Estimating the motion parameters of sound sources using a network of compact arrays (PDF)

Urazghildiiev, I.R

IEEE Journal of Oceanic Engineering 48(4): 1270–1279 (2023)

DOI:  10.1109/JOE.2023.3288975

In this article, the problem of employing passive acoustics to estimate the position, speed, and heading angle of a moving source using a network of underwater compact arrays is considered. Maximum-likelihood (ML) estimators using angle-of-arrival (AOA), time-difference-of-arrival (TDOA), and a combination of AOA/TDOA estimates are developed. The estimation accuracy provided by the AOA-based, TDOA-based, and hybrid estimators is evaluated using Cramér–Rao bounds (CRB), statistical simulations, and an in situ test. Test results demonstrate that practical accuracy provided by the proposed algorithms strongly depends on deviations in speed and heading angles from their average values.

Anatomical measurements of dugong auditory systems for evoked potential studies (PDF)

Ketten, D.R., K. Lucke, and J. M. Lanyon

The Effects of Noise on Aquatic Life (2024)

DOI: 10.1007/978-3-031-10417-6_77-1

Dugongs (Dugong dugon) are listed globally as “Vulnerable to Extinction,” raising substantial concerns for their welfare. Underwater sounds are potentially critical survival cues for dugongs, but there are few data on dugong hearing, much less on how ambient sounds, natural or anthropogenic, may affect dugongs.

A project was undertaken in 2022 to obtain auditory evoked potential (AEP) responses in wild Australian dugongs during health assessments. In support of that study, a parallel effort investigated cranial and auditory system anatomy of dugongs to determine optimal placements of hydrophones for delivering sound stimuli and of the recording electrodes for AEP response measurements. Relevant anatomical measurements were obtained from computerized tomography (CT) imaging and dissection of three dugong specimens collected in a previous study of stranded dugongs from northern Australia in collaboration with Dr. Helene Marsh and Dr. Donna Kwan of James Cook University.

The study demonstrated three external landmarks that allow triangulation of surface points closest to the middle ear, inner ear, auditory nerve, and brainstem of dugongs. These anatomical landmarks are proportionately spaced across animals, allowing placement calculations for animals tested in field studies regardless of body mass, age, and sex.

Measuring hearing sensitivity of wild Dugongs in Moreton Bay, Australia (PDF)

Lucke, K., J.M. Lanyon, and D.R. Ketten

The Effects of Noise on Aquatic Life (2024)

DOI: 10.1007/978-3-031-10417-6_94-1

A pilot study to measure hearing capabilities in wild dugongs (Dugong dugon) was conducted in Moreton Bay, Australia. To successfully obtain hearing measurements, an approach for measuring auditory responses in wild dugongs using neurophysiological measures was developed. Preparatory to the measurements, basic head anatomy of dugongs was investigated to optimize placements of the acoustic transmitting and receiving neuronal sensors. Three dugongs were selected as suitable candidates for the auditory measurements based on the results of a preliminary health assessment. Following the absence of observable responses by the first animal, click and sinusoidally amplitude modulated signals were used as acoustic stimuli for the second and third animals, eventually resulting in reproduceable and scalable neuronal responses. The recorded neuronal signals represent a proof of concept for the first auditory measurement in wild dugongs. Valuable insights were gathered during the pilot study allowing optimization of the procedure for a planned follow-up study which will test a larger number of wild dugongs.

Observed transmissions and ocean-ice-acoustic coupled modelling in the Beaufort Sea (PDF)

Barchay, D.R., S.B. Martin, P.C., Hines, J.M. Hamilton, M. Zykov, T. Deveau, P. Borys

The Journal of the Acoustical Society of America 154, 28-47 (2023)

