Seismic Air Gun Signals Research Articles

The impact of seismic survey exposure on the righting reflex and moult cycle of Southern Rock Lobster (Jasus edwardsii) puerulus larvae and juveniles

Anthropogenic aquatic noise is recognised as an environmental pollutant with the potential to negatively affect marine organisms. Seismic surveys, used to explore subseafloor oil reserves, are a common source of aquatic noise that have garnered attention due to their intense low frequency inputs and their frequent spatial overlap with coastal fisheries. Commercially important Southern Rock Lobster (Jasus edwardsii) adults have previously shown sensitivity to signals from a single seismic air gun. Here, the sensitivity of J. edwardsii juveniles and puerulus to the signals of a full-scale seismic survey were evaluated to determine if early developmental stages were affected similarly to adults, and the range of impact. To quantify impact, lobster mortality rates, dorsoventral righting reflex and progression through moult cycle were evaluated following exposure. Exposure did not result in mortality in either developmental stage, however, air gun signals caused righting impairment to at least 500 m in lobsters sampled immediately following exposure, as had previously been reported in adults with corresponding sensory system damage following exposure. Impairment resulting from close range (0 m) exposure appeared to be persistent, as previously reported in adults, whereas juveniles exposed at a more distant range (500 m) showed recovery, indicating that exposure at a range of 500 m may not cause lasting impairment to righting. Intermoult duration was (time between moults) significantly increased in juveniles exposed at 0 m from the source, indicating the potential for slowed development, growth, and physiological stress. These results demonstrate that exposure to seismic air gun signals have the potential to negatively impact early life history stages of Southern Rock Lobsters. The similarity of both the impacts and the sound exposure levels observed here compared to previous exposure using a single air gun offer validation for the approach, which opens the potential for accessible field-based experimental work into the impact of seismic surveys on marine invertebrates.

Three-dimensional propagation of seismic airgun signals in the Mississippi Canyon area of the Gulf of Mexico.

Seismic airgun signals recorded on two hydrophone arrays during an oil and gas survey were analyzed for investigation of three-dimensional (3D) underwater sound propagation in the Mississippi Canyon area. A 3D numerical model with realistic seafloor and oceanographic inputs has been established to explain the intensified canyon focusing seen in the airgun signals received at one of the arrays. This study was under a passive acoustic monitoring program for establishing a current baseline of natural and anthropogenic sound sources and levels in the Gulf of Mexico. The reported investigation provides insight into the propagation effects affecting underwater soundscape in the area.

Lobsters with pre-existing damage to their mechanosensory statocyst organs do not incur further damage from exposure to seismic air gun signals

Staotcysts, the mechanosensory organs common to many marine invertebrates, have shown sensitivity to aquatic noise. Previously, rock lobsters (Jasus edwardsii) from a remote site with little exposure to anthropogenic noise incurred persistent damage to the statocyst and righting reflex following exposure to seismic air gun signals. Here, J. edwardsii collected from a site subject to high levels of anthropogenic noise were exposed to an equivalent seismic air gun signal regime as the previous study of noise-naïve lobsters. Following exposure, both control and exposed treatments were found to have damage to the statocyst equivalent to that of noise-naïve lobsters following seismic exposure, which led to the conclusion that the damage was pre-existing and not exacerbated by seismic exposure. The source of the damage in the lobsters in this study could not be ascertained, but the soundscape comparisons of the collection sites showed that the noisy site had a 5–10 dB greater level of noise, equivalent to a 3–10 times greater intensity, in the 10–700 Hz range than was found at the remote collection site. In addition to the lack of further damage following seismic exposure, no disruption to the righting reflex was observed. Indeed, compared to the noise naïve lobsters, the lobsters here demonstrated an ability to cope with or adapt to the mechanosensory damage, indicating a need for better understanding of the ecological impacts of the damage caused by low frequency noise on marine organisms. More broadly, this study raises historical exposure to noise as a previously unrecognised but vitally important consideration for studies of aquatic noise.

