Seismic Airgun Surveying in Offshore Waters: What are the Effects on Marine Wildlife and What Can Be Done?

 

     While there seems to be a lot of talk about wind turbines killing birds and offshore windship traffic possibly killing some large whales, not much has been in the news, at least lately, about the effects of seismic airgun blasting on ocean mammals. We should, of course, try to limit harm to any wildlife, regardless of the energy source causing the harm, as much as possible.

     Seismic airguns release intense pulses of compressed air that propagate as powerful sound waves in the medium of ocean or sea waters. These waves are used as a sound source to penetrate tens of thousands of feet into the seabed to map the subsurface geology for the purpose of finding oil and gas. The compressed air, when released, produces a bubble as well as a very loud and high-decibel sound that propagates out from the source.  The graphics below depict the process.

 

 

A factsheet from Ocean.org describes how frequent and continuous these surveys are occurring:

 

Seismic airgun blasting characteristics:

> Loud blasts repeated every 10-12 seconds for days, weeks, or months at a time.

> 12-48 individual airguns are towed in each array; a single ship can tow up to 96 airguns.

> The surface area covered by the largest seismic array was 21 times larger than the National Mall in Washington, D.C.

> Seismic airgun sounds can be heard up to 2,500 miles from the source under some conditions, approximately the distance of a flight from New York to Los Angeles

 

      The tables below compare the natural ocean sounds (both abiotic and biotic) to human-made sounds. Marine animals rely upon sound for feeding, mating, avoiding predators, communicating, and navigating. The second table shows that seismic airguns have the highest decibel level of all anthropogenic sound sources in the ocean. However, some of the other sound sources are also very loud and worth limiting, if possible.

    

     At issue is the effect of seismic airguns on marine wildlife. Hearing loss due to the high-decibel sounds is a huge concern. According to a December 2018 factsheet by dosits.org:

 

“Sounds produced by seismic airguns have the potential to cause injury, hearing loss, behavioral changes, and masking in fishes, marine mammals, and invertebrates. However, data on the effects of airguns on marine life are limited. There are no studies of seismic airguns and their potential to cause death, mortal injury, or recoverable injury to wild fishes, and most behavioral studies have been conducted in a laboratory setting with freshwater species. Laboratory results do not necessarily reflect natural responses in the wild, and freshwater fishes, such as goldfish and zebrafish, are likely to respond very differently to a loud sound than a wild species such as Atlantic cod or tuna.”

     Environmental groups like Earthjustice have been speaking out against the use of seismic airguns for many years. As someone who has promoted animal welfare, including wildlife welfare, this is concerning to me. Of course, more needs to be understood since the negative auditory and other effects are not well established, However, studies of auditory damage to large mammals and fish that live in the ocean are not easy to conduct. Some studies have confirmed that auditory fatigue has occurred in some species resulting in a ‘temporary threshold shift (TTS)’ in the auditory systems of those affected species. This could result in noise-induced hearing loss, which can be temporary or permanent. How a particular animal is affected depends very much on its distance from the sound source. Thus, one mitigation method is to map the presence of the most affectable animals and wait till they are gone from the area. One study showed no TTS for exposed bottlenose dolphins. We still need to better understand the auditory stress these animals are enduring. An important question is how much of the hearing loss will be permanent as in a ‘permanent threshold shift (PTS)’.

     The issue of noise pollution in the oceans is an important one and seismic is not the only source. Ships propellers are a major source. Another source is suing pile drivers to drive offshore wind turbine foundations into place. Many of those are now using “bubble curtains,” literally curtains of bubbles to muffle the sound. Several species such as whales and dolphins rely on sounds to communicate. That becomes more difficult if there is chronic anthropogenic noise pollution in the water. As shown below, ocean acoustic levels can be measured and mapped. 

