The acoustic calls of blue whales off California with gender data

Spatial and temporal variability of the acoustic repertoire of Antarctic minke whales (Balaenoptera bonaerensis) in the Weddell Sea

Since the attribution of the bio-duck call to Antarctic minke whales (AMW Balaenoptera bonaerensis), different studies have retrospectively identified several bio-duck call types at various sites throughout the Southern Hemisphere. The function of their vocal behavior however, remains largely unknown. Further insights into their repertoire usage may help to reveal the function of their calls. Here, we use passive acoustic monitoring (PAM) data collected across six locations throughout the Weddell Sea (WS) in 2013 and from PALAOA Station (Ekström Ice Shelf, eastern WS) in 2015, 2016 and 2017. In 2013, we detected 11 bio-duck call types throughout the WS between May and December, with additional acoustic activity in February on the western recorder AMW calls fell into four general call clusters. Seasonal patterns of calls showed variability between locations and years. Furthermore, this is the first study to show that similar to other baleen whale species, AMWs also produce songs.

Distributed acoustic sensing recordings of low-frequency whale calls and ship noise offshore Central Oregon

Distributed acoustic sensing (DAS) is a technique that measures strain changes along an optical fiber to distances of ∼100 km with a spatial sensitivity of tens of meters. In November 2021, 4 days of DAS data were collected on two cables of the Ocean Observatories Initiative Regional Cabled Array extending offshore central Oregon. Numerous 20 Hz fin whale calls, northeast Pacific blue whale A and B calls, and ship noises were recorded, highlighting the potential of DAS for monitoring the ocean. The data are publicly available to support studies to understand the sensitivity of submarine DAS for low-frequency acoustic monitoring.

Acoustic and visual cetacean surveys reveal year-round spatial and temporal distributions for multiple species in northern British Columbia, Canada

Cetaceans spend most of their time below the surface of the sea, highlighting the importance of passive acoustic monitoring as a tool to facilitate understanding and mapping their year-round spatial and temporal distributions. To increase our limited knowledge of cetacean acoustic detection patterns for the east and west coasts of Gwaii Haanas, a remote protected area on Haida Gwaii, BC, Canada, acoustic datasets recorded off SG̱ang Gwaay (Sep 2009-May 2011), Gowgaia Slope (Jul 2017-Jul 2019), and Ramsay Island (Aug 2018-Aug 2019) were analyzed. Comparing overlapping periods of visual surveys and acoustic monitoring confirmed presence of 12 cetacean species/species groups within the study region. Seasonal patterns were identified for blue, fin, humpback, grey and sperm whale acoustic signals. Killer whale and delphinid acoustic signals occurred year-round on both coasts of Haida Gwaii and showed strong diel variation. Cuvier's, Baird's, beaked whale and porpoise clicks, were identified in high-frequency recordings on the west coast. Correlations between environmental factors, chlorophyll-a and sea surface temperature, and cetacean acoustic occurrence off Gwaii Haanas were also examined. This study is the first to acoustically monitor Gwaii Haanas waters for an extended continuous period and therefore serves as a baseline from which to monitor future changes.

Update on frequency decline of Northeast Pacific blue whale (Balaenoptera musculus) calls

Worldwide, the frequency (pitch) of blue whale (Balaenoptera musculus) calls has been decreasing since first recorded in the 1960s. This frequency decline occurs over annual and inter-annual timescales and has recently been documented in other baleen whale species, yet it remains unexplained. In the Northeast Pacific, blue whales produce two calls, or units, that, when regularly repeated, are referred to as song: A and B calls. In this population, frequency decline has thus far only been examined in B calls. In this work, passive acoustic data collected in the Southern California Bight from 2006 to 2019 were examined to determine if A calls are also declining in frequency and whether the call pulse rate was similarly impacted. Additionally, frequency measurements were made for B calls to determine whether the rate of frequency decline is the same as was calculated when this phenomenon was first reported in 2009. We found that A calls decreased at a rate of 0.32 Hz yr^-1 during this period and that B calls were still decreasing, albeit at a slower rate (0.27 Hz yr^-1) than reported previously. The A call pulse rate also declined over the course of the study, at a rate of 0.006 pulses/s yr^-1. With this updated information, we consider the various theories that have been proposed to explain frequency decline in blue whales. We conclude that no current theory adequately accounts for all aspects of this phenomenon and consider the role that individual perception of song frequency may play. To understand the cause behind call frequency decline, future studies might want to explore the function of these songs and the mechanism for their synchronization. The ubiquitous nature of the frequency shift phenomenon may indicate a consistent level of vocal plasticity and fine auditory processing abilities across baleen whale species.

Extraction of Energy Characteristics of Blue Whale Vocalizations Based on Empirical Mode Decomposition

This study extracts the energy characteristic distributions of the intrinsic mode functions (IMFs) and residue functions (RF) for a blue whale sound signal, with empirical mode decomposition (EMD) as the basic theoretical framework. A high-resolution marginal frequency characteristics extraction method, based on EMD with energy density intensity (EDI) parameters for blue B call vocalizations, was proposed. The extraction algorithm included six steps: EMD, energy analysis, marginal frequency (MF) analysis with EDI parameters, feature extraction (FE), classification, and Hilbert spectrum (HS) analysis. The blue whale sound sources were obtained from the website of the Scripps Whale Acoustics Lab of the University of California, San Diego, USA. The source is a type of B call with a time duration of 46.65 s, from which 59 analysis samples with a time duration of 180 ms were taken. The average energy distribution ratios of the IMF1, IMF2, IMF3, IMF4, and RF are 49.06%, 20.58%, 13.51%, 10.94% and 3.84%, respectively. New classification criteria and EDI parameters were proposed to extract the blue whale B call vocalization (BWBCV) characteristics. The analysis results show that the main frequency bands of the signal are distributed at 41–43 Hz in the MF of IMF1 for Class I BWBCV and 11–13 Hz in the MF of IMF2 for Class II BWBCV, respectively.

