The enigma of the mysterious sounds of the ocean solved

While in space no one can hear you scream, at the bottom of the ocean, sounds circulate and can be recorded, but sometimes it takes several years before they can be identified.

And so the mystery of an unknown noise in the Mariana archipelago finally seems to be solved. In 2014, low-pitched sounds followed by metallic echoes were recorded, detected during an acoustic survey over the Mariana Trench, off the coast of Guam. Scientists called them "Biotwangs". (A few seconds to listen to here).  

Initial hypotheses pointed to whale songs, but it was not possible to determine the species behind the sounds. Without visual evidence, it is difficult to say who was responsible, because scientists identify the source by seeing the animal produce its song. As Ann Allen, a NOAA researcher-oceanographer and co-author of the study, puts it,“It takes a lot of time, a lot of effort and a fair amount of luck”.

So it was with patience that scientists solved the enigma. While observing whales off the Mariana Islands, near the Mariana Trench in the North Pacific, scientists spotted Bryde's whales on ten occasions, and nine times they heard biotwangs. "Once, it’s a coincidence," explains Ann Allen. "Twice is happenstance. Nine times it's definitely a Bryde's whale." 

Once the whale had been identified, the scientists set about finding out where these specific sounds had been heard before. This involved a titanic task of analysis, with over 200,000 hours of audio recordings in the NOAA database. The scientists then teamed up with Google to use their artificial intelligence tools, which were "trained" to search for certain frequencies.

The study showed that this group of Bryde's whales forms a distinct population and indicated their location over several years. In 2016, for example, the whales were spotted in the north-western Hawaiian Islands because the location of their food had changed following an El Niño event.

By using AI to cross-reference data relating to the frequency of movements and location of whales with "climate and environmental factors", as Lauren Harrell from Google, who took part in the study, points out, we will be able to fine-tune actions to preserve these marine mammals.