Melanie E. Austin

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.

THE USE OF TESSELLATION IN THREE-DIMENSIONAL PARABOLIC EQUATION MODELING

A full three-dimensional parabolic equation model (MONM3D) has been developed that incorporates techniques that reduce the required number of model grid points and reduces computation time. The concept of tessellation is implemented in MONM3D, which allows the number of radial paths in the model grid to vary with range from the source, reducing the number of computational points in the horizontal plane. This design establishes a grid layout that is both numerically and computationally desirable. A benchmark test case is used to illustrate the accuracy and efficiency of the model.

Use of Preoperation Acoustic Modeling Combined with Real-Time Sound Level Monitoring to Mitigate Behavioral Effects of Seismic Surveys.

Underwater acoustic modeling is often used to estimate the injury radius around a seismic exploration source; only occasionally has it been applied to the mitigation of behavioral effects, where the safety boundary may extend to many kilometers. Such a mitigation strategy requires precise estimation of the sound field for many source locations and likely entails field validation over the course of the operation to ensure that mitigation regions are accurate. This article reviews the enactment of such an approach for a seismic survey off Sakhalin Island and examines how similar principles may be applied to other surveys under suitable conditions.

Computational grid design to improve three‐dimensional parabolic equation modeling efficiency.

One class of very accurate computer models that can be used to predict underwater acoustic fields is based on three‐dimensional (3‐D) solutions of the parabolic form of the reduced acoustic wave equation. 3‐D parabolic equation (PE) models contain differential operators in both depth and azimuth. These 3‐D solutions are very computationally intensive, but strategic definition of the model grid can save computation time. A 3‐D PE model (MONM3D) has been developed that incorporates techniques that reduce the required number of model grid points. The concept of tessellation is used to optimize the radial grid density as a function of range, reducing the required number of grid points in the horizontal planes of the grid. The model marches the solution out in range along several radial propagation paths emanating from a source position. Tessellation, as implemented in MONM3D, allows the number of radial paths in the model grid to depend on range from the source. In addition, the model incorporates a higher‐or...

Effects of riverine seismic air‐gun exposure on fish hearing

Seismic airguns produce considerable amounts of acoustic energy that have the potential to affect marine life. This study investigated the effects of exposure to an airgun array in the Mackenzie River Delta on the hearing of three fish species: northern pike (Esox lucius), broad whitefish (Coregonus nasus), and lake chub (Couesius plumbeus). Fish were placed in cages in 1.9 m of water and exposed to 5 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 auditory evoked potentials (AEPs). Threshold shifts were found for exposed fish as compared to controls in the northern pike and lake chub, with recovery within 24 h 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 a 2D airgun array used in a river seismic survey. Care must be taken in extrapolation to other species in other environm...

Acoustic particle velocity and intensity calculations from tri‐axial pressure gradient measurements

In July 2004 Fisheries and Oceans Canada supported a study to investigate effects of seismic airgun signals on hearing organs of freshwater fish in the Mackenzie River at Inuvik, NWT Canada. The study required particle velocity measurements for correlation with observed biological effects. JASCO Research built a pressure gradient measurement apparatus consisting of four hydrophones mounted at the vertices of a triangular‐pyramid frame. The system was used to measure differential pressure from the airgun events simultaneously in three perpendicular axial directions. An attached depth‐compass sensor monitored the depth and orientation of the system. Hydrophone separations were chosen to be small relative to the acoustic wavelength so that measured differential pressures correctly approximated the pressure gradients along each axis. Particle accelerations were computed directly from pressure gradients following Euler’s linearized momentum equation, and particle velocities were computed by integrating particl...

Acoustic characterization of exploration drilling in the Chukchi and Beaufort seas

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.

Techniques in sound propagation modeling for noise impact assessment in three‐dimensionally variable environments.

Sound generated in the ocean by human activities has the potential to be disturbing or harmful to marine fauna. Environmental assessments of offshore industrial activities must often include noise impact studies for regulatory approval. Such noise impact studies examine the spatial extent of underwater noise using a computer model to estimate the propagation loss between a noise source and a grid of surrounding receiver points, providing the information necessary for the effective assessment and management of anthropogenic marine noise. Models based on the solution of the parabolic form of the wave equation can be used to generate very accurate acoustic field estimations in range‐dependent environments. While parabolic equation (PE) codes can also be configured to accurately handle three‐dimensional (3‐D) propagation effects, the numerical techniques they require can be very computationally intensive. Pseudo‐3‐D PE solutions are typically computed to prevent prohibitively long model run times. The implica...

Marine mammal vocalizations: Spectrum analysis.

Marine mammals communicate underwater using sounds at different frequencies. Some whales speak using low frequency moans, and others communicate using high frequency whistles and clicks. Some sing notes that sweep over different frequencies. Come hear some of the amazing sounds that whales, seals, and walrus make! Look at spectrum plots to see which frequencies make up the sounds. See if you can match pictures of spectrogram plots with the sounds you hear. Also explore the sounds made by common man‐made noise sources in the ocean such as ships, sonars, and geophysical survey equipment. In this demonstration, you will learn how to distinguish low frequency and high frequency sounds, both by ear and by eye, through a computer based matching game. You will click on an image of a marine mammal, or a man‐made noise source, to hear an audio clip of the sound that each makes. After hearing the sound, try to guess which of the presented spectrum plots matches the sound you heard.

Acoustic monitoring of pile driving activities at the proposed NaiKun wind farm site.

Underwater sound level measurements were obtained during marine pile driving activities at the proposed NaiKun wind farm site in Hecate Strait, British Columbia, Canada. Three hollow steel piles 0.9 m in diameter were driven into the seafloor to secure in place a truss to support a meteorological instrumentation mast. The activities involved both vibro‐hammering and impact hammering. Measurements were collected at 10 m range to fulfill regulatory requirements for real‐time monitoring of the near‐source sound pressure levels and also at a selection of longer ranges to allow a characterization of the propagation conditions of the environment. A bubble curtain was utilized to mitigate the underwater noise generated by impact hammering after trial measurements over a few hammer strikes showed that unmitigated levels exceeded a regulatory threshold. Results from this study were used to derive source level estimates for a subsequent sound propagation modeling study conducted as part of the environmental assessm...