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.     

FRIENDS OF WILDLIFE SOUND AT NSA

ABSTRACT

The problem of categorization arises in any classification system because classes should be discrete while the characteristics of most natural objects and aspects of nature are more or less gradual. In systematics, this problem usually is solved by creating several levels of categories, such as class, order, family, genus and species. In the existing killer whale discrete call classification, only two levels occur—call type and call subtype. In this paper we describe structural categories at a broader level than call type in the discrete sounds of killer whales and compare these categories between and within vocal clans in a community of resident killer whales from Southeast Kamchatka, Russian Far East, and also with killer whales outside this community. We found four main classes of discrete calls in the repertoire of resident killer whales from Southeast Kamchatka. The calls of Southeast Kamchatka transient killer whales and Sakhalin killer whales do not fall into these classes. This suggests that the resident killer whale community from Southeast Kamchatka has some rules defining the structure of calls which are typical for this community. Consequently, all resident killer whales from Southeast Kamchatka can be said to share the same vocal tradition.     

Horizontal transmission of vocal traditions in killer whale (<Emphasis Type="Italic">Orcinus orca</Emphasis>) dialects

Unlike most other mammals, killer whales are capable of vocal learning and learn the dialect of their natal pod from their mothers. The classical model of killer whale dialect development suggests that the repertoire of calls is learned only “vertically” from mother to offspring, and calls evolve gradually with time by random drift caused by the accumulation of copying errors. However, some observations suggest that not only “vertical” (from mother to offspring) vocal learning can occur in killer whales, but also “horizontal” (between adult animals). In this study we analyzed the distribution of different call types and similarity of calls from the same type in different pods of killer whales from Kamchatka waters to estimate the probability of existence of interpod horizontal transmission of vocal traditions in killer whales. We found that the degree of similarity of K1 calls and K5 calls in different pods can differ. This situation contradicts the classical hypothesis and is possible in two cases: if different call types change with various speed in different pods, or if horizontal transmission of call features takes place. The distribution of K4 and K10 call types across pods also suggests the existence of horizontal transmission: K4 calls occur in the dialects of five of ten pods, and K10 calls, in six of ten pods, but only one pod has both K4 and K10 calls. Our results suggest that the real picture of the distribution of call features and call types in killer whale dialects contradicts the classical hypothesis of killer whale dialect evolution through the accumulation of copying errors.     

UNDERWATER NOISE OF WHALE-WATCHING BOATS AND POTENTIAL EFFECTS ON KILLER WHALES (ORCINUS ORCA), BASED ON AN ACOUSTIC IMPACT MODEL

Underwater noise of whale-watching boats was recorded in the popular killer whale-watching region of southern British Columbia and northwestern Washington State. A software sound propagation and impact assessment model was applied to estimate zones around whale-watching boats where boat noise was audible to killer whales, where it interfered with their communication, where it caused behavioral avoidance, and where it possibly caused hearing loss. Boat source levels ranged from 145 to 169 dB re 1 μPa @ 1 m, increasing with speed. The noise of fast boats was modeled to be audible to killer whales over 16 km, to mask killer whale calls over 14 km, to elicit a behavioral response over 200 m, and to cause a temporary threshold shift (TTS) in hearing of 5 dB after 30–50 min within 450 m. For boats cruising at slow speeds, the predicted ranges were 1 km for audibility and masking, 50 m for behavioral responses, and 20 m for TTS. Superposed noise levels of a number of boats circulating around or following the whales were close to the critical level assumed to cause a permanent hearing loss over prolonged exposure. These data should be useful in developing whale-watching regulations. This study also gave lower estimates of killer whale call source levels of 105–124 dB re 1 μPa.     

TWO TYPES OF BLUE WHALE CALLS RECORDED IN THE GULF OF ALASKA

At one time blue whales were found throughout the Gulf of Alaska, however, none have been sighted there in post-whaling era surveys. To determine if blue whales ( Balaenoptera musculus ) might now occur in the Gulf of Alaska, an array of hydrophones was deployed there in October 1999. Data were retrieved in May 2000 and in June 2001. Spectrograms from a random subsample comprising 15% of the ∼63,000 h of data were visually examined for blue whale calls. Call types attributed to both northeastern and northwestern Pacific blue whales were recorded. Both of these call types were recorded seasonally from the initial deployment date in October 1999 through the third week of December 1999 and then from July 2000 through mid-December 2000. Both call types were regularly recorded on the same hydrophone at the same time indicating clear temporal and spatial overlap of the animals producing these calls. Two blue whale call types were recorded in the Gulf of Alaska suggesting that perhaps two stocks use this area. The northeastern call type has now been documented from the equator up to at least 55°N in the eastern North Pacific.     