Assessing potential perception of shipping noise by marine mammals in an arctic inlet

Shipping is increasing in Arctic regions, exposing marine mammals to increased underwater noise. Noise analyses often use unweighted broadband sound pressure levels (SPL) to assess noise impacts, but this does not account for the animals' hearing abilities at different frequencies. In 2018 and 2019, noise levels were recorded at five and three sites, respectively, along a shipping route in an inlet of Northern Baffin Island, Canada. Broadband SPLs (10 Hz-25 kHz), unweighted and with auditory weighing functions from three marine mammal groups, were compared between times ore carriers (travelling < 9 knots) were present or absent. Clearly audible distances of shipping noise and exposure durations were estimated for each weighting function relative to vessel direction, orientation, and year. Auditory weighting functions had significant effects on the potential perception of shipping noise. Bowhead whales (Balaena mysticetus) experienced similar SPLs to unweighted levels. Narwhals (Monodon monoceros) and ringed seals (Pusa hispida) experienced lower SPLs. Narwhals were unlikely to clearly perceive shipping noise unless ships were in close proximity (<3 km) and ambient noise levels were low. Detectability propagation models of presumed noise exposure from shipping must be based on the hearing sensitivities of each species group when assessing noise impacts on marine mammals.

Seasonal Trends and Diel Patterns of Downsweep and SEP Calls in Chilean Blue Whales

To learn more about the occurrence and behaviour of a recently discovered population of blue whales, passive acoustic data were collected between January 2012 and April 2013 in the Chiloense ecoregion of southern Chile. Automatic detectors and manual auditing were used to detect blue whale songs (SEP calls) and D calls, which were then analysed to gain insights into temporal calling patterns. We found that D call rates were extremely low during winter (June–August) but gradually increased in spring and summer, decreasing again later during fall. SEP calls were absent for most winter and spring months (July–November) but increased in summer and fall, peaking between March and April. Thus, our results support previous studies documenting the austral summer residency of blue whales in this region, while suggesting that some individuals stay longer, highlighting the importance of this area as a blue whale habitat. We also investigated the daily occurrence of each call type and found that D calls occurred more frequently during dusk and night hours compared to dawn and day periods, whereas SEP calls did not show any significant diel patterns. Overall, these findings help to understand the occurrence and behaviour of endangered Chilean blue whales, enhancing our ability to develop conservation strategies in this important Southern Hemisphere habitat.

Baseline assessment of ocean ambient noise in the western Clarion Clipperton Zone, Pacific Ocean

Ocean noise in the western Clarion Clipperton Zone, Pacific Ocean was recorded for 5 min every hour during 2017 and 2018, at a depth of 300 m. The monthly and hourly mean spectrum levels in the 20-1000 Hz band were calculated, along with their skewness, kurtosis, percentile distributions, and spectral probability densities. The high noise levels at low frequencies generated from distant shipping and vocalizations of whales were found to range between 70 and 100 dB (<100 Hz) and 64-93 dB (100-200 Hz), respectively. The noise levels at high frequencies (>200 Hz), which are typically dominated by wind, were found to be low, ranging from 53 to 75 dB. At frequencies above 200 Hz, noise levels in winter were approximately 5 dB higher than those in summer, consistent with the seasonal variations in wind speed. Fin whales, blue whales, and fishes also potentially contributed to variations in the baseline of ambient noise.

Estimating minke whale relative abundance in the North Atlantic using passive acoustic sensors

Estimates of abundance and their changes through time are key elements of marine mammal conservation and management. Absolute marine mammal abundance in a region of the open ocean is often difficult to attain. However, methods of estimating their abundance based on passive acoustic recordings are becoming increasingly employed. This study shows that passive acoustic monitoring of North Atlantic minke whales with a single hydrophone provides sufficient information to estimate relative population abundance. An automated detector was developed for minke whale pulse trains and an approach for converting its output into a relative abundance index is proposed by accounting for detectability as well as false positives and negatives. To demonstrate this technique, a 2 y dataset from the seven sites of the Atlantic Deepwater Ecosystem Observatory Network project on the U.S. east coast was analyzed. Resulting relative abundance indices confirm pulse train-calling minke whale presence in the deep waters of the outer continental shelf. The minkes are present December through April annually with the highest abundance near the site offshore of Savannah, Georgia.

Geographically distinct blue whale song variants in the Northeast Pacific

The Northeast Pacific (NEP) population of blue whales Balaenoptera musculus musculus is currently managed as a single stock. We investigated the fine-scale frequency characteristics of 1 NEP blue whale song unit, the B call. We analyzed B calls from passive acoustic data collected between 2010 and 2013 at 2 low-latitude sites, Palmyra Atoll and the Hawaiian Islands, and 3 higher-latitude sites, off southern California, off Washington state and in the Gulf of Alaska. Frequency measurements were extracted along the contour of the third harmonic from each call, and data from each region were compared. Calls from the Gulf of Alaska and Hawai‘i presented a downshift in frequency, beginning just past the midway point of the contour, which was not present in calls recorded from southern California or Palmyra Atoll. Calls from Washington displayed intermediate characteristics between those from the other 2 high-latitude sites. Cluster analysis resulted in consistent grouping of call contours from Washington and southern California, in what we termed the NEP B1 variant, while contours from Hawai‘i and the Gulf of Alaska were grouped together, as a NEP B2 variant. Frequency differences were also observed among the variants; the Gulf of Alaska displayed the highest frequency on average, followed by Washington, then southern California. Consistent with other studies, a yearly decline in the frequency of B calls was also observed. This discovery of at least 2 geographically distinct variants provides the first evidence of vocally distinct subpopulations within the NEP, indicating the possibility of a need for finer-scale population segmentation.

