Whales can be difficult to monitor and study. a new approach – using fiber optic cables – may change that – ScienceDaily
Whales are huge, but they live in an even larger environment: the world’s oceans. Researchers use a range of tools to study their whereabouts, including satellite tracking, aerial surveys, observations and deploying individual hydrophones to listen to their calls. But now, for the first time, researchers have succeeded in listening to whales passively – essentially, spying on them – using existing undersea fiber optic cables.
The technique, called Distributed Acoustic Sensing, or DAS, uses an instrument called an interrogator to tap into a fiber optic system, turning the extra unused fibers 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 feed during the summer.
“I think this can change the field of marine bioacoustics,” said Léa Bouffaut, the first author of a paper just published in Frontiers in Marine Sciences. Bouffaut was a post-doctoral fellow at NTNU, the Norwegian University of Science and Technology, when she worked on this research and is now at the K. Lisa Yang Center for Conservation Bioacoustics at Cornell University, where she continues to d extend this work.
Fiber optic cables are everywhere
Bouffaut said the beauty of the system is that it could allow researchers to take advantage of an existing global network.
“Deploying hydrophones is extremely expensive. But fiber optic cables are all over the world and accessible,” she said. “It could be a bit like how satellite imagery coverage of the Earth has allowed scientists from many different fields to do many different kinds of studies of the Earth. To me, this system could become like satellites in the ocean.”
Bouffaut said other types of whale monitoring that rely on sound often only provide one or a few points of location information from a hydrophone. Point locations provide limited coverage of an area and, of course, are not evenly distributed across all oceans, which can make it difficult for researchers to study migration routes, for example.
In contrast, DAS not only allows researchers to detect whale vocalizations, but they can also use the fiber network to locate where whales are in space and time, with unprecedented spatial resolution, a she declared.
“With this system, which is what we can essentially call a hydrophone array, we have the ability to cover a much larger area for monitoring. And because we’re getting the sound from multiple angles, we can even tell where was the animal — the position of the animal. And that’s a huge advantage. And if we go even further, which still requires a bit of extra work, it could be done in real time, which would be a real game-changer for acoustic whale tracking,” said her colleague Hannah Joy Kriesell, one of the paper’s co-authors.
Can hear ships, earthquakes
The technology also allows researchers to “hear” other sounds carried in water, from large tropical storms to earthquakes to ships, said Martin Landrø, an NTNU geophysicist who was a co-author of the item. Landrø is also the head of the Center for Geophysical Prediction, a research-based innovation center funded by the Research Council of Norway.
We detected at least four or five different major storms that occurred and were able to go back to weather data and identify them by name.
“If something is moving near or making an acoustic noise near this fiber, which is buried in the seabed, we can measure it,” he said. “So what we saw was a lot of ship traffic, of course, a lot of earthquakes, and we were also able to detect distant storms. And finally, whales. We detected at least 830 vocalizations of whales in total.” Landrø said detection of distant storms was possible due to low-frequency seismic signals generated by waves from large storms. This method of detecting large storms from low-frequency waves at great distances was established by oceanographer Walter Munk in 1963, when he measured the waves of Antarctic storms on the Pacific island of Samoa, a said Landrø.
“We were able to see the storms that happened in the South Atlantic at 13,000 kilometers away on the low frequency part of the data, and we were able to determine the distance to the storm,” he said. “We detected at least four or five different major storms that occurred and were able to go back to the weather data and identify them by name.”
COVID-19 and a trip to Svalbard
The researchers worked with Sikt, the Norwegian Agency for Shared Services in Education and Research, which provided access to 250 km of fiber optic cable in Svalbard, buried in the seabed between the main town of archipelago, Longyearbyen, and Ny-Ålesund, a research colony. on a peninsula to the northwest. The cable runs from a sheltered fjord, called Isfjorden, to the open sea, where 120 km of cable has been used as a hydrophonic network.
The search group also included Alcatel Submarine Networks Norway, which provided the interrogators – the instruments that allowed the group to tap into the Sikt fiber optic cable.
