Underwater robot tracks sperm whale conversations in real time

By linking whale behaviour with environmental pressures, the technology could inform more precise, evidence-based policy decisions such as when to reduce ship speeds, reroute traffic or implement fishing restrictions to minimise disruption in sensitive areas

Deep beneath the ocean surface, sperm whales swim through the dark waters, clicking to each other in bursts of sound that can travel for kilometres (miles). Now, scientists say they are beginning to follow those exchanges in real time using an autonomous underwater robot that can track whales by listening to their ⁠voices.

Sperm whales use clicks to navigate and hunt, and also produce patterned sequences of clicks, known as "codas," that are thought to play a role ⁠in communication. Scientists first identified that sperm whales vocalize in 1957. But understanding how they communicate has remained ‌difficult because these marine mammals dive to depths of ​more than 1.6 km (one mile) for around 50 minutes each hour, making continuous observation challenging.

"The underwater glider is listening for whales via four hydrophones and then steering itself toward them using a feature called backseat driver," said David Gruber, founder and CEO of Project CETI, professor of biology and environmental sciences at Baruch College at the City University of New York and a co-author of the study published this week in the ​journal Scientific Reports. "When the glider detects the distinctive ⁠vocalizations of sperm whales, the software on board identifies where that sound is coming from and automatically communicates with the glider's navigation system to change directions and follow the whale," Gruber added.

A glider is a small robot that slowly changes its buoyancy, becoming slightly heavier to sink and lighter to rise. "You can think of it as a quiet, long-distance explorer, more like a soaring ⁠albatross than a motorized ‌vehicle, steadily travelling through the ocean while listening and gathering information as it goes," Gruber said. Traditional tracking methods rely on suction tags that fall off after a few days or on stationary sensors that lose ‌contact when whales move away. Project CETI also deploys hydrophones - underwater devices that detect and record sounds - towed from boats.

What makes the new robotic system different, Gruber said, is that ⁠it "can make decisions in real time while it's still underwater," rather than recording acoustic data for later analysis. Previous methods allowed scientists to reconstruct where a whale had been, but not actively follow it ‌at the moment. The new approach "continuously updates the glider's path so it can stay with a single whale for ‌extended periods - potentially months," Gruber said. The ability to track whales for longer periods marks what Gruber called a shift "from ‌brief encounters to continuous relationships," allowing scientists to stay with the same whale or group instead of relying on short, opportunistic ‌glimpses and to see patterns in how whales coordinate, socialize and respond to their environment over time.

Such data could also help answer longstanding questions about how sperm whales communicate. "By following mother-calf pairs over time, we can begin to see how calves pick up vocal patterns from their mothers," Gruber said.

The system could ⁠also reveal how whales react ⁠to human activity, allowing researchers to track the way their communication changes in the presence of human-made noise and offering a clearer picture of how shipping, offshore construction or fishing affect them.

By linking whale behaviour with environmental pressures, the technology could inform more precise, evidence-based policy decisions such as when to reduce ship speeds, reroute traffic or implement fishing restrictions to minimize disruption in sensitive areas, the researchers said. Developing the system "brings us closer to understanding another form of intelligence on Earth, which has implications not just for conservation, but for how we think about communication and life beyond our own species," Gruber added.

Yet, precise localisation remains a challenge, as the glider can detect ​the direction of a whale but not its exact position, limiting its ability to distinguish between individual whales and track them ​accurately. Communication is another constraint. The robot must surface every ​few hours to send and receive updates, making long-term, real-world monitoring less seamless.

For Gruber, the moment the glider acted on its own offered the first real glimpse of what ​this technology could become.

"We're beginning to build systems that can operate independently and respond to the natural world as it unfolds," Gruber said.