Alexander O. MacGillivray

Effects of exposure to seismic airgun use on hearing of three fish species

Seismic airguns produce considerable amounts of acoustic energy that have the potential to affect marine life. This study investigates the effects of exposure to a 730 in.3 airgun array on hearing of three fish species in the Mackenzie River Delta, the northern pike (Esox lucius), broad whitefish (Coregonus nasus), and lake chub (Couesius plumbeus). Fish were placed in cages in the 1.9 m of water and exposed to five or 20 airgun shots, while controls were placed in the same cage but without airgun exposure. Hearing in both exposed and control fish were then tested using the auditory brainstem response (ABR). Threshold shifts were found for exposed fish as compared to controls in the northern pike and lake chub, with recovery within 24 hours of exposure, while there was no threshold shift in the broad whitefish. It is concluded that these three species are not likely to be substantially impacted by exposure to an airgun array used in a river seismic survey. Care must be taken, however, in extrapolation to other species and to fishes exposed to airguns in deeper water or where the animals are exposed to a larger number of airgun shots over a longer period of time.

Marine mammal audibility of selected shallow-water survey sources

Most attention about the acoustic effects of marine survey sound sources on marine mammals has focused on airgun arrays, with other common sources receiving less scrutiny. Sound levels above hearing threshold (sensation levels) were modeled for six marine mammal species and seven different survey sources in shallow water. The model indicated that odontocetes were most likely to hear sounds from mid-frequency sources (fishery, communication, and hydrographic systems), mysticetes from low-frequency sources (sub-bottom profiler and airguns), and pinnipeds from both mid- and low-frequency sources. High-frequency sources (side-scan and multibeam) generated the lowest estimated sensation levels for all marine mammal species groups.

COMPILE—A Generic Benchmark Case for Predictions of Marine Pile-Driving Noise

The prediction of underwater noise emissions from impact pile driving during near-shore and offshore construction activities and its potential effect on the marine environment has been a major field of research for several years. A number of different modeling approaches have been suggested recently to predict the radiated sound pressure at different distances and depths from a driven pile. As there are no closed-form analytical solutions for this complex class of problems and for a lack of publicly available measurement data, the need for a benchmark case arises to compare the different approaches. Such a benchmark case was set up by the Institute of Modelling and Computation, Hamburg University of Technology (Hamburg, Germany) and the Organisation for Applied Scientific Research (TNO, The Hague, The Netherlands). Research groups from all over the world, who are involved in modeling sound emissions from offshore pile driving, were invited to contribute to the first so-called COMPILE (a portmanteau combining computation, comparison, and pile) workshop in Hamburg in June 2014. In this paper, the benchmark case is presented, alongside an overview of the seven models and the associated results contributed by the research groups from six different countries. The modeling results from the workshop are discussed, exhibiting a remarkable consistency in the provided levels out to several tens of kilometers. Additionally, possible future benchmark case extensions are proposed.

A model for underwater sound levels generated by marine impact pile driving

Marine impact pile driving generates very high underwater sound pressures, which can harm aquatic life. Environmental assessments for pile driving projects typically require acoustic impact zones for marine mammals and fish to be estimated in advance. A computer model that predicts the radiated acoustic field from impact driving of cylindrical piles has been developed. A lumped-mass model of the hammer, which predicts the force generated at the top of the pile, is coupled to a 1-D finite-difference model of radial and axial stress waves in a cylindrical pile. The radiated pressure is computed by matching the velocity boundary condition at the pile wall using a superposition of monopole sources distributed over the length of the pile in a layered 2-D fluid medium. The transfer function for the monopoles is computed using the near-field Hankel transform for radial particle velocity at the pile wall. Standard ocean acoustic modeling techniques are used to compute the Mach wave propagating away from the pile....

Modeling underwater sound propagation from an airgun array using the parabolic equation method

A technique for modeling sound propagation from an airgun array using the parabolic equation (PE) method is presented that takes into full account the far‐field, angle‐dependent directionality pattern of the array. This is achieved by generating a PE starting field for the array by summing together shaded, phase‐shifted replicas of the PE self‐starter. The array starter has been implemented using the RAM parabolic equation code. Validation comparisons are presented of field predictions generated using the array starter against exact normal mode solutions for an array source computed using ORCA. Examples of synthetic waveform airgun array calculations are also presented. The array starter method can be used to accurately predict pressure waveforms from an airgun array in the ocean environment provided that the modeler knows (or can compute) ‘‘notional’’ far‐field source signatures for individual airguns in the array.

