Seals Take Hearing Tests—and Offer Insight Into Arctic Drilling's Impact on Marine Mammals

How will Shell’s Arctic drilling affect marine mammals in the Chukchi Sea?
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(Photo: Joel Garlich-Miller/USFWS)

(Photo: Joel Garlich-Miller/USFWS)

The Arctic Ocean is hopping right now. Royal Dutch Shell plans to start drilling for oil in the Chukchi Sea later this month, and its two massive drill rigs, the Polar Pioneer and the Noble Discoverer, are garnering most of the attention. But let’s not forget the rigs’ sizable entourage of 30 support vessels and seven aircraft—all vehicles for noise.

The resulting cacophony—which includes seismic surveys, drilling, and helicopters shuttling supplies to ships dozens of times per week—could dramatically affect the Arctic’s whales, walruses, and seals.

“In the Arctic, I can’t emphasize how novel an activity this is,” says Natural Resources Defense Council attorney Giulia Good Stefani. “It really is a whole new level of disturbance for an area already experiencing rapid change and stress.”

By Shell’s own count from its spectacularly calamitous exploratory drilling efforts in the Chukchi three summers ago, marine mammals abound in the frigid waters. That summer, company observers counted 8,678 Pacific walruses, 1,386 seals, 1,179 whales, and 61 polar bears.

The oil giant has already suffered a major blow this year, thanks to its decision to ignore established regulations to protect this bevy of marine mammals. Shell had been planning to drill in two spots nine miles apart, but late last month the Obama administration nixed that plan after green groups, including EarthJustice, Oceana, and NRDC, sent a letter highlighting the illegality of the move. Under a 2013 United States Fish and Wildlife permit, the company must maintain a 15-mile buffer between rigs to avoid significantly harming Pacific walruses, and Shell is now re-evaluating whether it can use both rigs. The company’s prized Chukchi Sea Burger prospect is near Hanna Shoal, an area 75 miles off the coast where the large pinnipeds feed. Human noise, scientists think, may cause the animals to abandon food and swim to haul-out sites, which are increasingly farther away as sea ice shrinks and walruses are forced to return to land.

“I think it's really important that people consider the acoustic impact Shell will have on the Chukchi this summer—not just from drilling but also from the flotilla of support vessels they will be using,” says Kate Stafford, a University of Washington oceanographer who studies acoustics. This week, Stafford and colleagues will deploy an underwater robot to zigzag up the Chukchi Sea, monitoring marine mammals and ambient noise.

The work could help provide valuable insight that’s currently lacking. “There’s a lot we don’t know,” says Brandon Southall, an expert in marine mammals and human sounds at SEA-Inc and the University of California-Santa Cruz, and the former director of the National Oceanic and Atmospheric Association’s Ocean Acoustics Program. That includes specifics on how different animals hear, how sound affects communication and behavior, and how it might affect reproduction.

Here’s what scientists do know:


There’s a lot of noise associated with oil exploration and drilling. “From earlier monitoring done in 2012, we know that, from a sound perspective, drilling is actually a minor contributor to sound,” Southall says. But the other activities—seismically surveying the sea floor, busting up sea ice, drilling to anchor the vessels—generate a heck of a clamor, which can travel for miles underwater.


One thing the activities have in common is that they create mostly low-frequency sounds. Low-frequency noise covers larger expanses of the sea and can disturb, and potentially harm, animals that hear it—especially those that communicate at those same frequencies.

So far, most of the research on how noise affects marine mammals has been done in labs—thus, the study subjects have been fairly small species. “So no baleen whales,” Southall says. But based on a whale’s anatomy and the types of sounds they make, as well as field observations of how various wildlife respond to navy sonar and industry noises, Southall suspects that whales are the most vulnerable to drilling in the Arctic. Seals, sea lions, and walruses probably can’t hear noises as low as whales can. Meanwhile, dolphins and porpoises pick up high-frequency sounds.

Jillian Sills and her colleagues at the Pinniped Cognition and Sensory Systems Laboratory at U.C. Santa Cruz recently reported that the hearing of spotted and ringed seals is more sensitive than was previously thought—both on land (where they rest, molt, give birth, and nurse) and underwater (where they hunt)—and that the animals hear better at lower frequencies.

To measure the species’ hearing, Sills worked with seals that had been orphaned as pups and couldn’t be returned to the wild. She trained them to participate in hearing tests similar to those humans take in doctors’ offices, where the participant raises her hand when she hears a sound. Similarly, the seals touched a target when they heard a sound and remained still when they didn’t. A correct response earned the adorable pinniped a fish reward.


Imminent death from loud, low noises isn’t a big concern. “It’s not that these animals are going to float up dead,” Southall says. Rather, it’s that the ruckus might interfere with their communication or their ability to detect predators or prey. “Like if you’re in a noisy restaurant,” says Southall, “you can still hear somebody, but you both have to talk a little louder and you might miss some things. So there are consequences—but they’re more subtle and difficult to quantify.”

Sills has found that ringed and spotted seals are “quite good” at listening for specific sounds within typical ocean background noise. But there’s certainly a possibility, she says, that more noise could mask the seals’ detection of approaching predators or messages from their kin. Now Sills and her colleagues are examining how seismic air guns may interfere with the animals’ hearing—both during and after the “boom” rings out.

As for how noise affects behavior, most of the evidence is anecdotal. Seals, though skittish on land, seem fairly tolerant of noise in water. Bowhead whales tend to hightail it out of the area. Walruses have been known to flee, too, particularly when they’re on land, which can cause youngsters to be trampled to death.

Southall says a number of factors likely come into play, such as whether the species is a hunted one, if the sound is similar to a predator’s signal, and how rich the pickings in the place are: “If they’re in an area with a lot of food, they might just stay there and suck it up.” As scientists work to better understand the immediate effects of anthropogenic racket, they’re also digging into the longer-term effects, such as changes in feeding, survival, and reproduction.


Even as Shell readies to drill, environmental groups are pursuing several legal attacks to try to stop what they say is too risky a venture. Earth Justice has filed several lawsuits on behalf of green groups, including NRDC and the Sierra Club. The lawsuits challenge FWS’s assessment of travel corridors between haul-outs and the shoal; the sale of 30 million acres of the Chukchi to Shell; and approval of the company’s exploration plan, alleging that the government didn’t adequately assess the environmental threats.

Should the lawsuits fail to halt or slow drilling, if Shell does find oil, it’ll take at least a decade to build the necessary infrastructure to pump it. And if the company is successful, others will undoubtedly take to Arctic waters, too. That means we’re potentially looking at decades of increasing disturbances at the top of the world, in a place that climate change is altering more rapidly than anywhere else on the planet. That makes figuring out how the din affects marine mammals—and mitigating development to safeguard those species—more important than ever.

This post originally appeared on Earthwire as “Bringing the Noise” and is re-published here under a Creative Commons license.