BOEM clarifies airgun noise position

Chief environmental officer says there is no evidence that offshore seismic surveys have adverse impacts on animal populations

Alan Bailey

Petroleum News

On March 9 William Brown, chief environmental officer for the Bureau of Ocean Energy Management, issued a science note clarifying BOEM’s views on the impact of offshore seismic surveys on marine animals and refuting claims that surveys damage animal populations.

A marine seismic survey typically involves towing an array of air guns behind a seismic vessel. The airguns are fired at regular intervals, sending pulses of sound through the water column and into the rock strata below the seafloor. Echoes of the sound pulses are recorded through receivers called geophones, with the recordings subsequently being used to construct images of subsurface geologic structures.

At question are the impacts of the sound pulses on marine animals.

Brown said that a previous BOEM science note, published in August 2014, had stated that “to date, there has been no documented scientific evidence of noise from air guns being used in geological and geophysical … seismic activities adversely impacting animal populations.” However, there have been public statements citing the findings of BOEM research, claiming that many thousands of marine mammals will be killed or injured as a consequence of offshore seismic surveying, Brown said.

According to one Website “seismic air gun testing being proposed in the Atlantic will injure 138,000 whales and dolphins and disturb millions more according to government estimates,” Brown said. But statements of this type misrepresent BOEM’s evaluation of the potential environmental impacts of seismic surveying, he said.

In conducting this type of evaluation, government regulators assess whether a proposed survey program will comply with the Marine Mammals Protection Act, an act that prohibits the “take” of marine mammals, other than takes that are unintended and incidental, and that have been approved by an appropriate federal agency. Legally, a take can be something as simple as the minor disturbance of an animal.

However, the evaluation of the impact of an offshore activity on an animal species is conducted at the level of the entire animal stock, and not on the basis of impacts on individual animals, Brown explained.

To qualify for federal approval, an offshore activity and its associated takes can only have a negligible impact on that animal stock, with no adverse impacts on the animals’ rates of recruitment or survival, Brown said. And the BOEM issuance of an offshore seismic permit is predicated on the permit applicant obtaining appropriate incidental take authorizations. Those authorizations are designed to ensure that each animal species can sustain a population level appropriate to the carrying capacity of the species habitat and the health of the surrounding ecosystem, Brown said.

In the case of BOEM’s evaluation of possible seismic surveying in the Atlantic, the agency estimated the potential take of more than 1 million bottlenose dolphins, for example, but with less than 12,000 of these takes having significant impacts on individual animals. These numbers err on the side of caution, given mitigation measures such as wildlife exclusion zones mandated around airguns, Brown said. And dolphin stocks in the Gulf of Mexico have not been impacted by seismic surveys that are routinely carried out in that region, he said.

Brown did, however, argue for further research into the impacts of offshore seismic surveying on marine wildlife, to better understand the nature of those impacts.