Allopatric humpback whales of differing generations share call types between foraging and wintering grounds

Humpback whales (Megaptera novaeangliae) are a cosmopolitan baleen whale species with geographically isolated lineages. Despite last sharing an ancestor ~ 2-3 million years ago, Atlantic and Pacific foraging populations share five call types. Whether these call types are also shared between allopatric breeding and foraging populations is unclear, but would provide further evidence that some call types are ubiquitous and fixed. We investigated whether these five call types were present on a contemporary foraging ground (Newfoundland, 2015-2016) and a historic breeding ground (Hawaii, 1981-1982). Calls were classified using aural/visual (AV) characteristics; 16 relevant acoustic variables were measured and a Principal Component Analysis (PCA) was used to examine within-call and between-population variation. To assess whether between-population variation influenced classification, all 16 variables were included in classification and regression tree (CART) and random forest analyses (RF). All five call types were identified in both populations. Between-population variation in combined acoustic variables (PC1, PC2, PC3) was lower within call types than among call types, and high agreement between AV and quantitative classification (CART: 83% agreement; RF: 77% agreement) suggested that acoustic characteristics were more similar within than among call types. Findings indicate that these five call types are shared across allopatric populations, generations, and behavioural contexts.

Food talk: 40-Hz fin whale calls are associated with prey biomass

Animals use varied acoustic signals that play critical roles in their lives. Understanding the function of these signals may inform about key life-history processes relevant for conservation. In the case of fin whales (Balaenoptera physalus), that produce different call types associated with different behaviours, several hypotheses have emerged regarding call function, but the topic still remains in its infancy. Here, we investigate the potential function of two fin whale vocalizations, the song-forming 20-Hz call and the 40-Hz call, by examining their production in relation to season, year and prey biomass. Our results showed that the production of 20-Hz calls was strongly influenced by season, with a clear peak during the breeding months, and secondarily by year, likely due to changes in whale abundance. These results support the reproductive function of the 20-Hz song used as an acoustic display. Conversely, season and year had no effect on variation in 40-Hz calling rates, but prey biomass did. This is the first study linking 40-Hz call activity to prey biomass, supporting the previously suggested food-associated function of this call. Understanding the functions of animal signals can help identifying functional habitats and predict the negative effects of human activities with important implications for conservation.

Source level and vocalizing depth estimation of two blue whale subspecies in the western Indian Ocean from single sensor observations

The source level (SL) and vocalizing source depth (SD) of individuals from two blue whale (BW) subspecies, an Antarctic blue whale (Balaenoptera musculus intermedia; ABW) and a Madagascar pygmy blue whale (Balaenoptera musculus brevicauda; MPBW) are estimated from a single bottom-mounted hydrophone in the western Indian Ocean. Stereotyped units (male) are automatically detected and the range is estimated from the time delay between the direct and lowest-order multiply-reflected acoustic paths (multipath-ranging). Allowing for geometric spreading and the Lloyd's mirror effect (range-, depth-, and frequency-dependent) SL and SD are estimated by minimizing the SL variance over a series of units from the same individual over time (and hence also range). The average estimated SL of 188.5 ± 2.1 dB re 1μPa measured between [25-30] Hz for the ABW and 176.8 ± 1.8 dB re. 1μPa measured between [22-27] Hz for the MPBW agree with values published for other geographical areas. Units were vocalized at estimated depths of 25.0 ± 3.7 and 32.7 ± 5.7 m for the ABW Unit A and C and, ≃20 m for the MPBW. The measurements show that these BW calls series are stereotyped in frequency, amplitude, and depth.

Automatic detection and classification of baleen whale social calls using convolutional neural networks

Passive acoustic monitoring has proven to be an indispensable tool for many aspects of baleen whale research. Manual detection of whale calls on these large data sets demands extensive manual labor. Automated whale call detectors offer a more efficient approach and have been developed for many species and call types. However, calls with a large level of variability such as fin whale (Balaenoptera physalus) 40 Hz call and blue whale (B. musculus) D call have been challenging to detect automatically and hence no practical automated detector exists for these two call types. Using a modular approach consisting of faster region-based convolutional neural network followed by a convolutional neural network, we have created automated detectors for 40 Hz calls and D calls. Both detectors were tested on recordings with high- and low density of calls and, when selecting for detections with high classification scores, they were shown to have precision ranging from 54% to 57% with recall ranging from 72% to 78% for 40 Hz and precision ranging from 62% to 64% with recall ranging from 70 to 73% for D calls. As these two call types are produced by both sexes, using them in long-term studies would remove sex-bias in estimates of temporal presence and movement patterns.

Multiple pygmy blue whale acoustic populations in the Indian Ocean: whale song identifies a possible new population

Blue whales were brought to the edge of extinction by commercial whaling in the twentieth century and their recovery rate in the Southern Hemisphere has been slow; they remain endangered. Blue whales, although the largest animals on Earth, are difficult to study in the Southern Hemisphere, thus their population structure, distribution and migration remain poorly known. Fortunately, blue whales produce powerful and stereotyped songs, which prove an effective clue for monitoring their different ‘acoustic populations.’ The DGD-Chagos song has been previously reported in the central Indian Ocean. A comparison of this song with the pygmy blue and Omura’s whale songs shows that the Chagos song are likely produced by a distinct previously unknown pygmy blue whale population. These songs are a large part of the underwater soundscape in the tropical Indian Ocean and have been so for nearly two decades. Seasonal differences in song detections among our six recording sites suggest that the Chagos whales migrate from the eastern to western central Indian Ocean, around the Chagos Archipelago, then further east, up to the north of Western Australia, and possibly further north, as far as Sri Lanka. The Indian Ocean holds a greater diversity of blue whale populations than thought previously.

