Oil and gas companies rely on seismic airguns to understand what lies under the ocean floor. By bouncing sound waves off the floor, they can uncover potential energy deposits. But scientists and conservationists say such testing should be eliminated because of the unintended consequences on marine animals.

These blasts of compressed air can have powerful impacts on the marine ecosystem, some of which we're just now beginning to understand.

How seismic airguns work

Seismic airguns blast compressed air into the ocean at regular intervals, sometimes as often as once every 10 seconds, according to Woods Hole Coastal and Marine Science Center. Each blast of air creates a sound wave that travels to the ocean floor and bounces back up to the vessel's hydrophones, giving a computer system a picture of the floor's geological features. This data can determine whether or not there's the potential for an oil or gas well. The guns are towed behind a ship in a long chain or net and emit an acoustic pulse as the vessel sails through the ocean.

The process basically looks like this from the back of the vessel:

Near the end of the video, around the 13-second mark, you hear a thump and see a burst of water around the devices; that's the airguns firing. Even over the sound of the vessel and the wind, the thump is loud enough to be detected by the camera's microphone. According to the National Resource Defense Council (NRDC), what you'd hear under the ocean sounds like this.

It sounds like an explosive charge going off, except under the ocean. If that sound was going off every 10 seconds around you, it'd be cause for concern, especially since the highest decibel level for seismic airguns is 160 decibels, a level set by the Bureau of Ocean Energy Management (BOEM). That's basically the decibel level of a jet taking off or the blast of a shotgun. Some airguns can go to higher levels, including in the 250-260 range.

The effects of seismic airguns

The ramifications of these pulses can be severe, according to scientists. A 2013 review of seismic airgun studies found that the blasts can cover an area of 115,831 square miles (300,000 square kilometers) and raise the background noise of the ocean by around 20 decibels for weeks or even months. One study cited in the review found that the blasts could be heard 2,485 miles (4,000 kilometers) away from the survey vessel.

Given the sheer scope and noise level of the airguns, their ability to influence marine life is considerable. A 2017 study found that seismic ocean surveys resulted in a two- to threefold increase in the deaths of adult and larval zookplanton, the foundation on which the marine ecosystem is built. The sounds also killed larval krill, the tiny creatures that play an oversized role in the marine food web.

When it comes to marine mammals, like various whale species, airguns can lead to a variety of dangers and side effects. This can include temporary and permanent hearing impairment, stress responses, avoidance responses, changes in vocalizations or drowning out vocalizations entirely.

A krill floating in water Even the tiny krill is affected by seismic airgun surveys. (Photo: RLS Photo/Shutterstock)

Different whales respond differently. A group of 250 fin whales stopped singing for nearly a month during a seismic survey. This may have interfered with their reproductive functions. A separate blue whale population exhibited the opposite behavior, vocalizing more in the presence of seismic surveys, and researchers suggested that they were attempting to compensate for the increase noise presence.

Multiple species, including dolphins, sperm whales, pilot whales and killer whales, exhibited either long-range or localized avoidance for seismic surveys, pushing them outside their normal ranges or avoiding their preferred feeding areas. In addition, some strandings have been linked to the airgun surveys.

Fish exhibit a range of behavioral responses, including "freezing" or becoming more active, depending on the species. At sites where seismic airgun surveys were conducted, catch rates are severely reduced, sometimes up to 90 percent, even as far away as 19 miles from the survey site.

The lead author on the 2103 review, Lindy Weilgart, told Inverse that there is "no longer any scientifically valid doubt" about the dangers airguns pose to marine life.

The latest on seismic airgun surveys

A vessel trails a seismic airgun array behind it Scientists have found that seismic airgun surveys have negative effects on marine life. (Photo: Leo Francin/Shutterstock)

It's been more than 30 years since seismic surveys were conducted in the Atlantic Ocean. During the Obama administration, seismic survey applications were denied, and the administration placed a ban on oil and gas drilling in the Atlantic. In April 2017, President Donald Trump issued an executive order that called for a "streamlining" of seismic survey permits. It was intended to help implement a five-year-plan to tap offshore oil and gas deposits in federal waters.

The surveys have been met with litigation from conservation organizations like the Center for Biological Diversity, Oceana and the NRDC. On Feb. 20, their motion to stop the the seismic surveys was merged with similar lawsuits filed by 16 South Carolina coastal communities and the state's Small Business Chamber of Commerce. South Carolina's governor and attorney general, both Republicans, supported the merged lawsuits.

"Bombarding endangered whales with deafening blasts to search for dirty oil is indefensible. The court should prevent the devastating harm seismic airgun blasting would do to marine life," said Kristen Monsell, ocean legal director with the Center for Biological Diversity. "There's strong bipartisan opposition to Trump's proposal to allow offshore drilling in the Atlantic. We need to leave that oil in the ground and call off this sonic attack on North Atlantic right whales and other animals."

North American right whales calve in the Atlantic Ocean. Their population is estimated to be around 450 individuals.

Legislation in the U.S. House of Representatives is currently making its way through that chamber. U.S. Rep. Joe Cunningham (D-S.C.) introduced the Coastal Economies Protection Act on Jan. 8. That bill would place a 10-year moratorium on offshore drilling. Cunningham, who worked as an ocean engineer for five years, hopes to get the bill through committees by April.

Plans for seismic testing in Alaska's Arctic National Wildlife Refuge were stopped early in February. The prevention of seismic testing did not impede the Department of Interior's plan to offer leases for 1.5 million acres of ocean to oil and gas companies by the end of 2019, however. The companies would simply have to buy land without knowing what potential reserves are underwater.

How seismic blasting affects marine animals
Seismic airguns used to find oil and gas wells can lead to animals losing their hearing, abandoning habits and disrupt their mating and foraging activities.