Back in 2017, researchers were recording the chatter of Omura’s whales off the coast of Madagascar when they picked up the powerful song of another species: the blue whale, the largest animal to ever live on the planet and one of the loudest.
In some ways, this wasn’t surprising. Blue whales had previously been documented in this area of the western Indian Ocean and they are known to be talkative creatures, with each population emitting unique songs. But the vocalizations recorded nearly four years ago had never been heard before, leading scientists to conclude that they had discovered an entirely new population of blue whales.
Stretching up to 110 feet and weighing up to 150 tons, blue whales swim through all of the world’s major oceans, with the exception of the Arctic. These mammoth creatures produce intense, low frequency vocalizations that can travel more than 600 miles underwater, allowing them to communicate across vast distances. And yet—in spite of their gargantuan size, wide distribution and loquaciousness—blue whales are elusive animals. They spend little time at the surface of the water, for one, and their numbers have been severely depleted by past decades of whaling. While blue whale songs have been “extensively studied,” only around a dozen distinct ditties have ever been documented, according to Katherine J. Wu of the New York Times.
So when scientists were able to pick up a novel blue whale tune, it was "quite remarkable," says Salvatore Cerchio, director of the African Aquatic Conservation Fund's Cetacean Program and co-author of a new study in the journal Endangered Species Research. Experts had previously identified “two or three” blue whale subspecies in the Indian Ocean, structured into four distinct populations, according to the study authors. Now, a new cohort had entered the picture. It is possible that this group had been conflated with another population, but it may have gone entirely undetected until Cerchio and his fellow researchers recorded its signature song.
In the wake of this discovery, the new song was detected again by Cerchio’s colleagues, who were recording humpback whales off the coast of Oman, in the Arabian Sea. The calls were, in fact, more prevalent in this area than in the western Indian Ocean—a particularly significant find because no acoustic data had previously been collected from blue whales in the Arabian Sea. Researchers had speculated that blue whales there belonged to another population observed off the coast of Sri Lanka, but now they were able to give this group a unique identification.
In 2018, the researchers reported their finds to the Scientific Committee of the International Whaling Commission, which prompted another team of researchers to realize that they too had recorded the new song, this time off the Chagos Archipelago in the central Indian Ocean. A pattern of the whales’ movement started to emerge, with the animals possibly favoring the northern Indian Ocean, the study authors write.
The team does not have genetic data to support its findings, but because blue whale melodies are unique to specific populations, these cetacean songs have been used to identify different groups.
“It’s like hearing different songs within a genre—Stevie Ray Vaughan versus B. B. King,” Cerchio tells the Times. “It’s all blues, but you know the different styles.”
As Earther’s Dharna Noor points out, the discovery of a new blue whale population comes as good news for the species, which was once aggressively hunted for its oil and remains endangered today. According to the International Whaling Commission (IWC), more than 300,000 blue whales in the Southern Hemisphere and another 20,000 in the North Atlantic and North Pacific were slaughtered during the first half of the 20th century. Blue whales have been protected by the IWC since 1966 and some populations are recovering. The species continues to be put at risk by ship strikes, entanglement in fishing gear, habitat degradation and other threats.
Given that it went unnoticed for so long, the new whale population is probably small and “in critical need of status assessment and conservation action,” according to the study authors. The group’s identification also highlights how much of ocean life—even when it comes to the largest sea creatures—has yet to be discovered.
"With all that work on blue whale songs, to think there was a population out there that no one knew about until 2017,” says Cerchio, “well, it kind of blows your mind."