CEE Trial with Simulated CAS Signals

On Friday, September 19^th we conducted a Controlled Exposure Experiment (CEE) trial with goose-beaked whales Ziphius cavirostris in our study area off Cape Hatteras. Our focal whale was ZcTag161, an adult male equipped with a satellite-linked dive recorder on September 4^th. The focal whale was accompanied by three other goose-beaked whales during the trial. In addition to ZcTag161, we had three other tagged whales in the vicinity that were also exposed to the sonar signals; the response of these whales will also be part of our analysis

ZcTag161- the focal whale in the CEE trial on September 19th. Photograph by Meghan Bradley

We generated simulated Continuous Active Sonar (CAS) signals with a brand-new sound source built specifically for this purpose, supported by funding from the Navy’s Living Marine Resources (LMR) program. Brandon Southall, the lead Principal Investigator for the Atlantic Behavioral Response Study (BRS), operated the source and modeled the acoustic propagation of the sonar signals in real time to ensure that we achieved our targeted Received Levels on the focal whale.

Preparing to deploy the sound source transmitting elements from the R/V Shearwater for a field test off Beaufort, NC on Thursday, September 18th. Photograph by Brandon Southall.

Field conditions were challenging on Friday, with a north breeze interacting with a strong northerly flow of the Gulf Stream to create very choppy conditions. Our tagging crew on the R/V Barber had hoped to deploy a Digital Acoustic Tag on one of the whales in the focal group, but this proved to be impossible. We were able to track ZcTag161 using the signals from the satellite tag, but even when we were very close to the group, it was difficult to photograph them, let alone deploy a tag.

The dive profile of ZcTag161 prior to, during, and following the exposure to simulated CAS signals on September 19th. The 30-minute exposure is indicted by the pink shading.

We conducted a 30-minute playback of the simulated sonar signal at 16:26 GMT (12:26 local time). ZcTag161 had been making a series of 25-minute dives prior to exposure but stayed submerged for 90 minutes following the playback. We are still in the process of examining the data we collected from the satellite-linked dive recorder. The R/V Shearwater tracked the whale overnight and was able to relocate ZcTag161 the next day in a different social grouping, now accompanied by an adult female and her calf. Such changes occur frequently with goose-beaked whales, but it is unclear whether they are more likely to occur after exposure to sonar signals.

The R/V Shearwater tracking ZcTag 161 of Cape Hatteras. Photograph by Kate Sutherland.

This was the second and last CEE trial of 2025. The first trial was with CAS signals generated by the USS Donald Cook in July. Each trial requires an enormous amount of work and coordination. We are very thankful for critical support from Rob Kalin at FACSFAC JAX, Ron Filipowicz from USFFC, and Joel Bell from NAVFAC. Thanks also go to our dedicated field team and the amazing crew of the R/V Shearwater.