Impacts of Seismic Survey Blasting on Marine Environment

By Sue Arnold

CEO, California Gray Whale Coalition

Photos by

Charmaine Coimbra


One of the most important outcomes of the PG&E HESS – whichever way it goes – is the raising of awareness on the issue of underwater noise and acoustic trauma. Considering the precedent which would be set by allowing 260dB to be blasted into the seabed, impacting a vital environmental and economically important marine ecosystem, noise issues have become front and center.

Commercial and recreational fishers, the tourist industry, whale-watching organizations, surfers, divers, and other operations which rely on the central coast’s marine life are under threat.

Southern Sea Otter-Piedra Blancas, CA

Thousands of animals will be impacted including whales, dolphins, harbor porpoises, sea otters, elephant seals, and many commercial fish species.

Any precedent set by the California Coastal Commission in approving a permit for PG&E would give the go-ahead for other highly destructive seismic operations at a time when noise in the marine environment has become the main focus for many scientists and researchers.

Noise has a devastating impact on the marine environment. Given recent research on the devastating impacts of underwater noise on fish, coral, larvae, eggs, and aquatic life, noise is up there with climate change and ocean acidification. As the oil and gas industry seek deposits to allow the continuing mad race to consumption – the main driver of the US economy – the west coast has been identified as holding more oil deposits than Saudi Arabia, according to Richard Charter, a Senior Fellow with the Ocean Foundation.

Indeed, when the California Gray Whale Coalition consulted some of its deep throat informants in the oil industry, the first response to the information that the source blast was 260dB was:

“Ah, they’re looking for oil deposits.”

The most important measurement in assessing potential damage is the received level of decibels. The received level changes as the geoacoustic parameters change (tides, wind, sea surface temperatures, salinity, ducting, thermoclines).

Acoustic signals can travel long distances depending on the state of the tides, wind, seabed and other parameters. Christopher Clark, Director of Bioacoustic Research Program, Cornell University, says one of the best examples of the distance underwater noise can travel is the recent Shell seismic survey on the west coast of Ireland.

“We could hear that noise 1500 miles away. The noise could be heard in Nova Scotia and Newfoundland.”

Clark says the cumulative impact of noise in the urbanized ocean environment seriously compromises whales. He uses this example:

“Imagine a space ship is over your village and it’s sending explosions down to every 10 seconds, driving everybody crazy. The choice is you either leave or die.  

“The acoustic world is 10% of what it should be. The whales social network is destroyed, their world seriously compromised, their immune and reproductive systems impacted by stress created by noise. Animals which rely on sound lose the opportunity to engage in basic life functions and social networks.

“When you tear at those networks constantly, what does it mean if 50% or more of their acoustic world is compromised?”

The use of sound for communication and detection in the marine environment is important for survival for marine animals. Marine animals

Northern Elephant Seals, Piedras Blancas, CA

depend on their hearing sensitivity to retain cohesion in groups, for echolocation to locate and capture food, for detection of predators, for sensing their physical and biological environment and for avoiding dangerous situations (including anthropogenic threats).

Impacts of acoustic trauma include:

  • Organ damage; physiological damage which may lead to death
  • Permanent Threshold Shift (PTS): a permanent shift in hearing sensitivity
  • Temporary Threshold Shift (TTS): a temporary effect upon hearing ( recoverable)
  • Behavioral responses which may span short-term startle responses to long-term avoidance of areas by animals or a change to movement pathways or migration routes.
  • Masking signals.

Some of the impacts are well summed up by Canadian bioacoustician Dr. Lindy Weilgart (1). Her list of potential impacts include:

  • Detectable Effects
  • Respiration rate
  • Swim speed
  • Vocalizations
  • Dive times
  • Depth times
  • Dive depth
  • Residence time
  • Distribution
  • Movement relative to sound source
  • Non-detectable Effects
  • Birth rate
  • Miscarriage rate
  • Pregnancy rate
  • Birth defects
  • Mating rate
  • Rate of finding mates
  • Lactation rate
  • Changes in mating dynamics
  • Death rate
  • Injury, disease, morbidity
  • Vulnerability to hazards, shipping, fishing nets
  • Vulnerability to predation
  • Growth rate
  • Feeding rate and changes in appetite
  • Change in echolocation ability

Great variation in hearing sensitivity among animals, due to evolutionary diversification of anatomical structures involved in hearing and selection pressures, govern the way different animals utilize sound. Every animal is unique.
1 Potential impacts of noise pollution on cetaceans as listed by Dr. Lindy Weilgart, Bioacoustician, and Dalhousie University, Nova Scotia.

