Techniques for distinguishing between impulsive and non-impulsive sound in the context of regulating sound exposure for marine mammals (PDF)

Martin, S.B., K. Lucke, and D.R. Barclay

J. Acoust. Soc. Am. 147: 2159-2176 (2020)

DOI: 10.1121/10.0000971

Regulations designed to mitigate the effects of man-made sounds on marine mammal hearing specify maximum daily sound exposure levels. The limits are lower for impulsive than non-impulsive sounds. The regulations do not indicate how to quantify impulsiveness; instead sounds are grouped by properties at the source. To address this gap, three metrics of impulsiveness (kurtosis, crest factor, and the Harris impulse factor) were compared using values from random noise and real-world ocean sounds. Kurtosis is recommended for quantifying impulsiveness. Kurtosis greater than 40 indicates a sound is fully impulsive. Only sounds above the effective quiet threshold (EQT) are considered intense enough to accumulate over time and cause hearing injury. A functional definition for EQT is proposed: the auditory frequency-weighted sound pressure level (SPL) that could accumulate to cause temporary threshold shift from non-impulsive sound as described in Southall, Finneran, Reichmuth, Nachtigall, Ketten, Bowles, Ellison, Nowacek, and Tyack [(2019). Aquat. Mamm. 45, 125–232]. It is known that impulsive sounds change to non-impulsive as these sounds propagate. This paper shows that this is not relevant for assessing hearing injury because sounds retain impulsive character when SPLs are above EQT. Sounds from vessels are normally considered non-impulsive; however, 66% of vessels analyzed were impulsive when weighted for very-high frequency mammal hearing.

The coastal Arctic marine soundscape near Ulukhaktok, Northwest Territories, Canada

Halliday, W.D., M.K. Pine, X. Mouy, P. Kortsalo, R.C. Hilliard, and S.J. Insley

Polar Biology 43: 623-636 (2020)

DOI: 10.1007/s00300-020-02665-8

The soundscape is an important habitat feature for marine animals, and climate change may cause large changes to the Arctic marine soundscape through sea ice loss and increased anthropogenic activity. We examined the marine soundscape over eight months near Ulukhaktok, Northwest Territories, Canada, and assessed the relative contribution of the geophony (wind and wave sounds), biophony (marine mammal and fish sounds), and anthrophony (noise from vessel traffic). Sound pressure levels (SPL) were significantly higher during the summer than during the autumn and winter, and these differences were caused by increased wind/waves and vessel traffic in the summer. Increased wind speed drove increased SPL, while increased ice concentration resulted in decreased SPL. When vessel traffic was closer, SPL was higher. Marine mammal and fish vocalizations did not influence SPL; however, timing of vocalizations of both whales and seals matched seasonal patterns shown in other studies within the region. Overall, the marine soundscape near Ulukhaktok varied greatly through time and may be prone to large changes in the future as the ice-free season continues to lengthen and more vessels travel through the region.

Using two drones to simultaneously monitor visual and acoustic behaviour of gray whales (Eschrichtius robustus) in Baja California, Mexico

