Low-frequency whale and seismic airgun sounds recorded in the mid-Atlantic Ocean

Beginning in February 1999, an array of six autonomous hydrophones was moored near the Mid-Atlantic Ridge (35 degrees N-15 degrees N, 50 degrees W-33 degrees W). Two years of data were reviewed for whale vocalizations by visually examining spectrograms. Four distinct sounds were detected that are believed to be of biological origin: (1) a two-part low-frequency moan at roughly 18 Hz lasting 25 s which has previously been attributed to blue whales (Balaenoptera musculus); (2) series of short pulses approximately 18 s apart centered at 22 Hz, which are likely produced by fin whales (B. physalus); (3) series of short, pulsive sounds at 30 Hz and above and approximately 1 s apart that resemble sounds attributed to minke whales (B. acutorostrata); and (4) downswept, pulsive sounds above 30 Hz that are likely from baleen whales. Vocalizations were detected most often in the winter, and blue- and fin whale sounds were detected most often on the northern hydrophones. Sounds from seismic airguns were recorded frequently, particularly during summer, from locations over 3000 km from this array. Whales were detected by these hydrophones despite its location in a very remote part of the Atlantic Ocean that has traditionally been difficult to survey.     

Vocal behavior of resident killer whale matrilines with newborn calves: the role of family signatures

Studies of the vocal behavior of resident killer whales or orcas, Orcinus orca, in British Columbia have shown that matrilines have unique call repertoires consisting of up to 17 different call types. These call types cannot be attributed exclusively to specific behaviors, and their function in social contexts is poorly understood. This study investigated the change in call patterns of three resident matrilines in a changed social environment, before and up to one year after the birth of a calf. Acoustic data were collected with a network of hydrophones and were supplemented by visual observations. Call use changed distinctly after the birth of a calf in all three observed matrilines. All call types that were recorded in control situations were also recorded in postbirth situations; however, aberrant versions of discrete calls and excitement calls made up a higher proportion of calls after birth. Most conspicuously, family-specific call types occurred significantly more frequently in the days following a birth in two of the three matrilines and gradually returned to prebirth values within 2 weeks. Their increased use after a calf's birth may facilitate the learning process of this "acoustic family badge" and thereby help to recognize and maintain cohesion with family members.     

Seasonal variability and detection range modeling of baleen whale calls in the Gulf of Alaska, 1999-2002

Five species of large whales, including the blue (Balaenoptera musculus), fin (B. physalus), sei (B. borealis), humpback (Megaptera novaeangliae), and North Pacific right (Eubalaena japonica), were the target of commercial harvests in the Gulf of Alaska (GoA) during the 19th through mid-20th Centuries. Since this time, there have been a few summer time visual surveys for these species, but no overview of year-round use of these waters by endangered whales primarily because standard visual survey data are difficult and costly. From October 1999-May 2002, moored hydrophones were deployed in six locations in the GoA to record whale calls. Reception of calls from fin, humpback, and blue whales and an unknown source, called Watkins' whale, showed seasonal and geographic variation. Calls were detected more often during the winter than during the summer, suggesting that animals inhabit the GoA year-round. To estimate the distance at which species-diagnostic calls could be heard, parabolic equation propagation loss models for frequencies characteristic of each of each call type were run. Maximum detection ranges in the subarctic North Pacific ranged from 45 to 250 km among three species (fin, humpback, blue), although modeled detection ranges varied greatly with input parameters and choice of ambient noise level.     

