Acoustic occurrence of baleen whales, particularly blue, fin, and humpback whales, off eastern Canada, 2015-2017 (PDF)

Delarue, J.-Y., H. Moors-Murphy, K.A. Kowarski, G.E. Davis, I.R. Urazghildiiev, and S.B. Martin

Endangered Species Research 47: 265-289 (2022)

DOI: 10.3354/esr01176

Six baleen whale species occur off eastern Canada, but little is known of their year-round occurrence across this large region. This complicates identifying areas that are important to them and may require critical habitat designation, especially for those species considered at risk. This is particularly true between fall and spring because of a lack of visual survey effort. The main objective of this paper is to provide a year-round and pluriannual description of the minimum acoustic occurrence of baleen whales, particularly blue Balaenoptera musculus, fin B. physalus, and humpback whales Megaptera novaeangliae. We deployed 25 acoustic recorders off eastern Canada between May 2015 and November 2017, and the data were analyzed using a combination of automated detectors and manual validation to identify vocalizations produced by these species. Blue, fin, and humpback whales occurred off eastern Canada year-round, a finding which contrasts the traditional seasonal latitude migration narrative for these species. The Scotian Shelf region and Flemish Pass-Orphan Basin areas seem particularly important for these animals and should be the focus of future research. Sei B. borealis, minke B. acutorostrata, and North Atlantic right whale Eubalaena glacialis vocalizations also occurred in the data but were not adequately captured by the adopted methodology. Coarse patterns of occurrence are presented for these species as a foundation for more detailed analyses. This study is the first to cover eastern Canadian waters for an extended continuous period and provides a baseline against which future changes can be assessed.

The Beat Goes On: Humpback Whale Song Seasonality in Antarctic and South African Waters (PDF)

Shabangu, F.W. and K.A. Kowarski

Frontiers in Marine Science 9: 827324 (2022)

DOI: 10.3389/fmars.2022.827324

Little is known of the movements and seasonal occurrence of humpback whales (Megaptera novaeangliae) of South Africa and the Antarctic, populations once brought to near extinction by historic commercial whaling. We investigated the seasonal occurrence and diel-vocalizing pattern of humpback whale songs off the west coast of South Africa (migration route and opportunistic feeding ground) and the Maud Rise, Antarctica (feeding ground), using passive acoustic monitoring data collected between early 2014 and early 2017. Data were collected using acoustic autonomous recorders deployed 200-300 m below the sea surface in waters 855, 1,118 and 4,400 m deep. Acoustic data were manually analyzed for humpback whale vocalizations. While non-song calls were never identified, humpback whale songs were detected from June through December in South African waters, with a peak in percentage of acoustic occurrence around September/October in the austral spring. In Antarctic waters, songs were detected from March through May and in July (with a peak occurrence in April) where acoustic occurrence of humpback whales was negatively correlated to distance to the sea ice extent. Humpback whales were more vocally active at night than in the day at all recording sites. Detection range modelling indicates that humpback whale vocalizations could be detected as far as 18 and 45 km from recorders in South African and Antarctic waters, respectively. This study provides a multi-year description of the offshore acoustic occurrence of humpback whales off the west coast of South Africa and Maud Rise, Antarctica, regions that should continue to be monitored to understand these recovering populations.

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

Sweeney, S.O, J.M. Terhune, H. Frouin-Mouy, and P.A. Rouget

Journal of the Acoustical Society of America 151: 2310-2325 (2022)

DOI: 10.1121/10.0009956

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.

Changes in the acoustic activity of beaked whales and sperm whales recorded during a naval training exercise off eastern Canada (PDF)

Stanistreet, J.E., W.A.M. Beslin, K. Kowarski, S.B. Martin, A. Westell, and H.B. Moors-Murphy

Scientific Reports 12(1): 1973 (2022)