Frouin-Mouy, H., L. Tenorio-Hallé, A. Thode, S. Swartz, and J. Urbán

J. Exp. Mar. Biol. Ecol. 525: 151321 (2020)

DOI: 10.1016/j.jembe.2020.151321

This study provides an initial demonstration of a combined two-UAV (Unmanned Aerial Vehicle) system for measuring the underwater source levels and behavioural context of vocal and non-vocal marine mammal signals, information that is highly ecologically-relevant in terms of understanding how a species interacts and copes with conspecifics and its acoustic environment. Although the calls of a few species are well known, major gaps exist in our knowledge about the relationship between vocal output and behavioural context, gender and age for most species. Accurate parameter estimates (e.g., typical source levels, frequency ranges, and temporal characteristics of animal sounds) relevant to their behaviour (activities such as foraging, migrating, mating, or parental care) are needed to establish use of critical habitats (when monitored by acoustics) or to assess potential effects of anthropogenic sound exposure (including reduction of the detection space of sounds used for communication). […] We used two UAVs: one to obtain acoustic measurements close to the whales and another one to obtain overhead visual observations. […] Between 27 February and 17 March 2019, we simultaneously recorded underwater gray whale sounds and visual behavioural observations. During 92 min of underwater acoustic recordings, the acoustic drone recorded 11 call types. By time-synching underwater audio with the behavioural video, we obtained new insights into the source levels and functions of various quiet underwater sound that are difficult to impossible to obtain with standard methods. To our knowledge, no studies combining overhead visual observations and underwater acoustic recordings to describe acoustic behaviour and sound parameters of calls have been previously published.

Acoustic detections of Arctic marine mammals near Ulukhaktok, Northwest Territories, Canada

Halliday, W.D., M.K. Pine, S.J. Insley, R.N. Soares, P. Kortsalo, and X. Mouy

Can. J. Zool. 97(1): 72–80 (2019)

DOI: 10.1139/cjz-2018-0077

The Arctic marine environment is changing rapidly through a combination of sea ice loss and increased anthropogenic activity. Given these changes can affect marine animals in a variety of ways, understanding the spatial and temporal distributions of Arctic marine animals is imperative. We use passive acoustic monitoring to examine the presence of marine mammals near Ulukhaktok, Northwest Territories, Canada, from October 2016 to April 2017. We documented bowhead whale (Balaena mysticetus Linnaeus, 1758) and beluga whale (Delphinapterus leucas (Pallas, 1776)) vocalizations later into the autumn than expected, and we recorded bowhead whales in early April. We recorded ringed seal (Pusa hispida (Schreber, 1775)) vocalizations throughout our deployment, with higher vocal activity than in other studies and with peak vocal activity in January. We recorded bearded seals (Erignathus barbatus (Erxleben, 1777)) throughout the deployment, with peak vocal activity in February. We recorded lower bearded seal vocal activity than other studies, and almost no vocal activity near the beginning of the spring breeding season. Both seal species vocalized more when ice concentration was high. These patterns in vocal activity document the presence of each species at this site over autumn and winter and are a useful comparison for future monitoring.

Acoustic occurrence and behavior of ribbon seals (Histriophoca fasciata) in the Bering, Chukchi, and Beaufort seas

Frouin‑Mouy, H., X. Mouy, C.L. Berchok, S.B. Blackwell, and K.M. Stafford

Polar Biology 42: 657–674 (2019)

DOI: 10.1007/s00300-019-02462-y

Due to the difficulty of studying ice seals in their natural environment, distribution and movement patterns of ribbon seals (Histriophoca fasciata) over large spatio-temporal scales are poorly understood. In this study, we analyzed their distribution patterns in the Bering, Chukchi, and Beaufort seas, using passive acoustic data collected between August 2012 and July 2013 at 53 recording sites. Ribbon seal downsweeps were found using spectrogram correlation autodetection, at 30 of these recording sites. These detections were further manually analyzed to investigate the vocal repertoire and quantify the diel pattern in acoustic presence. We found that the Beaufort Sea shelf and the northern Bering Strait/southern Chukchi Sea are ecologically important for ribbon seals during the open-water season. Our results suggest that the northeastern Chukchi Sea serves as part of a migration corridor to and from the Chukchi Plateau and/or Beaufort Sea. In the Bering Sea, most detections occurred from February to June. Vocal activity was higher at nighttime than during the daytime prior to the peak calling period, while during the peak calling period, diel rhythm became less pronounced. The number of calls, proportional use of downsweeps, and bandwidth of downsweeps (estimated broadband source level 170–178 dB re 1 μPa-m) increased during the breeding period, from March to June, peaking in May. An additional call type, the “shuffle”, was identified in this study. These results improve our understanding of the migration, occurrence, and acoustic behavior of ribbon seals in the Bering, Chukchi, and Beaufort seas.

