Dark, cold, and seemingly bottomless, the Mariana Trench is shrouded in mystery, being one of the least explored places on the planet. However, one of its secrets was finally revealed by identifying a rare whale species to be the source of an unusual sound coming from the trench called a “biotwang.”
In 2014, autonomous underwater gliders collected passive acoustic data that translated to a strange noise no longer than 4 seconds. The sound started as a low-frequency groan followed by a high-pitched, mechanical resonance that researchers likened to sound effects from Star Trek and Star Wars. In 2016, researchers initially hypothesized that the sound was a baleen whale call based on preliminary analysis, but there was insufficient evidence to confirm the claim. Most people would not associate the sound with a whale call unless they studied the animals, according to Ann Allen, a research oceanographer in the U.S. National Oceanic and Atmospheric Administration (NOAA).
The mystery was solved when Allen and a team of researchers from NOAA went on a month-long expedition in the Mariana Islands near the trench to observe marine mammals in 2018. They spotted groups of Bryde’s whales ten times during observation, and nine times out of the ten, they recorded the biotwangs using underwater microphones. This repeated pattern made the connection between the whales and the unusual sound clear after that. As Allen said to Scientific American, “Once, it’s a coincidence. Twice is happenstance. Nine times, it’s definitely a Bryde’s whale.”
Bryde’s whales — pronounced “BROO-dus” — are rare to come across since they are spread all over the ocean in tropical and subtropical climates. The solitary creatures are constantly on the move and prefer deeper waters, making them one of the least studied members of the baleen family. With this discovery, however, scientists can have much more insight into the behavior of these whales.
“As Allen said to Scientific American, ‘Once, it’s a coincidence. Twice is happenstance. Nine times, it’s definitely a Bryde’s whale.’”
To corroborate their finding, the team needed to analyze audio recordings from underwater hydrophones to find other times that this whale sound was heard, which consisted of 200,000 hours of acoustic data. Due to the sheer volume of data, Allen reached out to Google for AI tools to help facilitate the analysis process. Together, Allen and a data science team at Google created an app that used AI to create spectrograms from the audio data and then develop algorithms to identify the specific biotwang frequencies. Data that would have taken years to analyze only took a few hours, to the amazement of the researchers.
In the study the team recently published, they established that the whales they had observed near the trench were part of a unique Bryde’s whale population based on the results from the app. Other acoustic data from the past showed them that Bryde’s whales were also seasonally located in the Western North Pacific, which matched their migration patterns and indicated that there are specific populations that frequent different areas and produce their own biotwangs. The study was groundbreaking as the researchers previously had no way of identifying or differentiating the whale populations.
The intensity of the biotwangs was also linked to the location of the whales’ food source as they shifted because of environmental conditions. Having knowledge of the whales’ behavior in real-time using these AI models can help support preservation efforts as climate change continues to affect weather patterns and the marine ecosystem. As this AI technology evolves in the future, it can be applied to study other elusive species to extend the efforts to protect biodiversity and continue the exploration of our mysterious oceans.
