A new blue whale population has been discovered in the Arabian Sea and Western Indian Ocean according to a study recently published in the journal Endangered Species Research. The conclusion is based not on sightings or DNA samples, but rather on recordings of the unique whale songs that distinguish this whale population from other blue whales in the region.

At up to 100 feet long and weighing up to 170 tonnes, blue whales are the largest creatures ever to exist on the earth. Nevertheless, they are often easier to hear than to see.

The unusual song was picked up at three different underwater locations separated by 3,500 kilometers (2,175 miles) of ocean. First recorded in 2017 off the coast of Madagascar, these unique calls were later identified in the western Arabian Sea, off the coast of Oman, and also in the Chagos Archipelago in the central Indian Ocean.

“It’s like hearing different songs within a genre — Stevie Ray Vaughan versus B.B. King,” said Salvatore Cerchio, a marine mammal biologist at the African Aquatic Conservation Fund in Massachusetts and the study’s lead author. “It’s all blues, but you know the different styles.”

“It was quite remarkable to find a whale song in your data that was completely unique, never before reported, and recognize it as a blue whale,” says Cerchio. “With all that work on blue whale songs, to think there was a population out there that no one knew about until 2017, well, it kind of blows your mind.”