South Georgia blue whales five decades after the end of whaling

Blue whales Balaenoptera musculus at South Georgia were heavily exploited during 20th century industrial whaling, to the point of local near-extirpation. Although legal whaling for blue whales ceased in the 1960s, and there were indications of blue whale recovery across the wider Southern Ocean area, blue whales were seldom seen in South Georgia waters in subsequent years. We collated 30 yr of data comprising opportunistic sightings, systematic visual and acoustic surveys and photo-identification to assess the current distribution of blue whales in the waters surrounding South Georgia. Over 34000 km of systematic survey data between 1998 and 2018 resulted in only a single blue whale sighting, although opportunistic sightings were reported over that time period. However, since 2018 there have been increases in both sightings of blue whales and detections of their vocalisations. A survey in 2020 comprising visual line transect surveys and directional frequency analysis and recording (DIFAR) sonobuoy deployments resulted in 58 blue whale sightings from 2430 km of visual effort, including the photo-identification of 23 individual blue whales. Blue whale vocalisations were detected on all 31 sonobuoys deployed (114 h). In total, 41 blue whales were photo-identified from South Georgia between 2011 and 2020, none of which matched the 517 whales in the current Antarctic catalogue. These recent data suggest that blue whales have started to return to South Georgia waters, but continued visual and acoustic surveys are required to monitor any future changes in their distribution and abundance.

Acoustic seasonality, behaviour and detection ranges of Antarctic blue and fin whales under different sea ice conditions off Antarctica

Descriptions of seasonal occurrence and behaviour of Antarctic blue and fin whales in the Southern Ocean are of pivotal importance for the effective conservation and management of these endangered species. We used an autonomous acoustic recorder to collect bioacoustic data from January through September 2014 to describe the seasonal occurrence, behaviour and detection ranges of Antarctic blue and fin whale calls off the Maud Rise, Antarctica. From 2479 h of recordings, we detected D- and Z-calls plus the 27 Hz chorus of blue whales, the 20 and 99 Hz pulses of fin whales and the 18-28 Hz chorus of blue and fin whales. Blue whale calls were detected throughout the hydrophone deployment period with a peak occurrence in February, indicating continuous presence of whales in a broad Southern Ocean area (given the modelled detection ranges). Fin whale calls were detected from January through July when sea ice was present on the latter dates. No temporal segregation in peaks of diel calling rates of blue and fin whales was observed in autumn, but a clear temporal segregation was apparent in summer. Acoustic propagation models suggest that blue and fin whale calls can be heard as far as 1700 km from the hydrophone position in spring. Random forest models ranked month of the year as the most important predictor of call occurrence and call rates (i.e. behaviour) for these whales. Our work highlights areas around the Maud Rise as important habitats for blue and fin whales in the Southern Ocean.

Timing is everything: Drivers of interannual variability in blue whale migration

Blue whales need to time their migration from their breeding grounds to their feeding grounds to avoid missing peak prey abundances, but the cues they use for this are unknown. We examine migration timing (inferred from the local onset and cessation of blue whale calls recorded on seafloor-mounted hydrophones), environmental conditions (e.g., sea surface temperature anomalies and chlorophyll a), and prey (spring krill biomass from annual net tow surveys) during a 10 year period (2008-2017) in waters of the Southern California Region where blue whales feed in the summer. Colder sea surface temperature anomalies the previous season were correlated with greater krill biomass the following year, and earlier arrival by blue whales. Our results demonstrate a plastic response of blue whales to interannual variability and the importance of krill as a driving force behind migration timing. A decadal-scale increase in temperature due to climate change has led to blue whales extending their overall time in Southern California. By the end of our 10-year study, whales were arriving at the feeding grounds more than one month earlier, while their departure date did not change. Conservation strategies will need to account for increased anthropogenic threats resulting from longer times at the feeding grounds.

Baleen whale acoustic presence and behaviour at a Mid-Atlantic migratory habitat, the Azores Archipelago

The identification of important areas during the annual life cycle of migratory animals, such as baleen whales, is vital for their conservation. In boreal springtime, fin and blue whales feed in the Azores on their way to northern latitudes while sei whales migrate through the archipelago with only occasional feeding. Little is known about their autumn or winter presence or their acoustic behaviour in temperate migratory habitats. This study used a 5-year acoustic data set collected by autonomous recorders in the Azores that were processed and analysed using an automated call detection and classification system. Fin and blue whales were acoustically present in the archipelago from autumn to spring with marked seasonal differences in the use of different call types. Diel patterns of calling activity were only found for fin whales with more calls during the day than night. Sei whales showed a bimodal distribution of acoustic presence in spring and autumn, corresponding to their expected migration patterns. Diel differences in sei whale calling varied with season and location. This work highlights the importance of the Azores as a migratory and wintering habitat for three species of baleen whales and provides novel information on their acoustic behaviour in a mid-Atlantic region.

Information limitation and the dynamics of coupled ecological systems

The dynamics of large ecological systems result from vast numbers of interactions between individual organisms. Here, we develop mathematical theory to show that the rate of such interactions is inherently limited by the ability of organisms to gain information about one another. This phenomenon, which we call 'information limitation', is likely to be widespread in real ecological systems and can dictate both the rates of ecological interactions and long-run dynamics of interacting populations. We show how information limitation leads to sigmoid interaction rate functions that can stabilize antagonistic interactions and destabilize mutualistic ones; as a species or type becomes rare, information on its whereabouts also becomes rare, weakening coupling with consumers, pathogens and mutualists. This can facilitate persistence of consumer-resource systems, alter the course of pathogen infections within a host and enhance the rates of oceanic productivity and carbon export. Our findings may shed light on phenomena in many living systems where information drives interactions.

