Underwater Blast Noise Measurements in Very Shallow Water

Jorge E. Quijano

IEEE Journal of Oceanic Engineering

DOI: 10.1109/JOE.2026.3693581

This article presents measurements and a model-based analysis of the acoustic noise generated by underwater charges (of weights 0.78–13.28 kg TNT equivalent) detonated in very shallow water (≤4-m depth) within a bay with a limited line-of-sight acoustic path toward open and deeper waters. Four bottom-mounted and one mid-water acoustic recorders at ranges 70–1000 m (water depths 4–60 m) were used to measure blast signatures of 48 detonations. Measurements at close range allowed for characterization of the frequency-dependent performance of a bubble curtain mitigation system, and verification of the agreement between the measured data and a theoretical model of an underwater explosion. Measurements at longer ranges provided empirical curves of the peak (PK) level and sound exposure level (SEL) as a function of range, which are more representative for acoustically enclosed locations than current models for confined detonations found in the literature. The measurements indicate strong attenuation outside the bay of the high-frequency oscillations characteristic of the blast shockwave, likely due to the effect of bathymetry features. Modeling of blast noise using the parabolic equation method successfully represented the PK and SEL characteristics of the blasts, but also highlighted the need to refine the seabed geoacoustic model and the bathymetry of the area.

From simple to sophisticated: characterization of new signals in the expanding vocal repertoire of the East Indian Ocean pygmy blue whale

Jolliffe, C.D., C.R. McPherson, R.D. McCauley, and G. Genty

Frontiers in Marine Science 13: 1821993 (2026)

DOI: 10.3389/fmars.2026.1821993

In an underwater world, acoustic signaling is an important aspect of the social communication of marine mammal species with the complexity of a species’ vocal repertoire often considered to reflect the social complexity of the population. The acoustic behavior of blue whales is relatively well studied, though much of what is known is limited to the characteristically loud, low frequency songs that are believed to be produced as a reproductive display by male animals. Blue whales are known to produce song units outside of stereotypical song sequences, along with short duration down swept signals known as ‘D calls’ leading researchers to believe their acoustic communication, and by proxy their social cognition is relatively less complex when compared to other baleen whales such as humpback and bowhead whales. Drawing from a multidecadal data set of acoustic recorders deployed throughout the migratory range of blue whales, this paper characterizes four previously undescribed signals for the East Indian Ocean pygmy blue whales and presents the first known evidence of a large baleen whale producing these social sounds in stereotyped patterned sequences that bear similarity to song. This indicates a higher level of complexity in the social communication of blue whales than previously understood and provides further support that blue whales have a higher level of social cognition than has been considered previously.

Geographe bay as an opportunistic foraging habitat for baleen whales

Genty, G., C.D. Jolliffe, J.C. Perkins, and C.R. McPherson

Marine Biology 173(6): 91 (2026)

DOI: 10.1007/s00227-026-04830-9

Geographe Bay, located along the southwest coast of Western Australia, is increasingly recognised as a region of ecological significance for migrating baleen whales. This study investigates the bay’s potential role as an opportunistic feeding ground, particularly for species such as pygmy blue whales, which are typically considered krill specialists but may exhibit dietary flexibility under varying prey conditions. Over three years, drone-based observations recorded frequent whale defecation events, with faecal colouration consistently ranging from green to yellow, hues commonly associated with copepod digestion due to their carotenoid content. To examine the underlying prey availability, this study provides the first investigation of applying environmental DNA metabarcoding on plankton tows within bay to assess food availability for baleen whales. A total of 3.2 million quality-filtered reads were assigned to 600 amplicon sequence variants (ASVs), with Arthropoda dominating the assemblage. Notably, the copepod order Calanoida accounted for over 20% of total reads and up to 95% of the relative abundance at individual transects. Key calanoid taxa included Clausocalanus furcatus, Temora turbinata, and Paracalanus indicus, all consistently detected across the transects. The strong dominance of copepods, paired with behavioural evidence and faecal pigmentation, supports the hypothesis that whales may be actively feeding in Geographe Bay. These findings highlight Geographe Bay as not only a sheltered resting habitat, particularly for mother/calf pairs, but also an energetically valuable area that may help buffer whales against variable offshore prey availability.