     A 2013 study by Canadian scientist Lindy Weilgart and the Okeanos Foundation laid out the problem with airguns:

 

“Noise from a single seismic airgun survey, used to discover oil and gas deposits hundreds of kilometers under the sea floor, can blanket an area of over 300,000 km2, raising background noise levels 100-fold (20 dB), continuously for weeks or months (IWC 2005, IWC 2007). Seismic airgun surveys are loud enough to penetrate hundreds of kilometers into the ocean floor, even after going through thousands of meters of ocean. Since this exposes large portions of a cetacean population to chronic noise, the International Whaling Commission’s Scientific Committee noted “…repeated and persistent acoustic insults [over] a large area…should be considered enough to cause population level impacts.” (IWC 2005). A recent report by the Convention on Biological Diversity noted that “...there are increasing concerns about the long-term and cumulative effects of noise on marine biodiversity...” and “...there is a need to...take measures [to] minimise our noise impacts on marine biodiversity...” and “...effective management of anthropogenic noise in the marine

environment should be regarded as a high priority for action at the national and regional level...” (CBD 2012).”

 

“Nieukirk et al. (2012) analyzed 10 years of recordings from the Mid-Atlantic Ridge, finding that seismic airguns were heard at distances of 4,000 km from survey vessels and present 80-95% of the days/month for more than 12 consecutive months in some locations. When several surveys were recorded simultaneously, whale sounds were masked (drowned out), and the airgun noise became the dominant part of background noise levels.”

 

     Masking is important as studies have shown that some whale species will stop communicating during an airgun survey and resume when the survey ends. Whales communicate to mate, and it seems very likely that seismic airguns can disrupt their mating. One blue whale population, instead of stopping communicating, actually tried to communicate more while modifying their vocalizations. Whales also tend to move away from the seismic sound sources. Many of the studies suggest that responses to the airguns differ among species and even among different groups of the same species. Studies also suggest that species like whales will dive deep less often when airguns surveys are in progress. Less biological diversity in the vicinity of airgun surveys has been observed. It has also been observed that seismic air guns have probably caused some whale strandings and deaths as well, particularly in beaked whales. This acoustic stress or acoustic trauma to marine organisms needs more research. More importantly, perhaps, there is a need for less acoustically destructive marine seismic sources that impact sea life. Along with effects on ocean mammals, impacts have been observed on marine turtles, fish, and invertebrates.

“At least 37 marine species have been shown to be affected by seismic airgun noise. These impacts range from behavioral changes such as decreased foraging, avoidance of the noise, and changes in vocalizations through displacement from important habitat, stress, decreased egg viability and growth, and decreased catch rates, to hearing impairment, massive injuries, and even death by drowning or strandings. Seismic airgun noise must be considered a serious marine environmental pollutant.”

The paper also notes that “…seismic airguns are the second highest contributor of human-caused underwater noise in total energy output per year, following only nuclear and other explosions…”

     A 2003 paper in Marine Technology Society Journal underscores that there was considerable uncertainty about the specifics of airgun effects on sea life:

“Physical/physiological effects could include hearing threshold shifts and auditory damage as well as non-auditory disruption, and can be directly caused by sound exposure or the result of behavioral changes in response to sounds, e.g. recent observations suggesting that exposure to loud noise may result in decompression sickness. Direct information on the extent to which seismic pulses could damage hearing are difficult to obtain and as a consequence the impacts on hearing remain poorly known. Behavioral data have been collected for a few species in a limited range of conditions. Responses, including startle and fright, avoidance, and changes in behavior and vocalization patterns, have been observed in baleen whales, odontocetes, and pinnipeds and in some cases these have occurred at ranges of tens or hundreds of kilometers. However, behavioral observations are typically variable, some findings are contradictory, and the biological significance of these effects has not been measured.”

Earthjustice mentions the discovery in 2021 of a threatened subspecies of Gulf of Mexico whale, or Rice whale and that they are likely affected by seismic airgun activity. In 2021 Earthjustice participated in a lawsuit against the Biden administration, stopping a Gulf of Mexico lease sale. During the Trump administration when there was consideration of exploring for oil & gas in the Atlantic Ocean to begin with seismic airgun surveying, there was pushback from many environmental groups, some fishing groups, and marine conservation groups.