DOI: 10.1121/10.0019942

An ocean-ice-acoustic coupled model is configured for the Beaufort Sea. The model uses outputs from a data assimilating global scale ice-ocean-atmosphere forecast to drive a bimodal roughness algorithm for generating a realistic ice canopy. The resulting range-dependent ice cover obeys observed roughness, keel number density, depth, and slope, and floe size statistics. The ice is inserted into a parabolic equation acoustic propagation model as a near-zero impedance fluid layer along with a model defined range-dependent sound speed profile. Year-long observations of transmissions at 35 Hz from the Coordinated Arctic Acoustic Thermometry Experiment and 925 Hz from the Arctic Mobile Observing System source were recorded over the winter of 2019–2020 on a free-drifting, eight-element vertical line array designed to vertically span the Beaufort duct. The ocean-ice-acoustic coupled model predicts receive levels that reasonably agree with the measurements over propagation ranges of 30–800 km. At 925 Hz, seasonal and sub-seasonal ocean and ice driven variations of propagation loss are captured in the data and reproduced in the model.

On definitions of signal duration, evaluated on close-rangeairgun signals (PDF)

Muller J. A., R, M. A. Ainslie, and M. B. Halvorsen

DOI: 10.1121/10.0019747

Journal of the Acoustical Society of America 153, 3513–3521 (2023)

In impact assessments for underwater noise, the duration of a transient signal is often expressed by the 90%-energy signal duration s90%. Consequently, the rms sound pressure is computed over this duration. Using a large set of measurements on marine-seismic airgun signals, it is shown that s90% is often very close to the interval between the primary and secondary pulse (the bubble period) or a small integer multiple thereof. In this situation s90% is a measure of the duration of the relative silence between primary and secondary peaks, which is not the intended measure. Rarely, s90% quantifies the duration of the main peak, leading to a much lower value of s90%. Since the number of peaks included in s90% is sensitive to the nature of the signal, relatively small differences in the signal lead to large differences in s90%, causing instability in any metric based on s90%, e.g., the rms sound pressure. Alternative metrics are proposed that do not exhibit these weaknesses. The consequences for the interpretation of sound pressure level of a transient signal, and the benefits of using a more stable metric than s90% are demonstrated. VC 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.

Impact of mobile offshore drilling units on Odontocetes (PDF)

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

The Effects of Noise on Aquatic Life (2023)

DOI: 10.1007/978-3-031-10417-6_103-1

Anthropogenic sounds can negatively impact marine mammals, limiting their ability to effectively forage or communicate, displacing them from a portion of their range, or causing physical harm. To date, potential impacts of sounds associated with mobile offshore drilling units (MODUs) on cetaceans have not been investigated. Acoustic recordings were collected at 1–2 km and 20–40 km from three MODUs to investigate variation in the acoustic occurrence of odontocetes with distance from the MODUs.

The West Aquarius MODU, West Hercules MODU, and Stena Forth MODU acoustic measurements lasted for at least 2 months each and included at least 1 min in 20 with high enough sampling rates to record the echolocation clicks of delphinids, beaked whales, and sperm whales. Recordings in the general area of the operations from previous years were also available. A comparison of the odontocete acoustic presence near the operations to the acoustic presence at longer distances showed a substantial difference in acoustic occurrence for dolphins, pilot whales, and beaked whales that could not be attributed to masking of detections by sounds from the operations.

Measurements of underwater radiated noise from mobile offshore drilling units (PDF)

Austin, M.E., S.B. Martin, C.R. McPherson

The Effects of Noise on Aquatic Life (2023)

DOI: 10.1007/978-3-031-10417-6_7-1

Mobile offshore drilling units (MODUs) are used to drill oil and gas wells in the ocean. For deeper water operations, there are two common forms of MODUs: semisubmersible rigs and drillships. Over the past several years, JASCO Applied Sciences measured MODU drilling operations by semisubmersibles and drillships, including platforms that were moored with anchors or that held position using dynamic positioning (DP) thrusters. The MODUs were accompanied by support vessels on standby, with additional vessels conducting resupply operations during the drilling campaigns. The measurements were performed in response to regulators requesting verification of the vessel source levels and the distances where the sounds were expected to either injure or disturb marine life.