Harbor Seal Behavior Under Shipping Noise: A Coupled Soundscape and Agent-Based Modeling Approach

Schaffeld, T., N. Maurer, A.S. Frankel, M.-N.R. Matthews, F. Campo, F. Pace, R. Racca, D.A. Nachtsheim, J.G. Schnitzler, U. Siebert, A. Gilles

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_125-1

The harbor seal (Phoca vitulina) is a sentinel top predator in the North Sea, inhabiting regions with high shipping activity. The rapid expansion of offshore wind farms (OWFs) is expected to further increase vessel traffic and underwater noise levels. The population-relevant behavioral consequences for harbor seals remain difficult to infer from tagging or visual surveys alone due to limited sample sizes, uneven coverage, and strong interindividual variability. This chapter presents a methodological framework that couples a large-scale, time-varying vessel noise soundscape with a telemetry-informed agent-based model (ABM) to explore potential future scenarios and mitigation efforts. Behavioral parameters were derived from 13 seals equipped with sound and movement sensing biologgers (DTAGs). Simulated animals were programmed with empirically derived parameters within four defined behavioral states, while the behavioral response functions are integrated as state-probability modifiers. Four scenarios are defined: a 2018 baseline, OWF-2030 and OWF-2050 traffic projections, and a speed-reduction policy within marine protected areas. The chapter provides a reproducible blueprint for constructing, parameterizing, and coupling soundscape and ABM components, enabling transparent what-if analyses beyond the reach of observational studies.

Empirical Relationships of Particle Motion and Pressure Soundscapes Along the US Eastern Continental Shelf

Jones, I.T., S.B. Martin, and J.L. Miksis-Olds

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_71-1

Acoustic particle motion is the primary sensory cue for fish and aquatic invertebrate hearing, yet underwater soundscape studies usually only report sound pressure levels. In the free field, particle motion magnitudes are often approximated by the ratio of sound pressure to acoustic impedance, which only requires single hydrophone pressure measurements. However, this scaling does not always apply near the seafloor, e.g., within ¼ acoustic wavelength, and never in the near field. This study compared measured sound pressure with measured particle motion from hydrophone arrays near the seafloor, at ten offshore sites on the US Eastern Continental Shelf ranging from the Gulf of Maine to Florida. In a 50 Hz decidecade band, >75% of measured particle motion level data exceeded sound pressure-impedance relationship estimates by over 3 dB, but this relationship was closer for 100 and 400 Hz decidecade bands. These relationships were region-specific, with the difference between measured particle motion and impedance relationship estimates being significantly lower (more negative) in the Gulf of Maine compared to southern sites. The results inform the potential error and overlooked variability of particle motion levels when only relying on sound pressure-impedance relationship estimates of particle motion, particularly over short (60 s) time integrations.

Sound Source Characterization for the World’s Largest Floating Offshore Wind Farm Hywind Tampen

Kriesell, H.J., A.S. Aniceto, R.D.J. Burns, K.M. Murvoll, J. Weissenberger, and S.J. Welch

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_79-1

Floating offshore wind farms represent a major advancement in renewable energy, enabling deployment in deepwater regions with stronger wind speeds. By 2035, they could account for up to one-third of offshore wind energy production. Hywind Tampen, in 2025 the world’s largest floating offshore wind farm, consists of 11 turbines with 94.6 MW total capacity, supporting the decarbonization of offshore oil and gas operations and serving as a platform for environmental research.