     A 2017 study published in Nature determined that zooplankton can be killed by seismic airgun blasting at a distance of up to 1.2km, much further than previously thought.  

     The table below shows the dose-response type of relationship between the sound exposure levels that whales receive from different airgun arrays and their avoidance of the loud areas.

 

     The Bureau of Ocean Energy Management released a Record of Decision in 2014 regarding seismic airgun surveys in the Atlantic Ocean. The Bureau’s Chief Environmental Officer noted at the time:

“To date, there has been no documented scientific evidence of noise from air guns used in geological and geophysical (G&G) seismic activities adversely affecting marine animal populations or coastal communities. This technology has been used for more than 30 years around the world. It is still used in U.S. waters off of the Gulf of Mexico with no known detrimental impact to marine animal populations or to commercial fishing.”

“While there is no documented case of a marine mammal or sea turtle being killed by the sound from an air gun, it is possible that at some point where an air gun has been used, an animal could have been injured by getting too close. Make no mistake, airguns are powerful, and protections need to be in place to prevent harm. That is why mitigation measures -- like required distance between surveys and marine mammals and time and area closures for certain species -- are so critical.”

Thus, he argues that while the evidence for harm is not there, it is logical to assume that closeness to the source, or the dose-response relationship dictates potential harm. He noted that environmental groups were often misrepresenting the facts, that sound propagated in water is of a lower intensity than sound propagated in air.

“A large air gun is loud, although it is not 100,000 times louder than a jet. Measured comparably in decibels, an air gun is about as loud as one jet taking off. Scientists who specialize in acoustics confirm that sounds in water and sounds in air that have the same pressures have very different intensities (which is a measure of energy produced by the source) because the density of water is much greater than the density of air, and because the speed of sound in water is much greater than the speed of sound in air. For the same pressure, the higher density and higher speed make sound in water less intense than sound in air.”

“We do not know what a whale, dolphin, or turtle actually experiences when it hears an air gun. Many marine mammal species -- but not the baleen whales including North Atlantic right whales -- have reduced sensitivity to sound signals that are in the same frequency range as airplanes and air gun arrays. Some whales appear to move away from surveys, indicating that they probably don't like the noise, but bottlenose dolphins have often been observed swimming toward surveying vessels, and ride bow waves along the vessels.”

However, he may be downplaying some of the obvious harms like masking and interfering with the animals mating and feeding activities.

 

What are Some Potential Solutions?

     As mentioned, clearly, more research needs to be done to better quantify the potential harms. In 2017 Oceana made the following recommendations for proposed sesmic airgun surveys:

Ø   Sharing of data between companies, the government and the public so seismic airgun blasting happens only once and impacts are minimized.

Ø   Require that companies fund third party passive acoustic monitoring before, during and after seismic airgun blasting to observe any effects on marine life, archive acoustic data recordings and immediately stop seismic airgun surveys if animals are detected during the surveys.

Ø   Require third party visual observers to watch for whales, dolphins and sea turtles before, during and after the seismic airgun surveys, record sightings and immediately stop seismic airgun blasting if animals are within view.

Ø   Do not conduct seismic airgun blasting during endangered and threatened species calving or nesting seasons, or in Critical Habitat areas, Essential Fish Habitat, or in other areas important to the survival of fish, invertebrates, sea turtles or marine mammals.

     Previous to that, in the Bureau of Ocean Energy Management’s 2014 Record of Decision, they

made similar and more detailed recommendations including:

1)        Establishing an acoustic exclusion zone around vessels

2)        Visual monitoring by protected species observers stationed on vessels

3)        Stopping airgun use when animals get too close

4)        Ramping up airguns (before they reach full power)

5)        Passive acoustic monitoring (specifically for marine mammal vocalizations)

6)        Geographic separation of simultaneous surveys

They also recommended no airguns during specific species-specific time periods and off-limits areas known as acoustic exclusion zones where no airguns can operate and those that operate nearby should be of lower decibels.

