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.

Modeling potential masking of echolocating sperm whales exposed to continuous 1–2 kHz naval sonar (PDF)

von Benda-Beckmann, A.M., S. Isojunno, M. Zandvliet, M.A. Ainslie, P.J. Wensveen, P.L. Tyack, P.H. Kvadsheim, F.P.A. Lam, and P.J.O. Miller

J. Acoust. Soc. Am. 149: 2908-2925 (2021)

DOI: 10.1121/10.0004769

Modern active sonar systems can (almost) continuously transmit and receive sound, which can lead to more masking of important sounds for marine mammals than conventional pulsed sonar systems transmitting at a much lower duty cycle. This study investigated the potential of 1–2 kHz active sonar to mask echolocation-based foraging of sperm whales by modeling their echolocation detection process. Continuous masking for an echolocating sperm whale facing a sonar was predicted for sonar sound pressure levels of 160 dB re 1 μPa2, with intermittent masking at levels of 120 dB re 1 μPa2, but model predictions strongly depended on the animal orientation, harmonic content of the sonar, click source level, and target strength of the prey. The masking model predicted lower masking potential of buzz clicks compared to regular clicks, even though the energy source level is much lower. For buzz clicks, the lower source level is compensated for by the reduced two-way propagation loss to nearby prey during buzzes. These results help to predict what types of behavioral changes could indicate masking in the wild. Several key knowledge gaps related to masking potential of sonar in echolocating odontocetes were identified that require further investigation to assess the significance of masking.

Ocean Sound Analysis Software Making Ambient Noise Trends Accessible (MANTA) (PDF)

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

Front. Mar. Sci. 8: 703650 (2021)

DOI: 10.3389/fmars.2021.703650

Making Ambient Noise Trends Accessible (MANTA) software is a tool for the community to enable comparisons between soundscapes and identification of ambient ocean sound trends required by ocean stakeholders. MANTA enhances the value of individual datasets by assisting users in creating thorough calibration metadata and internationally recommended products comparable over time and space to ultimately assess ocean sound at any desired scale up to a global level. The software package combines of two applications: MANTA Metadata App, which allows users to specify information about their recordings, and MANTA Data Mining App, which applies that information to acoustic recordings to produce consistently processed, calibrated time series products of sound pressure levels in hybrid millidecade bands. The main outputs of MANTA are daily.csv and NetCDF files containing 60-s spectral energy calculations in hybrid millidecade bands and daily statistics images. MANTA data product size and formats enable easy and compact transfer and archiving among researchers and programs, allowing data to be further averaged and explored to address user-specified questions.

Passive acoustic monitoring reveals spatio-temporal distributions of Antarctic and pygmy blue whales around central New Zealand (PDF)

Warren, V.E., A. Širović, C. McPherson, K.T. Goetz, C.A. Radford, and R. Constantine

Frontiers in Marine Science 7: 1162 (2021)

DOI: 10.3389/fmars.2020.575257

Effective management of wild animal populations relies on an understanding of their spatio-temporal distributions. Passive acoustic monitoring (PAM) is a non-invasive method to investigate the distribution of free-ranging species that reliably produce sound. Critically endangered Antarctic blue whales (Balaenoptera musculus intermedia) (ABWs) co-occur with pygmy blue whales (B. m. brevicauda) (PBWs) around New Zealand. Nationally, both are listed as “data deficient” due to difficulties in access and visual sub-species identification. PAM was used to investigate the distributions of blue whales via sub-species specific song detections in central New Zealand. Propagation models, incorporating ambient noise data, enabled the comparison of detections among recording locations in different marine environments. ABW detections peaked during austral winter and spring, indicating that New Zealand, and the South Taranaki Bight (STB) in particular, is a migratory corridor for ABWs. Some ABW calls were also detected during the breeding season (September and October). PBW calls were highly concentrated in the STB, particularly between March and May, suggesting that an aggregation of PBWs may occur here. Therefore, the STB is of great importance for both sub-species of blue whale. PBW detections were absent from the STB during parts of austral spring, but PBWs were detected at east coast locations during this time. Detection area models were valuable when interpreting and comparing detections among recording locations. The results provide sub-species specific information required for management of critically endangered ABWs and highlight the relative importance of central New Zealand for both sub-species of blue whale.