This work synthesizes findings from a sound source characterization study of operational turbines and assesses potential impacts on marine life. Using a directional hydrophone array within the wind farm and two omnidirectional hydrophones outside, the study identified narrowband sound emissions below 200 Hz, with prominent tones at ~25 and ~75 Hz. Median broadband source levels ranged from 156.5 to 163.8 dB re 1 μPa2m2, approximately 3 dB lower than levels recorded in a previous study for smaller turbines at the wind farm in Hywind Scotland, indicating a nonlinear relationship between turbine size and sound levels. Transient, impulsive sounds from the mooring system, previously reported at Hywind Scotland, were absent. Noise modeling showed no risk of injury to fish or marine mammals, with temporary threshold shifts occurring only within 150 m.

Sound Pressure Kurtosis Analysis for Impact Pile Driving Including Noise Mitigation

Peng, Y., H.Ö. Sertlek, and A. Tsouvalas

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_111-2

Impact pile driving generates intense and impulsive underwater noise, which can have significant effects on marine life. As sound waves propagate away from the pile–water and pile–soil interfaces, their pressure characteristics evolve under the influence of seabed and sea surface reflections. Understanding these sound pressure waveform properties is essential for selecting appropriate metrics to assess noise impact on marine species, particularly in relation to established environmental noise thresholds. Commonly used exposure metrics, such as cumulative sound exposure level (SEL) and peak sound pressure level (Lp, pk), provide important information but may not fully capture the complexity of noise impact across different species. Current impact assessments classify sound into only two mutually exclusive categories: impulsive and nonimpulsive. However, in reality, pulse length can vary with range and strike repetition rate. Given the impulsive nature of impact pile driving noise, this study investigates sound pressure kurtosis as a complementary metric to quantify the impulsiveness of noise signals across various sediment types. Furthermore, the study models the application of a noise mitigation system, specifically an air-bubble curtain, to evaluate its effect on noise emission and subsequent changes in kurtosis. The findings provide insights into the variability of sound pressure kurtosis in both mitigated and unmitigated cases, offering a comprehensive understanding of the acoustic characteristics of impact pile driving noise and its potential effects on marine ecosystems.

Future Ship Noise Scenarios: Probabilistic Forecasting Using Sound Maps

MacGillivray, A.O., T. Lloyd, H.Ö. Sertlek, and M.A. Ainslie

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_91-1

Underwater radiated noise (URN) from shipping is a pervasive marine pollutant that affects marine wildlife and habitats globally. Although various technological and operational measures have been proposed to reduce ship URN emissions, no mandatory international roadmap for their adoption exists, unlike for greenhouse gases. To address this gap, and to support environmental assessments and policymaking, the Navis Sonus (NAVISON) project, funded and managed by the European Maritime Safety Agency (EMSA), developed a new probabilistic method for rapidly generating URN foresight scenarios in European seas. This method produces forecasts by combining component sound map layers for different mitigation measures, according to joint probability tables for a given scenario. Separate sound map layers are generated for propeller cavitation noise and machinery (main and auxiliary engine) noise for several ship types. Spatially varying adjustment factors are associated with these layers for each distinct mitigation measure. Combining and adjusting these layers according to their joint probabilities offers managers a practical and efficient method to assess multiple scenarios without recalculating the underlying sound map layers. This approach provides a flexible marine spatial planning tool to enable evaluation of future URN management strategies.

What Is Vessel AIS Missing, and Why Do We Care?

Miksis-Olds, J.L., I.T. Jones, S.B. Martin, and K.D. Heaney

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_100-1

The global automatic identification system (AIS) enables the tracking and identification of vessels equipped with an AIS transponder. Vessel AIS detections are now being incorporated into soundscape models as one of many input parameters for sound level predictions that also include wind data, sound speed profile, seafloor composition, and bathymetry data. Recent efforts to compare soundscape models to acoustic measurements along the Atlantic Outer Continental Shelf (OCS) as part of the Atlantic Deepwater Ecosystem Observatory Network (ADEON) indicated site-specific differences between model predictions and sound level measurements. Hypothesized causal mechanisms of the model-measurement discrepancies include the spatial variability of seafloor composition impacting sound propagation, contribution of biological signals, and fidelity of vessel AIS data. This work directly addresses the question of vessel AIS fidelity by comparing AIS detections to passive acoustic detections with the understanding that not all vessels have an AIS transponder, and not all vessels with transponders have them turned on all the time. Results indicate that AIS fidelity is regionally specific and related to water depth, distance to shipping lane, and distance from land. Understanding the spatial variability of AIS fidelity will likely play an important role in future soundscape models and predictions.