DOI: 10.1038/s41598-022-05930-4

Experimental research has shown that beaked whales exhibit strong avoidance reactions to naval active sonars used during antisubmarine warfare training exercises, including cessation of echolocation and foraging activity. Behavioural responses to sonar have also been linked to strandings and mortality. Much of the research on the responses of beaked whales and other cetaceans to naval active sonar has occurred on or near U.S. naval training ranges, and the impacts of sonar in other regions remain poorly understood, particularly as these impacts, including mortality, are likely to go unobserved in offshore areas. In September 2016 the multinational naval exercise ‘CUTLASS FURY 2016’ (CF16) was conducted off eastern Canada. We used passive acoustic recordings collected in the region to quantify the occurrence and characteristics of sonar signals, measure ambient noise levels, and assess changes in the acoustic activity of beaked and sperm whales. The number of hours per day with echolocation clicks from Cuvier’s beaked whales and sperm whales were significantly reduced during CF16, compared to the pre-exercise period in 2016 (sperm whales) and to control data from 2015 (both species). Clicks from an unidentified Mesoplodont beaked whale species, sporadically detected prior to CF16, were absent during the exercise and for 7 days afterward. These results suggest that beaked and sperm whales ceased foraging in the vicinity of CF16 and likely avoided the affected area. Such disturbance may have energetic, health, and fitness consequences.

Offshore wind energy development: Research priorities for sound and vibration effects on fishes and aquatic invertebrates (PDF)

Popper, A.N. L. Hice-Dunton, E. Jenkins, D.M. Higgs, J. Krebs, A. Mooney, A. Rice, L. Roberts, F. Thomsen, K. Vigness-Raposa, D. Zeddies, and K.A. Williams

J. Acoust. Soc. Am. 151: 205–215 (2022)

DOI: 10.1121/10.0009237

There are substantial knowledge gaps regarding both the bioacoustics and the responses of animals to sounds associated with pre-construction, construction, and operations of offshore wind (OSW) energy development. A workgroup of the 2020 State of the Science Workshop on Wildlife and Offshore Wind Energy identified studies for the next five years to help stakeholders better understand potential cumulative biological impacts of sound and vibration to fishes and aquatic invertebrates as the OSW industry develops. The workgroup identified seven short-term priorities that include a mix of primary research and coordination efforts. Key research needs include the examination of animal displacement and other behavioral responses to sound, as well as hearing sensitivity studies related to particle motion, substrate vibration, and sound pressure. Other needs include: identification of priority taxa on which to focus research; standardization of methods; development of a long-term highly instrumented field site; and examination of sound mitigation options for fishes and aquatic invertebrates. Effective assessment of potential cumulative impacts of sound and vibration on fishes and aquatic invertebrates is currently precluded by these and other knowledge gaps. However, filling critical gaps in knowledge will improve our understanding of possible sound-related impacts of OSW energy development to populations and ecosystems.

International harmonization of procedures for measuring and analyzing of vessel underwater radiated noise (PDF)

Ainslie, M.A., S.B. Martin, K.B. Trounce, D.E. Hannay, J.M. Eickmeier, T.J. Deveau, K. Lucke, A.O. MacGillivray, V. Nolet, and P. Borys

Marine Pollution Bulletin 174: 113124 (2022)

DOI: 10.1016/j.marpolbul.2021.113124

The habitat of the endangered southern resident killer whale (SRKW) overlaps major international shipping lanes near the Port of Vancouver, British Columbia. Shipping is a dominant source of underwater noise, which can hinder SRKW key life functions. To reduce environmental pressure on the SRKWs, Vancouver Fraser Port Authority offers incentives for quieter ships. However, the absence of a widely accepted underwater radiated noise (URN) measurement procedure hinders the determination of relative quietness. We review URN measurement procedures, summarizing results to date from two Canadian-led projects aimed at improving harmonization of shallow-water URN measurement procedures: One supports the International Organization for Standardization (ISO) in the development of a URN measurement standard; the other supports the alignment of URN measurement procedures developed by ship classification societies. Weaknesses in conventional shallow-water URN metrics are identified, and two alternative metrics proposed. Optimal shallow-water measurement geometry is identified.

A modeling comparison of the potential effects on marine mammals from sounds produced by marine vibroseis and air gun seismic sources (PDF)

