the day and night compared to dawn and dusk at most sites. The variability shown in these results emphasizes the importance of assessing basic biological patterns and variations in the probability of detection before progressing to further analysis, such as density estimation, where the effects of uneven sampling effort could significantly influence results.

Presence and seasonal variation of deep diving foraging odontocetes around Kauai, Hawaii using remote autonomous acoustic recorders

Ecological acoustic recorders (EARs) were moored off the bottom in relatively deep depths (609-710 m) at five locations around the island of Kauai. Initially, the EARs had an analog-to-digital sample rate of 64 kHz with 30-s recordings every 5 min. After the second deployment the sampling rate was increased to 80 kHz in order to better record beaked whale biosonar signals. The results of the 80 kHz recording are discussed in this manuscript and are the results of three deployments over a year's period (January 2010 to January 2011). Five categories of the biosonar signal detection of deep diving odontocetes were created, short-finned pilot whales, sperm whales, beaked whales, Risso's dolphins, and unknown dolphins. During any given day, at least one species of these deep diving odontocetes were detected. On many days, several species were detected. The biosonar signals of short-finned pilot whales were detected the most often with approximately 30% of all the signals, followed by beaked and sperm whales approximately 22% and 21% of all clicks, respectively. The seasonal patterns were not very strong except in the SW location with distinct peak in detection during the months of April-June 2010 period.

Long term passive acoustics monitoring reveals differences in deep diving Odontocetes foraging strategies

Beaked whales, sperm whales, pilot whales, and Risso's dolphins perform deep dives to feed on prey in the deep sea. They use echolocation to detect prey, and echolocation can be monitor as a proxy of their foraging activities. Ecological acoustic recorders were deployed to monitor in time the echolocation signals of pilot whales, Risso's dolphins, beaked whales, and sperm whales near Josephine Seamount (Portugal), in the Ligurian Sea (Italy), and along the Kona coast of the island of Hawaii. Data analysis was performed using two automatic detector/classification systems: Marine Mammal Monitoring on Navy Ranges (M3R), developed at the Naval Undersea Warfare Center Division in Newport, USA, and a custom MATLAB program. An operator-supervised custom MATLAB program was used to validate the classification performance, which was higher than 85% for each category. Results show that pilot whales and Risso's dolphins concentrate their feeding effort mainly during the night. The foraging activity of beaked and sperm whales is variable, and different patterns are observed at different locations. Prey behavior might play a central role in driving the foraging activity of deep divers, but to date, the reasons why such activity varies between species that might feed on similar food resources remains unknown.

Comparisons of beaked whale signals recorded in eastern Atlantic to known beaked whales signals

Beaked whales are a group of more than 20 genetically confirmed species; they are very elusive and were among the least known species until a few years ago. Because of their sensitivity to sonar, an increased research effort dedicated to these species and in particular to their signals started 10 years ago. Despite this effort, the signals of many beaked whale species remain unknown. Signals of Blainville’s (Mesoplodon densirostris), Cuvier’s (Ziphius cavirostris), Gervais’ (Mesoplodon europaeus), and Northern Bottlenose Whales (Hyperoodon ampullatus) have been studied and described in different articles. The signals of three unknown species (different from the above mentioned species signals) have been reported. All seven species produce upsweep frequency modulated signals which seem species specific. In 2010, NATO Undersea Research Centre (NURC) conducted a sea-trial in Eastern Atlantic Ocean, Southwest of Portugal. Three different types of beaked whale signals were recorded. The characteristics of these signals will be presented and compared to the known signals of beaked whales. The conclusions of this analysis will be presented.

Localization of humpback whale signals with two directional frequency analysis and recording sonobouys

For many years, the navy has used directional frequency analysis and recording (DIFAR) sonobouys to record and track ships. DIFAR sonobouys compute acoustic particle velocity for two bimodal perpendicular hydrophone elements, which, with a magnetic compass, gives a directional bearing to the sound recorded on a third omnidirectional hydrophone. Use of DIFAR represents an easily deployable alternative method to standard time-difference of arrival localization with towed or bottom-mounted hydrophone arrays. In this study, we used two tethered DIFAR sonobouys to record and track playbacks of humpback whale song. GPS positions of playbacks were recorded. Digital signals were recorded at the sonobouy before multiplexing. Song units were recorded on both sonobouys, and then matched between sonobouys using time from the sonobouy GPS. To localize the signals, azimuths from the DIFAR sonobouys were combined with the time difference of arrival parabola to create a three-dimensional likelihood surface that gives the probabilities that a signal originated at a specific point in space. The locations with maximum likelihood were used to estimate source level of whale calls, and singing whales were tracked over time. Comparisons will be made between DIFAR methods and GPS locations from the playback boat, to ground-truth this localization methodology.