Sound production by North Atlantic right whales (Eubalaena glacialis) in surface active groups

The surface active group (SAG) is the most commonly observed surface social behavior of North Atlantic right whales. Recordings were made from 52 SAGs in the Bay of Fundy, Canada between July and September, from 1999 to 2002. The call types recorded from these groups were similar to those described previously for Southern right whales (Eubalaena australis), with six major call types being termed scream, gunshot, blow, upcall, warble, and downcall. The percentage of total calls of each call type depended on the group size and composition. The most common call type recorded was the scream call. The scream calls were produced by the focal female in a SAG. Production of other sound types can be attributed to whales other than the focal female, with gunshot and upcalls produced by males, and warble calls produced by female calves. The source levels for these sounds range from 137 to 162 dB rms re 1 ,tPa-m for tonal calls and 174 to 192 dB rms for broadband gunshot sounds.     

Sounds produced by Norwegian killer whales, Orcinus orca, during capture

To date very little is still known about the acoustic behavior of Norwegian killer whales, in particular that of individual whales. In this study a unique opportunity was presented to document the sounds produced by five captured killer whales in the Vestfjord area, northern Norway. Individuals produced 14 discrete and 7 compound calls. Two call types were used both by individuals 16178 and 23365 suggesting that they may belong to the same pod. Comparisons with calls documented in Strager (1993) showed that none of the call types used by the captured individuals were present. The lack of these calls in the available literature suggests that call variability within individuals is likely to be large. This short note adds to our knowledge of the vocal repertoire of this population and demonstrates the need for further studies to provide behavioural context to these sounds.     

Detection range modeling of blue whale calls in Southwestern Indian Ocean

In the Southwestern Indian Ocean, one year of continuous acoustic data from calibrated hydrophones maintained by the International Monitoring System provided data on blue whale calls from two subspecies Antarctic and pygmy blue whales. Using an automatic detection method with a fixed threshold, both call types were detected and received levels were measured for each detected call. By using a parabolic equation loss model configured with the precise characteristics of the biological source, hydroacoustic station, and environment in the study area, distances at which calls could be detected were estimated. These methods were used to define the maximum detection range around each array of hydrophones and the influence of the seasonal variation of the ambient noise and sound velocity on the detection ranges. Results showed that detection ranges were critically dependent on the choice of the biological source’s input parameters, including frequency bandwidth and source level. Over the course of the year, detection distances were different for both subspecies; the pygmy blue whale seemed to be consistently closer to the station than the Antarctic blue whale. The distribution of the estimated distances confirmed the presence of both subspecies of blue whales near the Crozet Islands showing the importance of this sub-Antarctic area for these endangered species, especially during the austral summer feeding season.     

Blue and fin whale call source levels and propagation range in the Southern Ocean

Blue (Balaenoptera musculus) and fin whales (B. physalus) produce high-intensity, low-frequency calls, which probably function for communication during mating and feeding. The source levels of blue and fin whale calls off the Western Antarctic Peninsula were calculated using recordings made with calibrated, bottom-moored hydrophones. Blue whales were located up to a range of 200 km using hyperbolic localization and time difference of arrival. The distance to fin whales, estimated using multipath arrivals of their calls, was up to 56 km. The error in range measurements was 3.8 km using hyperbolic localization, and 3.4 km using multipath arrivals. Both species produced high-intensity calls; the average blue whale call source level was 189+/-3 dB re:1 microPa-1 m over 25-29 Hz, and the average fin whale call source level was 189+/-4 dB re:1 microPa-1 m over 15-28 Hz. Blue and fin whale populations in the Southern Ocean have remained at low numbers for decades since they became protected; using source level and detection range from passive acoustic recordings can help in calculating the relative density of calling whales.     

Low frequency vocalizations attributed to sei whales (Balaenoptera borealis)

Low frequency (<100 Hz) downsweep vocalizations were repeatedly recorded from ocean gliders east of Cape Cod, MA in May 2005. To identify the species responsible for this call, arrays of acoustic recorders were deployed in this same area during 2006 and 2007. 70 h of collocated visual observations at the center of each array were used to compare the localized occurrence of this call to the occurrence of three baleen whale species: right, humpback, and sei whales. The low frequency call was significantly associated only with the occurrence of sei whales. On average, the call swept from 82 to 34 Hz over 1.4 s and was most often produced as a single call, although pairs and (more rarely) triplets were occasionally detected. Individual calls comprising the pairs were localized to within tens of meters of one another and were more similar to one another than to contemporaneous calls by other whales, suggesting that paired calls may be produced by the same animal. A synthetic kernel was developed to facilitate automatic detection of this call using spectrogram-correlation methods. The optimal kernel missed 14% of calls, and of all the calls that were automatically detected, 15% were false positives.     

