Both scientists and 关键字3sailors alike have recorded unique, strange noises in the ocean for decades. They sound guttural, and alien.

The sound is dubbed the "bio-duck" — though it doesn't sound like a duck — and you can hear an example of a recording below. Researchers have now reanalyzed one of these mysterious recordings from 1982, documented in the Pacific Ocean's South Fiji Basin, and concluded that it's a conversation between different animal speakers.

"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," Ross Chapman, an underwater acoustics researcher from the University of Victoria and an author of the research, said in a statement.

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At first, earlier listeners thought the deep sea sounds weren't natural. "They heard this sound, which is a low-frequency pulse of sound which is very regular. It almost sounds mechanical," Denise Risch, a National Oceanic and Atmospheric Administration marine biologist, previously noted. "So if you first hear it, you wouldn't necessarily think it's an animal, but it's very loud and very pervasive. You could hear it in the wintertime across the Southern Ocean."

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Scientists recorded these unusually mechanical noises using an array of hydrophones, which detect underwater sounds, that they towed behind a vessel. The different hydrophones allowed the researchers to identify different speakers.

"We discovered that there were usually several different speakers at different places in the ocean, and all of them making these sounds," Chapman explained. "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."

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The stern of a ship towing a long array of underwater recording devices, called hydrophones. The hydrophones are in the water hundreds of yards behind the vessel. Credit: Ross Chapman

Earlier research concluded Minke whales, the smallest species of baleen whale, created these underwater sounds. Yet there was never any sighting of the whales coming up for air to confirm this.

It is clear, however, these unusual sounds are coming from animals. And it certainly wouldn't be surprising if it were whales. These intelligent, cultured marine mammals, for example, fill the ocean with song.