Whale Song in the Arctic

In a previous Orkney News article we reported on research about whale song: Songs are Being Learned by Whales on Shared Migration

At the other end of the planet , for the first time ever, researchers have succeeded in passively listening to whales — essentially, eavesdropping on them — using existing underwater fibre optic cables.

This audio is series of non-stereotyped arched sounds and down-sweeps, likely from a North Atlantic blue whale. Recorded using Distributed Acoustic Sensing. Credit: Léa Bouffaut et al.

The technique, called Distributed Acoustic Sensing, or DAS, uses an instrument called an interrogator to tap into a fibre optic system, turning unused, extra fibres in the cable into a long virtual array of hydrophones. The research was conducted in the Svalbard archipelago, in an area called Isfjorden, where baleen whales, such as blue whales, are known to forage during the summer.

Scientist Léa Bouffaut, explained:

“Deploying hydrophones is extremely expensive. But fibre optic cables are all around the world, and are accessible. This could be much like how satellite imagery coverage of the Earth has allowed scientists from many different fields to do many different types of studies of the Earth. To me, this system could become like satellites in the ocean.”

This schematic shows how the Distributed Acoustic Sensing, called DAS, works. A laser pulse is sent from the shore station through a fibre optic cable by an interrogator (a). The fibre has evenly spaced nodes on it, called defects (b). Underwater sounds cause the defects in the fibre to be slightly displaced, which delays the backscatter a signal back to the interrogator, which then interprets the time delay as a strain on the fibre. That in turn can be interpreted as acoustic data. Credit:

The technology also allows researchers to “hear” other sounds carried through the water, from large tropical storms to earthquakes and to ships passing by.

The researchers worked with Sikt, the Norwegian Agency for Shared Services in Education and Research, which provided access to 250 km of fibre optic cable in Svalbard, buried on the seabed between the archipelago’s main town, Longyearbyen, and Ny-Ålesund, a research settlement on a peninsula to the northwest. The cable goes from a sheltered fjord, called Isfjorden, and out into the open ocean, where 120 km of the cable was used as a hydrophonic array.

It is possible to see whales when they come to the surface to breathe, but sound is acknowledged as the best way to study whales because they’re otherwise very elusive.

The study, ‘Eavesdropping at the speed of light: distributed acoustic sensing of baleen whales in the Arctic’, was published in Frontiers in Marine Science

Categories: Science

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