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I have manually analyzed acoustic data (Oct-May 2009-2021) from a moored hydrophone in the Bering Strait (65.78, -168.57) — about 15 km from Little Diomede and 24 km from mainland Alaska.

The hydrophone (AURAL-M2) was deployed at 49 m depth and duty cycled, recording 12-25 minutes every hour (depending on the year). The sample rate was 16,384 Hz but I was only scanning ~0-2,000 Hz, looking specifically for bowhead whales.

I came upon this mysterious low-frequency vocalization (<5 sec with a frequency range of 50-300 Hz), and I was hoping for help identifying the species.

Keeping in mind that I wasn’t specifically looking for it, in 2019, I documented it April 6-7 and in 2020, I documented it April 18-22, 26 and May 1, perhaps suggesting a springtime visitor. That being said, when seals take over the soundscape April/ May [shakes fist], it can be hard to discern other vocalizations.

As you’ll see in the example spectrograms below, the calls occur in the midst of other animals calling – in this example during bowhead whale song and bearded seal trills. Bowhead whales and bearded seals have been present for each mystery vocalization.

  • The top left spectrogram (Fig A) shows a zoomed-out temporal snapshot (aka LTSA) of an 11-hour period on April 19, 2020, with frequencies spanning 0-3500 Hz. Each section represents 25 min of acoustic data.
  • The bottom left plot (Fig B) shows a zoomed in version – 25 seconds in duration with frequencies spanning 0-1500 Hz.
  • The right plot (Fig C) corresponds the to the SoundCloud recording (link below) and is a 12-second-long recording spanning 0-500 Hz. The vocalization can be heard 3 seconds into the recording. Try to ignore the higher frequency sounds still lingering in the recording!

Likely candidates are marine mammals or fish. It doesn't seem like bowhead because it doesn't look/sound like their other non-song vocalizations and was not present at other times bowhead whales were present. So I am leaning toward fish. But I know nothing of fish acoustics. :)

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http://soundcloud.com/user-355449841/bering_strait_mystery_vocalization

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Sounds like it could be a fish. I'd encourage you to check out the FishSounds.Net library, which is a freely available archive of soundclips and spectrograms of many species of fish. You can even search by region or by sound name (e.g. grunt, knock, moan), etc.

Based on your description and spectrogram, perhaps it could be polar cod or a meagre (?)

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