An airgun array source model accounting for high-frequency sound emissions during firing—Solutions to the IAMW source test cases (PDF)

MacGillivray, A.O.

IEEE J. Ocean. Eng. 44: 582-588 (2019)

DOI: 10.1109/JOE.2018.2853199

JASCO's Airgun Array Source Model (AASM) is a combined deterministic and stochastic model that separately treats the low-frequency and high-frequency components of signals produced by airgun arrays. The low-frequency module is based on solving the equations of motion for interacting spherical bubbles. The high-frequency module is based on a stochastic model of the airgun spectrum, which has been derived from a principal component regression analysis of the experimental data. This stochastic model determines the frequency spectrum of an airgun waveform during the rapid onset of a pressure that occurs when air is released from the gun chamber. AASM combines the output of these two modules to predict the source waveform of an airgun array over a wide frequency range (0-25 kHz). AASM was among the source models included in benchmark comparisons presented at the International Airgun Modeling Workshop (IAMW), held in Dublin, Ireland, in 2016. Results from the workshop showed that different source models agreed reasonably well at low frequencies (<200 Hz), but they diverged substantially at high frequencies (>1 kHz). To help better understand the reasons for a mismatch between source models, this paper presents solutions to the IAMW source test cases, calculated using AASM, as well as a detailed description of AASM's theoretical underpinnings.

Analytical and numerical propagation loss predictions for gradually range-dependent isospeed waveguides

Sertlek, H.Ö., M.A. Ainslie, and K.D. Heaney

IEEE J. Ocean. Eng. 44: 1240-1252 (2019)

DOI: 10.1109/JOE.2018.2865640

An analytical formulation for the calculation of the range and depth-dependence of propagation loss in isospeed water is introduced. The range-dependent bathymetry is handled with Weston's ray invariant approach, requiring a gradually varying water depth. The depth dependence of propagation loss is formulated using a transformation from an incoherent mode sum to an integral over angle, in the adiabatic approximation, and the results obtained in this way are tested by comparison with a full adiabatic normal mode sum. The validity of the adiabatic approximation itself is then investigated by means of a comparison with parabolic equation and coupled normal mode results for selected test cases from the Weston Memorial Workshop, held at the University of Cambridge in April 2010. Propagation loss calculations based on different methods are compared. The proposed analytical approach provides practical, fast and accurate results.

Composite underwater noise footprint of a shallow Arctic exploration drilling project

Quijano, J.E., D.E. Hannay, and M.E. Austin

IEEE J. Ocean. Eng. 44: 1228-1239 (2019)

DOI: 10.1109/JOE.2018.2858606

In this paper, we present the results of a comprehensive acoustic monitoring and modeling study of the composite underwater noise footprint of an exploration drilling project in shallow waters (46 m) in the northeastern Chukchi Sea. Measured acoustic source levels of multiple vessels and drilling equipment were used as inputs to theoretical propagation models. The models generated time-dependent wide-area noise fields, accounting for oceanographic and weather conditions and the time-dependent drilling activities and positions of multiple vessels. Modeling in increments of 1 h was performed over the full operations period, from July 7, 2015 to October 16, 2015. Model validation was carried out by comparing simulated results with high-resolution acoustic data acquired at multiple stations in the area. The study shows that noise radiating from up to 19 supporting vessels is usually dominant, but noise from certain drilling-related activities occasionally rises above vessel noise within a radius of 8 km from drill sites, limited to a few hours in durations. Modeled scenarios show that by constraining vessel positions to within a few kilometers of the drilling location, the extent of the 120 dB re 1 μPa noise footprint, as defined for single-well and concurrent double-well drilling operations, is contained within a nominal radius of 20 km. Broadband noise from drilling platforms and support vessels reached wind-generated ambient noise levels at ranges between 60 and 85 km from the drill site. Still, some tones and narrowband sounds may remain above the natural ambient noise at the same frequencies to longer ranges.