The social vocalization repertoire of east Australian migrating humpback whales (Megaptera novaeangliae)

Although the songs of humpback whales have been extensively studied, other vocalizations and percussive sounds, referred to as "social sounds," have received little attention. This study presents the social vocalization repertoire of migrating east Australian humpback whales from a sample of 660 sounds recorded from 61 groups of varying composition, over three years. The social vocalization repertoire of humpback whales was much larger than previously described with a total of 34 separate call types classified aurally and by spectrographic analysis as well as statistically. Of these, 21 call types were the same as units of the song current at the time of recording but used individually instead of as part of the song sequence, while the other 13 calls were stable over the three years of the study and were not part of the song. This study provides a catalog of sounds that can be used as a basis for future studies. It is an essential first step in determining the function, contextual use and cultural transmission of humpback social vocalizations.     

Effects of noise levels and call types on the source levels of killer whale calls

Accurate parameter estimates relevant to the vocal behavior of marine mammals are needed to assess potential effects of anthropogenic sound exposure including how masking noise reduces the active space of sounds used for communication. Information about how these animals modify their vocal behavior in response to noise exposure is also needed for such assessment. Prior studies have reported variations in the source levels of killer whale sounds, and a more recent study reported that killer whales compensate for vessel masking noise by increasing their call amplitude. The objectives of the current study were to investigate the source levels of a variety of call types in southern resident killer whales while also considering background noise level as a likely factor related to call source level variability. The source levels of 763 discrete calls along with corresponding background noise were measured over three summer field seasons in the waters surrounding the San Juan Islands, WA. Both noise level and call type were significant factors on call source levels (1-40 kHz band, range of 135.0-175.7 dB(rms) re 1 [micro sign]Pa at 1 m). These factors should be considered in models that predict how anthropogenic masking noise reduces vocal communication space in marine mammals.     

The acoustic calls of blue whales off California with gender data

The acoustic calls of blue whales off California are described with visual observations of behavior and with acoustic tracking. Acoustic call data with corresponding position tracks are analyzed for five calling blue whales during one 100-min time period. Three of the five animals produced type A-B calls while two produced another call type which we refer to as type D. One of the animals producing the A-B call type was identified as male. Pauses in call production corresponded to visually observed breathing intervals. There was no apparent coordination between the calling whales. The average call source level was calculated to be 186 dB re: 1 muPa at 1 m over the 10-110-Hz band for the type B calls. On two separate days, female blue whales were observed to be silent during respective monitoring periods of 20 min and 1 h.     

Intra- and intergroup vocal behavior in resident killer whales, Orcinus orca

Vocal communication within and between groups of individuals has been described extensively in birds and terrestrial mammals, however, little is known about how cetaceans utilize their sounds in their natural environment. Resident killer whales, Orcinus orca, live in highly stable matrilines and exhibit group-specific vocal dialects. Single call types cannot exclusively be associated with particular behaviors and calls are thought to function in group identification and intragroup communication. In the present study call usage of three closely related matrilines of the Northern resident community was compared in various intra- and intergroup contexts. In two out of the three matrilines significant changes in vocal behavior depending both on the presence and identity of accompanying whales were found. Most evidently, family-specific call subtypes, as well as aberrant and variable calls, were emitted at higher rates, whereas "low arousal" call types were used less in the presence of matrilines from different pods, subclans, or clans. Ways in which the observed changes may function both in intra- and intergroup communication.     