Two unit analysis of Sri Lankan pygmy blue whale song over a decade

Sri Lankan pygmy blue whale song consists of three repeated units: (1) low frequency pulsive unit, (2) frequency modulated (FM) upsweep, and (3) long tonal downsweep. The Unit 2 FM unit has up to three visible upsweeps with energy concentrated at approximately 40, 50, and 60 Hz, while the Unit 3 (∼100 Hz) tonal downsweep is the most distinct unit lasting 20-30 s. Spectral characteristics of the Units 2 and 3 song elements, along with ocean sound levels, were analyzed in the Indian Ocean from 2002 to 2013. The peak frequency of the tonal Unit 3 calls decreased from approximately 106.5 to 100.7 Hz over a decade corresponding to a 5.4% decrease. Over the same time period, the frequency content of the Unit 2 upsweeps did not change as dramatically with only a 3.1% change. Ambient sound levels in the vocalization bands did not exhibit equivalent patterns in amplitude trends. Analysis showed no increase in the ambient sound or compensated peak amplitude levels of the tonal downsweeps, eliminating the presence of a Lombard effect. Here it is proposed that each song unit may convey different information and thus may be responding to different selective pressures.

Marine mammal acoustic detections in the Greenland and Barents Sea, 2013 - 2014 seasons

While the Greenland and Barents Seas are known habitats for several cetacean and pinniped species there is a lack of long-term monitoring data in this rapidly changing environment. Moreover, little is known of the ambient soundscapes, and increasing off-shore anthropogenic activities can influence the ecosystem and marine life. Baseline acoustic data is needed to better assess current and future soundscape and ecosystem conditions. The analysis of a year of continuous data from three passive acoustic monitoring devices revealed species-dependent seasonal and spatial variation of a large variety of marine mammals in the Greenland and Barents Seas. Sampling rates were 39 and 78 kHz in the respective locations, and all systems were operational at a duty cycle of 2 min on, 30 min off. The research presents a description of cetacean and pinniped acoustic detections along with a variety of unknown low-frequency tonal sounds, and ambient sound level measurements that fall within the scope of the European Marine Strategy Framework (MSFD). The presented data shows the importance of monitoring Arctic underwater biodiversity for assessing the ecological changes under the scope of climate change.

Context-dependent variability in blue whale acoustic behaviour

Acoustic communication is an important aspect of reproductive, foraging and social behaviours for many marine species. Northeast Pacific blue whales (Balaenoptera musculus) produce three different call types-A, B and D calls. All may be produced as singular calls, but A and B calls also occur in phrases to form songs. To evaluate the behavioural context of singular call and phrase production in blue whales, the acoustic and dive profile data from tags deployed on individuals off southern California were assessed using generalized estimating equations. Only 22% of all deployments contained sounds attributed to the tagged animal. A larger proportion of tagged animals were female (47%) than male (13%), with 40% of unknown sex. Fifty per cent of tags deployed on males contained sounds attributed to the tagged whale, while only a few (5%) deployed on females did. Most calls were produced at shallow depths (less than 30 m). Repetitive phrasing (singing) and production of singular calls were most common during shallow, non-lunging dives, with the latter also common during surface behaviour. Higher sound production rates occurred during autumn than summer and they varied with time-of-day: singular call rates were higher at dawn and dusk, while phrase production rates were highest at dusk and night.

Estimating drift of directional sonobuoys from acoustic bearings

A maximum likelihood method is presented for estimating drift direction and speed of a directional sonobuoy given the deployment location and a time series of acoustic bearings to a sound source at known position. The viability of this method is demonstrated by applying it to two real-world scenarios: (1) during a calibration trial where buoys were independently tracked via satellite, and (2) by applying the technique to sonobuoy recordings of a vocalising Antarctic blue whale that was simultaneously tracked by photogrammetric methods. In both test cases, correcting for sonobuoy drift substantially increased the accuracy of acoustic locations.

Characterizing Chilean blue whale vocalizations with DTAGs: a test of using tag accelerometers for caller identification

Vocal behavior of blue whales (Balaenoptera musculus) in the Gulf of Corcovado, Chile, was analyzed using both audio and accelerometer data from digital acoustic recording tags (DTAGs). Over the course of three austral summers (2014, 2015, 2016), seventeen tags were deployed, yielding 124 hours of data. We report the occurrence of Southeast Pacific type 2 (SEP2) calls, which exhibit peak frequencies, durations, and timing consistent with previous recordings made using towed and moored hydrophones. We also describe tonal downswept (D) calls, which have not been previously described for this population. Since being able to accurately assign vocalizations to individual whales is fundamental for studying communication and for estimating population densities from call rates, we further examine the feasibility of using high-resolution DTAG accelerometers to identify low-frequency calls produced by tagged blue whales. We cross-correlated acoustic signals with simultaneous tri-axial accelerometer readings in order to analyze the phase match as well as the amplitude of accelerometer signals associated with low-frequency calls, which provides a quantitative method of determining if a call is associated with a detectable acceleration signal. Our results suggest that vocalizations from nearby individuals are also capable of registering accelerometer signals in the tagged whale's DTAG record. We cross-correlate acceleration vectors between calls to explore the possibility of using signature acceleration patterns associated with sounds produced within the tagged whale as a new method of identifying which accelerometer-detectable calls originate from the tagged animal.