Modelled and measured sound levels from a seismic survey in the Canadian Beaufort Sea

JASCO Applied Sciences performed acoustic modeling and measurements to calculate marine mammal exclusion zones for Chevron Canada Limited’s 2012 Sirluaq 3-D seismic program in the Canadian Beaufort Sea. The Sirluaq survey was located in deep water (>650 m), on and beyond the continental slope, and presented unique challenges from both modeling and measurement standpoints. The modeling was performed with JASCO’s Marine Operations Noise Model (MONM), which uses a parabolic-equation-based algorithm to accurately predict N×2-D sound propagation in ocean environments. Sound levels were measured with five calibrated Autonomous Multichannel Acoustic Recorder (AMAR) systems at distances of 50–50 000 m from the airgun array, in water depths ranging from 50 to 1500 m. The sensors were laid out to capture sound levels in both the broadside (perpendicular to survey line) and endfire (along the survey line) directions. The high-resolution digital recordings of seismic sounds were analyzed to determine peak and rms sound pressure levels (SPL), and sound exposure levels (SEL) as functions of range from the airgun array. The model estimates were generally conservative; however, the model predictions at the specific depth of the receivers accurately predicted the existence of a shadow zone and the overall transmission loss trend.

Measurements of industrial noise and vibration in artificial polar bear (Ursus maritimus) dens, Flaxman Island, Alaska.

Noise and ground vibration generated by environmental remediation activities were measured in man‐made polar bear (Ursus maritimus) dens at Flaxman Island, Alaska in Mar. 2002. The remediation activities involved use of heavy excavation equipment, ground vehicles, and blasting. Comparison of sound levels measured inside and outside the dens permitted estimation of the sound‐insulating properties of the dens. Vibration data were acquired from sensors placed in the tundra and in the snow of the den floors. Measurements of noise and vibration were made for the following vehicles: front‐end loader, trimmer, gravel hauler, fuel truck, pickup truck, Hagglunds tracked vehicle, and a Tucker Sno‐Cat. A single 8.7 kg blast event at 19 m underground, which was used to cut a well pipe, was recorded in the dens at distances from 500 to 1300 m. Additional noise and ground vibration data were obtained for Bell 212 and Bell 206 helicopters performing maneuvers above the dens. The man‐made dens were found to have good sou...

An acoustic modeling study of airgun noise from seismic surveys performed offshore British Columbia

A recent numerical modeling study has examined the propagation of underwater noise from potential seismic survey activity in Hecate Strait and Queen Charlotte Sound, Canada. Noise level predictions from this study are based on an integrated modeling approach incorporating an airgun array source model, a broadband transmission loss model, and an environmental model based on high resolution bathymetry, historical CTD casts and geophysical data. Details of the source model, transmission loss model and environmental model are discussed. Selected noise level predictions from the modeling study are presented. Results from this study will aid in evaluating potential environmental impacts of seismic exploration activity on marine ecosystems in British Columbia’s offshore region. [Work supported by BC MEM and NSERC.]

An airgun array source signature model for environmental impact assessments

Environmental impact assessments for seismic surveys often include estimates of radially propagating sound levels, which are used to determine marine mammal impact zones. Sound levels may be estimated using computer‐based acoustic modelling techniques but these require an accurate description of the survey source signature—arrays of airguns, in particular, have complex, highly directional source functions that depend on the array layout. To address this requirement, an airgun array source signature model has been developed for the purpose of underwater noise level prediction. The source model is based on published descriptions of the physics of airgun bubble oscillations and radiation [A. Ziolkowski, Geophys. J. R. Astron. Soc. 21, 137–161 (1970)] and includes the effects of port throttling, motion damping and bubble interactions. The output of the model is a collection of notional signatures which may be used to compute the source function of the array in any direction. Free parameters in the model have ...

Noise exposure from commercial shipping for the southern resident killer whale population

This study assesses vessel-noise exposure levels for Southern Resident Killer Whales (SRKW) in the Salish Sea. Kernel Density Estimation (KDE) was used to delineate SRKW summer core areas. Those areas were combined with the output of a regional cumulative noise model describing sound level variations generated by commercial vessels (1/3-octave-bands from 10 Hz to 63.1 kHz). Cumulative distribution functions were used to evaluate SRKWs noise exposure from 15 vessel categories over three zones located within the KDE. Median cumulative noise values were used to group categories based on the associated exposure levels. Ferries, Tugboats, Vehicle Carriers, Recreational Vessels, Containers, and Bulkers showed high levels of exposure (Leq-50th > 90 dB re 1 μPa) within SRKW core areas. Management actions aiming at reducing SRKW noise exposure during the summer should target the abovementioned categories and take into consideration the spatial distribution of their levels of exposure, their mechanical and their operational characteristics.