Overall, drillships had higher source levels than semisubmersibles. Moored platform sound levels decreased with drilling depth and hole diameter. The signatures of moored platforms featured tones from different types of rotating machinery. When platforms or nearby support vessels were holding station using DP, the tonal signatures were obscured by DP thruster sounds. All measurements of underwater radiated noise from platforms using DP contained sounds from ultrashort baseline (USBL) beacons at 25–27 kHz.

Measuring vessel underwater radiated noise in shallow water (PDF)

MacGillivray, A.O., S.B. Martin, M.A. Ainslie, J.N. Dolman, Z. Li, and G.A. Warner

The Journal of the Acoustical Society of America 153, 1506 (2023)

DOI: 10.1121/10.0017433

Performing reproducible vessel source level (SL) measurements is complicated by seabed reflections in shallow water. In deep water, with a hydrophone far from the seabed, it is straightforward to estimate propagation loss (PL) and convert sound pressure level (SPL) into SL using the method codified in the international standard ISO 17208-2 [International Organization for Standardization (ISO), Geneva, Switzerland (2019)]. Estimating PL is more difficult in shallow water because of the way that sound reflects from the seabed such that multiple propagation paths contribute to SPL. Obtaining reproducible SL measurements in shallow water requires straightforward and robust methods to estimate PL. From May to July 2021, a field experiment evaluated different methods of measuring vessel SL in shallow water. The same vessels were measured many times in water depths of 30, 70, and 180 m. In total, 12 079 SL measurements were obtained from 1880 vessel transits and 16 hydrophones, distributed across 3 moored vertical line arrays and 2 moored horizontal line arrays. The experiment confirmed that it is possible to obtain reproducible vessel SL estimates in shallow water comparable to within ±2.5 dB of ISO-compliant measurements in deep water and repeatable to within ±1.5 dB.

Vector acoustic properties of underwater noise from impact pile driving measured within the water column (PDF)

Dahl PH, A.O. MacGillivray, and R. Racca

Frontier Marine Science 10:1146095.

DOI: 10.3389/fmars.2023.1146095

Vector acoustic properties of the underwater noise originating from impact pile driving on steel piles has been studied, including the identification of features of Mach wave radiation associated with the radial expansion of the pile upon hammer impact. The data originate from a 2005 study conducted in Puget Sound in the U.S. state of Washington, and were recorded on a four-channel hydrophone system mounted on a tetrahedral frame. The frame system measured the gradient of acoustic pressure in three dimensions (hydrophone separation 0.5 m) from which estimates of kinematic quantities, such as acoustic velocity and acceleration exposure spectral density, were derived. With frame at a depth of 5 m in waters 10 m deep, the data provide an important look at vector acoustic properties from impact pile driving within the water column. Basic features of the Mach wave are observed in both dynamic (pressure) and kinematic measurements, most notably the delay time TT leading to spectral peaks separated in frequency by 1/T∼ 1061/T∼ 106 Hz, where TT equals the travel time of the pile radial deformation over twice the length of the pile. For the two piles studied at range 10 and 16 m, the strike-averaged sound exposure level (SEL) was ∼∼ 177 dB re 1μ1μPa2Pa2-s and the acceleration exposure level (AEL) was 122-123 dB re μμm2m2/s4/s4 s. The study demonstrates an approximate equivalence of observations based on dynamic and kinematic components of the underwater acoustic field from impact pile driving measured within the water column.

Methods to measure underwater sound sources from oil and gas activities (PDF)

De Jong, C.A.F., M.B. Halvorsen, D.E. Hannay, and M. A. Ainslie

The Effects of Noise on Aquatic Life (2023)

DOI: 10.1007/978-3-031-10417-6_37-1

In 2021, the International Association of Oil and Gas Producers (IOGP) published a report in which measurement procedures are described that enable the acoustic characterization of underwater sound sources associated with seismic acquisition, high-resolution geophysical surveys, and production of oil and gas. These procedures are designed to provide consistency and comparability of independently carried out measurements. An initial review of existing methods revealed that there was some commonality in reported measurements of airgun arrays and high-resolution geophysical sources, but very few reports or publications included all relevant parameters. Achieving comparability in measurements requires precise nomenclature and clear documentation of the various choices made concerning measurement geometry, instrumentation, and processing. The measurement procedures describe requirements and recommendations for equipment selection, calibration, placement in depth and range, sampling rates, and operational measurement procedures for the three source types. Signal analysis methods are specified, as well as reporting content and formats for the acoustic results and relevant metadata. Where possible, calculation procedures are described to determine source metrics from the measured acoustic field, which can be used as input for environmental impact assessments for future projects.