Divergence of a stereotyped call in northern resident killer whales

Northern resident killer whale pods (Orcinus orca) have distinctive stereotyped pulsed call repertoires that can be used to distinguish groups acoustically. Repertoires are generally stable, with the same call types comprising the repertoire of a given pod over a period of years to decades. Previous studies have shown that some discrete pulsed calls can be subdivided into variants or subtypes. This study suggests that new stereotyped calls may result from the gradual modification of existing call types through subtypes. Vocalizations of individuals and small groups of killer whales were collected using a bottom-mounted hydrophone array in Johnstone Strait, British Columbia in 2006 and 2007. Discriminant analysis of slope variations of a predominant call type, N4, revealed the presence of four distinct call subtypes. Similar to previous studies, there was a divergence of the N4 call between members of different matrilines of the same pod. However, this study reveals that individual killer whales produced multiple subtypes of the N4 call, indicating that divergence in the N4 call is not the result of individual differences, but rather may indicate the gradual evolution of a new stereotyped call.     

Directional frequency and recording (DIFAR) sensors in seafloor recorders to locate calling bowhead whales during their fall migration

Bowhead whales, Balaena mysticetus, migrate west during fall approximately 10-75 km off the north coast of Alaska, passing the petroleum developments around Prudhoe Bay. Oil production operations on an artificial island 5 km offshore create sounds heard by some whales. As part of an effort to assess whether migrating whales deflect farther offshore at times with high industrial noise, an acoustical approach was selected for localizing calling whales. The technique incorporated DIFAR (directional frequency and recording) sonobuoy techniques. An array of 11 DASARs (directional autonomous seafloor acoustic recorders) was built and installed with unit-to-unit separation of 5 km. When two or more DASARs detected the same call, the whale location was determined from the bearing intersections. This article describes the acoustic methods used to determine the locations of the calling bowhead whales and shows the types and precision of the data acquired. Calibration transmissions at GPS-measured times and locations provided measures of the individual DASAR clock drift and directional orientation. The standard error of the bearing measurements at distances of 3-4 km was approximately 1.35 degrees after corrections for gain imbalance in the two directional sensors. During 23 days in 2002, 10,587 bowhead calls were detected and 8383 were localized.     

Sounds from airguns and fin whales recorded in the mid-Atlantic Ocean, 1999-2009

Between 1999 and 2009, autonomous hydrophones were deployed to monitor seismic activity from 16° N to 50° N along the Mid-Atlantic Ridge. These data were examined for airgun sounds produced during offshore surveys for oil and gas deposits, as well as the 20?Hz pulse sounds from fin whales, which may be masked by airgun noise. An automatic detection algorithm was used to identify airgun sound patterns, and fin whale calling levels were summarized via long-term spectral analysis. Both airgun and fin whale sounds were recorded at all sites. Fin whale calling rates were higher at sites north of 32° N, increased during the late summer and fall months at all sites, and peaked during the winter months, a time when airgun noise was often prevalent. Seismic survey vessels were acoustically located off the coasts of three major areas: Newfoundland, northeast Brazil, and Senegal and Mauritania in West Africa. In some cases, airgun sounds were recorded almost 4000 km from the survey vessel in areas that are likely occupied by fin whales, and at some locations airgun sounds were recorded more than 80% days/month for more than 12 consecutive months.     

