Looking from the stern of the ship as it tows the long horizontal array of hydrophones. The tow cable can be seen going through the metal horn at the stern. The hydrophone array is several hundred meters behind the ship and about 200 meters deep.
News — MELVILLE, N.Y., Nov. 21, 2024 – Mysterious, repeating sounds from the depths of the ocean can be terrifying to some, but in the 1980s, they presented a unique look at an underwater soundscape.
In July 1982, researchers in New Zealand recorded unidentifiable sounds as a part of an experiment to characterize the soundscape of the South Fiji Basin. The sound consisted of four short bursts resembling a quack, which inspired the name of the sound “Bio-Duck.”
“The sound was so repeatable, we couldn’t believe at first that it was biological,” said researcher Ross Chapman from the University of Victoria. “But in talking to other colleagues in Australia about the data, we discovered that a similar sound was heard quite often in other regions around New Zealand and Australia.”
They came to a consensus that the sounds had to be biological.
Chapman will present his work analyzing the mystery sounds Thursday, Nov. 21, at 10:05 a.m. ET as part of the virtual 187th Meeting of the Acoustical Society of America, running Nov. 18-22, 2024.
“I became involved in the analysis of the data from the experiment in 1986,” Chapman said. “We discovered that the data contained a gold mine of new information about many kinds of sound in the ocean, including sounds from marine mammals.”
“You have to understand that this type of study of ocean noise was in its infancy in those days. As it turned out, we learned something new about sound in the ocean every day as we looked further into the data—it was really an exciting time for us,” he said.
However, the sounds have never been conclusively identified. There are theories the sounds were made by Antarctic Minke whales, since the sounds were also recorded in Antarctic waters in later years, but there was no independent evidence from visual sightings of the whales making the sounds in the New Zealand data.
No matter the animal, Chapman believes that the sounds could be a conversation. The data was recorded by an acoustic antenna, an array of hydrophones that was towed behind a ship. The uniqueness of the antenna allowed the researchers to identify the direction the sounds were coming from.
“We discovered that there were usually several different speakers at different places in the ocean, and all of them making these sounds,” Chapman said. “The most amazing thing was that when one speaker was talking, the others were quiet, as though they were listening. Then the first speaker would stop talking and listen to responses from others.”
He will present the waveform and spectrum of the recordings during his session, as well as further evidence that the work was a conversation between multiple animals.
“It’s always been an unanswered issue in my mind,” Chapman said. “Maybe they were talking about dinner, maybe it was parents talking to children, or maybe they were simply commenting on that crazy ship that kept going back and forth towing that long string behind it.”
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