Using Nuclear Bomb Detectors, Scientists Overhear the Secret Songs of a Never-Before-Seen Pygmy Blue Whale Population

In the vast depths of the ocean, pygmy blue whales are hard to spot despite their immense size—the length of two buses. Luckily, they’re loud enough to eavesdrop on.

With the help of a network of deep sea, nuclear bomb-detecting microphones, researchers have now found an entirely new population of these whales lurking in the Indian Ocean, simply by listening in on their distinct song patterns, reports Angela Heathcote for Australian Geographic. This group is the fifth known pygmy blue whale population residing in the Indian Ocean, which makes the area a thriving locale for the species.

Scientists identified the new population of pygmy blue whales while analyzing almost two decades’ worth of acoustic data from underwater nuclear bomb detectors in the bottom of the Indian Ocean, according to a study published April 22 in Scientific Reports.

Run by the international Comprehensive Nuclear-Test-Ban Treaty Organization, the deep-sea mics are meant to listen for illegal nuclear bomb tests in the ocean. The organization’s long-term data collection incidentally came in handy for monitoring whale populations when the recordings inadvertently picked up their songs.

“[Whales’] songs are like a fingerprint that allows us to track them as they move over thousands of kilometres,” says the study’s lead author Emmanuelle Leroy, a bioacoustician at the University of New South Wales in Sydney, Australia (UNSW Sydney), in a statement.

Whale songs can be used to differentiate between species. Nuances in these songs sometimes indicate the presence of new populations within a species across different regions. Blue whales are repetitive vocalists, crooning their choruses at regular intervals for hours. Some populations of blue whales have been belting the same ballad since the 1960s, Leroy tells Australian Geographic. Nevertheless, the songs of blue whales differ across populations in duration, structure and number of sections.

“Humpback whales are like jazz singers. They change their songs all the time,” says senior author Tracey Rogers, a marine ecologist at UNSW Sydney, in a statement. “Blue whales, on the other hand, are more traditional. They sing very structured, simple songs.”

The newly identified throng of pygmy blue whales sings in three parts. The first part is the most complex, followed by two more basic parts, reports Harry Baker for Live Science. The new population is named “Chagos” after the group of islands close to where the whales’ songs were detected.

“We found them not only in the central Indian Ocean, but as far north as the Sri Lankan coastline and as far east in the Indian Ocean as the Kimberley coast in northern Western Australia,” says Rogers in a statement.

Researchers analyzed recordings from 2002 to 2018. The anthem of the still unseen Chagos whales has prevailed for 18 years, according to Rogers. Because the song has persisted for so long, the team presumes it belongs to a whole population of pygmy blue whales living in the ocean, not just a few lone stragglers. But how many whales belong to this newfound population remains unclear, per Live Science.

Blue whales once flourished in the oceans, tallying up to around 350,000 strong—until the whaling industry decimated their populations by 99 percent by the mid-1960s. To date, only 5,000 to 10,000 blue whales remain in the Southern Hemisphere. Modern-day blue whales face new threats of collisions with shipping vessels and entanglement in fishing gear, so their population still hasn’t fully recovered.

To protect any species, scientists need to know how many individuals make up a given population. But blue whales are notoriously shy, making conservation efforts challenging. They travel alone or in small groups and prefer to stay submerged underwater, rarely breaching the surface—unlike other more flamboyant types of whales.

The new study strikes a heartening chord with conservationists as “it increases the global population that we did not realize was there before,” says Rogers to Australian Geographic.

The researchers plan to revisit the bomb detector data to learn more about how the Chagos population has changed over the last two decades, including how it has adapted to climate change. The acoustic monitoring network will also be valuable to the scientists for monitoring the population in the future, including their distribution, migration patterns and population numbers, reports Katie Camero for Miami Herald.

“Discovering a new population is the first step to protecting it,” says Leroy.

Shi En Kim | | READ MORE

Shi En Kim is a Washington, D.C.-based freelance science journalist. Her work has appeared in National Geographic, Scientific American, the Atlantic, Popular Science and others. In 2021, she interned at Smithsonian magazine as an AAAS Mass Media Fellow.