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

Frouin‑Mouy, H., X. Mouy, J. Pilkington, E. Küsel,L. Nichol, T. Doniol‑Valcroze, and L. Lee

Scientific Reports 12, 19272 (2022).

DOI: 10.1038/s41598-022-22069-4

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.

Acoustic monitoring and analyses of air gun, pile driving, vessel, and ambient sounds during the 2015 seismic surveys on the Sakhalin shelf (PDF)

Rutenko, A.N., M.M. Zykov, V.A. Gritsenko, M. Yu. Fershalov, M.R. Jenkerson, D.S. Manulchev, R. Racca, and V.E. Nechayuk

Environmental Monitoring and Assessment 194 (Suppl 1): 744 (2022)

DOI: 10.1007/s10661-022-10021-y

During the summer of 2015, four 4D seismic surveys were conducted on the northeastern Sakhalin shelf near the feeding grounds of the Korean-Okhotsk (western) gray whale (Eschrichtius robustus) population. In addition to the seismic surveys, onshore pile driving activities and vessel operations occurred. Forty autonomous underwater acoustic recorders provided data in the 2 Hz to15 kHz frequency band. Recordings were analyzed to evaluate the characteristics of impulses propagating from the seismic sources. Acoustic metrics analyzed comprised peak sound pressure level (PK), mean square sound pressure level (SPL), sound exposure level (SEL), T100%, T90% (the time intervals that contain the full and 90% of the energy of the impulse), and kurtosis. The impulses analyzed differed significantly due to the variability and complexity of propagation in the shallow water of the northeast Sakhalin shelf. At larger ranges, a seismic precursor propagated in the seabed ahead of the acoustic impulse, and the impulses often interfered with each other, complicating analyses. Additional processing of recordings allowed evaluation and documentation of relevant metrics for pile driving, vessel sounds, and ambient background levels. The computed metrics were used to calibrate acoustic models, generating time resolved estimates of the acoustic levels from seismic surveys, pile driving, and vessel operations on a gray whale distribution grid and along observed gray whale tracks. This paper describes the development of the metrics and the calibrated acoustic models, both of which will be used in work quantifying gray whale behavioral and distribution responses to underwater sounds and to determine whether these observed responses have the potential to impact important parameters at the population level (e.g., reproductive success).

Gray whale density during seismic surveys near their Sakhalin feeding ground (PDF)

Gailey, G., M.M. Zykov, O. Sychenko, A. Rutenko, A.L. Blanchard, L.A.M. Aerts, and R.H. Melton

Environmental Monitoring and Assessment 194 (Suppl 1): 739 (2022)

DOI: 10.1007/s10661-022-10025-8

Oil and gas development off northeastern Sakhalin Island, Russia, has exposed the western gray whale population on their summer-fall foraging grounds to a range of anthropogenic activities, such as pile driving, dredging, pipeline installation, and seismic surveys. In 2015, the number of seismic surveys within a feeding season surpassed the level of the number and duration of previous seismic survey activities known to have occurred close to the gray whales’ feeding ground, with the potential to cause disturbance to their feeding activity. To examine the extent that gray whales were potentially avoiding areas when exposed to seismic and vessel sounds, shore-based teams monitored the abundance and distribution of gray whales from 13 stations that encompassed the known nearshore feeding area. Gray whale density was examined in relation to natural (spatial, temporal, and prey energy) and anthropogenic (cumulative sound exposure from vessel and seismic sounds) explanatory variables using Generalized Additive Models (GAM). Distance from shore, water depth, date, and northing explained a significant amount of variation in gray whale densities. Prey energy from crustaceans, specifically amphipods, isopods, and cumaceans also significantly influenced gray whale densities in the nearshore feeding area. Increasing cumulative exposure to vessel and seismic sounds resulted in both a short- and longer-term decline in gray whale density in an area. This study provides further insights about western gray whale responses to anthropogenic activity in proximity to and within the nearshore feeding area. As the frequency of seismic surveys and other non-oil and gas anthropogenic activity are expected to increase off Sakhalin Island, it is critical to continue to monitor and assess potential impacts on this endangered population of gray whales.