Determining the dependence of marine pile driving sound levels on strike energy, pile penetration, and propagation effects using a linear mixed model based on damped cylindrical spreading (PDF)

Martin, S.B. and D.R. Barclay

J. Acoust. Soc. Am. 146: 109-121 (2019)

DOI: 10.1121/1.5114797

Acoustic recordings were made during the installation of four offshore wind turbines at the Block Island Wind Farm, Rhode Island, USA. The turbine foundations have four legs inclined inward in a pyramidal configuration. Four bottom mounted acoustic recorders measured received sound levels at distances of 541–9067 m during 24 pile driving events. Linear mixed models based on damped cylindrical spreading were used to analyze the data. The model's random effects coefficients represented useful information about variability in the acoustic propagation conditions. The received sound levels were dependent on the angle between pile and seabed, strike energy, and pile penetration (PP). Deeper PPs increased sound levels in a frequency dependent manner. The estimated area around the piles where auditory injury and disturbance to marine life could occur were not circular and changed by up to an order of magnitude between the lowest and highest sound level cases. The study extends earlier results showing a linear relationship between the peak sound pressure level and per-strike sound exposure level. Recommendations are made for how to collect and analyze pile driving data. The results will inform regulatory mitigations of the effects of pile driving sound on marine life, and contribute to developing improved pile driving source models.

Displaying bioacoustic directional information from sonobuoys using “azigrams” (PDF)

Thode, A.M., T. Sakai, J. Michalec, S. Rankin, M.S. Soldevilla, B. Martin, and K.H. Kim

J. Acoust. Soc. Am. 146: 95–102 (2019)

DOI: 10.1121/1.5114810

The AN/SSQ-53 Directional Frequency Analysis and Recording (DIFAR) sonobuoy is an expendable device that can derive acoustic particle velocity along two orthogonal horizontal axes, along with acoustic pressure. This information enables computation of azimuths of low-frequency acoustic sources from a single compact sensor. The standard approach for estimating azimuth from these sensors is by conventional beamforming (i.e., adding weighted time series), but the resulting “cardioid” beampattern is imprecise, computationally expensive, and vulnerable to directional noise contamination for weak signals. Demonstrated here is an alternative multiplicative processing scheme that computes the “active intensity” of an acoustic signal to obtain the dominant directionality of a noise field as a function of time and frequency. This information is conveniently displayed as an “azigram,” which is analogous to a spectrogram, but uses color to indicate azimuth instead of intensity. Data from several locations demonstrate this approach, which can be computed without demultiplexing the raw signal. Azigrams have been used to help diagnose sonobuoy issues, improve detectability, and estimate bearings of low signal-to-noise ratio signals. Azigrams may also enhance the detection and potential classification of signals embedded in directional noise fields.

Localizing sources using a network of asynchronous compact arrays (PDF)

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

IEEE J. Ocean. Eng. 45(3): 1091-1098 (2019)

DOI: 10.1109/JOE.2019.2915913

This paper considers the problem of passive acoustic localization of sources using a network of stationary compact arrays of acoustic sensors providing azimuth and elevation measurements of detected sounds. The maximum-likelihood estimator and Cramér-Rao bounds are derived. The localization accuracy is evaluated using statistical simulations and in situ tests. The plots of azimuth, range, and position estimation accuracy are presented. Test results demonstrated that superefficient position estimates with an error lower than the Cramér-Rao bounds can be achieved for surface vessels and other sound sources with known depths.

