Exploring movement patterns and changing distributions of baleen whales in the western North Atlantic using a decade of passive acoustic data

Six baleen whale species are found in the temperate western North Atlantic Ocean, with limited information existing on the distribution and movement patterns for most. There is mounting evidence of distributional shifts in many species, including marine mammals, likely because of climate‐driven changes in ocean temperature and circulation. Previous acoustic studies examined the occurrence of minke (Balaenoptera acutorostrata) and North Atlantic right whales (NARW; Eubalaena glacialis). This study assesses the acoustic presence of humpback (Megaptera novaeangliae), sei (B. borealis), fin (B. physalus), and blue whales (B. musculus) over a decade, based on daily detections of their vocalizations. Data collected from 2004 to 2014 on 281 bottom‐mounted recorders, totaling 35,033 days, were processed using automated detection software and screened for each species' presence. A published study on NARW acoustics revealed significant changes in occurrence patterns between the periods of 2004–2010 and 2011–2014; therefore, these same time periods were examined here. All four species were present from the Southeast United States to Greenland; humpback whales were also present in the Caribbean. All species occurred throughout all regions in the winter, suggesting that baleen whales are widely distributed during these months. Each of the species showed significant changes in acoustic occurrence after 2010. Similar to NARWs, sei whales had higher acoustic occurrence in mid‐Atlantic regions after 2010. Fin, blue, and sei whales were more frequently detected in the northern latitudes of the study area after 2010. Despite this general northward shift, all four species were detected less on the Scotian Shelf area after 2010, matching documented shifts in prey availability in this region. A decade of acoustic observations have shown important distributional changes over the range of baleen whales, mirroring known climatic shifts and identifying new habitats that will require further protection from anthropogenic threats like fixed fishing gear, shipping, and noise pollution.     

'Megapclicks': acoustic click trains and buzzes produced during night-time foraging of humpback whales (Megaptera novaeangliae)

Humpback whales (Megaptera novaeangliae) exhibit a variety of foraging behaviours, but neither they nor any baleen whale are known to produce broadband clicks in association with feeding, as do many odontocetes. We recorded underwater behaviour of humpback whales in a northwest Atlantic feeding area using suction-cup attached, multi-sensor, acoustic tags (DTAGs). Here we describe the first recordings of click production associated with underwater lunges from baleen whales. Recordings of over 34000 'megapclicks' from two whales indicated relatively low received levels at the tag (between 143 and 154dB re 1 microPa pp), most energy below 2kHz, and interclick intervals often decreasing towards the end of click trains to form a buzz. All clicks were recorded during night-time hours. Sharp body rolls also occurred at the end of click bouts containing buzzes, suggesting feeding events. This acoustic behaviour seems to form part of a night-time feeding tactic for humpbacks and also expands the known acoustic repertoire of baleen whales in general.     

Observations of cetaceans in the south-east Atlantic sector of the Southern Ocean,during summer 2008

Knowledge of cetacean species composition and their distribution in the south-east Atlantic sector of the Southern Ocean is scarce. During a survey in February–March 2008, systematic whale sightings were carried out along transect lines following the 5° and 15° E meridians between 35° and 67° S. In total, 67 toothed whales and 126 baleen whales were observed. Both fin whales (four animals) and Antarctic minke whales Balaenoptera bonaerenses (three animals) in addition to 16 individuals of unidentified species were among the observed baleen whales. The dominating baleen whale species in our study was humpback whales Megaptera novaeangliae with 108 individuals observed. They occurred single or in groups up to seven individuals (N _mean = 2.5 ind) and eight of the counts were of calves. The relationship between humpback whale occurrence and environmental variables including Antarctic krill (Euphausia superba) abundance from acoustic recordings, hydrography, bathymetry and production was tested using general additive models. Only temperature increased the predictive power of the model with whale occurrence increasing with the decreasing temperature in more southern areas.     