Real-time acoustic monitoring with telemetry to mitigate potential effects of seismic survey sounds on marine mammals: a case study offshore Sakhalin Island (PDF)

Rutenko, A.N., M.M. Zykov, V.A. Gritsenko, M.Y. Fershalov, M.R. Jenkerson, R. Racca, and V.E. Nechayuk

Environmental Monitoring and Assessment 194 (Suppl 1): 745 (2022)

DOI: 10.1007/s10661-022-10019-6

Exxon Neftegas Ltd. (ENL) carried out three 4D seismic surveys during the summer of 2015. Seismic operations in two of these fields (Odoptu and Chayvo) ensonified the nearshore feeding area of Korean-Okhotsk (western) gray whales (Eschrichtius robustus), potentially disturbing feeding activities. Following model-based optimization of the source design to minimize its lateral acoustic footprint, pre-season modeling was used to compute the acoustic exposure along each survey line. Real-time acoustic data facilitated implementation of mitigation measures aimed to minimize disturbance of whales. Acoustic data originated from underwater recorders deployed on the seafloor. Two complementary approaches were used to transmit recorded sound data to a computer housed at the Central Post (CP), where decisions regarding mitigation shut downs were made. In the first approach, a limited bandwidth (2–2000 Hz) sampling of the data was transmitted via cable to a surface buoy, which relayed these data to a shore station up to 15 km away via digital VHF telemetry. At the shore station, acoustic impulses from the seismic surveys were processed to compute impulse characteristics in the form of estimates of sound exposure level and peak sound pressure level, as well as one-minute-average 1/3-octave power spectral density coefficients, which were then transmitted to the CP via the internet. In the second, the pulse characteristics were computed through algorithms running on an onboard processor in each recorder’s surface buoy and sent directly to the CP computer via an Iridium satellite uplink. Both methods of data transfer proved viable, but Iridium transmission achieved the goal without the need for any shore based relay stations and is therefore more operationally efficient than VHF transmission. At the CP, analysts used the real-time acoustic data to calibrate and adjust the output of pre-season acoustical model runs. The acoustic footprint for the active seismic source, advancing synchronously with the motion of the seismic vessel and changing as the sound propagation environment changed, was computed from the calibrated and adjusted model output and integrated through the software Pythagoras with locations of gray whales provided by shore-based observers. This enabled analysts to require air gun array shutdowns before whales were exposed to mean square sound pressure levels greater than the behavioral response threshold of 163 dB re 1 μPa^2. The method described here provides a realistic means of mitigating the possible effects of air guns at a behavioral response level, whereas most seismic surveys rely on pre-established mitigation radii to manage the risk of injury to a whale.

Seismic surveys near gray whale feeding areas off Sakhalin Island, Russia: assessing impact and mitigation effectiveness (PDF)

Aerts, L.A.M., M.R. Jenkerson, V.E. Nechayuk, G. Gailey, R. Racca, A.L. Blanchard, L.K. Schwarz, and H.R. Melton

Environmental Monitoring and Assessment 194 (Suppl 1): 746 (2022)