Two researchers traveled to Longyearbyen in June 2020, at the start of the COVID-19 pandemic, and were able to use the interrogator for 40 days, listening along the 120 km long cable.
“The fiber optic cable between Longyearbyen and Ny-Ålesund, which was put into production in 2015 after 5 years of planning and preparatory work and mainly financed by our ministry, was intended to serve the research community and the geodetic station of Ny Ålesund with a high and resilient communication capacity,” said Olaf Schjelderup, Sikt’s national R&E network manager and another co-author of the paper. “The DAS whale detection and observation experience shows a use completely new of this type of fiber optic infrastructure, resulting in excellent and unique science.”
Schjelderup noted that another benefit of the experiment was the high-throughput data communication capability provided by Norway’s R&E network (named mUninett), which allowed near real-time streaming of raw data from the sensor unit. DAS in Longyearbyen to Trondheim. .
“Researchers could, from Trondheim, almost instantly start studying signal records from the sea outside Svalbard. This is a very good example of a paradigm shift in distributed data collection,” did he declare. “What has been done in Svalbard here paves the way for more of these types of fiber optic sensors to be deployed as permanent infrastructure – collecting and processing data from different geographies and locations in near time. real – both for research and for different operational purposes.”
7 terabytes per day
Bouffaut and Kriesell, a researcher in NTNU’s Electronic Systems Department, worked on analyzing the experiment’s 40 days of round-the-clock data. In total, they had to analyze 7 terabytes per day, or about 250 terabytes of data for the entire period. They started by looking at signals from locations on the fiber 10km apart, which “made it manageable,” Bouffaut said.
The challenge, in addition to the amount of data involved, was that “we are looking for signals without knowing exactly what to expect. This is new technology and a new type of data that no one has looked at to find whales” , said Bouffaut. said.
The work was painstaking, but “it was very, super exciting, especially when we started seeing whale signals,” Bouffaut said. “But I often get this question, even from bioacousticians: how do you know it’s a whale? And I say, ‘how do you know it’s a whale when you recorded from a hydrophone? We recognized the frequency, the pattern, the repetition, and we listened to it.'”
Bouffaut added that now that researchers know the data better, they could train machine learning models to simplify and automate the data analysis process.
Bouffaut and Kriesell identified so-called stereotypical calls for North Atlantic blue whales outside of Isfjorden. These types of calls are associated with male vocalizations. They also saw what are called D-calls, which are low-pitched vocalizations that can be made by males, females, and calves. They detected these calls inside the sheltered waters of the fjord. Previous researchers have linked D calls to foraging or social contexts, the researchers said.
The Changing Arctic
Bouffaut said the value of this type of system is particularly evident in the Arctic, where warming due to climate change is occurring two to three times faster than average.
“The Arctic is changing very rapidly. And the animal and human use of the region is changing as fast as the ice is melting,” Bouffaut said.
Whales such as blue whales are not yet year-round users of the area, but as the ice melts that could change, she noted.
At the same time, the disappearance of the ice cover is opening up the Arctic to increased shipping, fishing and other activities, such as tourism.
“So if the whales are changing their uses of that area, and maybe using that area for more than foraging or for activities where they’re very vulnerable, then having that kind of technology can help us monitor these changes,” Bouffaut said.
It is possible to see whales as they come to the surface to breathe, but sound is recognized as the best way to study whales because they are otherwise very elusive”. Thus, by studying their sound production, their cries and their vocalizations, we can learn We can know where they are in different seasons, and how and where they migrate, so we get a lot of information from listening to them,” Kriesell said.
And if DAS can be set up so that the information can be analyzed in real time, the information could be relayed to vessels traveling in waters where the whales feed or socialize, and inform stakeholders for direct conservation action. , said Bouffaut.
“We could potentially reduce the risk of collisions with whales. That would be a really big deal,” Kriesell added. “Arctic ice is melting and ship traffic has increased dramatically in the Arctic. And that’s a problem for animals. So if we have a way to let ships know where whales are in real time, we could stop or at least reduce the risk of collision with ships.