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Fin whale near the Azores: Where the feeding grounds of the whales are shifting to is important information for scientists
Photo: Luis Quinta / Nature Picture Library / IMAGO
Thousands of kilometers of fiber optics connect the continents at the bottom of the oceans, and the lines transmit many terabytes of data every day.
But since the operators lay many cables in addition to the active lines, so to speak, researchers are already looking for other applications.
A Norwegian research team has now succeeded in using the "dark fiber" lines as antennas to search for whales.
This is possible because baleen whales broadcast their famous songs at very low frequencies.
They can therefore be heard over long distances and also cause the data lines on the sea floor to vibrate.
By sending light of a special wavelength through the unused optical fibres, the scientists from the University of Trondheim were able to register these vibrations from the coast.
They present their method in a recent article in the journal »Frontiers in Marine Science«.
The method of "Distributed Acoustic Sensing" - in short: DAS - proved to be surprisingly effective.
The research group was not only able to distinguish the different types of whale songs, but also to determine the position of the animals.
The technology is only made possible by tiny impurities in the glass fibers that slow down the light signals.
Through targeted queries, the researchers can transform each section of a 120-kilometer fiber optic cable into an underwater listening station.
Scientists could use the method to explore the changed territories and routes of the whales.
In order for a worldwide network to emerge, however, they would need many more inactive submarine cables.
The amount of data is also a problem.
Even in the limited test run, the researchers had to analyze seven terabytes of data per day to separate the whale songs from the sounds of propellers and other underwater echoes.
DAS could also benefit other research, such as detecting earthquakes.
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