From Behavioral Experiments to Fisheries Impacts: A Collaborative Evaluation of Seismic Survey Effects on Snow Crab and Groundfish

Morris, C.J., K. Nguyen, S.B. Martin, J. Hanlon, M. Piersiak, L. Gullage, M. Brake, J. Xu, D. Schornagel, et al.

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_104-1

To assess the impacts of seismic surveying on commercial fisheries offshore Newfoundland and Labrador, Canada, a series of collaborative studies was conducted with the fishing industry, oil and gas sector, and regulatory agencies. Here, an overview of marine seismic surveying in this region is provided with summary findings from experiments that incorporated industry-based seismic surveying. Field studies and complementary laboratory experiments showed undetectable or inconsistent effects of seismic surveying sound on snow crab and catch rates. In contrast, in situ observations on groundfish revealed species-specific behavioral changes in depth use, activity, or feeding patterns when a seismic survey vessel was operating within 60 km and when sound pressure levels exceeded 120 dB re 1 μPa2. Stakeholders were involved from planning stages and through the publication process, ensuring a focus on industry priorities which included realistic impacts of seismic surveying on commercial fishing grounds measured by controlled scientific field experiments. This collaborative approach produced accepted information to support the development of effective mitigation measures.

A Shift Towards Quantitative Cumulative Impact Assessments for Data Poor Marine Mammal Species: A Novel Approach for the Australian Context

Jolliffe, C.D., C.R. McPherson, and B.L. Southall

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_70-1

Marine fauna are vulnerable to a variety of acute and chronic stressors that act across varying spatial and temporal scales. The evaluation of the effect of these stressors requires consideration of the key threats and impact pathways, and the cumulative effect of anthropogenic pressures from all aspects of a project in concert with projects and long-term environmental change. Migratory species, particularly those that migrate across jurisdictional boundaries, may be exposed to pressures that compromise the recovery or health of the population that are not manageable under any one country’s legislation. Thus, the evaluation of cumulative impacts in a meaningful manner requires careful consideration of pressures at biologically meaningful spatial and temporal scales. Complex models predicting the population consequence of disturbance are increasingly being used to understand the potential significance of anthropogenic pressures on populations. While incredibly valuable, information to parametrize these models are not available for many species and populations. This chapter presents a semi-quantitative framework for the prediction of cumulative impacts on migratory marine mammal populations, with examples of how this may be applied using the Australian legislative and environmental context.

A ship noise rating system for underwater vessel noise reduction targets

Matthews, M.-N.R., J.N. Dolman, Z. Li, D.E. Hannay, and A. Cosandey-Godin

Marine Pollution Bulletin 228: 119483 (2026)

DOI: 10.1016/j.marpolbul.2026.119483

To support Canada's efforts in addressing underwater radiated noise (URN), a novel ship noise rating system was developed using the distribution of Radiated Noise Levels (RNL) measurements from over 49,000 transits of 5947 different ships. The system sets category-specific URN targets for nine ship categories and allows for URN evaluations using semi-controlled measurements made during routine ship operations. The approach extends the framework recommended by the national Underwater Vessel Noise Reduction Targets (UVNRT) Working Group, by using scaled RNL measurements to account for operating condition differences during measurements, and vessel dimensional differences within the same ship category. Ships are rated according to their URN quartile, allowing for future refinements as vessel RNL distributions evolve. Integration into automated monitoring tools, including the Boundary Pass Underwater Listening Station, facilitates cost-effective ratings of large numbers of ships and allows for data-driven refinements. The rating system contributes to Canada's development of ship URN management methods and target setting approaches and provides information to support the country's continued engagement at the International Maritime Organization (IMO) as international policy frameworks evolve.