Potential benefits of vessel slowdowns on endangered southern resident killer whales (PDF)

Joy, R., D. Tollit, J. Wood, A. MacGillivray, Z. Li, K. Trounce, and O. Robinson

Frontiers in Marine Science 6: 344 (2019)

DOI: 10.3389/fmars.2019.00344

A voluntary commercial vessel slowdown trial was conducted through 16 nm of shipping lanes overlapping critical habitat of at-risk southern resident killer whales (SRKW) in the Salish Sea. From August 7 to October 6, 2017, the trial requested piloted vessels to slow to 11 knots speed-through-water. […] Slowdown results were compared to ‘Baseline’ noise of the same region, matched across lunar months. […] A regional vessel noise model predicted noise for a range of traffic volume and vessel speed scenarios for a 1133 km^2 ‘Slowdown region’ containing the 16 nm of shipping lanes. A temporally and spatially explicit simulation model evaluated the changes in traffic volume and speed on SRKW in their foraging habitat within this Slowdown region. The model tracked the number and magnitude of noise-exposure events that impacted each of 78 (simulated) SRKW across different traffic scenarios. These disturbance metrics were simplified to a cumulative effect termed ‘potential lost foraging time’ that corresponded to the sum of disturbance events described by assumptions of time that whales could not forage due to noise disturbance. […]

Slowing deep-sea commercial vessels reduces underwater radiated noise (PDF)

MacGillivray, A.O., Z. Li, D.E. Hannay, K.B. Trounce and O.M. Robinson

J. Acoust. Soc. Am. 146: 340-351 (2019)

DOI: 10.1121/1.5116140

During 2017, the Vancouver Fraser Port Authority's Enhancing Cetacean Habitat and Observation program carried out a two-month voluntary vessel slowdown trial to determine whether slowing to 11 knots was an effective method for reducing underwater radiated vessel noise. The trial was carried out in Haro Strait, British Columbia, in critical habitat of endangered southern resident killer whales. During the trial, vessel noise measurements were collected next to shipping lanes on two hydrophones inside the Haro Strait slowdown zone, while a third hydrophone in Strait of Georgia measured vessels noise outside the slowdown zone. Vessel movements were tracked using the automated identification system (AIS), and vessel pilots logged slowdown participation information for each transit. An automated data processing system analyzed acoustical and AIS data from the three hydrophone stations to calculate radiated noise levels and monopole source levels (SLs) of passing vessels. Comparing measurements of vessels participating in the trial with measurements from control periods before and after the trial showed that slowing down was an effective method for reducing mean broadband SLs for five categories of piloted commercial vessels: containerships (11.5 dB), cruise vessels (10.5 dB), vehicle carriers (9.3 dB), tankers (6.1 dB), and bulkers (5.9 dB).

Sound exposure level as a metric for analyzing and managing underwater soundscapes (PDF)

Martin, S.B., C. Morris, K. Bröker, and C. O’Neill

J. Acoust. Soc. Am. 146: 135-149 (2019)

DOI: 10.1121/1.5113578

The auditory frequency weighted daily sound exposure level (SEL) is used in many jurisdictions to assess possible injury to the hearing of marine life. Therefore, using daily SEL to describe soundscapes would provide baseline information about the environment using the same tools used to measure injury. Here, the daily SEL from 12 recordings with durations of 18–97 days are analyzed to: (1) identify natural soundscapes versus environments affected by human activity, (2) demonstrate how SEL accumulates from different types of sources, (3) show the effects of recorder duty cycling on daily SEL, (4) make recommendations on collecting data for daily SEL analysis, and (5) discuss the use of the daily SEL as an indicator of cumulative effects. The autocorrelation of the one-minute sound exposure is used to help identify soundscapes not affected by human activity. Human sound sources reduce the autocorrelation and add low-frequency energy to the soundscapes. To measure the daily SEL for all marine mammal auditory frequency weighting groups, data should be sampled at 64 kHz or higher, for at least 1 min out of every 30 min. The daily autocorrelation of the one-minute SEL provides a confidence interval for the daily SEL computed with duty-cycled data.