Passive acoustic monitoring of Cook Inlet beluga whales (Delphinapterus leucas)

The endangered beluga whale (Delphinapterus leucas) population in Cook Inlet, AK faces threats from a variety of anthropogenic factors, including coastal development, oil and gas exploration, vessel traffic, and military activities. To address existing gaps in understanding about the occurrence of belugas in Cook Inlet, a project was developed to use passive acoustic monitoring to document the year-round distribution of belugas, as well as killer whales (Orcinus orca), which prey on belugas. Beginning in June 2009, ten moorings were deployed throughout the Inlet and refurbished every two to eight months. Despite challenging conditions consisting of strong tidal currents carrying debris and seasonal ice cover, 83% of mooring deployments were successfully recovered. Noise from water flow, vessel traffic, and/or industrial activities was present at several sites, potentially masking some signals. However, belugas were successfully detected at multiple locations. Detections were relatively common in the upper inlet and less common or absent at middle and lower inlet locations. Killer whale signals were also recorded. Some seasonal variability in the occurrence of both belugas and killer whales was evident.

Species-specific beaked whale echolocation signals

Beaked whale echolocation signals are mostly frequency-modulated (FM) upsweep pulses and appear to be species specific. Evolutionary processes of niche separation may have driven differentiation of beaked whale signals used for spatial orientation and foraging. FM pulses of eight species of beaked whales were identified, as well as five distinct pulse types of unknown species, but presumed to be from beaked whales. Current evidence suggests these five distinct but unidentified FM pulse types are also species-specific and are each produced by a separate species. There may be a relationship between adult body length and center frequency with smaller whales producing higher frequency signals. This could be due to anatomical and physiological restraints or it could be an evolutionary adaption for detection of smaller prey for smaller whales with higher resolution using higher frequencies. The disadvantage of higher frequencies is a shorter detection range. Whales echolocating with the highest frequencies, or broadband, likely lower source level signals also use a higher repetition rate, which might compensate for the shorter detection range. Habitat modeling with acoustic detections should give further insights into how niches and prey may have shaped species-specific FM pulse types.

High-frequency modulated signals of killer whales (Orcinus orca) in the North Pacific

Killer whales in the North Pacific, similar to Atlantic populations, produce high-frequency modulated signals, based on acoustic recordings from ship-based hydrophone arrays and autonomous recorders at multiple locations. The median peak frequency of these signals ranged from 19.6-36.1 kHz and median duration ranged from 50-163 ms. Source levels were 185-193 dB peak-to-peak re: 1 μPa at 1 m. These uniform, repetitive, down-swept signals are similar to bat echolocation signals and possibly could have echolocation functionality. A large geographic range of occurrence suggests that different killer whale ecotypes may utilize these signals.

Characteristics of biosonar signals from the northern bottlenose whale, Hyperoodon ampullatus

The biosonar pulses from free-ranging northern bottlenose whales (Hyperoodon ampullatus) were recorded with a linear hydrophone array. Signals fulfilling criteria for being recorded close to the acoustic axis of the animal (a total of 10 clicks) had a frequency upsweep from 20 to 55 kHz and durations of 207 to 377 μs (measured as the time interval containing 95% of the signal energy). The source level of these signals, denoted pulses, was 175-202 dB re 1 μPa rms at 1 m. The pulses had a directionality index of at least 18 dB. Interpulse intervals ranged from 73 to 949 ms (N = 856). Signals of higher repetition rates had interclick intervals of 5.8-13.1 ms (two sequences, made up of 59 and 410 clicks, respectively). These signals, denoted clicks, had a shorter duration (43-200 μs) and did not have the frequency upsweep characterizing the pulses of low repetition rates. The data show that the northern bottlenose whale emits signals similar to three other species of beaked whale. These signals are distinct from the three other types of biosonar signals of toothed whales. It remains unclear why the signals show this grouping, and what consequences it has on echolocation performance.

High-frequency modulated signals of killer whales (Orcinus orca) in the North Pacific

High-frequency modulated signals of killer whales (<i>Orcinus orca</i>) in the North Pacific

Masking of southern resident killer whale signals by commercial ship noise.