From Documented Impacts to Cross-Taxa Perspectives: Towards a Framework for Assessing Vulnerability to Underwater Noise

Calonge, A., H. Eicher, A.-S. Krång, E. Debusschere, K. de Jong, K. McQueen, M.A. Ainslie, M. den Held, B. Rumes, J. Schnitzler

The Effects of Noise on Aquatic Life IV, Springer Nature Switzerland, Cham (2026)

DOI: 10.1007/978-3-031-94229-7_31-1

The escalating threat of aquatic noise to marine life underscores the urgency of setting scientifically grounded underwater noise limits. The Marine Strategy Framework Directive (MSFD) Descriptor 11 provides a policy lever to mitigate pressures arising from underwater noise. Achieving this goal requires that underwater radiated noise (URN) management shifts from a primarily pressure-based approach, focused on quantifying environmental sound pressure, towards a risk-based, ecosystem-oriented framework. This approach requires the selection of indicator species to relate noise vulnerability to impacts on populations. As part of the Interreg North Sea DEMASK project, the need for a multi-criteria framework for selecting indicator species from multiple taxa is introduced, with the overarching goal of assessing vulnerability to URN. The framework should combine a range of attributes related to the sound sensitivity and production of the animal, documented impacts of URN, and attributes describing the species’ general vulnerability related to life-history traits and socio-ecological status. Here, an overview of documented impacts of URN on mammals, fish, and invertebrates in the North Sea is presented, with the aim of motivating a multi-criteria, cross-taxa framework in selecting indicator species to support an adaptive and impact-focused vulnerability assessment.

Collaborating for Conservation: A Summary of Current and Future Directions in Blue Whale Science

Capri D. Joliffe, K. Edyvane, G. Genty, R. D. McCauley, C. McPherson, D. Barlow, B. L. Southall, L. Irvine, T. A. Branch, C. Jenner, M. Jenner, C. Burton, G. Whittome, P. Gill, G. Russell, B. Elsdon, J. Quintas

Aquatic Conservation: Marine and Freshwater Ecosystems (2026)

DOI: 10.1002/aqc.70331

The blue whale has been the focus of considerable research effort worldwide, yet significant gaps remain in the understanding of this species' ecology, behaviour, distribution and resilience to anthropogenic pressures. This review synthesizes insights from an international workshop held during the 25th Biennial Conference on the Biology of Marine Mammals 2024 hosted in Perth, Western Australia, which convened over 40 scientists specializing in blue whale research. The workshop aimed to consolidate the current state of knowledge, identify key research gaps and develop collaborative strategies to advance blue whale science with a focus on the local population of blue whales, the eastern Indian Ocean pygmy blue (EIOPB) whale. With research efforts into the species intensifying in recent years, there exist considerable opportunities for collaboration across research groups to avoid unnecessary duplication of effort and maximize the value of research efforts. Further, filling critical knowledge gaps that limit conservation and effective population management will require holistic studies focused not only on blue whales but on their prey species, krill and the mechanistic links between environmental drivers, krill and blue whales.

Estimating sediment properties using a new source level function for wind-driven underwater sound derived from long-term archival data (PDF)

Martin, S.B. and M. Siderius.

