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The Atlantic Behavioral Response Study, led by Duke University, had it's first successful controlled experimental exposure with continuously active sonar from a U.S. Navy ship!

The R/V Shearwater had a very busy day on Sunday, July 21^st. They started at first light by deploying a High Frequency Recording Package (HARP) in our study area off Cape Hatteras. They deployed the HARP in a depth of about 1,000 m – it will record the vocalizations of goose-beaked whales (Ziphius cavirostris) and other cetaceans for a year, before being retrieved next summer. The HARP recordings will also allow researchers to assess the presence of anthropogenic sounds in the study area, such as the presence of vessels, distant seismic exploration activity, or the use of tactical sonars in Navy training exercises.

The HARP loaded on the back deck of the RV Shearwater.

Then, in mid-morning, the team coordinated with the USS Thomas Hudner, a guided missile destroyer, to conduct a controlled experimental exposure trial with Continuous Active Sonar (CAS) signals with three tagged goose-beaked whales. The focal whale was Zc150, which they tagged a week earlier and tracked before, during, and after the exposure to document its response.

USS Thomas Hudner at Naval Station Mayport. U.S. Navy photo by Mass Communication Specialist 1st Class Brian G. Reynolds.

In accordance with the experimental design, the Thomas Hudner completed a full 60-minute CAS transmission sequence at a distance of approximately 25 km from Zc150.  The research team deployed dipping hydrophones near the focal whale before, during and after the exposure and the CAS signal was audible at expected levels in our recordings. Prior to the start of the experimental trial, the team had been running acoustic propagation models in real time. This enabled them to ensure that the CAS signals were clearly audible to the whale but not loud enough to cause any potential distress.

Deploying a satellite-linked dive recorder on Zc150 on July 14th. Photograph by Anne Harshbarger.<

The CAS signals are in the same frequency range but quite different in structural and temporal patterns from the Pulsed Active Sonar (PAS) signals that they have been working with for the past few years. This was the research team's first experimental exposure with this type of active military sonar, and, to our knowledge, this is the first experimental playback of CAS signals to goose-beaked whales. They conducted an 8-hour focal follow of Zc150 from the R/V Shearwater to assess its potential response to the CAS signals. The whale moved a short distance away from the track of the Hudner but did not travel far. The team is still working through its dive records received via satellite.

Read about this and other projects on the Duke Read Lab Blog. For more about the Atlantic BRS project, see the project profile.