Impulsive Knocks Recorded Underwater in Glacier Bay

Notes on Sound Clips
The recordings below were made by the National Park Service, using a hydrophone that is anchored near the mouth of Glacier Bay, Alaska for the purpose of monitoring ambient noise. The recordings are intended to provide examples of the types of natural and manmade sounds that occur in Glacier Bay National Park.

Impulsive Knocks Recorded in Glacier Bay

Recorded in 2022-2023, the first two sets of sounds are believed to be made by harbor seals. A 2009 field recording made near two humpback whales demonstrates that whales can make similar, but much louder, impulsive sounds.
 

Single, Double, and Triple Impulsive Knocks

These sounds are examples of three different types of impulsive knocks observed on recordings from remote cabled hydrophone in Glacier Bay, Alaska. Researchers now believe these are made by harbor seals. On average, impulsive knocks have a mean peak frequency of 1.1 kHz are 0.128 sec duration, and occupy the entire 20 Hz – 21.9 kHz band. In the case of double and triple pulse knocks, the pulses occur 0.267 sec apart on average.
 
Spectrograms showing frequency (1 - 22 kilohertz) on the vertical axis and time on the horizontal axis.
Single, Double, and Triple Impulsive knocks recorded on spectrograms showing frequency (1 - 22 kilohertz) on the vertical axis and time on the horizontal axis.

NPS / C. Gabriele

 

  • Single Impulsive Knock


    Single pulse knock recorded September 19, 2022, 23:41:50 amplified by 6 decibels

    Credit / Author:
    NPS / C. Gabriele
    Audio Transcript
 

  • Double Impulsive Knock


    Double pulse recorded May 15, 2023, 13:36:16, amplified by 6 decibels.

    Credit / Author:
    NPS / C. Gabriele
    Audio Transcript
 

  • Triple Impulsive Knock


    Triple pulse recorded September 20, 2022 05:35:28 amplified by 6 decibels.

    Credit / Author:
    NPS / C. Gabriele
    Audio Transcript
 

Call and Response Knocks?

 
sound spectrogram showing frequency (1 - 11 kilohertz) on the vertical axis and time on the horizontal axis. Letters A and B are superimposed to represent two possible animals.
One or two animals making impulsive knocks sounds together. Sound spectrogram shows frequency (1 - 11 kilohertz) on the vertical axis and time on the horizontal axis. Researchers believe that these sounds are made by harbor seals

NPS / C. Gabriele

 

  • Two or More Animals Impulsive Knocks


    A 45-second recording of two or more animals making impulsive knocks, denoted A and B, on April 19, 2017 at 09:48:41. Researchers think these are sounds made by humpback whales.

    Credit / Author:
    NPS / C. Gabriele
    Audio Transcript
 

Field Recording of Loud Snaps Made by a Humpback Whale

 
sound spectrograms showing frequency (1 - 11 kilohertz) on the vertical axis and time on the horizontal axis.
Sound spectrogram showing frequency (1 - 24 kilohertz) on the vertical axis and time on the horizontal axis. Recorded on a hydrophone (underwater microphone) near Bartlett Cove, Glacier Bay National Park.

NPS / C. Gabriele

 

  • Loud Impulsive Snaps


    Loud impulsive “snaps” recorded while male humpback whale (ID #1065) was observed chasing female (#1019) within 300 m of research vessel in Icy Strait, Alaska, September 29, 2009. Social sounds and song audible (and visible) in background. This recording demonstrates that humpback whales produce loud broadband pulses in Alaska.

    Credit / Author:
    NPS / C. Gabriele
    Audio Transcript

Last updated: April 4, 2025

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Glacier Bay National Park & Preserve
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Gustavus, AK 99826

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907 697-2230

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