How fiber optic cables helped researchers eavesdrop on whales

Scientists “eavesdrop” on whales in the Arctic using fiber optic cables. In July, a group of scientists published a study that used a practical method commonly used to monitor the cables themselves and to track the activity of baleen whales in the Arctic. The researchers say similar studies could change the way scientists collect data on marine life.

Under the oceans, fiber optic cables carry internet traffic around the world. They have also become a common tool for scientists in the field who want to collect and access data in real time. In particular, 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 is the first time wildlife monitoring has been conducted through a technique called distributed acoustic sensing, the study said.

“[With] distributed acoustic detection, we may be able to have better coverage,” said Léa Bouffaut, who co-authored the study as a student at the Norwegian University of Science and Technology. The edge. “This could open up new possibilities in locations that were either too complicated to reach or in regions where governments are unable to fund new projects like this,” said Bouffaut, now a researcher at the K. Lisa Yang Center for Conservation Bioacoustics. Cornell University.

Fiber optic cables crisscross vast tracts of the seabed

Whale researchers like Bouffaut typically use hydrophones to monitor whale activity underwater. Although the hydrophone provides good quality data, it can only cover a limited number of areas. Hydrophones are usually deployed about 10 to 20 kilometers apart, Bouffaut explained. This relatively close proximity gives scientists a good idea of ​​where whales might be, a method similar to using cell phone triangulation to detect the location where a phone call was made. But the oceans are huge, and even a large network of hydrophones can only detect a small area. Fiber optic cables, on the other hand, traverse huge parts of the seabed.

Distributed acoustic sensing is already being used to monitor the health of submarine cables and can alert communications companies to problems such as a line break. It works because a fiber in the cable is connected to a so-called interrogator, a device that measures whether a fiber optic cable is functional, explains Bouffaut. The interrogator sends pulses of light 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 happening near the cable, whether that’s an anchor dropped close to a cable or a whale singing nearby.

Here the sound of the whales has been recorded by the virtual hydrophones.

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

Just like fiber optic cables pick up vibrations from an earthquake, the cable can pick up the sounds through seismic vibrations that bounce off the fins of male whales. Yes, fins. Apparently, male whales can make songs of fin whales through a “series of repeated short and low-frequency pulses that resemble air rifle blasts,” the study said.

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

“We need scientific evidence of what they do and how they do it”

“We need scientific evidence of what they do and how they do it,” Bouffaut explained to The edge. Using fiber optic cables, researchers can see when whales have been attacked by boats, become entangled 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 monitor whales as they recover and cope with a commercial whaling industry.

Now that researchers have collected the data for their research, Bouffaut is looking for other applications of the recording technology. Some curiosities 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 leverage the idea that because we can receive the data in real time, we can interact with the data in real time,” Bouffaut said. “This is something that I believe could be helpful to the bioacoustics community because there are many conservation issues that require real-time monitoring.”

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