Recorded by underwater microphones, the unexplained sound—a low, sonorous grunting followed by a squeaky, mechanical echo like a frog burping in space—first rumbled through a computer speaker about a decade ago. Baffled researchers called it the “biotwang.”
“You’ve got this low-frequency portion, like a moan,” says Lauren Harrell, a data scientist at Google’s AI for Social Good team, adding her own impression of a hearty groan. “Then you have the higher-frequency component that sounds, to me, like the original Star Trek Enterprise ship—the ‘bip boo, bip boo’ sound.”
Autonomous underwater gliders first encountered the odd noise in 2014 echoing near the miles-deep Mariana Trench in the western Pacific Ocean. Researchers couldn’t identify its source, but they had a theory. “There are enough other Star Wars–sounding whale calls that they guessed it was made by a baleen whale,” says Ann Allen, a research oceanographer at the U.S. National Oceanic and Atmospheric Administration. But, she adds, “anybody who’s not familiar with whales would never think this was made by an animal.”
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Hear the biotwang for yourself:
Confirming which marine creature makes a particular unusual noise isn’t easy: it requires a person on a boat to see and identify the source at exactly the same time the sound is heard. “It takes a lot of time, a lot of effort and a fair amount of luck,” Allen says.
That’s how Allen, Harrell and their colleagues finally solved the biotwang mystery, which they describe in Frontiers in Marine Science. While surveying whales off the Mariana Islands, an archipelago near the trench of the same name, noaa researchers saw an enigmatic baleen species called the Bryde’s whale (Balaenoptera edeni) 10 times. These rarely observed whales have a vast range spanning much of the ocean, making them hard to study. On nine of the occasions when Bryde’s whales turned up, the researchers also heard the biotwang. “Once, it’s a coincidence,” Allen says. “Twice is happenstance. Nine times, it’s definitely a Bryde’s whale.”
After identifying the source, the scientists reviewed years’ worth of audio data from underwater hydrophones to figure out where this specific whale sound had previously been heard. But according to Allen, noaa’s growing database has more than 200,000 hours of such recordings. “It’s so much data that it’s simply impossible to analyze [manually],” says Olaf Meynecke, who studies baleen whales as a research fellow at Griffith University in Australia and wasn’t involved in the study.
“We seem to be so detached from, or simply have no access to, this amazing acoustic underwater world. I think it’s about time that we change that.” —Olaf Meynecke Griffith University
When analyzing audio data for another project, Allen had been “flabbergasted” by the huge volumes of information to slog through. At one point, she says, her dad suggested, “Just get Google to do it for you.” So Allen reached out to company staff, and, to her surprise, they agreed. Google provided AI tools that helped to speed up her analysis by transforming audio data into an image called a spectrogram and then training algorithms to look for certain frequencies using image recognition.
The new study lays out the evidence associating biotwangs with Bryde’s whales in the western North Pacific. The data suggest that the animals the researchers studied are members of a distinct Bryde’s whale population and showed where in the ocean they were found during different seasons and years—something that had previously been challenging to discern because scientists couldn’t easily tell different populations of the elusive whales apart. In 2016, after a strong El Niño led to a shift in the location of the whales’ food (largely krill, sardines and anchovies), there were lots of biotwangs—even in the northwestern Hawaiian Islands, an area these whales ventured into only under certain climate conditions. This correlation could mean that their movements are at least partially determined by their prey’s distribution, which changes with environmental conditions.
Once scientists know where and when these whales travel, Harrell says, AI models could “connect those data to climate and environmental factors” and thus support protection efforts. As climate change worsens and El Niño and its cold-water counterpart, La Niña, potentially undergo changes,“these whales will have to travel farther—and they may have to work a little harder to find food,” Allen says.
The data-processing technology isn’t perfect. “These algorithms can only search for a frequency they know,” Meynecke says. Baleen whale vocalizations change over time and between populations. But because the tools are open source, other scientists can use them to discover more about whale language. “We seem to be so detached from, or simply have no access to, this amazing acoustic underwater world,” he says. “I think it’s about time that we change that.”
[Audio credit: “A Complex Baleen Whale Call Recorded in the Mariana Trench Marine National Monument,” by Sharon L. Nieukirk et al., in Journal of the Acoustical Society of America, Vol. 140, No. 3; September 2016]