Matthews, M.-N.R., D.S. Ireland, D.G. Zeddies, R.H. Brune, and C.D. Pyć

J. Mar. Sci. Eng. 9(1): 12 (2021)

DOI: 10.3390/jmse9010012

Concerns about the potential environmental impacts of geophysical surveys using air gun sources, coupled with advances in geophysical surveying technology and data processing, are driving research and development of commercially viable alternative technologies such as marine vibroseis (MV). MV systems produce controllable acoustic signals through volume displacement of water using a vibrating plate or shell. MV sources generally produce lower acoustic pressure and reduced bandwidth (spectral content) compared to air gun sources, but to be effective sources for geophysical surveys they typically produce longer duration signals with short inter-signal periods. Few studies have evaluated the potential effects of MV system use on marine fauna. In this desktop study, potential acoustic exposure of marine mammals was estimated for MV and air gun arrays by modeling the source signal, sound propagation, and animal movement in representative survey scenarios. In the scenarios, few marine mammals could be expected to be exposed to potentially injurious sound levels for either source type, but fewer were predicted for MV arrays than air gun arrays. The estimated number of marine mammals exposed to sound levels associated with behavioral disturbance depended on the selection of evaluation criteria. More behavioral disturbance was predicted for MV arrays compared to air gun arrays using a single threshold sound pressure level (SPL), while the opposite result was found when using frequency-weighted sound fields and a multiple-step, probabilistic, threshold function.

A reference spectrum model for estimating source levels of marine shipping based on Automated Identification System data (PDF)

MacGillivray, A. and C. de Jong

J. Mar. Sci. Eng. 9: 369 (2021)

DOI: 10.3390/jmse/9040369

Underwater sound mapping is increasingly being used as a tool for monitoring and managing noise pollution from shipping in the marine environment. Sound maps typically rely on tracking data from the Automated Information System (AIS), but information available from AIS is limited and not easily related to vessel noise emissions. Thus, robust sound mapping tools not only require accurate models for estimating source levels for large numbers of marine vessels, but also an objective assessment of their uncertainties. As part of the Joint Monitoring Programme for Ambient Noise in the North Sea (JOMOPANS) project, a widely used reference spectrum model (RANDI 3.1) was validated against statistics of monopole ship source level measurements from the Vancouver Fraser Port Authority-led Enhancing Cetacean Habitat and Observation (ECHO) Program. These validation comparisons resulted in a new reference spectrum model (the JOMOPANS-ECHO source level model) that retains the power-law dependence on speed and length but incorporates class-specific reference speeds and new spectrum coefficients. The new reference spectrum model calculates the ship source level spectrum, in decidecade bands, as a function of frequency, speed, length, and AIS ship type. The statistical uncertainty (standard deviation of the deviation between model and measurement) in the predicted source level spectra of the new model is estimated to be 6 dB.

A review of big data analysis methods for baleen whale passive acoustic monitoring (PDF)

Kowarski, K.A. and H. Moors-Murphy

Marine Mammal Science 37: 652-673 (2021)

DOI: 10.1111/mms.12758

Many organizations collect large passive acoustic monitoring (PAM) data sets that need to be efficiently and reliably analyzed. To determine appropriate methods for effective analysis of big PAM data sets, we undertook a literature review of baleen whale PAM analysis methods. Methodologies from 166 studies (published between 2000–2019) were summarized, and a detailed review was performed on the 94 studies that recorded more than 1,000 hr of acoustic data (“big data”). Analysis techniques for extracting baleen whale information from PAM data sets varied depending on the research observed. A spectrum of methodologies was used and ranged from manual analysis of all acoustic data by human experts to completely automated techniques with no manual validation. Based on this assessment, recommendations are provided to encourage robust research methods that are comparable across studies and sectors, achievable across research groups, and consistent with previous work. These include using automated techniques when possible to increase efficiency and repeatability, supplementing automation with manual review to calculate automated detector performance, and increasing consistency in terminology and presentation of results. This work can be used to facilitate discussion for minimum standards and best practices to be implemented in the field of marine mammal PAM.

A Terminology Standard for Underwater Acoustics and the Benefits of International Standardization (PDF)

Ainslie, M.A., M.B. Halvorsen, and S.P. Robinson

IEEE J. Ocean. Eng. 47: 179-200 (2021)

