In 2014, researchers monitoring acoustic recordings from the Mariana Archipelago picked up an unusual whale vocalization with both low- and high-frequency components. It seemed to be a whale call, but it sounded more mechanical than biological and has since been dubbed a "biotwang."
Now a separate team of scientists has developed a machine-learning model to scan a dataset of recordings of whale vocalizations from various species to help identify the source of such calls. Combining that analysis with visual observations allowed the team to identify the source of the biotwang: a species of baleen whales called Bryde's (pronounced "broodus") whales. This should help researchers track populations of these whales as they migrate to different parts of the world, according to a recent paper published in the journal Frontiers in Marine Science.
Marine biologists often rely on a powerful tool called passive acoustic monitoring for long-term data collection of the ocean's acoustic environment, including whale vocalizations. Bryde's whale calls tend to be regionally specific, per the authors. For instance, calls in the eastern North Pacific are pretty well documented, with frequencies typically falling below 100 Hz, augmented by harmonic frequencies as high as 400 Hz. Far less is known about the sounds made by Bryde's whales in the western and central North Pacific, since for many years there were only three known recordings of those vocalizations—including a call dubbed "Be8" (starting at 45 Hz with multiple harmonics) and mother-calf calls.
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