Repeated call sequences and behavioural context in long-finned pilot whales off Cape Breton,Nova Scotia,Canada

Repeated calls are part of the vocal repertoire of a diverse array of species, often presented in sequences that take time and effort on the part of the signal producer. Rhythmic repeated call sequences make up a significant portion of long-finned pilot whale (Globicephala melas) vocal production, yet the function of these sequences has not been investigated until now. In this study, we explored the relationship between behavioural context and the presence of these vocal sequences using recordings of a population of pilot whales found off Cape Breton, Nova Scotia, Canada. We used a binomial logit-link generalized linear model to look for possible predictors of the presence of repeated call sequences. They were more common in recordings of socializing whales than in those of whales in other behavioural states, and least common in resting whales. These vocal repetitions were also more common with larger group size. These results suggest that sequences function in maintaining contact and cohesion within this social species, possibly also serving in individual or group identification. The context of repeated call sequences indicate that they are not primarily mother–calf interactions, as they are heard just as commonly from groups without young. Future studies of pilot whale repeated call sequences should include individual-level behaviour and detailed acoustic calling context.     

The Relationship between Vessel Traffic and Noise Levels Received by Killer Whales (Orcinus orca)

Whale watching has become increasingly popular as an ecotourism activity around the globe and is beneficial for environmental education and local economies. Southern Resident killer whales (Orcinus orca) comprise an endangered population that is frequently observed by a large whale watching fleet in the inland waters of Washington state and British Columbia. One of the factors identified as a risk to recovery for the population is the effect of vessels and associated noise. An examination of the effects of vessels and associated noise on whale behavior utilized novel equipment to address limitations of previous studies. Digital acoustic recording tags (DTAGs) measured the noise levels the tagged whales received while laser positioning systems allowed collection of geo-referenced data for tagged whales and all vessels within 1000 m of the tagged whale. The objective of the current study was to compare vessel data and DTAG recordings to relate vessel traffic to the ambient noise received by tagged whales. Two analyses were conducted, one including all recording intervals, and one that excluded intervals when only the research vessel was present. For all data, significant predictors of noise levels were length (inverse relationship), number of propellers, and vessel speed, but only 15% of the variation in noise was explained by this model. When research-vessel-only intervals were excluded, vessel speed was the only significant predictor of noise levels, and explained 42% of the variation. Simple linear regressions (ignoring covariates) found that average vessel speed and number of propellers were the only significant correlates with noise levels. We conclude that vessel speed is the most important predictor of noise levels received by whales in this study. Thus, measures that reduce vessel speed in the vicinity of killer whales would reduce noise exposure in this population.     

Annual Acoustic Presence of Fin Whale (Balaenoptera physalus) Offshore Eastern Sicily,Central Mediterranean Sea

In recent years, an increasing number of surveys have definitively confirmed the seasonal presence of fin whales (Balaenoptera physalus) in highly productive regions of the Mediterranean Sea. Despite this, very little is yet known about the routes that the species seasonally follows within the Mediterranean basin and, particularly, in the Ionian area. The present study assesses for the first time fin whale acoustic presence offshore Eastern Sicily (Ionian Sea), throughout the processing of about 10 months of continuous acoustic monitoring. The recording of fin whale vocalizations was made possible by the cabled deep-sea multidisciplinary observatory, “NEMO-SN1”, deployed 25 km off the Catania harbor at a depth of about 2,100 meters. NEMO-SN1 is an operational node of the European Multidisciplinary Seafloor and water-column Observatory (EMSO) Research Infrastructure. The observatory was equipped with a low-frequency hydrophone (bandwidth: 0.05 Hz–1 kHz, sampling rate: 2 kHz) which continuously acquired data from July 2012 to May 2013. About 7,200 hours of acoustic data were analyzed by means of spectrogram display. Calls with the typical structure and patterns associated to the Mediterranean fin whale population were identified and monitored in the area for the first time. Furthermore, a background noise analysis within the fin whale communication frequency band (17.9–22.5 Hz) was conducted to investigate possible detection-masking effects. The study confirms the hypothesis that fin whales are present in the Ionian Sea throughout all seasons, with peaks in call detection rate during spring and summer months. The analysis also demonstrates that calls were more frequently detected in low background noise conditions. Further analysis will be performed to understand whether observed levels of noise limit the acoustic detection of the fin whales vocalizations, or whether the animals vocalize less in the presence of high background noise.     

Exposure to seismic survey alters blue whale acoustic communication

The ability to perceive biologically important sounds is critical to marine mammals, and acoustic disturbance through human-generated noise can interfere with their natural functions. Sounds from seismic surveys are intense and have peak frequency bands overlapping those used by baleen whales, but evidence of interference with baleen whale acoustic communication is sparse. Here we investigated whether blue whales (Balaenoptera musculus) changed their vocal behaviour during a seismic survey that deployed a low-medium power technology (sparker). We found that blue whales called consistently more on seismic exploration days than on non-exploration days as well as during periods within a seismic survey day when the sparker was operating. This increase was observed for the discrete, audible calls that are emitted during social encounters and feeding. This response presumably represents a compensatory behaviour to the elevated ambient noise from seismic survey operations.     