 

Marine Vibroseis

     Another solution is the ongoing development of marine vibroseis. Vibroseis refers to the practice of using vibrations as a sonic source for seismic surveying. Terrestrial vibroseis, with vibrator trucks, is the wave source for about half of land seismic surveying, with dynamite making up the other half.

     Sesimic airguns have been standard for marine seismic since the late 1960s. Geokinetics began deploying their AquaVib marine vibroseis in 2017 as an alternative to airguns. They note that the sound from AquaVib puts the same amount of energy into the water but over a longer time interval (50msec) rather than the short time interval that airguns blast. This results in a much lower sound and decibel level. The marine vibrators that Geokinetics uses are 16ft by 9ft in size. They have advantages over airguns in that they can be used in shallow water areas which are both underexplored due to difficulty of surveying but also due to environmental restrictions in sensitive coastal environments. Airgun arrays must carry large air compressors which require larger vessels that cannot operate in shallow water. AquaVib was designed for operation in shallow water rather than to alleviate environmental or animal welfare concerns.

     PGS/TGS makes marine vibrators as shown below. They note the pros and cons of marine vibroseis in a December 2017 article:

“Marine vibrators are not a new idea but the various designs, with a short-lived application over the past few decades, suffered from similar flaws: Operationally cumbersome, messy and inefficient hydraulic components, narrow frequency bandwidth, and so on. Whilst the PGS marine vibrator concepts elegantly use only electric driver mechanisms and emit relatively uniform amplitudes over the traditional 5-100 Hz frequency range, industry interest has not been historically motivated by the environmental and efficiency ambitions that have recently surged to prominence worldwide. Due to the growing opposition to air guns in many areas and extreme cost pressures in the global industry climate, it may now be time to enter a new era in marine seismic survey technology and allocate more E&P company funding to the commercialization of marine vibrator technology.”

     These problems and issues will likely have to be well worked out before the industry adopts marine vibroseis as it does not yet appear that vibroseis data is comparable in quality to data acquired with airguns. That could change at some point in the future, and it would be nice for marine species if it does.

     Since 2011, ExxonMobil, Shell and Total have sponsored much of the research for the development of marine vibroseis technology, in a project known as the Marine Vibrator Joint Industry Project. Some environmental groups want to force the offshore oil & gas industry to adopt marine vibroseis but only if and until the harms are better quantified that is not likely to happen unless the data quality improves.

 

 

     In January 2022, Shearwater GeoServices, Equinor, and a few other companies made an agreement to “accelerate the development and commercialisation of a sustainable marine vibratory source technology to minimise environmental footprint and enhance data quality from seismic data acquisition.” Once fully developed they expect an improvement in data quality. If this occurs, then airgun use will decrease.

 

     Those so-called acoustic exclusion zones have also spurred research into making seismic airgun blasts lower decibel events. This involves reconfiguring the arrays to produce an adequate sonic source, but one with a lower decibel output. Decreasing the sound exposure level (SEL) threshold can be done, but thus far only in a limited sense by changing airgun array configurations.

 

References:

UNDERSTANDING AIRGUNS, SEISMIC SURVEYS, AND THEIR POTENTIAL FOR EFFECTS ON MARINE ANIMALS. Discovery of Sound in the Sea. www.dosits.org. December 2018. SeismicsFactSheet_DOSITS_vs3

A Review of The Effects of Seismic Surveys on Marine Mammals. Jonathan Gordon, Douglas Gillespie, John Robert Potter, and Alexandros Frantzis. December 2003. Marine Technology Society Journal 37(4):16-34. (PDF) A Review of The Effects of Seismic Surveys on Marine Mammals (researchgate.net)

Offshore Oil & Gas Exploration: Seismic Airgun Blasting. Oceana.org. Seismic Factsheet. 2017. https://usa.oceana.org/wp-content/uploads/sites/4/662/seismic_fact_sheet_long_final_7-25_0.pdf