Observations and Bayesian location methodology of transient acoustic signals (likely blue whales) in the Indian Ocean, using a hydrophone triplet

A notable sequence of calls was encountered, spanning several days in January 2003, in the central part of the Indian Ocean on a hydrophone triplet recording acoustic data at a 250 Hz sampling rate. This paper presents signal processing methods applied to the waveform data to detect, group, extract amplitude and bearing estimates for the recorded signals. An approximate location for the source of the sequence of calls is inferred from extracting the features from the waveform. As the source approaches the hydrophone triplet, the source level (SL) of the calls is estimated at 187 ± 6 dB re: 1 μPa-1 m in the 15-60 Hz frequency range. The calls are attributed to a subgroup of blue whales, Balaenoptera musculus, with a characteristic acoustic signature. A Bayesian location method using probabilistic models for bearing and amplitude is demonstrated on the calls sequence. The method is applied to the case of detection at a single triad of hydrophones and results in a probability distribution map for the origin of the calls. It can be extended to detections at multiple triads and because of the Bayesian formulation, additional modeling complexity can be built-in as needed.

Towards population-level conservation in the critically endangered Antarctic blue whale: the number and distribution of their populations

Population-level conservation is required to prevent biodiversity loss within a species, but it first necessitates determining the number and distribution of populations. Many whale populations are still depleted due to 20th century whaling. Whales are one of the most logistically difficult and expensive animals to study because of their mobility, pelagic lifestyle and often remote habitat. We tackle the question of population structure in the Antarctic blue whale (Balaenoptera musculus intermedia) – a critically endangered subspecies and the largest extant animal – by capitalizing on the largest genetic dataset to date for Antarctic blue whales. We found evidence of three populations that are sympatric in the Antarctic feeding grounds and likely occupy separate breeding grounds. Our study adds to knowledge of population structure in the Antarctic blue whale. Future research should invest in locating the breeding grounds and migratory routes of Antarctic blue whales through satellite telemetry to confirm their population structure and allow population-level conservation.

Vast assembly of vocal marine mammals from diverse species on fish spawning ground

Observing marine mammal (MM) populations continuously in time and space over the immense ocean areas they inhabit is challenging but essential for gathering an unambiguous record of their distribution, as well as understanding their behaviour and interaction with prey species. Here we use passive ocean acoustic waveguide remote sensing (POAWRS) in an important North Atlantic feeding ground to instantaneously detect, localize and classify MM vocalizations from diverse species over an approximately 100,000 km(2) region. More than eight species of vocal MMs are found to spatially converge on fish spawning areas containing massive densely populated herring shoals at night-time and diffuse herring distributions during daytime. We find the vocal MMs divide the enormous fish prey field into species-specific foraging areas with varying degrees of spatial overlap, maintained for at least two weeks of the herring spawning period. The recorded vocalization rates are diel (24 h)-dependent for all MM species, with some significantly more vocal at night and others more vocal during the day. The four key baleen whale species of the region: fin, humpback, blue and minke have vocalization rate trends that are highly correlated to trends in fish shoaling density and to each other over the diel cycle. These results reveal the temporospatial dynamics of combined multi-species MM foraging activities in the vicinity of an extensive fish prey field that forms a massive ecological hotspot, and would be unattainable with conventional methodologies. Understanding MM behaviour and distributions is essential for management of marine ecosystems and for accessing anthropogenic impacts on these protected marine species.

Software for real-time localization of baleen whale calls using directional sonobuoys: A case study on Antarctic blue whales

Directional frequency analysis and recording (DIFAR) sonobuoys can allow real-time acoustic localization of baleen whales for underwater tracking and remote sensing, but limited availability of hardware and software has prevented wider usage. These software limitations were addressed by developing a module in the open-source software PAMGuard. A case study is presented demonstrating that this software provides greater efficiency and accessibility than previous methods for detecting, localizing, and tracking Antarctic blue whales in real time. Additionally, this software can easily be extended to track other low and mid frequency sounds including those from other cetaceans, pinnipeds, icebergs, shipping, and seismic airguns.

Calls of Bryde's whale (Balaenoptera edeni) recorded in the Gulf of California (L)

A total of 109 recordings aiming to identify Bryde's whale calls were collected from the Gulf of California, Mexico, during field trips performed from January 2010 to June 2014. Vocalizations were recorded only when no calves were observed. Four types of calls were identified. Calls similar to the Be4 call type previously reported for the Eastern Tropical Pacific region and South of California were recorded. In addition, three calls, not reported in previous studies of the Bryde's whale, have also been identified. The identification of these calls, which were labeled Be10, Be11, and Be12, enables expansion of the known acoustic repertoire of this species, which is currently poorly documented. The identification of three previously unreported calls and the confidence given by careful visual confirmation of the whale species and number of individuals contribute to make this study a significant contribution toward the acoustic monitoring of Bryde's whale.

Designing an effective mark-recapture study of Antarctic blue whales

To properly conserve and manage wild populations, it is important to have information on abundance and population dynamics. In the case of rare and cryptic species, especially in remote locations, surveys can be difficult and expensive, and run the risk of not producing sample sizes large enough to produce precise estimates. Therefore, it is crucial to conduct preliminary analysis to determine if the study will produce useable estimates. The focus of this paper is a proposed mark-recapture study of Antarctic blue whales (Balaenoptera musculus intermedia). Antarctic blue whales were hunted to near extinction up until the mid- 1960s, when commercial exploitation of this species ended. Current abundance estimates are a decade old. Furthermore, at present, there are no formal circumpolar-level cetacean surveys operating in Antarctic waters and, specifically, there is no strategy to monitor the potential recovery of Antarctic blue whales. Hence the work in this paper was motivated by the need to inform decisions on strategies for future monitoring of Antarctic blue whale population. The paper describes a model to predict the precision and bias of estimates from a proposed survey program. The analysis showed that mark-recapture is indeed a suitable method to provide a circumpolar abundance estimate of Antarctic blue whales, with precision of the abundance, at the midpoint of the program, predicted to be between 0.2 and 0.3. However, this was only if passive acoustic tracking was utilized to increase the encounter rate. The analysis also provided guidance on general design for an Antarctic blue whale program, showing that it requires a 12-year duration; although surveys do not necessarily need to be run every year if multiple vessels are available to clump effort. Mark-recapture is based on a number of assumptions; it was evident from the analysis that ongoing analysis and monitoring of the data would be required to check such assumptions hold (e.g., test for heterogeneity), with the modeling adjusted as needed.

