Mysterious Underwater Sound That Baffled Scientists Finally Identified

For decades, scientists were puzzled by sounds picked up on underwater recordings in Antarctic waters and off Australia's west coast.

But now, the so-called "bio-duck" sounds are thought to belong to Antarctic minke whales, specifically Balaenoptera bonaerensis.

The Antarctic minke whale was recently identified as the source of the mysterious bio-duck sound. (Image source: Wikimedia)

"Our results solve the mystery around the source of the bio-duck sound, which is one of the most prevalent sounds in the Southern Ocean during austral winter and can now be attributed unequivocally to the Antarctic minke whale," the study authors wrote. "These results have important implications for our understanding of this species, which is of particular priority to the International Whaling Commission."

The sound, which was first described in the 1960s, is heartbeat-like or even quack-like, hence the name bio-duck. Take a listen:

"In the beginning, no one really knew what it was," lead researcher Denise Risch, a marine biologist with the National Oceanic and Atmospheric Administration, told LiveScience.

At first, it was thought the sound could be the result of human activities, like submarines. The sound was highly repetitive and occurred at an interval of about 3.1 seconds.

The researchers tagged some of the whale species and were able to record audio, matching the bio-duck sound with other descriptions in published literature.

"We analyzed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species," the authors wrote in the study's abstract. "This finding allows the interpretation of a wealth of long-term acoustic recordings for this previously acoustically concealed species, which will improve our understanding of the distribution, abundance and behaviour of Antarctic minke whales."

The technique of using audio recordings to track such metrics is also an attractive option in areas like the Antarctic, where visual surveys might not always be feasible or cost effective.

The observations were published in the Royal Society journal Biology Letters.

(H/T: io9)

Front page image via Shutterstock.