DOI: 10.1109/JOE.2021.3085947

Applications of underwater acoustics include sonar, communication, geophysical imaging, acoustical oceanography, and bioacoustics. Specialists typically work with little interdisciplinary interaction, and the terminology they employ has evolved separately in each discipline, to the point that transdisciplinary misunderstandings are common. Furthermore, increasing societal concern about possible detrimental effects of underwater noise on aquatic animals has led national and international regulators to require monitoring of underwater noise, with a consequent need for interdisciplinary harmonization of terminology. By adopting a common language, we facilitate the effective communication of concepts and information in underwater acoustics, whether for research, technology, or regulation. In the words of William H. Taft, “Don’t write so that you can be understood, write so that you can’t be misunderstood.” Clear definitions of widely used terms are needed, such as those used for the characterization of sound fields (e.g., “soundscape” and “ambient noise”), sound sources (“source level” and “source waveform”), sound propagation (“transmission loss” and “propagation loss”), and sound reception (“hearing threshold” and “frequency weighting function”). Terms that are used synonymously in one application have different meanings in another (examples include “hearing threshold” versus “detection threshold” and “transmission loss” versus “propagation loss”). Distinct definitions for these and many other acoustic terms are provided in a standard published in April 2017 by the International Organization for Standardization, ISO 18405. This article summarizes ISO 18405 and the process that led to the published definitions, including the reasons for omitting some terms.

Automatic data selection for validation: A method to determine cetacean occurrence in large acoustic data sets (PDF)

Kowarski, K.A., J.J.-Y. Delarue, B.J. Gaudet, and S.B. Martin

JASA Express Letters 1: 051201 (2021)

DOI: 10.1121/10.0004851

Passive acoustic monitoring (PAM) can inform wildlife management by providing information on the distribution of cetaceans. This paper presents an automatic data selection for validation (ADSV) method to effectively identify all species acoustically present in large PAM data sets. The ADSV method involves the application of automated detectors, the automated selection of a portion of data for manual review, and the evaluation/optimization of automated detectors. Using an exemplar data set, results from the ADSV method were compared to a more intensive systematic manual review method. The two methods were found to have similar species occurrence results (hourly occurrence matching 73%–100%).

Bowhead whales overwinter in the Amundsen Gulf and Eastern Beaufort Sea (PDF)

Insley, S.J., W.D. Halliday, X. Mouy, and N. Diogou

R. Soc. Open Sci. 8: 202268 (2021)

DOI: 10.1098/rsos.202268

The bowhead whale is the only baleen whale endemic to the Arctic and is well adapted to this environment. Bowheads live near the polar ice edge for much of the year and although sea ice dynamics are not the only driver of their annual migratory movements, it likely plays a key role. Given the intrinsic variability of open water and ice, one might expect bowhead migratory plasticity to be high and linked to this proximate environmental factor. Here, through a network of underwater passive acoustic recorders, we document the first known occurrence of bowheads overwintering in what is normally their summer foraging grounds in the Amundsen Gulf and eastern Beaufort Sea. The underlying question is whether this is the leading edge of a phenological shift in a species' migratory behaviour in an environment undergoing dramatic shifts due to climate change.

Characterization of the acoustic output of single marine-seismic airguns and clusters: The Svein Vaage dataset (PDF)

Prior, M.K., M.A. Ainslie, M.B. Halvorsen, I. Hartstra, R.M. Laws, A.O. MacGillivray, R. Müller, S. Robinson, and L. Wang

J. Acoust. Soc. Am. 150: 3675-3692 (2021)

DOI: 10.1121/10.0006751

The acoustical output of marine-seismic airguns is determined from recordings of the sound pressure made on hydrophones suspended below a floating barge from which the airguns are also deployed. The signals from multiple types of airguns are considered and each type is operated over a range of deployment depths and chamber pressures. The acoustical output is characterized in terms of a “source waveform” with dimensions of the pressure-times-distance and in an infinite idealized medium, could be divided by the source-receiver distance to give the sound pressure at that receiver. In more realistic environments, the source waveform may be used to predict the pressure at any arbitrary receiver position simply by the application of a time-domain transfer function describing the propagation between the source and receiver. The sources are further characterized by metrics such as the peak source waveform and energy source level. These metrics are calculated in several frequency bands so that the resulting metrics can be used to characterize the acoustical output of the airguns in terms of their utility for seismic image-processing or possible effects on marine life. These characterizations provide reference data for the calibration of models that predict the airguns' acoustical output. They are validated via comparisons of the acoustic pressure measured on far-field hydrophones and predicted using the source waveforms. Comparisons are also made between empirically derived expressions relating the acoustic metrics to the chamber volume, chamber pressure, and deployment depth and similar expressions from the literature.