Individual right whales call louder in increased environmental noise

The ability to modify vocalizations to compensate for environmental noise is critical for successful communication in a dynamic acoustic environment. Many marine species rely on sound for vital life functions including communication, navigation and feeding. The impacts of significant increases in ocean noise levels from human activities are a current area of concern for the conservation of marine mammals. Here, we document changes in calling behaviour by individual endangered North Atlantic right whales (Eubalaena glacialis) in increased background noise. Right whales, like several bird and primate species, respond to periods of increased noise by increasing the amplitude of their calls. This behaviour may help maintain the communication range with conspecifics during periods of increased noise. These call modifications have implications for conservation efforts for right whales, affecting both the way whales use sound to communicate and our ability to detect them with passive acoustic monitoring systems.     

Evidence that ship noise increases stress in right whales

Baleen whales (Mysticeti) communicate using low-frequency acoustic signals. These long-wavelength sounds can be detected over hundreds of kilometres, potentially allowing contact over large distances. Low-frequency noise from large ships (20-200 Hz) overlaps acoustic signals used by baleen whales, and increased levels of underwater noise have been documented in areas with high shipping traffic. Reported responses of whales to increased noise include: habitat displacement, behavioural changes and alterations in the intensity, frequency and intervals of calls. However, it has been unclear whether exposure to noise results in physiological responses that may lead to significant consequences for individuals or populations. Here, we show that reduced ship traffic in the Bay of Fundy, Canada, following the events of 11 September 2001, resulted in a 6 dB decrease in underwater noise with a significant reduction below 150 Hz. This noise reduction was associated with decreased baseline levels of stress-related faecal hormone metabolites (glucocorticoids) in North Atlantic right whales (Eubalaena glacialis). This is the first evidence that exposure to low-frequency ship noise may be associated with chronic stress in whales, and has implications for all baleen whales in heavy ship traffic areas, and for recovery of this endangered right whale population.     

Blue whales respond to simulated mid-frequency military sonar

Mid-frequency military (1–10 kHz) sonars have been associated with lethal mass strandings of deep-diving toothed whales, but the effects on endangered baleen whale species are virtually unknown. Here, we used controlled exposure experiments with simulated military sonar and other mid-frequency sounds to measure behavioural responses of tagged blue whales (Balaenoptera musculus) in feeding areas within the Southern California Bight. Despite using source levels orders of magnitude below some operational military systems, our results demonstrate that mid-frequency sound can significantly affect blue whale behaviour, especially during deep feeding modes. When a response occurred, behavioural changes varied widely from cessation of deep feeding to increased swimming speed and directed travel away from the sound source. The variability of these behavioural responses was largely influenced by a complex interaction of behavioural state, the type of mid-frequency sound and received sound level. Sonar-induced disruption of feeding and displacement from high-quality prey patches could have significant and previously undocumented impacts on baleen whale foraging ecology, individual fitness and population health.     

Estimation of minke whale abundance from an acoustic line transect survey of the Mariana Islands

The minke whale is one of the most abundant species of baleen whales worldwide, yet is rarely sighted in subtropical waters. In the North Pacific, they produce a distinctive sound known as the “boing,” which can be used to acoustically localize individuals. A vessel‐based survey using both visual and passive acoustic monitoring was conducted during the spring of 2007 in a large (616,000 km²) study area encompassing the Mariana Islands. We applied line transect methods to data collected from a towed hydrophone array to estimate the abundance of calling minke whales in our study area. No minke whales were sighted, but there were hundreds of acoustic detections of boings. Computer algorithms were developed to localize calling minke whales from acoustic recordings, resulting in over 30 independent localizations, a six‐fold increase over those estimated during the survey. The two best estimates of abundance of calling minke whales were determined to be 80 and 91 animals (0.13 and 0.15 animals per 1,000 km2, respectively; CV = 34%). These are the first density and abundance estimates for calling minke whales using towed hydrophone array surveys, and the first estimates for this species in the Mariana Islands region. These are considered minimum estimates of the true number of minke whales in the study area.     