DOI: 10.1007/s10661-022-10016-9

In 2015, two oil and gas companies conducted seismic surveys along the northeast coast of Sakhalin Island, Russia, near western gray whale (Eschrichtius robustus) feeding areas. This population of whales was listed as Critically Endangered at the time of the operations described here but has been reclassified as Endangered since 2018. The number and duration of the 2015 seismic surveys surpassed the level of previous seismic survey activity in this area, elevating concerns regarding disturbance of feeding gray whales and the potential for auditory injury. Exxon Neftegas Limited (ENL) developed a mitigation approach to address these concerns and, more importantly, implemented a comprehensive data collection strategy to assess the effectiveness of this approach. The mitigation approach prioritized completion of the seismic surveys closest to the nearshore feeding area as early in the season as possible, when fewer gray whales would be present. This was accomplished by increasing operational efficiency through the use of multiple seismic vessels and by establishing zones with specific seasonal criteria determining when air gun shutdowns would be implemented. These zones and seasonal criteria were based on pre-season modeled acoustic footprints of the air gun array and on gray whale distribution data collected over the previous 10 years. Real-time acoustic and whale sighting data were instrumental in the implementation of air gun shutdowns. The mitigation effectiveness of these shutdowns was assessed through analyzing short-term behavioral responses and shifts in gray whale distribution due to sound exposure. The overall mitigation strategy of an early survey completion was assessed through bioenergetics models that predict how reduced foraging activity might affect gray whale reproduction and maternal survival. This assessment relied on a total of 17 shore-based and 5 vessel-based teams collecting behavior, distribution, photo-identification, prey, and acoustic data. This paper describes the mitigation approach, the implementation of mitigation measures using real-time acoustic and gray whale location data, and the strategy to assess impacts and mitigation effectiveness.

Western gray whale behavioral response to seismic surveys during their foraging season (PDF)

Gailey, G., O. Sychenko, M.M. Zykov, A. Rutenko, A. Blanchard, and R.H. Melton

Environmental Monitoring and Assessment 194 (Suppl 1): 740 (2022)

DOI: 10.1007/s10661-022-10023-w

Gray whales utilizing their foraging grounds off northeastern Sakhalin Island, Russia, have been increasingly exposed to anthropogenic activities related to oil and gas development over the past two decades. In 2015, four seismic vessels, contracted by two operators, conducted surveys near and within the gray whale feeding grounds. Mitigation and monitoring plans were developed prior to the survey and implemented in the field, with real-time data transfers to assist the implementation of measures aimed at minimizing impacts of acoustic exposure. This study examined the behavioral response of gray whales relative to vessel proximities and sounds generated during seismic exploration. Five shore-based teams monitored gray whale behavior from 1 June to 30 September using theodolite tracking and focal follow methodologies. Behavioral data were combined with acoustic and benthic information from studies conducted during the same period. A total of 1270 tracks (mean duration = 0.9 h) and 401 focal follows (1.1 h) were collected with gray whales exposed to sounds ranging from 59 to 172 dB re 1 μPa^2 SPL. Mixed models were used to examine 13 movement and 10 respiration response variables relative to “natural,” acoustic, and non-acoustic explanatory variables. Water depth and behavioral state were the largest predictors of gray whale movement and respiration patterns. As vessels approached whales with increasing seismic/vessel sound exposure levels and decreasing distances, several gray whale movement and respiration response variables significantly changed (increasing speed, directionality, surface time, respiration intervals, etc.). Although the mitigation measures employed could have reduced larger/long-term responses and sensitization to the seismic activities, this study illustrates that mitigation measures did not eliminate behavioral responses, at least in the short-term, of feeding gray whales to the activities.

Seasonal song ontogeny in western North Atlantic humpback whales: drawing parallels with songbirds (PDF)

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

Bioacoustics (Advance Online Publication)

DOI: 10.1080/09524622.2022.2122561

The use of song as a reproductive display is common in the animal kingdom; however, for many taxa, little is known of song ontogeny. Male humpback whales produce elaborate songs on low latitude breeding grounds in winter and begin to sing on high latitude feeding grounds in late summer, yet songs from the two locations are rarely compared. Seasonal song ontogeny in western North Atlantic humpback whales was explored by comparing songs recorded in high latitude feeding grounds (Canada in spring 2016 and fall 2016 to winter 2017) with songs recorded in a low latitude breeding ground (Dominican Republic in winter and spring 2017). High-quality song samples were selected, and every phrase annotated. Song theme order, song duration, and number of phrase repetitions were compared across samples. The most variability in theme order was found between November and December in the Canadian recordings, a phase in song ontogeny that may be important for learning. Song duration gradually increased, via an increase in phrase repetitions, through the breeding season, before peaking in the Dominican Republic between January and March. A comparison to oscine bird seasonal song ontogeny revealed many similarities, highlighting potentially similar physiological processes between humpback whales and songbirds.

