Aerial image of blue whale breathing at the water’s surface.
Credit: NOAA Photo Library/Flikr, CC BY 2.0

For the first time, scientists tapped into an unused fiber-optic cable to record whale calls ringing through Norway’s Svalbard archipelago.

Fiber-optic cables carry vast amounts of data between continents and underly 1.2 million kilometers of ocean floor globally.

Researchers eavesdropped on North Atlantic blue whales, the largest animal on Earth, calling out to each other within the fjord-sheltered waters and the open ocean. The whales migrate from as far south as the subtropics to Svalbard’s northern waters in summer, and during late June to early August 2020, blue whales and other cetaceans vocalized more than 800 times. (Other species caught on tape may have included fin, humpback, and sei whales.)

A ubiquitous presence on the seafloor—fiber-optic cables—captured the songs. The cables carry vast amounts of data between continents and underly 1.2 million kilometers of ocean floor globally. On land and sea, recent advancements in acoustics have enabled scientists to tap into this worldwide network for their own interests: sensing volcanic rumbles in Iceland, tracking ships in the Mediterranean, and even recording the revelry of the Rose Parade in Pasadena, Calif.

But fiber optics have never been used to detect whale songs before. Researchers often rely on underwater microphones, or hydrophones, to study whale calls. But hydrophones cost money to deploy at sea, whereas fiber-optic cables have already been deployed.

The latest research relied on a spare fiber-optic cable running through Isfjorden, a fjord in Svalbard. The scientists placed a laser-pulsing instrument called an interrogator at the end of a 120-kilometer cable in the coastal city of Longyearbyen.

The interrogator transformed the cable into a hypersensitive distributed acoustic sensor. As it pulsed lasers into the cable, the lasers hit infinitesimal impurities in the fibers and backscattered. When acoustic waves from whale songs lightly pushed on the cable, the interrogator sensed that the backscatter changed ever so slightly, revealing a signal.

Vocalizations from the Deep

The fiber-optic eavesdropping may have wide-ranging applications. One advantage of fiber optics over traditional ocean acoustics, for example, is its instantaneous nature. Signals travel along the cable at the speed of light, and if algorithms interpret the data swiftly, scientists could obtain a real-time understanding of whale whereabouts. (Hydrophones, in contrast, can’t transmit data remotely while underwater; sending acoustics data through radio waves simply consumes too much power.)

Scientists worry that climate change is altering whale migration, and real-time monitoring could help determine the extent. The data could also help gauge the health of whale populations. Fin whales and other baleen species have been recovering since international whaling ceased in 1982, but because whales’ species range is vast, researchers struggle to grasp the success of their recovery.

“This technology, I think, can change our way of seeing the ocean.”

“This technology, I think, can change our way of seeing the ocean,” said lead author Léa Bouffaut, who completed the work at the Norwegian University of Science and Technology. Bouffaut published the research in Frontiers in Marine Science.

In addition to tracking whale movement and migration, the fiber-optic network could contribute to whale conservation. “Ship strikes are a conservation concern for many whale species, especially in areas where major shipping lanes crisscross migration routes or critical habitats for feeding and breeding,” said Holger Klinck, the director of the K. Lisa Yang Center for Conservation Bioacoustics at the Cornell Lab of Ornithology. Although Klinck was not involved in the present study, Bouffaut now also conducts research at the K. Lisa Yang Center.

“This information could be relayed to vessels operating in the area, requesting them to slow down to reduce the risk of striking a whale,” said Klinck.

The Potential of Fiber Optics

Although the study was successful in the coastal North Atlantic, researchers say we won’t be able to listen to whales in the middle of the ocean just yet. Repeaters spaced along fiber-optic cables strengthen telecommunication signals but also block the lasers from the interrogators. For now, the machine can sense signals only from the shore to the first repeater, often about 50 to 70 kilometers offshore.

“We were able to see storms that occurred in the South Atlantic 13,000 kilometers away.”

And as with any new technique, the fiber-optic eavesdropping must be tested alongside existing methods, said Klinck.

Bouffaut received funding from the Research Centre for Arctic Petroleum Exploration of Norway. One application of the technology could include harnessing whale calls to seismically map the seabed for resources, she said.

The scientists also observed far-distant weather, a phenomenon first proved possible by oceanographer Walter Munk in 1963. “We were able to see storms that occurred in the South Atlantic 13,000 kilometers away on the low-frequency part of the data, and we could determine the distance to the storm,” said Martin Landrø, an author of the study and a geophysicist at the Norwegian University of Science and Technology. “We detected at least four or five different large storms that occurred, and we could go back to the meteorological data and identify them by name.”

—Jenessa Duncombe (@jrdscience), Staff Writer

Citation: Duncombe, J. (2022), Wiretapped cables and the songs of whales, Eos, 103, Published on 22 July 2022.
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