Scientists have been “eavesdropping” on whales in the Arctic using fiber-optic cables. In July, a group of scientists published a study that took a practical method usually used to monitor the cables themselves and used it to monitor the activity of baleen whales in the Arctic. The researchers say similar studies could transform how scientists collect data on marine life. 

Under the oceans, fiber-optic cables carry internet traffic around the world. They have also become a usual tool for scientists in the field who would like to collect and access data in real time. Notably, they can be used to detect earthquakes, including aftershocks that go undetected by traditional seismic stations. In this case, those cables were used to detect whale sounds. It’s the first instance of wildlife monitoring being done through a technique called distributed acoustic sensing, the study notes. 

“[With] distributed acoustic sensing, we can potentially have better coverage,” Léa Bouffaut, who co-authored the study as a student at the Norwegian University of Science and Technology, told The Verge. “This may open new possibilities in locations that were either too complicated to access or in regions where governments are not able to fund new projects like this,” said Bouffaut, now a researcher at Cornell University’s K. Lisa Yang Center for Conservation Bioacoustics.

Whale researchers like Bouffaut usually use hydrophones to monitor underwater whale activity. Though the hydrophone provides good quality data, it can only cover so much ground. Hydrophones are typically deployed around 10 to 20 kilometers away from each other, Bouffaut explained. This relatively close proximity gives scientists a good idea of where whales might be located, a method similar to using cellphone tower triangulation to detect the location of where a phone call was made. But the oceans are huge, and even a large network of hydrophones can only observe a small area. Fiber-optic cables, in contrast, crisscross huge areas of the seafloor. 

Distributed acoustic sensing is already used to check up on the health of undersea cables and can alert communications companies to problems, like a break in the line. It works because a fiber in the cable is connected to something called an interrogator, a device that measures whether a fiber-optic cable is functional, Bouffaut explains. The interrogator sends light pulses to the fiber-optic cable at regular intervals. Sounds or vibrations can disrupt the cable and the pulses passing through it. By observing the changes in the light reaching the interrogator, researchers can determine what’s going on near the cable, whether that’s an anchor dropped close to a cable or a whale singing nearby.