Minimal COVID-19 quieting measured in the deep offshore waters of the U.S. Outer Continental Shelf (PDF)

Miksis-Olds, J.L., B.S. Martin, K. Lowell, C. Verlinden, and K.D. Heaney

JASA Express Letters 2: 090801 (2022)

DOI: 10.1121/10.0013999

Using a 2-year time series (2019–2020) of 1-min sound pressure level averages from seven sites, the extension of COVID-related quieting documented in coastal soundscapes to deep (approximately 200–900 m) waters off the southeastern United States was assessed. Sites ranged in distance to the continental shelf break and shipping lanes. Sound level decreases in 2020 were observed at sites closest to the shelf break and shipping lanes but were inconsistent with the timing of shipping changes related to a COVID-19 slowdown. These observations are consistent with increased numbers of vessel tracks in 2020 compared to 2019 at a majority of sites.

A functional regression analysis of vessel source level measurements from the Enhancing Cetacean Habitat and Observation (ECHO) database (PDF)

MacGillivray, A.O., L.M. Ainsworth, J. Zhao, J.N. Dolman, D.E. Hannay, H. Frouin-Mouy, K.B. Trounce, and D.A. White

Journal of the Acoustical Society of America 152: 1547-1563 (2022)

DOI: 10.1121/10.0013747

Measurements of the source levels of 9880 passes of 3188 different large commercial ships from the Enhancing Cetacean Habitat and Observation (ECHO) program database were used to investigate the dependencies of vessel underwater noise emissions on several vessel design parameters and operating conditions. Trends in the dataset were analyzed using functional regression analysis, which is an extension of standard regression analysis and represents a response variable (decidecade band source level) as a continuous function of a predictor variable (frequency). The statistical model was applied to source level data for six vessel categories: cruise ships, container ships, bulk carriers, tankers, tugs, and vehicle carriers. Depending on the frequency band and category, the functional regression model explained approximately 25%–50% of the variance in the ECHO dataset. The two main operational parameters, speed through water and actual draft, were the predictors most strongly correlated with source levels in all of the vessel categories. Vessel size (represented via length overall) was the design parameter with the strongest correlation to underwater radiated noise for three categories of vessels (bulkers, containers, and tankers). Other design parameters that were investigated (engine revolutions per minute, engine power, design speed.

Cetacean acoustic occurrence on the US Atlantic Outer Continental Shelf from 2017 to 2020 (PDF)

Kowarski, K.A., S.B. Martin, E.E. Maxner, C.B. Lawrence, J.J.-Y. Delarue, and J.L. Miksis-Olds

Marine Mammal Science (Advanced Online Publication)

DOI: 10.1111/mms.12962

Long-term distribution data for cetaceans are lacking, inhibiting the ability of management bodies to assess trends and react appropriately. Such is true even along the US Atlantic Outer Continental Shelf (OCS) where previous passive acoustic monitoring programs have laid the groundwork for monitoring cetacean occurrence over a multidecadal scale. Here, we continue and expand the scope of previous acoustic programs, providing a synopsis of the monthly cetacean acoustic occurrence from late 2017 to late 2020. Acoustic data were collected using bottom-mounted autonomous recorders located at seven stations along the OCS in depths of 212–900 m. Automated cetacean vocalization detector-classifiers were applied, and the resulting automated detections directed the manual review of a subset of the data by analysts. Only manual detections informed the occurrence results. Six baleen whale species and at least eight toothed whale species occurred in the region with diversity increasing in winter. In considering previous monitoring program results, we found evidence that some mysticete whales are spending less time in the region annually, confirmed that some species occur farther offshore than previously reported, and identified two previously unreported areas utilized by beaked whales. For effective species management, these findings must be considered, and monitoring programs continued.