Quantitative Soundscape Analysis to Understand Multidimensional Features (PDF)

Wilford, D.C., J.L. Miksis-Olds, S.B. Martin, D.R. Howard, K. Lowell, A.P. Lyons, and M.J. Smith

Frontiers in Marine Science 8: 672336 (2021)

DOI: 10.3389/fmars.2021.672336

A methodology for the analysis of soundscapes was developed in an attempt to facilitate efficient and accurate soundscape comparisons across time and space. The methodology consists of a collection of traditional soundscape metrics, statistical measures, and acoustic indices that were selected to quantify several salient properties of marine soundscapes: amplitude, impulsiveness, periodicity, and uniformity. The metrics were calculated over approximately 30 h of semi-continuous passive acoustic data gathered in seven unique acoustic environments. The resultant metric values were compared to a priori descriptions and cross-examined statistically to determine which combination most effectively captured the characteristics of the representative soundscapes. The best measures of amplitude, impulsiveness, periodicity, and uniformity were determined to be SPLrms and SPLpk for amplitude, kurtosis for impulsiveness, an autocorrelation based metric for periodicity, and the Dissimilarity index for uniformity. The metrics were combined to form the proposed “Soundscape Code,” which allows for rapid multidimensional and direct comparisons of salient soundscape properties across time and space. This initial characterization will aid in directing further analyses and guiding subsequent assessments to understand soundscape dynamics.

Spatio-temporal summer distribution of Cumberland Sound beluga whales (Delphinapterus leucas) in Clearwater Fiord, Nunavut, Canada (PDF)

Booy, K.V., X. Mouy, S.H. Ferguson, and M. Marcoux

Arctic Science 7: 394–412 (2021)

DOI: 10.1139/as-2019-0031

The Cumberland Sound (Nunavut, Canada) beluga whale (Delphinapterus leucas (Pallas, 1776)) population has been designated as threatened and updated biological information about summer distribution is required for a sound recovery plan. Variation in aerial survey counts are speculated to occur due to movement of belugas in and out of the fiord, and there is still uncertainty related to their distribution within key summer habitat. To address these knowledge gaps, non-invasive passive acoustic monitoring (PAM) systems were deployed in August of 2010 and 2011. An automated detector was used to determine presence/absence and quantify calls by recorder site. Results were verified by partial manual analysis of 20% of the files. The detector had a minimum accuracy of 85% for presence/absence and 42% for call quantification. Belugas were detected primarily at the uppermost site of Clearwater Fiord, with detections subsiding with increasing proximity to the fiord entrance. Diel variation in call patterns were quantified at two separate sites in different years, but no correlation was observed between tidal cycles and number of detections. This study indicates that Cumberland Sound beluga may prefer sites at the head of Clearwater Fiord. Further research is required to identify which environmental variables contribute to this observed summer distribution.

Temperature-driven seasonal and longer term changes in spatially averaged deep ocean ambient sound at frequencies 63–125 Hz (PDF)

Ainslie, M.A., R.K. Andrew, B.M. Howe, and J.A. Mercer

J. Acoust. Soc. Am. 149: 2531–2545 (2021)

DOI: 10.1121/10.0003960

The soundscape of the Northeast Pacific Ocean is studied with emphasis on frequencies in the range 63–125 Hz. A 34-year (1964–1998) increase and seasonal fluctuations (1994–2006) are investigated. This is achieved by developing a simple relationship between the total radiated power of all ocean sound sources and the spatially averaged mean-square sound pressure in terms of the average source factor, source depth, and sea surface temperature (SST). The formula so derived is used to predict fluctuations in the sound level in the range 63–125 Hz with an amplitude of 1.2 dB and a period of 1 year associated with seasonal variations in the SST, which controls the amount of sound energy trapped in the sound fixing and ranging (SOFAR) channel. Also investigated is an observed 5 dB increase in the same frequency range in the Northeast Pacific Ocean during the late 20th century [Andrew, Howe, Mercer, and Dzieciuch (2002). ARLO 3, 65–70]. The increase is explained by the increase in the total number of ocean-going ships and their average gross tonnage.

The Accuracy of Bearing Estimates of Wideband Signals Produced by Marine Animals

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

IEEE J. Ocean. Eng. 46: 1057-1067 (2021)

DOI: 10.1109/JOE.2020.3040703

The problem of estimating bearings of impulsive wideband acoustic signals produced by vocalizing animals and received by a compact array of synchronized sensors is addressed. The accuracy provided by the maximum-likelihood (ML), the beamformer (BF), and the time-difference-of-arrival (TDOA) based estimators is evaluated by simulations and in situ tests and compared with the Cramér-Rao bounds. Test results demonstrated that the ML estimator and BF provided similar bearing estimation accuracy for all types of signals. They are more accurate than the TDOA-based estimator for mid- and low-frequency impulsive signals. The accuracy of the TDOA-based estimates comes close to the ML- and BF-based estimates when the signal bandwidth increases. TDOA-based estimators outperformed the BFs and the ML algorithms when estimating the bearings of clicks. The empirical standard deviations provided by the ML/BF and TDOA-based estimators were 0.2° ...3° and 2°...70° for mid- and low-frequency impulsive signals and 5.0° and 0.6° for clicks, respectively.