It’s important to consider the effects of cumulative exposures on mortality, physiology and behavior. Consideration of the effects of exposure to multiple impacts and the time between signals (one every few seconds, for example) need to be made. Investigation of a larger temporal length of exposure to repeated signals (repeated exposures several hours, days, weeks, months later) needs to be undertaken.

Man-made underwater noise covers a large range of frequencies, and the way in which a species is impacted by the sound will depend on the

Gray Whale Calf, Baja California

frequency range it can hear, the level of sound (or energy) and its frequency spectrum (Nedwell et al. 2004).

It is clear from the smorgasbord of current research on noise impacts in the ocean that the PG&E HESS presents an unacceptable risk to the marine environment.

The PG&E HESS is remarkable for its lack of adequate mitigation measures. With no real-time sensors there’s no way of determining the received levels which marine animals are exposed to. At least three days could pass before this information is available under the proposed system. As received levels of noise can change on an hourly basis depending on the tides, wind, seawater temperature and so many factors, the damage caused by received levels could be very difficult to determine with a three-day waiting period.

Worse still is the problem of who would carry out necropsies, when and where and how long would it take for the results to be made available? As there are only audiograms for 11 species of cetaceans, the probability of a decision-indicating acoustic trauma is the cause of death is remote. Most cetaceans sink to the seafloor when they die and it may be days and weeks or never before any corpse comes ashore.

Audiograms for other marine life are not yet available. Given the delays involved in determining the cause of death, the seismic operation is unlikely to be stopped as powering down seismic arrays is an expensive operation.

Listed below are some of the basic information which has been ignored by the PG&E HESS. National Marine & Fisheries have also failed to take into account these essential parameters.


Impacts of noise sources need to take into account noise characteristics including sound level, noise duration, frequency, sound propagation characteristics of the area; the sensitivity of species of concern; physical robustness; size and age of species; life history and relative population sensitivity; timing of different stages of life history; animal distribution and abundance; migration patterns and whether the species can or are likely to move away from the noise if distressed by it (2). And whether a new area is capable of supporting their survival needs given competition and disease risks.


In order to assess the impacts of underwater noise the following information is essential:

  • key marine species likely to be present in the region and their sensitive periods be identified.
  • the noise signature of the construction technologies described.
  • ambient sea noise measured
  • sound propagation models run to predict transmission of key underwater noise sources (3)
  • cumulative impact of combined noise and impacts of continuing noise over many years
  • shipping noise

2 Environment Impacts of Underwater Noise Associated With Harbor Works Port Hedland. C P Kent, R. McCauley, A Duncan for SKM/BHP Billiton August 2009
3 Ibid

Susanna Blackwell is a bioacoustics expert who has worked on noise data in the Arctic environment.
She says that there currently is no modelling which can demonstrate the cumulative impacts of a seismic study:

“Modeling enables scientists and acousticians to look at the worse case scenario in terms of the sound speed profile. Modeling does not assess the effects on animals. Models are purely to determine sound level and sound source verification. Models do not take into account the levels of noise which observer planes, ships, multibeam scanners or sidescanners involved in any seismic project create. Modeling can be inaccurate and 0.5 dB can make a 20 km difference.” 

“Sound source verification can take up to three days. In some cases it can take four hours but unless the verification of received levels is done in real time, it’s almost pointless to ask for the levels.”

Brandon Southall is also a recognized expert on acoustic trauma in the marine environment. He has expressed concern at the lack of real-time sensors and the lack of triggers which would indicate damage is occurring.

John Calambokidis of Cascadia Research in Washington has indicated his concern over the project.

“I do not think that looking for strandings is a very effective way to examine mortality since we have shown in some previous work that only a small proportion of cetaceans that die show up as strandings. I do think there is greater potential for displacement and disruption of feeding than acknowledged and certainly our understanding of the impact of these types of surveys is very poor.

“I think they have not made any attempt to even advance to knowledge of the impact of these types of surveys by conducting a more thorough study related to this survey.

Adult Gray Whale, Baja California

“They have made no attempt to even attempt to photo-ID or document the individual whales exposed to the airgun survey so we can at least attempt to examine the long-term consequences of exposure to this sound (something that has not been done previously and is clearly needed). We have large long-term catalogs of the individual IDs for the majority of the humpback and blue whales that feed off California and a portion of the fin whales.”


The Convention on Biological Diversity Secretariat’s Subsidiary Body on Scientific Technical and Technological Advice, Sixteenth Meeting, April 30-May 5, 2012, considered a paper on impacts of underwater noise entitled: “Scientific Synthesis of Underwater Noise on Marine and Coastal Biodiversity and Habitats.”