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.     

Changes in the acoustic behavior of resident bottlenose dolphins near operating vessels

Maritime traffic is an issue of major ecological concern, and vessel noise may be an important source of disturbance for coastal cetaceans. In the Sado estuary, Portugal, core habitat areas of a small resident population of bottlenose dolphins (Tursiops truncatus) overlap with routes of intense maritime traffic, which presents an opportunity to assess vocal responses of these dolphins to specific vessel noise sources. Field recordings of dolphin vocalizations were made from April to November 2011, using a calibrated system. Dolphin behavior and group size were recorded, as well as the operating boat condition (no boats or specific boat type) in a 1,000 m radius. Spectral analyses of vocalizations allowed the categorization and quantitative analysis of echolocation click trains and social calls, including whistles. Mean overall call rates decreased significantly in the presence of operating vessels. Creaks (fast click trains) were significantly reduced in the presence of ferry boats. Significant differences were also observed in the whistles' minimum, maximum, and start frequencies. These changes in call emission rates and temporary shifts in whistles characteristics may be a vocal response to the proximity of operating vessels, facilitating communication in this busy, noisy estuary.     

Call types of Bigg’s killer whales (Orcinus orca) in western Alaska: using vocal dialects to assess population structure

Bigg’s killer whales (Orcinus orca; i.e. ‘transient’ ecotype), as apex predators, are important to the dynamics of marine ecosystems, but little is known about their population structure in western Alaska. Currently, all Bigg’s killer whales in western Alaska are ascribed to a single broad stock for management under the US Marine Mammal Protection Act. However, recent nuclear microsatellite and mitochondrial DNA analyses indicate that this stock is likely comprised of genetically distinct sub-populations. In accordance with what is known about killer whale vocal dialects in other locations, we used the spatial distribution of group-specific call types to investigate the population structure of Bigg’s killer whales in this part of Alaska. Digital audio recordings were collected from 33 Bigg’s killer whale encounters throughout the Aleutian and Pribilof Islands in the summers of 2001–2007 and 2009–2010. Recorded calls were qualitatively classified into discrete types and then quantitatively described using 12 structural and time-frequency measures. Resulting call categories were validated using a random forest approach. A total of 36 call types and subtypes were identified across the entire study area, and regional patterns of call type use revealed three distinct dialects which correspond to proposed genetic delineations. Our results suggest that there are at least three acoustically and genetically distinct sub-populations in western Alaska, and we present an initial catalogue for this area describing the regional vocal repertoires of Bigg’s killer whale call types.     

Vocal activity of tropical dolphins is inhibited by the presence of killer whales,Orcinus orca

Research has suggested killer whale (Orcinus orca) predation may affect cetacean vocal behavior; however, few data exist to test this hypothesis. Data collected during 40,976 km of visual and acoustic shipboard surveys in the tropical Pacific Ocean, including 1,232 detections of 13 species, were examined to determine if changes in dolphin vocal activity could be attributed to the presence of killer whales. Generalized linear models and Random Forest analyses were used to test the hypothesis that dolphin vocal activity was related to the distance and time to the nearest killer whale sighting. Both results show that dolphin vocalizations were inversely correlated with the temporal proximity of killer whales (P < 0.05). Despite the relative rarity of killer whales in the tropics, they appear to influence vocal behavior of nearby dolphin schools. This disruption in communication may not significantly impact interactions necessary for survival in tropical waters where killer whale density is low. However, in temperate climates, where increased productivity supports a greater abundance of killer whales, this interruption in communication may have a greater impact. The lower incidence of whistling dolphins in temperate waters may be related to the greater abundance of killer whales in these areas.     

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.     

Seasonal detection of three types of “pygmy” blue whale calls in the Indian Ocean

The Indian Ocean is an area in which a rich suite of cetacean fauna, including at least two subspecies of blue whale, is found; yet little information beyond stranding data and short‐term surveys for this species is available. Pygmy blue whale (Balaenoptera musculus spp.) call data are presented that provide novel information on the seasonal and geographic distribution of these animals. Acoustic data were recorded from January 2002 to December 2003 by hydrophones at three stations of the International Monitoring System, including two near the subequatorial Diego Garcia Atoll and a third southwest of Cape Leeuwin, Australia. Automated spectrogram correlation methods were used to scan for call types attributed to pygmy blue whales. Sri Lanka calls were the most common and were detected year‐round off Diego Garcia. Madagascar calls were only recorded on the northern Diego Garcia hydrophone during May and July, whereas Australia calls were only recorded at Cape Leeuwin, between December and June. Differences in geographic and seasonal patterns of these three distinct call types suggest that they may represent separate acoustic populations of pygmy blue whales and that these “acoustic populations” should be considered when assessing conservation needs of blue whales in the Indian Ocean.     