Underwater Target Localization Using Opportunistic Ship Noise Recorded on a Compact Hydrophone Array (PDF)

Mirzaei Hotkani, M., J.-F. Bousquet, S.A. Seyedin, B. Martin, and E. Malekshahi

Acoustics 3: 611-629 (2021)

DOI: 10.3390/acoustics3040039

In this research, a new application using broadband ship noise as a source-of-opportunity to estimate the scattering field from the underwater targets is reported. For this purpose, a field trial was conducted in collaboration with JASCO Applied Sciences at Duncan’s Cove, Canada in September 2020. A hydrophone array was deployed in the outbound shipping lane at a depth of approximately 71 m to collect broadband noise data from different ship types and effectively localize the underwater targets. In this experiment, a target was installed at a distance (93 m) from the hydrophone array at a depth of 25 m. In this study, a matched field processing (MFP) algorithm is utilized for localization. Different propagation models are presented using Green’s function to generate the replica signal; this includes normal modes in a shallow water waveguide, the Lloyd-mirror pattern for deep water, as well as the image model. We use the MFP algorithm with different types of underwater environment models and a proposed estimator to find the best match between the received signal and the replica signal. Finally, by applying the scatter function on the proposed multi-channel cross correlation coefficient time-frequency localization algorithm, the location of target is detected.

An Assessment of the Potential Risks of Seismic Surveys to Affect Snow Crab Resources (PDF)

C. J. Morris, D. Cote, B. Martin, R Saunders-Lee, M. Rise, and J. Hanlon

Environmental Studies Research Funds report ; 220

publications.gc.ca/pub?id=9.910796&sl=0

Concerns were expressed by Snow Crab harvesters in the Newfoundland and Labrador region about the potential impacts of seismic oil and gas surveying on catch rates near commercial fishing areas. The impacts of ocean noise are a known societal concern, heightened by significant gaps in ecological understanding of the potential existing and future long-term effects on marine life. This study, funded by the Environmental Studies Research Fund (ESRF), was conducted in collaboration with local stakeholders, with significant participation from the snow crab fishing industry, from the planning stages through to completion. The purpose of this project was to examine effects of seismic exploration on the commercial Snow Crab fishery.

Vocal behavior of the endangered splendid toadfish and potential masking by anthropogenic noise (PDF)

Pyć , C.D., J. Vallarta , A.N. Rice, D.G. Zeddies, E.E. Maxner, and S.L. Denes

Conservation Science and Practice 3(5): e352 (2021)

DOI: 10.1111/csp2.352

Vessel‐related noise is a potential stressor for coral reef fauna. The Parque Nacional Arrecifes de Cozumel (PNAC) is a Mexican Marine Protected Area that is exposed to pervasive vessel traffic. PNAC is also the primary range of splendid toadfish (Sanopus splendidus, family Batrachoididae), an IUCN red‐listed soniferous fish for which vessel noise may represent a threat. We conducted a passive acoustic monitoring survey during summer of 2017 at Paraiso Reef in PNAC and obtained the first scientific recordings from splendid toadfish, enabling a vocal characterization of the species. We simultaneously collected data on sound levels of vessels passing near the reef. High noise levels of cruise ship and small motorboat traffic caused elevated anthropogenic sound pressure levels for up to 15 hr per day in the same bandwidth as toadfish vocalizations. A single cruise ship added up to 4 dB above nighttime ambient levels while small motorboat traffic added up to 7 dB. The overlap of toadfish vocalizations and vessel‐related noise highlights the susceptibility of splendid toadfish to acoustic masking and reduction in communication space throughout the day, warranting further study. Because acoustic communication is critical to toadfish reproductive success, noise from cruise ships and small motorboats may threaten splendid toadfish individuals or population viability.

Application of damped cylindrical spreading to assess range to injury threshold for fishes from impact pile driving (PDF)

Ainslie, M.A., M.B. Halvorsen, R.A.J. Müller, and T. Lippert

J. Acoust. Soc. Am. 148: 108–121 (2020)

DOI: 10.1121/10.0001443

Environmental risk assessment for impact pile driving requires characterization of the radiated sound field. Damped cylindrical spreading (DCS) describes propagation of the acoustic Mach cone generated by striking a pile and predicts sound exposure level (L_E) versus range. For known water depth and sediment properties, DCS permits extrapolation from a measurement at a known range. Impact assessment criteria typically involve zero-to-peak sound pressure level (L_p,pk), root-mean-square sound pressure level (L_p,rms), and cumulative sound exposure level (L_E,cum). To facilitate predictions using DCS, L_p,pk and L_p,rms were estimated from L_E using empirical regressions. Using a wind farm construction scenario in the North Sea, DCS was applied to estimate ranges to recommended thresholds in fishes. For 3500 hammer strikes, the estimated L_E,cum impact ranges for mortal and recoverable injury were up to 1.8 and 3.1 km, respectively. Applying a 10 dB noise abatement measure, these distances reduced to 0.29 km for mortal injury and 0.65 km for recoverable injury. An underlying detail that produces unstable results is the averaging time for calculating L_p,rms, which by convention is equal to the 90%-energy signal duration. A stable alternative is proposed for this quantity based on the effective signal duration.