THE EFFECTS OF SEISMIC SURVEYS ON MARINE ORGANISMS. University of Georgia. February 2021. Microsoft Word - Effect of Seismic Surveys on Marine Organisms 10.docx (uga.edu)

Seismic Airgun Blasting in the Atlantic Ocean: Case Overview. Earthjustice. May 18, 2021. Seismic Airgun Blasting in the Atlantic Ocean - Earthjustice

There’s a Biodiversity Crisis, and Oil and Gas Are Making It Worse. Alison Cagle. Earthjustice. March 16, 2023. There's a Biodiversity Crisis, and Oil and Gas Are Making It Worse - Earthjustice

Leading Scientists Set the Record Straight on Seismic Airgun Blasting in the Atlantic: “Seismic Activity is Likely to Have Significant, Long-lasting, and Widespread Impacts”. Oceana. Press Release Date: March 10, 2015.  Leading Scientists Set the Record Straight on Seismic Airgun Blasting in the Atlantic: “Seismic Activity is Likely to Have Significant, Long-lasting, and Widespread Impacts” | Oceana

A Review of the Impacts of Seismic Airgun Surveys on Marine Life.Lindy Weilgart, Ph.D. Department of Biology Dalhousie University, Halifax, Nova Scotia and Okeanos Foundation Darmstadt,  Germany. November 14, 2013.  mcbem-2014-01-submission-seismic-airgun-en.pdf (cbd.int)

Air guns used in offshore oil exploration can kill tiny marine life. Jeff Tollefson. Nature volume 546, pages586–587 (2017).  Air guns used in offshore oil exploration can kill tiny marine life | Nature

Widely used marine seismic survey air gun operations negatively impact zooplankton. Robert D. McCauley, Ryan D. Day, Kerrie M. Swadling, Quinn P. Fitzgibbon, Reg A. Watson & Jayson M. Semmens. Nature Ecology & Evolution volume 1, Article number: 0195 (2017). Widely used marine seismic survey air gun operations negatively impact zooplankton | Nature Ecology & Evolution

Air Gun Arrays: Setting the Scene for a New Era. 2019.  industry_insights2019_04_air-gun-fundamentals.pdf (pgs.com)

Airgun arrays for marine seismic surveys - physics and directional characteristics. Alec J Duncan. Centre for Marine Science and Technology, Curtin University, Perth, Australia. Acoustics 2017 Perth.  p88.pdf (acoustics.asn.au)

A safe alternative to the seismic airgun. Molly Lempriere. Offshore Technology. June 16, 2017. A safe alternative to the seismic airgun - Offshore Technology (offshore-technology.com)

REPORT OF THE WORKSHOP ON ALTERNATIVE TECHNOLOGIES TO SEISMIC AIRGUN SURVEYS FOR OIL AND GAS EXPLORATION AND THEIR POTENTIAL FOR REDUCING IMPACTS ON MARINE MAMMALS. Held by Okeanos - Foundation for the Sea. Monterey, California, USA. 31st August – 1st September, 2009. Edited by Lindy Weilgart, Ph.D.  Prologue (dal.ca)

MARINE VIBROSEIS: A SAFER ALTERNATIVE TO SEISMIC AIRGUNS FOR THE NORTH ATLANTIC RIGHT WHALE. APRIL 23, 2019. KBASTOLLA. Debating Science. University of Massachusetts. April 23. 2019. Marine Vibroseis: A Safer Alternative to Seismic Airguns for the North Atlantic Right Whale – Debating Science (umass.edu)

Protecting whales from the noise people make in the ocean. Chris Baraniuk. BBC. February 27, 2020. Protecting whales from the noise people make in the ocean (bbc.com)

Marine Vibrators Get Closer to Reality. PGS/TGS. December 13, 2017. Marine Vibrators Get Closer to Reality | Oil and Gas Exploration | Marine Seismic Acquisition | PGS

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