Effects of a seismic survey on movement of free-ranging Atlantic cod (PDF)

van der Knaap, I., J. Reubens, L. Thomas, M.A. Ainslie, H.V. Winter, J. Hubert, B. Martin, and H. Slabbekoorn

Current Biology 31(7): 1555-1562 (2021)

DOI: 10.1016/j.cub.2021.01.050

Geophysical exploration of the seabed is typically done through seismic surveys, using airgun arrays that produce intense, low-frequency-sound pulses that can be heard over hundreds of square kilometers, 24/7. Little is known about the effects of these sounds on free-ranging fish behavior. Effects reported range from subtle individual change in activity and swimming depth for captive fish to potential avoidance and changes in swimming velocity and diurnal activity patterns for free-swimming animals. However, the extent and duration of behavioral responses to seismic surveys remain largely unexplored for most fish species. In this study, we investigated the effect of a full-scale seismic survey on the movement behavior of free-swimming Atlantic cod (Gadus morhua). We found that cod did not leave the detection area more than expected during the experimental survey but that they left more quickly from 2 days to 2 weeks after the survey. Furthermore, during the exposure, cod decreased their activity, with time spent being “locally active” (moving small distances, showing high body acceleration) becoming shorter, and time spent being “inactive” (moving small distances, having low body acceleration) becoming longer. Additionally, diurnal activity cycles were disrupted with lower locally active peaks at dusk and dawn, periods when cod are known to actively feed. The combined effects of delayed deterrence and activity disruption indicate the potential for seismic surveys to affect energy budgets and to ultimately lead to population-level consequences.

Hybrid millidecade spectra: A practical format for exchange of long-term ambient sound data (PDF)

Martin, S.B., B.J. Gaudet, H. Klinck, P.J. Dugan, J.L. Miksis-Olds, D.K. Mellinger, D.A. Mann, O. Boebel, C.C. Wilson, D.W. Ponirakis, and H. Moors-Murphy

JASA Express Letters 1(1): 011203 (2021)

DOI: 10.1121/10.0003324

This Letter proposes a frequency scaling for processing, storing, and sharing high-bandwidth, passive acoustic spectral data that optimizes data volume while maintaining reasonable data resolution. The format is a hybrid that uses 1 Hz resolution up to 455 Hz and millidecade frequency bands above 455 Hz. This hybrid is appropriate for many types of soundscape analysis, including detecting different types of soundscapes and regulatory applications like computing weighted sound exposure levels. Hybrid millidecade files are compressed compared to the 1 Hz equivalent such that one research center could feasibly store data from hundreds of projects for sharing among researchers globally.

Where, when, and why do western North Atlantic humpback whales begin to sing? (PDF)

Kowarski, K., S. Cerchio, H. Whitehead, and H. Moors-Murphy

Bioacoustics 31: 450-469 (2021)

DOI: 10.1080/09524622.2021.1972838

At the onset of the winter breeding season, male humpback whales begin a prominent breeding behaviour, singing. Early songs are produced on summer feeding grounds prior to migration, but little is known about the proximate cues for the initiation of this behaviour, nor where or when it begins. We document the phenology of humpback whale singing along the western North Atlantic coast ranging from Newfoundland and Labrador, Canada to Massachusetts, USA through the fall-winter of 2015-16 (seven stations) and 2016-17 (three stations). Acoustic data from static recorders were categorised as containing humpback whale non-song calls, song fragments, or full songs. First heard in September, singing occurred throughout the fall-winter, but was not regular until October. Latitude, temperature, photoperiod, sea surface pressure, and wind speed were considered as potential explanatory variables for four definitions of song onset using forward stepwise regression. Final models included the environmental variables with photoperiod negatively correlated to singing (coefficient = −657; p-value = 0.04). Reliable environmental cues, such as photoperiod, may produce a heritable physiological response, resulting in whales acquiring the capacity and motivation to sing, with the subsequent timing and nature of song production influenced by other factors.

