Whale songs are heard over a fiber-optic cable – wissenschaft.de

Until now, if researchers wanted to record whale songs, they had to rely on individual underwater microphones. Innovative technology now makes it possible to discover the sounds of giant marine mammals on a much larger scale: with the help of fiber-optic cables already laid on the sea floor. The cables are so sensitive to the smallest vibrations that even the sound waves emitted by the whales are reflected in the signal. In an experiment conducted in the Arctic Ocean, researchers were able to use this data to locate whales within a few metres.

Despite their size, whales are often difficult to track in vast oceans. While local observations and satellite images of surfacing whales allow researchers to draw conclusions about the occurrence and migration of giant marine mammals, they only provide an incomplete picture. Underwater microphones, called aquatic microphones, which record whale songs, cover only a small area at a time. Especially in light of the changing activities of whales and humans in the context of climate change, it is important for researchers to obtain more accurate data on where whales are located so that they can protect the animals more effectively.

Satellites in the ocean

A team led by Léa Bouffaut of the Norwegian University of Science and Technology in Trondheim has successfully tested a new approach that could make it possible to track whales across large areas of the ocean based on their songs and possibly even monitor them in real time. To do this, the researchers used and tapped into fiber-optic cables located on the sea floor using a technology called Distributed Acoustic Sensing (DAS). DAS technology makes it possible to transmit optical pulses over unused fibers of a fiber-optic cable with the help of an interrogation device and assessment of transit time. Vibrations in the cable affect the signal propagation time. So the system is already used to detect earthquakes.

Bufo and her team focused on the much weaker tremors: those that cause the sound waves of whales’ calls. “I think this could change the field of marine bioacoustics,” says Lea Buffo. “Using water is very expensive. But fiber-optic cables are scattered all over the world and are easily accessible. From my point of view, this system could become something like satellites in the ocean.”

A new kind of data

The research was conducted in the Svalbard archipelago in Norway. In this part of the Arctic Ocean, baleen whales forage for blue whales during the summer. For 44 days, the researchers recorded the signals from the fiber-optic cables laid there and received a massive amount of data of about seven terabytes per day. “If anything moves or makes a sound near these fibers buried on the sea floor, we can measure it,” says Martin Landru, a fellow of Bofo. “So we saw a lot of shipping traffic, of course a lot of earthquakes, and we could even see storms in the distance. And finally: whales. In total, we recorded at least 830 whale calls.”

One of the challenges at first was to correctly interpret the signals. “We were looking for signals without knowing exactly what to expect,” Buffo explains. “It’s a new technology and a new kind of data that no one has used before to search for whales.” However, by analyzing frequency, pattern, and frequency, they were able to clearly identify whale songs in the data being produced. With this knowledge, it will be possible in the future to train models for machine learning and thus simplify and automate data analysis.

Contribute to the protection of whales

“With this system we have the potential to cover a large area of ​​observation,” says Buffo colleague Hannah Joy Cresel. “And since we receive sound from multiple angles, we can even determine the position of the animal. If we go further, which still requires some extra work, it could be in real time, which would really be a huge step forward for observing vocal whales.” Move and thus avoid collision with whales. Especially if shipping traffic increases in the Arctic as the ice sheet melts, this could be of great importance to protecting whales.

Source: Léa Bouffaut (Norwegian University of Science and Technology (NTNU), Trondheim) et al, Frontiers in Marine Science, doi: 10.3389/fmars.2022.901348

© wissenschaft.de – Elena Bernard