Exposure to seismic air gun signals causes physiological harm and alters behavior in the scallop Pecten fumatus

Seismic surveys map the seabed using intense, low-frequency sound signals that penetrate kilometers into the Earth's crust. Little is known regarding how invertebrates, including economically and ecologically important bivalves, are affected by exposure to seismic signals. In a series of field-based experiments, we investigate the impact of exposure to seismic surveys on scallops, using measurements of physiological and behavioral parameters to determine whether exposure may cause mass mortality or result in other sublethal effects. Exposure to seismic signals was found to significantly increase mortality, particularly over a chronic (months postexposure) time scale, though not beyond naturally occurring rates of mortality. Exposure did not elicit energetically expensive behaviors, but scallops showed significant changes in behavioral patterns during exposure, through a reduction in classic behaviors and demonstration of a nonclassic "flinch" response to air gun signals. Furthermore, scallops showed persistent alterations in recessing reflex behavior following exposure, with the rate of recessing increasing with repeated exposure. Hemolymph (blood analog) physiology showed a compromised capacity for homeostasis and potential immunodeficiency, as a range of hemolymph biochemistry parameters were altered and the density of circulating hemocytes (blood cell analog) was significantly reduced, with effects observed over acute (hours to days) and chronic (months) scales. The size of the air gun had no effect, but repeated exposure intensified responses. We postulate that the observed impacts resulted from high seabed ground accelerations driven by the air gun signal. Given the scope of physiological disruption, we conclude that seismic exposure can harm scallops.

The impact of seismic air gun exposure on the haemolymph physiology and nutritional condition of spiny lobster, Jasus edwardsii

There is a critical knowledge gap regarding the impacts of seismic air gun signals on the physiology of adult crustaceans. We conducted four controlled field experiments to examine the impact of seismic acoustic signals on spiny lobster, Jasus edwardsii. Seismic air gun exposure suppressed total haemocyte count (THC) for up to 120days post-exposure, suggesting a chronic negative impact of immune competency. THC levels after 365days post-exposure, were elevated two fold, potentially indicating an immune response to infection. Haemolymph refractive index was reduced after 120days post exposure in one experiment, suggesting a chronic impairment of nutritional condition. There was no effect of air gun exposure on 24 haemolymph biochemical parameters, hepatopancreas index or survival. Collectively these results indicate that the biochemical haematological homeostasis of J. edwardsii is reasonably resilient to seismic acoustic signals, however, air gun exposure may negatively influence the lobster's nutritional condition and immunological capacity.

Is low frequency ocean sound increasing globally?

Low frequency sound has increased in the Northeast Pacific Ocean over the past 60 yr [Ross (1993) Acoust. Bull. 18, 5-8; (2005) IEEE J. Ocean. Eng. 30, 257-261; Andrew, Howe, Mercer, and Dzieciuch (2002) J. Acoust. Soc. Am. 129, 642-651; McDonald, Hildebrand, and Wiggins (2006) J. Acoust. Soc. Am. 120, 711-717; Chapman and Price (2011) J. Acoust. Soc. Am. 129, EL161-EL165] and in the Indian Ocean over the past decade, [Miksis-Olds, Bradley, and Niu (2013) J. Acoust. Soc. Am. 134, 3464-3475]. More recently, Andrew, Howe, and Mercer's [(2011) J. Acoust. Soc. Am. 129, 642-651] observations in the Northeast Pacific show a level or slightly decreasing trend in low frequency noise. It remains unclear what the low frequency trends are in other regions of the world. In this work, data from the Comprehensive Nuclear-Test Ban Treaty Organization International Monitoring System was used to examine the rate and magnitude of change in low frequency sound (5-115 Hz) over the past decade in the South Atlantic and Equatorial Pacific Oceans. The dominant source observed in the South Atlantic was seismic air gun signals, while shipping and biologic sources contributed more to the acoustic environment at the Equatorial Pacific location. Sound levels over the past 5-6 yr in the Equatorial Pacific have decreased. Decreases were also observed in the ambient sound floor in the South Atlantic Ocean. Based on these observations, it does not appear that low frequency sound levels are increasing globally.

Assessing marine ecosystem acoustic diversity across ocean basins

Concurrent with the elevation of the concern over the state of sound in the ocean, advances in terrestrial acoustic monitoring techniques have produced concepts and tools that may be applicable to the underwater world. Several index values that convey information related to acoustic diversity with a single numeric measurement made from acoustic recordings have been proposed for rapidly assessing community biodiversity. Here we apply the acoustic biodiversity index method to low frequency recordings made from three different ocean basins to assess its appropriateness for characterizing species richness in the marine environment. Initial results indicated that raw acoustic entropy (H) values did not correspond to biological patterns identified from individual signal detections and classification. Noise from seismic airgun activity masked the weaker biological signals and confounded the entropy calculation. A simple background removal technique that subtracted an average complex spectrum characteristic of seismic exploration signals from the average spectra of each analysis period that contained seismic signals was applied to compensate for salient seismic airgun signals present in all locations. The noise compensated (HN) entropy index was more reflective of biological patterns and holds promise for the use of rapid acoustic biodiversity in the marine environment as an indicator of habitat biodiversity and health.