Systematic source level measurements of whale watching vessels and other small boats (PDF)

Wladichuk, J.L., D.E. Hannay, A.O. MacGillivray, Z. Li, and S. Thornton

Journal of Ocean Technology 14(3): 108-126 (2019)

JOT Article page

Marine mammals rely heavily on sound for foraging, communicating, and navigating. As noise in the ocean increases, their ability to perform these important life functions can be affected. In the past decade, numerous studies have expanded our awareness of the effects of anthropogenic noise on marine life. Improving our knowledge of how sound impacts marine mammals is particularly important in coastal waters where the spatial distributions of vessels and marine mammals overlap, as exemplified by the critical habitat for the endangered Southern Resident killer whale (Orcinus orca). The impacts of small vessel traffic (including the commercial and recreational whale watching that is directed on this population) has been difficult to assess as there is a data gap for small vessel noise emissions. In this study, two autonomous marine acoustic recorders were deployed in transboundary Haro Strait (British Columbia, Canada, and Washington State, USA) from July to October 2017 to measure sound levels produced by whale watching vessels and other small boats. […]

The presence of large whale species in Clayoquot Sound and its offshore waters

Burnham, R.E., D.A. Duffus, and X. Mouy

Continental Shelf Research 177: 15–23 (2019)

DOI: 10.1016/j.csr.2019.03.004

Large whale populations in the northeast Pacific were severely reduced by whaling, with many showing limited recovery. Their use of offshore waters and limited knowledge of life histories has hindered studies focused on estimating population numbers and mapping habitat use. Acoustic recordings, using vocalizations as a marker of whale presence, may be the first step in re-establishing baseline knowledge of species presence over time and space. Recordings from both stationary and mobile platforms, covering waters from coastal to shelf-break and offshore waters, show spatial segregation in the dominant species recorded. Inshore recordings are dominated by more coastally-focused species, whereas fin (Balaenoptera physalus) blue (Balaenoptera musculus) and sperm whales (Physeter macrocephalus) are primarily heard in the shelf-break zones. Calls tentatively described for sei whales (Balaenoptera borealis) are also noted. Calls matching those previously described to these species as breeding and foraging calls were found. Acoustic monitoring surveys like this study are needed to better map presence and habitat use of these rare and endangered species, ultimately leading to the identification and protection of areas important to population recovery.

Western North Atlantic humpback whale fall and spring acoustic repertoire: Insight into onset and cessation of singing behavior (PDF)

Kowarski, K., H. Moors-Murphy, E. Maxner, and S. Cerchio

J. Acoust. Soc. Am. 145: 2305–2316 (2019)

DOI: 10.1121/1.5095404

Humpback whale songs have been described worldwide and studies exploring non-song vocal behavior continue to expand; however, studies on the transition periods when whales shift to and from the seasonal behavioral state of singing are lacking and may be potentially informative regarding the proximal factors controlling the onset and offset of humpback whale male singing. Acoustic recorders collected data off eastern Canada continuously from the Bay of Fundy in the fall of 2015 and near-continuously off northeast Nova Scotia in the spring of 2016. Humpback whale acoustic occurrence and behavior were identified by systematically reviewing a subset of acoustic recordings for presence before analyzing the highest quality recordings for behavior. The onset of singing in the fall was gradual over a period of about three weeks with an intermediate form, termed “song fragment,” occurring prior to full songs. In comparison, singing in the spring seemed to end abruptly with few song fragments. Song fragments could be produced by juveniles learning to sing for the first time or mature males preparing for breeding activities prior to migrating to southern breeding grounds. The authors propose an alternative hypothesis that the timing and manner of transitions could be driven by physiological processes similar to those documented in songbirds.

