Undersea fiber optic cables can be used to record whales and see what they're doing

Over the years, researchers have used a variety of techniques to study whale habitats in the ocean, including aerial surveys, direct observation, and sonar. Now, for the first time, they can passively listen to whales' "talks" (essentially eavesdropping) using existing undersea fiber optic cables.

With this system, called a hydrophone array, there is an opportunity to cover a much larger area for monitoring. And the sound is received in many angles, one can even tell where the animal was and the position of the animal, which is a big plus.

Basically, a fiber optic cable will carry light. Fiber optic cable is what gives you high-speed internet (if you're lucky enough to have high-speed internet), and researchers recently discovered that you can also turn these cables into seismic sensors. .

When cables are subjected to sound waves (as in earthquakes), light transmission is affected and this can be detected with specialized equipment. So a group of researchers thought why not try and also use this method to detect underwater sounds - such as those made by whales.

The technique, known as Distributed Acoustic Sensing (DAS), uses an instrument called an interrogator to tap into an optical fiber system, turning unused fibers in the cable into a hydrophone. The study was carried out in the Svalbard Islands in the Arctic Ocean, where baleen whales, blue whales and others feed during the summer.

"Sound travels five times faster in the ocean than it does in the air," said Leá Bouffaut, a researcher at the Center for Bioacoustics at Cornell University and first author of the study.

DAS allows scientists to detect whale voices and use their fiber-optic network to find whales' positions in both time and space, with exceptional spatial resolution.

While most whale species have recovered from the ban, many whale species are still threatened or critically endangered. They are subject to an increasing number of stressors caused by human activities, from ship collisions to noise pollution. In addition, changes in water and nutrient cycles due to chemical and plastic pollution are a growing problem.

Researchers largely rely on passive acoustic monitoring as a reliable way to study whales, from multi-sensory platforms to stationary automated archival recorders.

However, this work is very expensive so that most recorders are very sparse and uneven in density. Therefore, this study may yield a more effective and less expensive method.

The DAS technology will essentially act like a hydrophone, but it can cover a much larger monitoring area than other methods. Researchers can use it not only to detect whale voices, but also to determine the whale's position in both space and time, Bouffaut argues.

"Deploying the hydrophone in practice, it will be very expensive, but now, the network of undersea optical cables is densely unused and using fiber-optic cables like hydrophones will help us reduce a lot of costs," she said. . "This could be similar to the way satellites cover the Earth, allowing scientists from many different fields to do different types of research on the Earth. For me, this system could become a huge part of the world. satellites in the ocean".

The researchers have now worked with the Norwegian Research Service (Sikt), which has enabled access to more than 250km of fiber optic cable in Svalbard, between the archipelago's main town and a research settlement. The entire cable goes from the sheltered fjord (Isfjorden) and out to the open sea, where 120 km is used as a hydraulic array.

To conduct the study, two members of the research team traveled to the archipelago in June 2020 at the start of the Covid-19 pandemic. They partnered with Norwegian company Alcatel Submarine Networks, which provides interrogators - tools that allow researchers to mine data from Sikt fiber optic cables.

After reviewing more than 250 terabytes of data, the researchers identified stereotypical "calls" to North Atlantic blue whales outside Isfjorden. And usually the sound that males and females call each other.

The researchers concluded that more research is needed to see how this technology can be used to study and conserve whales, as it is an innovative method with so much potential.

"My hope is to further develop this technology and make it available to all those involved in marine conservation," Bouffaut said. "This technology can make the future of many whale species brighter."