Acousticians abuse Darwin: Multipath propagation of seismic airgun signals and bowhead whale calls in the Arctic Ocean, with evolutionary implications.

Evolutionary biologists have long noted that animals attempting long‐range communication often adjust their acoustic signals to compensate for or even exploit features of the acoustic propagation path. Here we present recordings of long‐range seismic exploration signals and bowhead whale calls detected on directional autonomous seafloor acoustic recorders deployed in the Beaufort Sea in 2008. Seismic signals that begin as broadband impulses geometrically disperse into FM downsweeps as they propagate over several kilometers range in shallow water waveguides parallel to the Alaskan coast, eventually becoming similar to bowhead FM sweeps in bandwidth and modulated structure, creating headaches for unfortunate scientists trying to create automated bowhead whale acoustic detectors. It is suggested that the similarity in structure between long‐range seismic signals and bowhead whales is not coincidental, but provides an enlightening example of how marine mammals, over evolutionary time scales, have optimized their acoustic signals to propagate long distances while retaining information. A broadband harmonic bowhead whale call is analyzed to examine the speculation. In general, stereotyped baleen whale calls might serve purposes beyond simple species identification in complex waveguide environments.

Automated detection and localization of nonstereotyped bowhead whale calls in the presence of seismic airgun signals, incorporating multiple directional autonomous recording packages (DASARs).

In 2007 and 2008, 35 directional autonomous recording packages (DASARs) [Greene et al., J. Acoust. Soc. Am. 116, 799–813 (2004)] were deployed at five sites over a 280 km swath in the Beaufort Sea to monitor the annual migration of the bowhead whale (Balaena mysticetus) population during seismic exploration activities. To expedite analysis, automated detection and localization methods are applied to each DASAR data set, employing a four-stage detection and classification algorithm. The first three stages consist of the detection phase, while the final classification stage uses image thresholding, morphological processing, edge detection, and image segmentation to extract key features of signals from equalized spectrograms. These features are then compared to results from other DASARS at a given site in order to identify a single call across all DASARs. Bearings from each DASAR are then crossed to provide a location. Manually reviewed data sets are used to optimize the algorithm parameters for a given site and a given set of environmental conditions. The total detection and classification performance of the combined DASAR set will be compared with the performance of a single DASAR. [Work supported by Shell Exploration and Production Company.]

Computer‐aided detection of non‐stereotyped bowhead whale calls in the presence of seismic airgun signals

In 2007 thirty‐five autonomous recording packages were deployed over a 150 mile swath in the Beaufort Sea to monitor the annual migration of the bowhead whale (Balaena mysticetus) population during seismic exploration activities. Over 1350 days worth of acoustic data were gathered, generating a need for computer‐aided assistance in detecting calls. Bowhead whales produce over ten types of frequency modulated calls, and the frequency range, duration, and fine structure of individual calls vary considerably even within each call type, creating difficulties when using simple matched‐filtering or spectrogram correlation. Numerous airgun signals also display frequency‐modulated structure, complicating the challenge. In this presentation a three‐stage process is presented for detecting arbitrary bowhead whale calls in the presence of seismic airgun signals, implemented in JAVA and MATLAB, with components extracted from the industry‐supported PAMGUARD software package. The first stage runs several "energy‐based" detectors simultaneously across multiple frequency bands to capture events, and a second stage analyzes the timing of these detections to remove regular periodic sequences, such as those expected from airguns. The final stage attempts to trace contours on spectrograms. Both genetic algorithms and direct optimization are used to optimize the program's 21 input parameters. [Work supported by Shell Exploration and Production Company].

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 particle accelerations. Acoustic intensity was computed from the product of acoustic pressure and particle velocity. The hydrophone precision imposed a limit on accuracy of particle velocity measurements at low frequencies. Likewise the fixed hydrophone spacings defined an upper frequency limit for applicability of this method.