Acoustic characterization of exploration drilling in the Chukchi and Beaufort seas

Austin, M.E., D.E. Hannay, and K.C. Bröker

Journal of the Acoustical Society of America 144: 115–123 (2018)

DOI: 10.1121/1.5044417

This paper characterizes underwater sound levels produced by three drilling units during offshore exploration drilling at three sites in the Beaufort and Chukchi seas. Received levels and spectra are reported as functions of distance during drilling and excavation of mudline cellars (MLCs). Sound levels emitted during MLC excavation exceeded those during drilling at all three sites, although this operation was much shorter in duration. Drilling sounds exhibited tones below 2 kHz, with harmonics present to 10 kHz, while MLC excavation sounds were broadband in character. Drilling sounds varied substantially between the three operations, whereas MLC excavation sounds were more consistent in amplitude and spectral distribution. Estimates of broadband and 1/3-octave band source levels were computed from measurements at 1 km range. The broadband drilling source levels were 168.6 dB re 1 μPa m for the Kulluk drilling unit, 174.9 dB re 1 μPa m for the drillship Noble Discoverer, and 170.1 dB re 1 μPa m for the semi-submersible Polar Pioneer. The received levels measured at 1 km during MLC excavation yielded source level estimates that were more consistent among sources: 191.8, 193.0, and 193.3 dB re 1 μPa for the Discoverer, Kulluk, and Polar Pioneer, respectively.

Assessing vessel slowdown for reducing auditory masking for marine mammals and fish of the western Canadian Arctic

Pine, M.K., D.E. Hannay, S.J. Insley, W.D. Halliday, and F. Juanes

Marine Pollution Bulletin 135: 290-302 (2018)

DOI: 10.1016/j.marpolbul.2018.07.031

Vessel slowdown may be an alternative mitigation option in regions where re-routing shipping corridors to avoid important marine mammal habitat is not possible. We investigated the potential relief in masking in marine mammals and fish from a 10 knot speed reduction of container and cruise ships. The mitigation effect from slower vessels was not equal between ambient sound conditions, species or vessel-type. Under quiet ambient conditions, a speed reduction from 25 to 15 knots resulted in smaller listening space reductions by 16–23%, 10–18%, 1–2%, 5–8% and 8% respectively for belugas, bowheads, bearded seals, ringed seals, and fish, depending on vessel-type. However, under noisy conditions, those savings were between 9 and 19% more, depending on the species. This was due to the differences in species' hearing sensitivities and the low ambient sound levels measured in the study region. Vessel slowdown could be an effective mitigation strategy for reducing masking.

Behavioral responses of harbor porpoises (Phocoena phocoena) to sonar playback sequences of sweeps and tones (3.5-4.1 kHz) (PDF)

Kastelein, R.A., L. Helder-Hoek, S. Van de Voorde, S. de Winter, S. Janssen, and M.A. Ainslie

Aquatic Mammals 44: 389-404 (2018)

DOI: 10.1578/AM.44.4.2018.389

Naval sonar signals may affect the behavior of harbor porpoises (Phocoena phocoena). The 53C sonar system produces 1,600 ms sonar signals in the 3.5 to 4.1 kHz band, each consisting of a sweep immediately followed by two tones which are separated by a 100 ms silence. Effects of sound pressure level (SPL) and duty cycle on the behavioral responses of two harbor porpoises to these sounds were investigated. Respiration rate, distance to the transducer, swimming speed, and the number of jumps during sound exposure and baseline periods were compared. Harbor porpoises were exposed to 30-min playbacks of 53C sonar sounds at five average received SPLs (Lrecs) with a duty cycle of 2.7%, and at six Lrecs with a duty cycle of 96%, under low ambient noise conditions. They did not respond to the sounds when the duty cycle was 2.7%, even at the maximum Lrec (143 dB re 1 μPa). When the duty cycle was 96%, only Porpoise 06 increased his respiration rate when the Lrec was ≥119 dB re 1 μPa, and he moved away from the transducer only at an Lrec of 143 dB re 1 μPa. At the same Lrec and duty cycle, the effect of 53C sonar sounds on harbor porpoise behavior was weaker than that of 1 to 2 kHz, 6 to 7 kHz, and 25 kHz sonar signals observed in previous studies.