A comparison of Northeast Atlantic killer whale (Orcinus orca) stereotyped call repertoires

Killer whale call repertoires can provide information on social connections among groups and populations. Killer whales in Iceland and Norway exhibit similar ecology and behavior, are genetically related, and are presumed to have been in contact before the collapse of the Atlanto-Scandian herring stock in the 1960s. However, photo-identification suggests no recent movements between Iceland and Norway but regular movement between Iceland and Shetland. Acoustic recordings collected between 2005 and 2016 in Iceland, Norway, and Shetland were used to undertake a comprehensive comparison of call repertoires of Northeast Atlantic killer whales. Measurements of time and frequency parameters of calls from Iceland (n = 4,037) and Norway (n = 1,715) largely overlapped in distribution, and a discriminant function analysis had low correct classification rate. No call type matches were confirmed between Iceland and Norway or Shetland and Norway. Three call types matched between Iceland and Shetland. Therefore, this study suggests overall similarities in time and frequency parameters but some divergence in call type repertoires. This argues against presumed past contact between Icelandic and Norwegian killer whales and suggests that they may not have been one completely mixed population.     

Spatial and temporal patterns in the calling behavior of beluga whales,Delphinapterus leucas,in Cook Inlet,Alaska

Cook Inlet beluga whales (CIBs) are an endangered population residing in Cook Inlet, Alaska. We characterized the calling behavior of CIBs to improve our understanding of sounds produced by this population. Bottom‐moored hydrophones were deployed at Eagle Bay in summer 2009 and at Trading Bay in summer and winter 2009. CIB sounds were qualitatively analyzed and categorized as a whistle, pulsed call, or click train. A total of 4,097 calls were analyzed, and 66 unique whistle contours were identified. Whistles were quantitatively analyzed using a custom Matlab program. A chi‐square test showed the call category usage at Eagle Bay during summer 2009 and those at Trading Bay during summer 2009 and winter 2009–2010 differed significantly (P < 0.001). Pulsed calls were more common during summer months, and click trains within the frequency band (12.5 kHz) were more common in Eagle Bay. The variation in calling behavior suggests differences in habitat usage or in the surrounding environment, including background noise. With the proposed development projects in Cook Inlet and the potential increase in ambient noise level due to ocean acidification, it is important to understand how this endangered population uses sound, and what anthropogenic factors may influence that use.     

Repeated call types in short‐finned pilot whales,Globicephala macrorhynchus

Four short‐finned pilot whales, Globicephala macrorhynchus, were tagged with digital acoustic recording tags (DTAGs) for a total of 30 h in the Bahamas during 2007. Spectrograms were made of all audible sounds, which were independently categorized by three observers. Of 4,098 calls, 1,737 (42%) were placed into 173 call types, which were defined as calls that occurred more than once. Of the 173 call types, 51 contained at least 10 calls (= 24), and were termed predominant call types (PCTs), which comprised 1,219 (70%) of categorized calls. PCTs tended to occur in sequences of the same call, which appeared to be produced by a single animal. However, matching interactions consisting of adjacent or overlapping calls of the same type were also observed, and some call types were recorded on more than one tag, suggesting that at least some calls are shared by members of a group or subgroup. These results emphasize the importance of categorizing calls before attempting to draw conclusions about call usage and possible effects of noise on vocal behavior.     

Seasonality of Antarctic minke whale (Balaenoptera bonaerensis) calls off the western Antarctic Peninsula

The Antarctic minke whale (Balaenoptera bonaerensis) is a difficult species to study because of its low visual detectability and preference for living within the sea ice habitat, accessible only by ice‐strengthened vessels. Recent identification of the Antarctic minke whale as the source of the seasonally ubiquitous bio‐duck call has allowed the use of this sound, as well as downsweeps, to investigate seasonality trends and diel patterns in Antarctic minke whale call production, and their relationship to sea ice cover. Passive acoustic data were collected using an autonomous Acoustic Recording Package (ARP) off the western Antarctic Peninsula. Bio‐duck calls were classified into four distinct call variants, with one variant having two subtypes. Bio‐duck calls were detected between April and November, with increasing call duration during the austral winter, indicating a strong seasonality in call production. Downsweeps, which were also attributed to Antarctic minke whales, were present throughout most months during the recording period, with a peak in July, and an absence in March and April. Both bio‐duck and downsweeps were significantly correlated with sea ice cover. No diel patterns were observed in bio‐duck calls or in downsweep call production at this site.