The endangered southern resident killer whales (SRKWs) emit sound to communicate with each other and to hunt fish. Communication or fishing are possible only within a distance (R) at which a signal can be detected. We determine detection distance by comparing the power spectra of the ambient noise and the received signal, with attention to the auditory response curve of the receiver. In Haro Strait, the center of the SRKW critical habitat, about 21 commercial ships per day, increases the ambient noise level by about 20 dB. To assess how ship noise may affect the SRKW communication and hunting, we define the fractional reduction in the zone of audibility at any location and time as the ratio of the area where signal detection is expected to occur in the increased noise regime to the maximum detection area expected under ideal conditions R2/Rmax2. We map the decreased zones of audibility in Haro Strait during average and extreme ship noise by combining field measurements of spreading rates with source power spectra (1–100 kHz) of common SRKW signals and typical ships.

Rhythmic analysis of sperm whale broadband acoustic signals.

Rhythmic analysis of sperm whale clicks, based on the static Fourier transform, was previously reported in the literature as a tool for extracting the acoustic signature of individual sperm whales [Andre and Kamminga, J. Mar. Biol. Ass. U.K. (2000)]. A new approach, originated from the algorithm developed for human motion analysis [Sabatier and Ekimov, “A Review of Human Signatures in Urban Environments Using Seismic and Acoustic Methods,” Proc. IEEE (2008)], is applied to study time‐dependent periodicity in sperm whale signals recorded in the Gulf of Mexico. The new approach for rhythmic analysis of sperm whales clicks, which are used for navigation purposes, shows the presence of stable temporal periodicity that could possibly be attributed to the acoustic portrait of individuals. [Research supported in part by SPAWAR.]

Temporal patterns in the acoustic signals of beaked whales at Cross Seamount

Seamounts may influence the distribution of marine mammals through a combination of increased ocean mixing, enhanced local productivity and greater prey availability. To study the effects of seamounts on the presence and acoustic behaviour of cetaceans, we deployed a high-frequency acoustic recording package on the summit of Cross Seamount during April through October 2005. The most frequently detected cetacean vocalizations were echolocation sounds similar to those produced by ziphiid and mesoplodont beaked whales together with buzz-type signals consistent with prey-capture attempts. Beaked whale signals occurred almost entirely at night throughout the six-month deployment. Measurements of prey presence with a Simrad EK-60 fisheries acoustics echo sounder indicate that Cross Seamount may enhance local productivity in near-surface waters. Concentrations of micronekton were aggregated over the seamount in near-surface waters at night, and dense concentrations of nekton were detected across the surface of the summit. Our results suggest that seamounts may provide enhanced foraging opportunities for beaked whales during the night through a combination of increased productivity, vertical migrations by micronekton and local retention of prey. Furthermore, the summit of the seamount may act as a barrier against which whales concentrate prey.

Communicative pulsed signals of beluga whales in the reproductive gathering off Solovetskii Island in the White Sea

Results of the perceptive and acoustic analysis of communicative pulsed signals recorded in a repro- ductive gathering of beluga whales off Solovetskii Island in the white sea are presented. The mean signal dura- tion varies from 0.04 to 1.52 s for various signal types, the pulse repetition rate on the average ranges from 13 to 1300 (possibly, 2700) impulses per second, and the mean peak frequency falls within 0.2 to 11.3 kHz. A high degree of similarity between the communicative pulsed signals produced by beluga whales from different pop- ulations is revealed.

Acoustical monitoring of finback whale movements on the New Jersey Shelf

Acoustical monitoring of finback whales is performed by using a data set collected over a 3-week period in December of 2003 on the New Jersey Shelf. One-second-duration 20-Hz signals of finback whales were recorded on three vertical line arrays (VLAs) and a bottomed horizontal line array (HLA.). One-second-duration pulses are separated by about 10 s and there is an approximately 2-min-long silent period between 10- to 18-min-long pulse trains. A 30- to 60-min silent period after 5 to 10 pulse trains is also common. Modal analysis of individual pulses indicated that most signals contained two acoustic modes. Arrival-time and group-speed differences of these modes are used for remote acoustic ranging. These modal characteristics are also exploited in a broadband matched-field algorithm for depth discrimination. Bearing estimation of individual whales is obtained by performing horizontal beamforming on the HLA data. Range estimation results are verified by time-of-flight triangulation using single hydrophone data from each VLA location. Acoustic monitoring results indicated that most finback whales traveled near the shelf break front where food might be abundant. Relations between silent periods and acoustic range/depth monitoring results are also investigated. [This work was supported by the ONR.]