Between June and August 2025, my fellow scientists of the Southeast Fisheries Science Center and crew of the NOAA Ship Gordon Gunter deployed a towed hydrophone array—an underwater microphone system—about 300 meters behind the ship. The goal? To detect the sounds produced by one species in particular: the endangered sperm whale in the Gulf of America.
This survey was focused on finding and studying these deep-diving giants. The scientists worked with the ship’s crew to transit through prime sperm whale habitat. Visual observers, drone operators, and acousticians were always on high alert—each using their specialized methods to detect these creatures.
Types of Sperm Whale Clicks
The towed hydrophone array picked up lots of sperm whale clicks on this 3-month trip. If the acousticians heard a whale before the visual observers spotted one, they were able to guide the ship toward the location. The array has multiple hydrophones, and measuring the tiny time differences when a click arrives at each one allowed them to pinpoint where the whale was. That’s teamwork at its finest, and it’s pretty cool, right?
But you might be wondering, what’s so special about these clicks besides helping to find the whales? Well, there’s actually a whole lot more to them!
Echolocation Clicks
Sperm whales produce different types of clicks. When they dive deep in search of food, they produce echolocation clicks to sense their environment and find their prey. They do this by listening for the echoes that bounce off of objects. The longer the echo takes to return, the farther away the object is. As they get closer to their prey, the two-way transit time for the clicks decreases, and they speed up their click rates until they’re making a rapid-fire sound called a “buzz” or a “creak.”
Caption: A waveform (top) and spectrogram (bottom) of sperm whale echolocation clicks ending in a buzz recorded from a tagged whale during the 2025 survey. Credit: NOAA Fisheries/Matthew Bowers, Laura Dias, Gina Rappucci, and Lynne Hodge (Permit #25867)
Fun Fact: Sperm whales make deep dives lasting on average 45 minutes in search of prey (including their favorite, squid!). Tagged sperm whales in the Gulf of America typically attempted 17 prey captures during each deep dive based on detected buzzes.
Codas
The acousticians aboard the Gordon Gunter also recorded many patterned, rhythmic groups of clicks called “codas.” The clicks of a coda are not random—they’re organized and can be combined into sequences. Scientists have discovered that sperm whales in different regions produce different codas, which help define “acoustic clans.” The shared codas within an acoustic clan are passed down through generations. Think of it like a secret knock or code that identifies a member of a group. We’re hoping to analyze the codas recorded during this trip along with those recorded during previous surveys to learn more about the different coda types in the northern Gulf of America. We can then compare our findings to other regions to see how they are similar or different.
A waveform (top) and spectrogram (bottom) with sperm whale codas recorded from a tagged whale from the June–August 2025 survey. Credit: NOAA Fisheries/Matthew Bowers, Laura Dias, Gina Rappucci, and Lynne Hodge (Permit #25867)
Fun Fact: Patterned, rhythmic groups of clicks are called “codas.”
Using Sounds to Estimate Body Size
But wait, there’s more! The clicks also contain information that can help estimate a sperm whale’s body length. This is all thanks to the incredible anatomy inside their massive heads. Basically, the whale produces a sound that bounces around inside its head before being focused and sent out as a super loud click. Seriously, sperm whale clicks are the loudest animal sound on Earth! This bouncing creates a multi-pulsed structure in the click. By measuring the time between pulses, known as the “inter-pulse interval,” we can estimate the size of the whale’s head. Since a mature sperm whale’s head is about one-third of its total body length (yes, it’s true!), we can then estimate its overall size. Amazing, right?
Fun fact: Did you know that the scientific name for sperm whale is Physeter macrocephalus, and macrocephalus means "big" (macro) "head" (cephalus)?
Supporting Technology
What was really exciting about the June–August 2025 survey was that there were so many techniques happening at the same time, which lets us verify our methods. For example, we can compare the body length estimates from our acoustic data with the pictures taken by the drone. This size information is important for understanding the demographic structure of the whales in the Gulf of America.
Now that the survey is over, we are analyzing the data back at the lab—not just to identify codas but also to get those body length estimates!
Video taken from the drone of three sperm whales beginning to take a deep dive. Credit: NOAA Fisheries/Melissa Cook (Permit #25867)
Funding and Partnership
This project is a collaboration between NOAA Fisheries and the University of Miami’s Cooperative Institute for Marine and Atmospheric Studies. It was funded through the Deepwater Horizon Open Ocean Trustee Implementation Group, as part of their Monitoring and Adaptive Management activities. These activities assess how projects restoring natural resources injured from the Deepwater Horizon oil spill are making progress toward recovery in the Gulf of America. All activities aboard the ship are conducted under a scientific research permit (Permit #25867) and approval from the NOAA Fisheries Institutional Animal Care and Use Committee.