A simulation study of acoustic-assisted tracking of whales for mark-recapture surveys

Collecting enough data to obtain reasonable abundance estimates of whales is often difficult, particularly when studying rare species. Passive acoustics can be used to detect whale sounds and are increasingly used to estimate whale abundance. Much of the existing effort centres on the use of acoustics to estimate abundance directly, e.g. analysing detections in a distance sampling framework. Here, we focus on acoustics as a tool incorporated within mark-recapture surveys. In this context, acoustic tools are used to detect and track whales, which are then photographed or biopsied to provide data for mark-recapture analyses. The purpose of incorporating acoustics is to increase the encounter rate beyond using visual searching only. While this general approach is not new, its utility is rarely quantified. This paper predicts the “acoustically-assisted” encounter rate using a discrete-time individual-based simulation of whales and survey vessel. We validate the simulation framework using existing data from studies of sperm whales. We then use the framework to predict potential encounter rates in a study of Antarctic blue whales. We also investigate the effects of a number of the key parameters on encounter rate. Mean encounter rates from the simulation of sperm whales matched well with empirical data. Variance of encounter rate, however, was underestimated. The simulation of Antarctic blue whales found that passive acoustics should provide a 1.7–3.0 fold increase in encounter rate over visual-only methods. Encounter rate was most sensitive to acoustic detection range, followed by vocalisation rate. During survey planning and design, some indication of the relationship between expected sample size and effort is paramount; this simulation framework can be used to predict encounter rates and establish this relationship. For a case in point, the simulation framework indicates unequivocally that real-time acoustic tracking should be considered for quantifying the abundance of Antarctic blue whales via mark-recapture methods.

Source levels of dugong (Dugong dugon) vocalizations recorded in Shark Bay

Dugongs (Dugong dugon) spend significant time in shallow, turbid waters and are often active at night, conditions which are not conducive to visual cues. In part, as a result, dugongs vocalize to gain or pass information. Passive acoustic recording is a useful tool for remote detection of vocal marine animals, but its application to dugongs has been little explored compared with other mammals. Aerial surveys, often used to monitor dugong distribution and abundance, are not always financially or logistically viable and involve inherent availability and perception bias considerations. Passive acoustic monitoring is also subject to sampling biases and a first step to identifying these biases and understanding the detection or communication range of animal calls is to determine call source level. In March 2012, four dugongs were fitted with satellite tags in Shark Bay, Western Australia by the Department of Environment and Conservation. During this, acoustic recordings were taken at 5.1 m range. Source levels for each of five call types (two types of chirp, bark, squeak, and quack) were estimated, assuming spherical spreading as the transmission loss. Mean source levels for these call types were 139 (n = 19), 135 (12), 142 (2), 158 (1), and 136 (9) dB re 1 μPa at 1 m, respectively.

Tracking dolphin whistles using an autonomous acoustic recorder array

Dolphins are known to produce nearly omnidirectional whistles that can propagate several kilometers, allowing these sounds to be localized and tracked using acoustic arrays. During the fall of 2007, a km-scale array of four autonomous acoustic recorders was deployed offshore of southern California in a known dolphin habitat at ~800 m depth. Concurrently with the one-month recording, a fixed-point marine mammal visual survey was conducted from a moored research platform in the center of the array, providing daytime species and behavior visual confirmation. The recordings showed three main types of dolphin acoustic activity during distinct times: primarily whistling during daytime, whistling and clicking during early night, and primarily clicking during late night. Tracks from periods of daytime whistling typically were tightly grouped and traveled at a moderate rate. In one example with visual observations, traveling common dolphins (Delphinus sp.) were tracked for about 10 km with an average speed of ~2.5 m s(-1) (9 km h(-1)). Early night recordings had whistle localizations with wider spatial distribution and slower travel speed than daytime recordings, presumably associated with foraging behavior. Localization and tracking of dolphins over long periods has the potential to provide insight into their ecology, behavior, and potential response to stimuli.

Temporal separation of two fin whale call types across the eastern North Pacific

Fin whales (Balaenoptera physalus) produce a variety of low-frequency, short-duration, frequency-modulated calls. The differences in temporal patterns between two fin whale call types are described from long-term passive acoustic data collected intermittently between 2005 and 2011 at three locations across the eastern North Pacific: the Bering Sea, off Southern California, and in Canal de Ballenas in the northern Gulf of California. Fin whale calls were detected at all sites year-round, during all periods with recordings. At all three locations, 40-Hz calls peaked in June, preceding a peak in 20-Hz calls by 3-5 months. Monitoring both call types may provide a more accurate insight into the seasonal presence of fin whales across the eastern North Pacific than can be obtained from a single call type. The 40-Hz call may be associated with a foraging function, and temporal separation between 40- and 20-Hz calls may indicate the separation between predominately feeding behavior and other social interactions.

