Examining the effects of depth, distance and sound propagation on the acoustic identification of odontocete species

Goal: to evaluate the effects of recording depth, animal behavior and sound propagation characteristics of the water column on whistles and clicks produced by delphinids

Time Period: May 2015 – September 2016

Our Role: to collect field recordings of free-ranging dolphins off Maui, the Big Island of Hawaii and San Diego, and from captive Navy trained dolphins in San Diego, using two vertical arrays of autonomous acoustic recorders. To perform classification analysis on the collected data, and collaborate with Oceanwide Science Institute (OSI) and Abakai International to carry out sound propagation analysis and acoustic localization.

Substantial advancements have been made in the identification of odontocete species based on the properties of their whistles and clicks. However, the suitability of species classifiers trained using data from the sea surface to analyze recordings obtained at depth is currently unknown. Bio-Waves, Inc. is working in collaboration with OSI to examine how species-specific signaling cues are affected depth, distance of the animals from the recorder, animal behavior and sound propagation. We are using both surface-deployed and bottom-moored vertical arrays of hydrophones and autonomous recorders to obtain recordings at different depths in the water column from a variety of free-ranging odontocete species and Navy trained captive dolphins stationed at known depths. We will use acoustic localization and sound propagation modeling to address the following questions:

  1. Does the depth at which dolphin whistles are recorded affect the signal properties observed?
  2. If so, does the performance of species classifiers developed using whistles recorded at the surface change when applied to data from bottom-moored recorders?
  3. Do reported species-specific click characteristics remain consistent across recording depths?
  4. If so, are the cues consistent across behaviors, such as diving, surface milling and travel?

The data obtained during this two year effort will be used to examine signal characteristics, localize signalers and model signal propagation between the source and the recorder. The data will also be used to test the performance of existing whistle classifiers on signals obtained at different depths. It is expected that the results of this effort will provide a better understanding of the classification methods presently being employed for marine mammal monitoring and mitigation, and will lead to greater confidence in their application.

Collaborators/Partners: Oceanwide Science Institute, Abakai International, LLC

Sponsors: Office of Naval Research, Navfac-Atlantic, U.S. Navy Living Marine Resources Program

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