In-air and underwater sounds of hooded seals during the breeding season in the Gulf of St. Lawrence (PDF)

Frouin-Mouy, H. and M.O. Hammill

J. Acoust. Soc. Am. 150: 281–293 (2021)

DOI: 10.1121/10.0005478

The hooded seal is a migratory species inhabiting the North Atlantic. Passive acoustic monitoring (PAM) conducted over spatial scales consistent with their known and potential habitat could provide insight into seasonal and spatial occurrence patterns of this species. Hooded seal airborne and underwater acoustic signals were recorded during the breeding season on the pack ice in the Gulf of St. Lawrence in March 2018 to better characterize their acoustic repertoire (notably underwater calls). In-air and underwater signals were classified into 12 and 22 types, respectively. Signals produced by males through the inflation and deflation of the proboscis and septum were the predominant sounds heard on the ice surface. Five of the 22 underwater signals were proboscis and septum noises. The remaining underwater signals (17) were categorized as voiced calls and further analyzed using two classification methods. Agreement with the initial subjective classification of voiced calls was high (77% for classification tree analysis and 88% for random forest analysis), showing that 12–13 call types separated well. The hooded seal's underwater acoustic repertoire is larger and more diverse than has been previously described. This study provides important baseline information necessary to monitor hooded seals using PAM.

Influence of propellers and operating conditions on underwater radiated noise from coastal ferry vessels

McIntyre, D., W. Lee, H. Frouin-Mouy, D. Hannay, and P. Oshkai

Ocean Engineering 232: 109075 (2021)

DOI: j.oceaneng.2021.109075

Underwater radiated noise from marine ships represents the largest source of anthropogenic noise in oceans the world over, representing a substantial and persistent stressor to the health of marine ecosystems. The radiated noise from vessels can often be related to their velocity, and slowing vessels in critical habitat areas has been shown to reduce the average level of ambient noise in those regions; however, universal speed limits ignore the significant variation in speed-noise behaviour between vessels. We investigated the underwater radiated noise signatures and levels from eight coastal ferry vessels each operating at a range of speeds in order to examine the underlying causes of the atypical speed-noise correlations. The analysis revealed discrete patterns associated with speed ranges, suggesting that the increase in noise radiated at low velocities that was observed from some vessels was the result of a change in the regime of the physical mechanism generating the sound. Propeller-induced cavitation is the strongest possible explanation for noise of this type. The present results suggest that controllable-pitch propellers may be susceptible to changes in cavitation regimes resulting in increased radiated noise when operated under reduced loads, a finding that corroborates previous model-scale experimental evidence of the same behaviour.

Localizing Sources Using a Network of Synchronized Compact Arrays (PDF)

Urazghildiiev, I.R. and D.E. Hannay

IEEE J. Ocean. Eng. 46: 1302-1312 (2021)

DOI: 10.1109/JOE.2021.3082758

The problem of passive acoustic estimating the position of a source using a network of synchronized underwater compact arrays is considered. Maximum-likelihood estimators using angle of arrival (AOA), time difference of arrival (TDOA), as well as a combination of AOA/TDOA estimates are developed. The localization accuracy provided by the AOA-based, TDOA-based, and hybrid estimators is evaluated using Cramér–Rao bounds, statistical simulations, and in situ test. Test results demonstrated that the efficiency of AOA-based and TDOA-based estimators strongly depends on variances of the AOA and TDOA estimates. Relative efficiency of the hybrid estimator is higher than any of the AOA-based and TDOA-based algorithms.

Marine soundscape variation reveals insights into baleen whales and their environment: a case study in central New Zealand (PDF)

Warren, V.E., C. McPherson, G. Giorli, K.T. Goetz, and C.A. Radford

Royal Society Open Science 8(3): 201503 (2021)

DOI: 10.1098/rsos.201503

Baleen whales reliably produce stereotyped vocalizations, enabling their spatio-temporal distributions to be inferred from acoustic detections. Soundscape analysis provides an integrated approach whereby vocal species, such as baleen whales, are sampled holistically with other acoustic contributors to their environment. Acoustic elements that occur concurrently in space, time and/or frequency can indicate overlaps between free-ranging species and potential stressors. Such information can inform risk assessment framework models. Here, we demonstrate the utility of soundscape monitoring in central New Zealand, an area of high cetacean diversity where potential threats are poorly understood. Pygmy blue whale calls were abundant in the South Taranaki Bight (STB) throughout recording periods and were also detected near Kaikōura during autumn. Humpback, Antarctic blue and Antarctic minke whales were detected in winter and spring, during migration. Wind, rain, tidal and wave activity increased ambient sound levels in both deep- and shallow-water environments across a broad range of frequencies, including those used by baleen whales, and sound from shipping, seismic surveys and earthquakes overlapped in time, space and frequency with whale calls. The results highlight the feasibility of soundscape analysis to quantify and understand potential stressors to free-ranging species, which is essential for conservation and management decisions.