Characteristics of gunshot sound displays by North Atlantic right whales in the Bay of Fundy

North Atlantic right whales (Eubalaena glacialis) produce a loud, broadband signal referred to as the gunshot sound. These distinctive sounds may be suitable for passive acoustic monitoring and detection of right whales; however, little is known about the prevalence of these sounds in important right whale habitats, such as the Bay of Fundy. This study investigates the timing and distribution of gunshot sound production on the summer feeding grounds using an array of five marine acoustic recording units deployed in the Bay of Fundy, Canada in mid-summer 2004 and 2005. Gunshot sounds were common, detected on 37 of 38 recording days. Stereotyped gunshot bouts averaged 1.5 h, with some bouts exceeding 7 h in duration with up to seven individuals producing gunshots at any one time. Bouts were more commonly detected in the late afternoon and evening than during the morning hours. Locations of gunshots in bouts indicated that whales producing the sounds were either stationary or showed directional travel, suggesting gunshots have different communication functions depending on behavioral context. These results indicate that gunshots are a common right whale sound produced during the summer months and are an important component in the acoustic communication system of this endangered species.

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.

Analysis and localization of blue whale vocalizations in the Solomon Sea using waveform amplitude data

During the Woodlark Basin seismic experiment in eastern Papua New Guinea (1999-2000), an ocean-bottom seismic array recorded marine mammal vocalizations along with target earthquake signals. The array consisted of 14 instruments, 7 of which were three-component seismometers with a fourth component hydrophone. They were deployed at 2.0-3.2 km water depth and operated from September 1999 through February 2000. While whale vocalizations were recorded throughout the deployment, this study focuses on 3 h from December 21, 1999 during which the signals are particularly clear. The recordings show a blue whale song composed of a three-unit phrase. That song does not match vocalization characteristics of other known Pacific subpopulations and may represent a previously undocumented blue whale song. Animal tracking and source level estimates are obtained with a Bayesian inversion method that generates probabilistic source locations. The Bayesian method is augmented to include travel time estimates from seismometers and hydrophones and acoustic signal amplitude. Tracking results show the whale traveled northeasterly over the course of 3 h, covering approximately 27 km. The path followed the edge of the Woodlark Basin along a shelf that separates the shallow waters of the Trobriand platform from the deep waters of the basin.

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.

Minke whale (Balaenoptera acutorostrata) boings detected at the Station ALOHA Cabled Observatory

Minke whales (Balaenoptera acutorostrata) in the tropical North Pacific are elusive and difficult to detect visually. The recent association of a unique sound called the "boing" to North Pacific minke whales has made it possible to use passive acoustics to investigate the occurrence of this species in Hawaiian waters. One year of recordings (17 February 2007-18 February 2008) made at the Station ALOHA Cabled Observatory were examined to investigate the characteristics of boings and temporal patterns in their occurrence at this site, located 100 km north of Oahu. Characteristics of boings exhibited low variability. Pulse repetition rate and duration measurements matched those for "central" or "Hawaii" boing types. Boings were detected from October until May, with a peak in March. Although no boings were detected from June to September, the absence of boings does not necessarily indicate the absence of minke whales. Significant diel variation in boing rate was not observed. The absence of a diel pattern in boing production suggests that day- or night-time acoustic surveys are equally acceptable methods for studying minke whale occurrence. Future research should include efforts to determine what other sounds are produced by minke whales in this area, and which age/sex classes produce boings.

Frequency synchronization of blue whale calls near Pioneer Seamount

Vocalizations of blue whales were recorded with a cabled hydrophone array at Pioneer Seamount, 50 miles off the California coast. Most calls occurred in repeated sequences of two-call pairs (A, then B). The B call is a frequency-modulated tone highly repeatable in form and pitch. A model of this sound is described which permits detecting very small frequency shifts. B calls are found to be aligned in frequency to about one part in 180. This requires very fine pitch discrimination and control over calling frequency, and suggests that synchronizing to a common frequency pattern carries some adaptive advantage. Some possibilities for acoustic sensing by whales requiring this fine frequency resolution are discussed.

Source level estimation of two blue whale subspecies in southwestern Indian Ocean

Blue whales produce intense, stereotypic low frequency calls that are particularly well suited for transmission over long distances. Because these calls vary geographically, they can be used to gain insight into subspecies distribution. In the Southwestern Indian Ocean, acoustic data from a triad of calibrated hydrophones maintained by the International Monitoring System provided data on blue whale calls from two subspecies: Antarctic and pygmy blue whales. Using time difference of arrival and least-squares hyperbolic methods, the range and location of calling whales were determined. By using received level of calls and propagation modeling, call source levels of both subspecies were estimated. The average call source level was estimated to 179+/-5 dB re 1 microPa(rms) at 1 m over the 17-30 Hz band for Antarctic blue whale and 174+/-1 dB re 1 microPa(rms) at 1 m over the 17-50 Hz band for pygmy blue whale. According to previous estimates, slight variations in the source level could be due to inter-individual differences, inter-subspecies variations and the calculation method. These are the first reported source level estimations for blue whales in the Indian Ocean. Such data are critical to estimate detection ranges of calling blue whales.

Seasonal changes in the vocal behavior of bowhead whales (Balaena mysticetus) in Disko Bay, Western-Greenland

Singing behavior has been described from bowhead whales in the Bering Sea during their annual spring migration and from Davis Strait during their spring feeding season. It has been suggested that this spring singing behavior is a remnant of the singing during the winter breeding season, though no winter recordings are available. In this study, the authors describe recordings made during the winter and spring months of bowhead whales in Disko Bay, Western-Greenland. A total of 7091 bowhead whale sounds were analyzed to describe the vocal repertoire, the singing behavior, and the changes in vocal behavior from February to May. The vocal signals could be divided into simple (frequency-modulated) calls (n=483), complex (amplitude-modulated) calls (n=635), and song notes (n=5973). Recordings from the end of February to middle of March were characterized by higher call rates with a greater diversity of call types than recordings made later in the season. This study is the first description of bowhead song from the stock in Western-Greenland during both the winter and spring months, and provides support for the hypothesis that song during the winter months contains more song notes than song from the spring making the winter song more variable.