The Journal of the Acoustical Society of America 159(1): 300–314 (2026)

DOI:10.1121/10.0042217

Wind-driven breaking waves generate the background sound throughout the ocean. An accurate source level for wind-driven breaking waves is needed for estimating the ambient sound levels needed for sound exposure modeling, environmental assessments, and assessing the detection performance of sonars. Previous models applied a constant roll-off of sound levels at −16 dB/decade at all wind speeds, and these models' source levels were flat at frequencies below ∼1000 Hz due to a lack of measurements. Here, we analyzed 16 long-term archival datasets with limited anthropogenic sound sources to estimate the wind-driven source level down to 100 Hz. We estimated the site-specific areic propagation loss (APL) using a ray-based model and then added the APL to the median received levels at each wind speed to obtain the source level. An equation for the areic dipole source level is provided that increases as wind speed cubed, like most other air-ocean coupling processes. The model may be used to estimate sediment properties (given a wind speed history and measured sound levels) or to estimate wind speeds (given the sediment type and measured sound levels). It is well suited for estimating ambient sound levels from wind for soundscape modeling. An open-source implementation is available.

Origins of natural and anthropogenic sounds in a coastal, seasonally ice-covered, Antarctic marine soundscape (PDF)

Van Den Hoff, J., J. Delarue, V.E. Warren, C. McPherson, J.L. Lieser, H. Achurch, P. Virtue, and B.S. Miller

Marine Ecology Progress Series 757:17-36(2025)

DOI: 10.3354/meps14813

Baseline characterisation of the acoustic underwater environment is integral to understanding changes in the soundscape of a location. We used passive acoustic monitoring to investigate the soundscape of a seasonally ice-covered, shallow marine environment close to a permanently occupied research station in Prydz Bay, East Antarctica, from July (winter ice cover) 2021 through to February (summer open water) 2022. We applied a suite of automated detectors to detect sounds, with manual analysis of a subset of recordings to validate automated detections and characterise detector performance. From July until late November, the landfast ice cover had a dampening effect on mean daily ambient underwater sound pressure levels. The anthropophony of the ice-covered environment included contributions from aircraft landings and the movements of over-ice vehicles. The biophony was most influenced by the sounds of Weddell, crabeater and leopard seals and Antarctic minke whales. Mean daily sound levels increased immediately as the ice cover decreased and the sea surface became exposed to the effects of wind. The soundscape of the open-water/drifting pack-ice environment then altered to include noise from ship and small boat activities and vocalisations of killer whales and leopard and Ross seals. The results demonstrate a study site with high seasonality in natural sound sources and an unprecedented contribution of noise from human activities during the period of ice cover. There is likely a year-round contribution of anthropogenic noise to the Antarctic coastal marine environment close to research stations that are often co-located with regional hot-spots in faunal occurrences.

A new era for underwater noise impact prediction and management (PDF)

Capri D. Joliffe

Acoustics 2025 — Sounds of the Sunset Coast, Joondalup, Western Australia (2025)

AAS2025/papers/p85

There is global consensus that anthropogenic underwater noise represents a ubiquitous pressure to marine fauna, with an increasing number of studies seeking to understand both the short- and longterm impact of noise exposure on various species. As our understanding of the full extent of threats and pressure to marine fauna populations grows, so too does concern regarding the impacts and management of noise generating activities from offshore industries. Regulators, proponent and EIA practitioners for offshore industries are faced with the challenge of integrating new scientific understandings and increasingly complex impact prediction tools within existing regulatory and management frameworks. Often these management frameworks are based around standardised mitigation measures and set and forget management approaches. These frameworks are limited in their ability to be adaptable to real time information, and often blind to the nuances of operational and environmental context. While the level of environmental impact that is acceptable will vary between environmental and regulatory contexts, EIA and mitigation approaches are often based around demonstrating that impacts are reduced to a level that is as low as practicable and fail to demonstrate that impacts will be managed to achieve a specific environmental outcome. Over the past decade, the technical capability surrounding noise impact prediction has significantly evolved, this has occurred alongside a growing body of information to inform species distribution and habitat use. As our ability to predict the impacts and risks of underwater noise grows, it becomes increasingly evident that set and forget mitigation measures fall short in managing impacts to an acceptable level. This highlights the need for pragmatic underwater noise management frameworks that are sensitive to environmental and operational context and adaptive in their implementation. This paper will discuss best practices in underwater noise impact 

