underwater cables: Tiny fiber-optic cables on seabed can do a lot more than you can imagine. Now, they can listen to silent whales. Here’s how
Existing underwater cables reveal another purpose
For years, fiber optic cables have connected countries by carrying internet traffic, phone calls, financial transactions and other digital communications across the ocean floor.
In 2020, researchers at the Norwegian University of Science and Technology (NTNU) discovered another use for these underwater cables. They found that the cables could act as passive listening devices. Using this system, they detected the deep sounds made by whales in the waters near Svalbard.
This success encouraged researchers to investigate whether these cables could provide more information about whales. Recent research has now shown that whales can be detected even when they are completely silent.
Tiny fiber optic cables on the seafloor can do more than you can imagine by detecting silent whales
Researchers found that whales create low-frequency pressure waves as they swim in the ocean. As the whale moves, its body pushes the water in front of it. This movement disturbs the surrounding water and nearby seafloor sediments. Fiber optic cables are sensitive enough to detect these changes.
Martin Landrø, director of NTNU’s Center for Geophysical Prediction and senior author of the study published in the Proceedings of the National Academy of Sciences (PNAS), explained that silent whales can still be detected because their movements create measurable disturbances. According to the researchers, no previous studies have focused on these low-frequency pressure waves for whale detection.
Pressure waves are harder to detect
The research team explained that low-frequency pressure waves weaken rapidly as they move through water. Large ships are much easier to detect because they push much more water than whales, said Robin Andre Rørstadbotnen, first author of the study and a postdoctoral researcher at the Center for Geophysical Prediction. Because whales move less water, they must dive into the water column before these pressure waves become detectable through fiber optic cables. Understanding this difference helped researchers improve detection methods.
Ships helped scientists understand whale movement
A large number of vessels, including cruise ships and research vessels, enter the waters around Svalbard throughout the year. The ships are equipped with Automatic Identification System (AIS). This system constantly reports the ship’s identity, position, speed and navigational route. The researchers compared AIS information with signals recorded by fiber optic cables.
Previous studies focused mainly on the sound made by ships. During recent research, scientists realized that they could also measure pressure waves created by ships moving through water. Since ship positions and speeds were already known through AIS data, researchers were able to compare the recorded pressure waves with actual ship motion. This helped them understand what similar pressure waves from whales might look like.
Physics played an important role in research
Scientists also relied on a physics equation published by Lord Rayleigh in 1917. The equation originally described how bubbles collapse in boiling water. While boiling water and ocean movement may seem unrelated, the same physical principles help explain the pressure waves produced by moving ships and whales, the researchers said.
Using the ship data together with the Rayleigh equation allowed the researchers to calibrate their observations. They were then able to interpret low-frequency signals with greater confidence. This was one of the most important findings of the research.
Blue whale confirms discovery
The research team received unexpected help from nature. A blue whale swam near the surface making vocal sounds. Fiber optic cables detected these sounds using methods developed during previous studies.
The whale then stopped making sounds and dived deeper into the ocean. Instead of losing track of the animal, the researchers examined low-frequency pressure wave data. They continued to track the whale successfully even after it fell silent. This confirmed that the new detection method worked. The researchers said the observation was possible because they already understood how pressure waves behave after examining the ships.
Existing wired networks can support protection
Scientists believe this discovery could be an important tool in whale conservation. Many whale populations have declined due to decades of commercial whaling. Although some populations have recovered, whale numbers remain difficult to estimate because these marine mammals travel across large areas of ocean.
Traditional monitoring relies heavily on whale vocalizations. But silent whales often remain unnoticed. The new technique could help scientists monitor whale populations more accurately without disturbing the animals. It also makes use of fiber optic cables that already exist under the oceans around the world.
More possibilities beyond whale watching
The research team has previously proposed several additional uses for underwater fiber optic cables. Scientists believe these cable networks can help detect earthquakes. They can also monitor subsea pipelines for possible damage or sabotage.
The researchers proposed combining cable observations with satellite information to build an Earth-Ocean-Atmosphere-Space Observatory. Such a system could improve the understanding of natural phenomena occurring on the planet. The ability to detect silent whales now adds another possible application to this growing list. Researchers believe that existing underwater communications infrastructure can support scientific research without installing entirely new monitoring systems.
Why is this discovery important?
This research shows that fiber optic communication cables can perform many tasks beyond carrying internet traffic. These cables, which detect pressure waves created by swimming whales, offer scientists another way to observe marine life. The expedition combines communications technology, ocean science, ship tracking and physics to improve whale watching.
The researchers believe this method could strengthen conservation efforts by helping scientists more accurately estimate whale populations and study whale behavior even when the animals remain silent beneath the ocean’s surface.
FAQ
Q1. How do fiber optic cables detect silent whales?
Fiber optic cables detect the low-frequency pressure waves created by whales moving through the water. Even without vocal sounds, these water disturbances reach the cables, allowing researchers to track whale movement beneath the ocean.
Q2. Why is this discovery important for whale conservation?
The method helps scientists detect whales that remain silent underwater. Better monitoring can improve population estimates, study migration patterns, support conservation planning, and increase understanding of marine ecosystems using existing cable networks.