Southern right whales show no behavioral response to low noise levels from a nearby unmanned aerial vehicle

Unmanned aerial vehicles (UAVs) are increasingly used for wildlife research and monitoring, but little information exists on their potential effect on marine mammals. We assessed the effects of a UAV on the behavior of southern right whales (Eubalaena australis) in Australia. Focal follows of ten right whale mother-calf pairs were conducted using a theodolite. Control data were recorded for 30 min, and then a DJI Inspire 1 Pro was flown above the whales for 10 min at 5 m altitude. Potential changes to horizontal behavior (swim speed and turning angle) and surfacing pattern (interbreath intervals) were investigated by comparing mother-calf behavior before and during UAV approaches. Changes in respiration rate were used to quantify energetic effects. We also explored acoustic cue perceptibility of the UAV at 5, 10, and 30 m altitude, by measuring the received UAV underwater noise level on whales equipped with acoustic tags (DTAGs). The received noise levels were 86.0 ± 3.9 dB re 1 μPa, while the measured ambient noise was 80.7 ± 7.3 dB re 1 μPa in the same frequency band (100–1,500 Hz). No behavioral response to the UAV was observed. This provides support for UAVs as a noninvasive tool to study baleen whale behavior and ecophysiology.     

Seasonal and Geographic Variation of Southern Blue Whale Subspecies in the Indian Ocean

Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four “acoustic populations” occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds.     

Exceptional occurrence of fossil baleen in shallow marine sediments of the Neogene Pisco Formation,Southern Peru

Fossil baleen is rare in the sedimentary record. This paper documents the exceptional occurrence of thirty seven fossil whale specimens with preserved baleen in the Neogene Pisco Formation during a transect survey in a limited area west of the Ica River Valley near the town of Ocucaje in southern Peru. The sedimentary layers consist of tuffaceous and diatomaceous sandstones, diatomaceous mudstones, and dolomites, deposited in a shallow marine embayment. Observations of modern whale carcasses on the seafloor and stranded individuals indicate that baleen detaches from the mouth of the whales very rapidly after death, and that bones deteriorate very rapidly as a result of scavenging activity and abrasion. In contrast, the bones of the Pisco Formation whales are exceptionally well preserved, and their baleen is often found in life position suspended from the rostrum. Sedimentary structures found associated with some skeletons indicate tidal and storm processes, suggesting that the environment was not anoxic. This exceptional occurrence of fossil baleen suggests early mineralization of the baleen attachment to the rostrum or rapid burial of the skeletons before any detachment or loss could occur.     

Visual and acoustic surveys for North Atlantic right whales,Eubalaena glacialis,in Cape Cod Bay,Massachusetts, 2001–2005: Management implications

North Atlantic right whales, Eubalaena glacialis, remain endangered, primarily due to excessive anthropogenic mortality. Current management protocols in US waters are triggered by identifying the presence of at least one right whale in a management area. We assessed whether acoustic detection of right whale contact calls can work as an alternative to visual aerial surveys for establishing their presence. Aerial survey and acoustic monitoring were conducted in Cape Cod Bay, Massachusetts, in 2001–2005 and used to evaluate and compare right whale detections. Over the 58 d with simultaneous aerial and acoustic coverage, aerial surveys saw whales on approximately two-thirds of the days during which acoustic monitoring heard whales. There was no strong relationship between numbers of whales seen during aerial surveys and numbers of contact calls detected on survey days. Results indicate acoustic monitoring is a more reliable mechanism than aerial survey for detecting right whales. Because simple detection is sufficient to trigger current management protocols, continuous, autonomous acoustic monitoring provides information of immediate management utility more reliably than aerial surveillance. Aerial surveys are still required to provide data for estimating population parameters and for visually assessing the frequency and severity of injuries from shipping and fishing and detecting injured and entangled right whales.     

ACOUSTIC COMMUNICATION SIGNALS OF MYSTICETE WHALES

ABSTRACT

Mysticete (baleen) whales produce a variety of vocalizations and sounds, but relatively few of these have been well described with accompanying behavior. This review concentrates on the vocalizations consistently associated with behavioral interactions or acoustic exchanges between or among conspecifics. These communication “signals” have been categorized for this review as contact calls of single animals outside of the breeding season (including cow-calf pairs), vocalizations reported during the breeding season (often designated as “songs”), and calls produced by active groups of whales that may or may not have a reproductive function. While much remains unknown, the data obtained thus far indicate that the social vocalizations of baleen whales have structural/functional similarities with those of other mammals and birds.     