Underwater noise from on-land blasting (PDF)

Quijano, J.E. and M.W. Koessler

JASA Express Letters 5(11): 113601 (2025)

DOI: 10.1121/10.0039805

The production of underwater noise from on-land detonations is of concern, especially near sensitive marine mammal habitats. Despite this, there is a lack of public experimental data to analyze the characteristics of this type of noise. This paper quantifies noise from near-water land detonations, based on measurements obtained at Bentinck Island Demolition Range, Vancouver Island. The measurements show that ground-to-water propagation is dominant and that air-to-water coupling via evanescent waves is also present but mostly perceptible only at close distances from the detonation. A simple wavenumber integration model is used to illustrate the depth dependency of the evanescent field.

Fractional octave and fractional decade frequency bands in acoustics: Historical review and recommendations

Ainslie, M.A., S.P. Robinson, and R. Barham

The Journal of the Acoustical Society of America 158, 3631–3644 (2025)

DOI: 10.1121/10.0039684

Frequency bands are used in acoustical analysis to group sound energy into meaningful bands that simplify frequency-dependent behavior or characterize the spectrum in a manner relevant to the perception of sound. Early frequency bands were typically based on the octave (oct) and submultiples, such as one-third of an octave (1/3 oct), and such base 2 bands were first standardized in the 1950s. Ten 1/3 oct bands span a frequency range close to 1 decade (dec), which made it convenient to divide each decade into ten equal parts, resulting in the specification of 1/10 dec (decidecade) bands by modern standards, replacing the previous 1/3 oct bands. Because 1/10 dec is approximately equal to 1/3 oct, these decidecade bands are sometimes referred to as “one-third octave” bands, even in international standards, leading to ambiguity. The historical evolution of frequency bands in acoustics is reviewed and it is proposed to distinguish clearly between 1 oct and 3/10 dec (or equivalently between one-third of an octave and one-tenth of a decade).

Environmental drivers of foraging by deep-diving cetaceans: Roles of mesoscale oceanography and light-driven cycles (PDF)

Clay, T.A., G. Carroll, M.A. Cimino, J.L. Miksis-Olds, K.A. Kowarski, A.P. Lyons, P.I. Miller, T.S. Moore, J.D. Warren, E.L. Hazen.

Progress in Oceanography Vol.239, 2025

DOI: 10.1016/j.pocean.2025.103581

Foraging by deep-diving marine predators is shaped by the interplay between oceanographic features and light-driven (diel and lunar) cycles that structure the three-dimensional distributions of their mesopelagic prey. While mesoscale features such as fronts and eddies are important for epipelagic predators, their role in driving the foraging behaviour of deep-divers remains poorly understood. We investigated bio-physical drivers of habitat use for dwarf and pygmy sperm whales Kogia spp. and beaked whales Mesoplodon spp. using three years of passive acoustic monitoring at seven sites on the Outer Continental Shelf of the northwest Atlantic Ocean. We analysed acoustic detections alongside satellite- and model-derived oceanographic variables spanning meso- and seasonal scales, and diel and lunar cycles. The two deepest sites, on the Blake Plateau (870 m) and the outer continental slope (790 m), emerged as foraging hotspots with year-round vocal presence of kogiid and beaked whales. Mesoscale activity associated with the Gulf Stream – including current strength and eddy kinetic energy – were foraging predictors, alongside sea surface temperature and primary productivity. However, site-specific habitat models explained only 3–37 % deviance. Blainville’s beaked whale M. densirostris foraging activity peaked during the full moon, likely due to lunar effects on prey concentrations at depth, while there was no clear diel variation for any detected beaked whale species. In contrast, kogiid foraging activity was elevated around sunrise and sunset. These findings suggest a role of near-surface features such as eddies in addition to light-driven cycles in shaping predator–prey dynamics, even in deep continental slope ecosystems.