How fiber-optic cables helped researchers eavesdrop on whales

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 WM Leader. “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.

Fiber-optic cables crisscross huge areas of the seafloor

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.  

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Here’s the sound of the whales captured by the virtual hydrophones.

Bouffaut calls the result “virtual hydrophones.” During the experiment, researchers placed these “virtual hydrophones” about four meters apart. The data received can be interpreted audibly, but it can be visualized as well. 

Similar to how fiber-optic cables pick up on vibrations from an earthquake, the cable can pick up the sounds through seismic vibrations that bounce off of the fins of male whales. Yep, fins. Apparently, male whale fins can make fin whale songs through a “series of repeated short and low frequency pulses that share similarities with airgun blasts,” according to the study. 

More data about baleen whales in particular could help fill in major gaps in our understanding of whale species, especially in the warming Arctic where this research took place. Even though they are some of the biggest animals on the planet, researchers don’t have enough information about some species of whale to know whether they are threatened or endangered. 

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“We need to have scientific evidence of what they’re doing and how they’re doing”

“We need to have scientific evidence of what they’re doing and how they’re doing,” Bouffaut explained to WM Leader. Using fiber-optic cables, researchers can tell when whales are getting struck by boats, getting caught in fishing gear, have migrated in a different direction, and as mentioned above, whether they are present in a specific region. The information collected is also essential to keeping tabs on whales as they recover and cope with a commercial whaling industry.

Now that researchers have collected the data for their study, Bouffaut is looking for other uses of the recording technology. Some curiosities that Bouffaut wants to keep in mind are whether they can only record at low frequencies, how many different species can be recorded, and how far researchers can record a whale.

“One of my hopes is that we can exploit the idea that because we can receive the data in real time, we can deal with the data in real time,” Bouffaut said. “This is something I believe can be helpful for the bioacoustics community because there are a lot of conservation issues that do require real-time monitoring.”

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