Status of the world's baleen whales

No global synthesis of the status of baleen whales has been published since the 2008 IUCN Red List assessments. Many populations remain at low numbers from historical commercial whaling, which had ceased for all but a few by 1989. Fishing gear entanglement and ship strikes are the most severe current threats. The acute and long‐term effects of anthropogenic noise and the cumulative effects of multiple stressors are of concern but poorly understood. The looming consequences of climate change and ocean acidification remain difficult to characterize. North Atlantic and North Pacific right whales are among the species listed as Endangered. Southern right, bowhead, and gray whales have been assessed as Least Concern but some subpopulations of these species ‐ western North Pacific gray whales, Chile‐Peru right whales, and Svalbard/Barents Sea and Sea of Okhotsk bowhead whales ‐ remain at low levels and are either Endangered or Critically Endangered. Eastern North Pacific blue whales have reportedly recovered, but Antarctic blue whales remain at about 1% of pre‐exploitation levels. Small isolated subspecies or subpopulations, such as northern Indian Ocean blue whales, Arabian Sea humpback whales, and Mediterranean Sea fin whales are threatened while most subpopulations of sei, Bryde's, and Omura's whales are inadequately monitored and difficult to assess.     

Interspecific relationships in density among the whale community in the Antarctic

Interspecific relationships in density among a whale community in Antarctic feeding grounds were examined using the sightings data derived from the systematic surveys conducted between 1978/1979 and 1987/1988. A clear difference in densities against the physiographic variables (the sea floor-slope type) was identified between baleen whales and toothed whales. Densities of sperm whales and ziphiids were low in the waters over the continental shelf where minke whales' densities were highest. This led to an apparent negative correlation in the density between minke and sperm whales, and minke whale and ziphiids. A significant positive correlation in density between minke and blue whales was identified. No association in density between minke and humpback whales was observed. Distribution of killer whales shows strong positive correlation with that of minke whales. The positive correlation existed between minke and blue whales, and minke and killer whales even when the effect of environmental variables was excluded. Analysis also revealed that the environmental variables, including physiographic variables, are major factors affecting the distributions and density of whales, especially between baleen whales and toothed whales. Accepted: 8 December 1999     

Proceedings of the SMBE Tri-National Young Investigators' Workshop 2005. Baleen whale phylogeny and a past extensive radiation event revealed by SINE insertion analysis

Baleen whales (suborder Mysticeti) comprise 11 extant species that are classified into four families. Although several phylogenetic hypotheses about these taxa have been proposed, their phylogenetic relationships remain confused. We addressed this problem using short interspersed repetitive element (SINE) insertion data, which now are regarded as almost ideal shared, derived characters at the molecular level. We reconstructed the phylogenetic relationships of baleen whales by characterizing 36 informative SINE loci. One of the intriguing conclusions is that balaenopterids and eschrichtiids radiated very rapidly during a very short evolutionary period. During this period, speciation occurred in balaenopterids and eschrichtiids while newly inserted SINE loci remains polymorphic. Later on, these SINEs were sorted incompletely into each lineage. Thus, there are now inconsistencies among species regarding the presence or absence of a given SINE. This is in sharp contrast to the phylogeny of toothed whales, for which no SINE inconsistencies have been found. Furthermore, we found monophyletic groupings between humpback and fin whales as well as between (sei+Bryde's) whales and blue whales, both of which have not previously been recognized. The comprehensive SINE insertion data, together with the mitochondrial DNA phylogeny that was recently completed (Sasaki, T., M. Nikaido, H. Healy et al. 2005. Mitochondrial phylogenetics and evolution of mysticete whales. Syst. Biol. 56:77-90; Rychel, A. L., T. W. Reeder, and A. Berta. 2004. Phylogeny of mysticete whales based on mitochondrial and nuclear data. Mol. Phylogenet. Evol. 32:892-901), provide a nearly complete picture of the evolutionary history of baleen whales.     

Blue whales respond to anthropogenic noise

Anthropogenic noise may significantly impact exposed marine mammals. This work studied the vocalization response of endangered blue whales to anthropogenic noise sources in the mid-frequency range using passive acoustic monitoring in the Southern California Bight. Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to stop calling at any time of day, showing no diel pattern in their sensitivity to sonar. Conversely, the likelihood of whales emitting calls increased when ship sounds were nearby. Whales did not show a differential response to ship noise as a function of the time of the day either. These results demonstrate that anthropogenic noise, even at frequencies well above the blue whales' sound production range, has a strong probability of eliciting changes in vocal behavior. The long-term implications of disruption in call production to blue whale foraging and other behaviors are currently not well understood.     