Vocal characteristics of pygmy blue whales and their change over time

Vocal characteristics of pygmy blue whales of the eastern Indian Ocean population were analyzed using data from a hydroacoustic station deployed off Cape Leeuwin in Western Australia as part of the Comprehensive Nuclear-Test-Ban Treaty monitoring network, from two acoustic observatories of the Australian Integrated Marine Observing System, and from individual sea noise loggers deployed in the Perth Canyon. These data have been collected from 2002 to 2010, inclusively. It is shown that the themes of pygmy blue whale songs consist of ether three or two repeating tonal sounds with harmonics. The most intense sound of the tonal theme was estimated to correspond to a source level of 179 ± 2 dB re 1 μPa at 1 m measured for 120 calls from seven different animals. Short-duration calls of impulsive downswept sound from pygmy blue whales were weaker with the source level estimated to vary between 168 to 176 dB. A gradual decrease in the call frequency with a mean rate estimated to be 0.35 ± 0.3 Hz/year was observed over nine years in the frequency of the third harmonic of tonal sound 2 in the whale song theme, which corresponds to a negative trend of about 0.12 Hz/year in the call fundamental frequency.     

North Pacific right whale up-call source levels and propagation distance on the southeastern Bering Sea shelf

Call source levels, transmission loss, and ambient noise levels were estimated for North Pacific right whale (Eubalaena japonica) up-calls recorded in the southeastern Bering Sea in autumn of 2000 and 2001. Distances to calling animals, needed to estimate source levels, were based on two independent techniques: (1) arrival-time differences on three or more hydrophones and (2) shallow-water dispersion of normal modes on a single receiver. Average root-mean-square (rms) call source levels estimated by the two techniques were 178 and 176 dB re 1 μPa at 1 m, respectively, over the up-call frequency band, which was determined per call and averaged 90 to 170 Hz. Peak-to-peak source levels were 14 to 22 dB greater than rms levels. Transmission loss was approximately 15?log(10)(range), intermediate between cylindrical and spherical spreading. Ambient ocean noise within the up-call band varied from 72 to 91 dB re 1 μPa(2)/Hz. Under average noise conditions, call spectrograms were detectable for whales at distances up to 100 km, but propagation and detection distance may vary depending on environmental parameters and anthropogenic noise. Obtaining distances to animals and acoustic detection range is a step toward using long-term passive acoustic recordings to estimate abundance for this critically endangered whale population.     

Automatic classification of killer whale vocalizations using dynamic time warping

A set of killer whale sounds from Marineland were recently classified automatically [Brown et al., J. Acoust. Soc. Am. 119, EL34-EL40 (2006)] into call types using dynamic time warping (DTW), multidimensional scaling, and kmeans clustering to give near-perfect agreement with a perceptual classification. Here the effectiveness of four DTW algorithms on a larger and much more challenging set of calls by Northern Resident whales will be examined, with each call consisting of two independently modulated pitch contours and having considerable overlap in contours for several of the perceptual call types. Classification results are given for each of the four algorithms for the low frequency contour (LFC), the high frequency contour (HFC), their derivatives, and weighted sums of the distances corresponding to LFC with HFC, LFC with its derivative, and HFC with its derivative. The best agreement with the perceptual classification was 90% attained by the Sakoe-Chiba algorithm for the low frequency contours alone.     

Acoustic properties of humpback whale songs

A vertical array of five hydrophones was used to measure the acoustic field in the vertical plane of singing humpback whales. Once a singer was located, two swimmers with snorkel gear were deployed to determine the orientation of the whale and position the boat so that the array could be deployed in front of the whale at a minimum standoff distance of at least 10 m. The spacing of the hydrophones was 7 m with the deepest hydrophone deployed at a depth of 35 m. An eight-channel TASCAM recorder with a bandwidth of 24 kHz was used to record the hydrophone signals. The location (distance and depth) of the singer was determined by computing the time of arrival differences between the hydrophone signals. The maximum source level varied between individual units in a song, with values between 151 and 173 dB re 1 microPa. One of the purposes of this study was to estimate potential sound exposure of nearby conspecifics. The acoustic field determined by considering the relative intensity of higher frequency harmonics in the signals indicated that the sounds are projected in the horizontal direction despite the singer being canted head downward anywhere from about 25 degrees to 90 degrees. High-frequency harmonics extended beyond 24 kHz, suggesting that humpback whales may have an upper frequency limit of hearing as high as 24 kHz.