Roughly a decade ago, a team of biologists glued audio recording devices onto the backs of a handful of elephant seals on the California coast. They wanted to know if the seals — identified as males by their cartoonish faces with trunk-like noses — make noises as they swim out to sea in search of food.
The recordings they brought back caught the researchers by surprise. There was no evidence of seals vocalizing while foraging, but the devices did pick up something else: the eerie, clicking calls of sperm whales, which sound like someone walking up a creaky staircase. Some of the calls also seemed to get louder, leading the researchers to believe that the seals were swimming toward the whales, and maybe even eavesdropping on them to find food.
Nothing much came of that discovery, but it has inspired marine biologists to use seals as a tool to eavesdrop on other marine life. Elephant seals spend about nine months each year at sea and travel across far reaches of the Pacific that would otherwise be difficult for scientists to survey. And like migratory birds, the seals return to the same spot year after year, so researchers can equip them with recording devices and retrieve them relatively easily.
As soon as next week, marine biologists at the University of California Santa Cruz (UCSC) will test out this slippery technique. They’ll attach acoustic monitors to a few northern elephant seals before the animals depart for a little over two months.
If all goes as planned, it will be the first time scientists use animals — rather than a network of underwater microphones — to spy on marine life in the deep ocean for longer than a few days. What they overhear could help scientists unlock the mysteries of elusive marine mammals, such as beaked whales, and understand how poorly known ecosystems are changing as the planet warms.
Why seals make such good spies
Scientists have used audio recording devices to monitor marine life for decades. It’s a common way to survey species like the rare vaquita porpoise. What makes this project unique, however, is that these devices won’t be fixed in place or dangling from a boat — they’re attached to living, breathing, moving animals.
Elephant seals might look clumsy on land, but they’re agile underwater creatures that make ideal marine sentinels. They spend months at a time foraging far offshore, not even returning home to sleep. The animals likely take naps while drifting a few hundred meters underwater, said Roxanne Beltran, an assistant professor at UCSC who’s co-leading the project.
Elephant seals descend as much as a mile underwater when hunting for small fish, squid, and even sharks, and that brings them within earshot of whales and other marine mammals. Conveniently enough, seals themselves don’t make much noise. “They’re not contaminating the data,” said Holger Klinck, an expert in bioacoustics at Cornell University who’s co-leading the project with Beltran. “They’re really only measuring what’s going on in their surroundings.”
Perhaps most importantly, the seals return to the same beach each year, which reduces the risk of losing equipment. For the project at UCSC, each recording device is roughly the size of an old cellphone and costs about $5,000. It isn’t capable of beaming acoustic data back to shore, Beltran said, so if you lose the device, you lose everything.
Using an epoxy adhesive, Beltran and Allison Payne, a doctoral researcher at UCSC, will glue recording devices onto three female seals at Año Nuevo Reserve in Northern California. (Females have a much higher survival rate and reliably head out to sea right after weaning their pups.) Beltran is building on research led by UCSC’s Dan Costa, who heads a project to monitor local seals that dates back to the 1960s.
Then they’ll wait. The seals will make it about a quarter of the way to Japan before turning back, in a trip that takes roughly 75 days. The device will record about 40 days of audio before the batteries run out, while other tags measure things like location, depth, and water temperature, leaving the scientists with lots of clues to what’s happening in a largely unknown stretch of ocean.
Uncovering mysteries of the deep
When the animals return, scientists will meet them on the beach and retrieve the devices before sending the seals on their way. (The devices don’t harm the seals or change their behavior, Beltran said.) Then they’ll run the audio through computer algorithms that separate out the unique sounds made by each species. A humpback whale can sound a bit like a whining puppy crossed with Chewbacca, for example, while orcas often sound like a metal detector gone haywire.
Payne will be listening closely for the echolocating clicks of beaked whales. This group of toothy marine animals, often gray or black and white, have eluded scientists for decades. “We know almost nothing about them,” she told Vox.
Beaked whales make up more than a quarter of living cetaceans (a group that includes dolphins, porpoises, and whales), but scientists don’t know where they go in the ocean or what they do, she said. They spend most of their time deep underwater and rarely surface for air, Payne added. There are more than 20 species of beaked whales, and much of what we know about them comes from carcasses that occasionally wash up on shore.
It’s hard to protect a species you don’t understand, Payne said. For example, researchers think that noise from shipping traffic harms beaked whales, but scientists can’t say for sure — because they simply don’t know what these animals are doing.
Researchers also hope to build an auditory archive of the ocean over years to understand how marine communities are changing, especially as the planet heats up. How, for example, is the giant patch of warm water in the Pacific Ocean, dubbed “the blob,” affecting marine communities? “The elephant seals can help us collect information where we have little to no data,” Klinck told Vox.
For now, Beltran and her team are just trying to prove that it can work. If it does, she hopes to scale it up and start collecting sounds in all kinds of marine environments — not just far offshore, but near the coast and even under Arctic ice. Perhaps in the future, legions of elephant seals will unwittingly survey the ocean in the name of science.