BLUE WHALE, BALAENOPTERA MUSCULUS, VOCALIZATIONS FROM THE WATERS OFF CENTRAL CALIFORNIA

Low-frequency calls produced by blue whales, Balaenoptera musculus , were recorded in the northeastern Pacific Ocean off central California. Two blue whales were sighted during a vessel-based marine mammal survey, and when sonobuoys were subsequently deployed, blue whale calls were recorded. A third recording was obtained during the survey from a blue whale that was not seen. Recordings with 15, 25, and 55 min of calls were obtained from these individuals. The three recordings all contain two-part, low-frequency calls with slight interindividual variation. The calls consist of an amplitude modulated (AM) signal with a mean center frequency of 16.5 Hz, followed by a downsweep whose mean center frequency sweeps from 18.2 Hz to 16.6 Hz. The recordings are compared with blue whale recordings from the Pacific and Atlantic Oceans. The geographic variability suggests that blue whale calls may be used as an acoustic indicator of stock identity.     

Red Shift,Blue Shift: Investigating Doppler Shifts,Blubber Thickness,and Migration as Explanations of Seasonal Variation in the Tonality of Antarctic Blue Whale Song

The song of Antarctic blue whales (Balaenoptera musculus intermedia) comprises repeated, stereotyped, low-frequency calls. Measurements of these calls from recordings spanning many years have revealed a long-term linear decline as well as an intra-annual pattern in tonal frequency. While a number of hypotheses for this long-term decline have been investigated, including changes in population structure, changes in the physical environment, and changes in the behaviour of the whales, there have been relatively few attempts to explain the intra-annual pattern. An additional hypothesis that has not yet been investigated is that differences in the observed frequency from each call are due to the Doppler effect. The assumptions and implications of the Doppler effect on whale song are investigated using 1) vessel-based acoustic recordings of Antarctic blue whales with simultaneous observation of whale movement and 2) long-term acoustic recordings from both the subtropics and Antarctic. Results from vessel-based recordings of Antarctic blue whales indicate that variation in peak-frequency between calls produced by an individual whale was greater than would be expected by the movement of the whale alone. Furthermore, analysis of intra-annual frequency shift at Antarctic recording stations indicates that the Doppler effect is unlikely to fully explain the observations of intra-annual pattern in the frequency of Antarctic blue whale song. However, data do show cyclical changes in frequency in conjunction with season, thus suggesting that there might be a relationship among tonal frequency, body condition, and migration to and from Antarctic feeding grounds.     

Fin Whale Sound Reception Mechanisms: Skull Vibration Enables Low-Frequency Hearing

Hearing mechanisms in baleen whales (Mysticeti) are essentially unknown but their vocalization frequencies overlap with anthropogenic sound sources. Synthetic audiograms were generated for a fin whale by applying finite element modeling tools to X-ray computed tomography (CT) scans. We CT scanned the head of a small fin whale (Balaenoptera physalus) in a scanner designed for solid-fuel rocket motors. Our computer (finite element) modeling toolkit allowed us to visualize what occurs when sounds interact with the anatomic geometry of the whale’s head. Simulations reveal two mechanisms that excite both bony ear complexes, (1) the skull-vibration enabled bone conduction mechanism and (2) a pressure mechanism transmitted through soft tissues. Bone conduction is the predominant mechanism. The mass density of the bony ear complexes and their firmly embedded attachments to the skull are universal across the Mysticeti, suggesting that sound reception mechanisms are similar in all baleen whales. Interactions between incident sound waves and the skull cause deformations that induce motion in each bony ear complex, resulting in best hearing sensitivity for low-frequency sounds. This predominant low-frequency sensitivity has significant implications for assessing mysticete exposure levels to anthropogenic sounds. The din of man-made ocean noise has increased steadily over the past half century. Our results provide valuable data for U.S. regulatory agencies and concerned large-scale industrial users of the ocean environment. This study transforms our understanding of baleen whale hearing and provides a means to predict auditory sensitivity across a broad spectrum of sound frequencies.