The United States is a signatory to this Convention and obliged under international law to abide by the provisions of the treaty. Any permission by the Federal and State governments or relevant agencies to the PG&E HESS would arguably be a violation by the US of the Convention.

“The Impacts of Underwater Noise on Marine Biodiversity”

5.  A variety of marine animals are known to be affected by anthropogenic noise. Negative impacts for at least 55 marine species (cetaceans, teleost fish, marine turtles and invertebrates) have been reported in scientific studies to date. (Please note sentences in bold are bolded by the Secretariat)

6. A wide range of effects of increased levels of sound on marine fauna have been documented both in laboratory and field conditions. The effects can range from mild behavioral responses to complete avoidance of the affected area, masking of important acoustic signals or cues , and in some cases serious physical injury or death. Low levels of sound can be inconsequential for many animals. However, as sound levels increase the elevated background noise can disrupt normal behavior patterns leading to less efficient feeding for example. Masking of important acoustic signals or cues can reduce communication between con-specifics and may interfere with larval orientation which could have implications for recruitment. Some marine mammals have tried to compensate for the elevated background noise levels by making changes in their vocalizations.

Intense levels of sound exposure have caused physical damage to tissues and organs of marine animals, and can lead to mortality, with lethal injuries of cetaceans documented in stranded individuals caught up in atypical stranding events. Lower sound levels have been shown to cause permanent or temporary loss of hearing in marine mammals and fish. Behavioral responses such a strong avoidance of the sound source can lead to habitat displacement.

7. There are increasing concerns about the long-term and cumulative effects of noise on marine biodiversity. The long-term consequences of chronic noise pollution for individuals and populations are still mainly unknown. Potential long-term impacts of reduced fitness and increased stress leading to health issues have been suggested. There is also growing concern of the cumulative effects of anthropogenic sound and other stressors and how this can affect populations and communities. The additional threat of living in a noisy environment may push already highly stressed animals into population decline with subsequent effects on marine communities and biodiversity.

8. Research is required to better understand the impacts of anthropogenic sound on marine biodiversity. The lack of scientific knowledge regarding the issue is also one of the most important limitations for effective management at the present time. There are high levels of uncertainty for noise effects on all marine taxa. Detailed research programs of noise effects on species, populations, habitats and ecosystems, plus also cumulative effects with others stressors, need to be put in place or consolidated where they exist. However, the extensive knowledge gaps also mean that prioritization will be required. Recommended priorities for research include species that are already highly threatened, endangered or particularly vulnerable through a combination of multiple stressors and intrinsic characteristics, but also representative groups of understudied taxa. Current knowledge for some faunal groups such as teleost fish, elasmobranch fish, marine turtles, seabirds and invertebrates is particularly lacking. Other priorities for acoustic related research are the identification and protection of critical habitats that endangered or threatened marine species depend on for important activities such as foraging or spawning.

9. There is a need to scale up the level of research and management efforts, to significantly promote greater awareness of

Northern Elephant Seal, Piedras Blancas, CA

the issue and to take measures minimize our noise impacts on marine biodiversity.

10. Effective management of anthropogenic noise in the marine environment should be regarded as a high priority for action at the national and regional level through the use of up-to-date mitigation measures based on the latest scientific understanding of the issue for marine species and habitats. Mitigation and management of anthropogenic noise through the use of spatio-temporal restrictions (STR) of activities has been recommended as the most practical and straightforward approach to reduce effects on marine animals.

It is very clear from the information and research available that the PG&E HESS is scientifically unacceptable and the potential damage so significant that any proper assessment could take years to ascertain.

Finally, when two Coalition representatives decided to doorstop the President of PG&E in downtown San Francisco, we were told to sit patiently and wait for a decision.

Two security people rolled up to ensure we were sent on our way.

That sums up the attitude of this influential company.


The California Gray Whale Coalition was set up five years ago with one sole purpose: to re-instate the Gray Whales under the provisions of the Endangered Species Act. The Coalition represents economic and environmental organizations as it recognizes the importance of the whales to the economies of Washington, Oregon and California. With more than 140 member organizations ranging from Mexico to Alaska, the Coalition is now the largest whale conservation coalition on the west coast of North America. Coalition members are active at the political level lobbying in the California Assembly and Senate and also the House and Senate in Washington, DC. For more information on the California Gray Whale and underwater noise issues in particular, please contact

Categories: Dolphins, Fisheries, Marine Mammal Rescue, nature, Northern Elephant Seal, Seismic Testing, Whales

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2 replies

  1. Great analysis. Thanks for your thoughtful research. I hope you submitted it to the Coastal Commission! This will be an ongoing issue and we will need to be vigilant.

  2. I am against the mining and destroying of our sea and nature.

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