For decades, scientists have relied on several methods to locate whales in the ocean. Some attach satellite transmitters to the animals, others deploy drones for aerial observations, while many use underwater hydrophones to record whale songs.
Each of these techniques, however, has significant limitations. Satellite tags can only track whales that have been fitted with transmitters. Drones have limited flight time and operating range. Hydrophones are effective only when whales are vocalizing.
Now, a new study has demonstrated an entirely different approach. Without relying on satellites or drones, researchers successfully tracked whales using the same fiber-optic cables that carry internet traffic across the seafloor.
Even more remarkably, the technology can detect whales while they are silently swimming.
How Can Undersea Fiber-Optic Cables Detect Whales?
The breakthrough relies on Distributed Acoustic Sensing (DAS), a technology that transforms submarine fiber-optic cables into continuous sensors stretching for tens or even hundreds of kilometers. The system measures extremely small strains occurring along the cable.
DAS has already been used to monitor earthquakes, ship traffic, and ocean waves. The new study shows that the same infrastructure can also detect whale movements.
Importantly, the system does not “listen” to whales.
As a whale swims, its massive body displaces millions of liters of seawater, generating hydrodynamic pressure disturbances that propagate toward the seafloor. These pressure changes cause microscopic deformation of the seabed sediments. Because fiber-optic cables are buried within these sediments, the tiny deformations stretch the cable ever so slightly, allowing the DAS system to record the signal.
In other words, the cable does not hear whales—it senses the subtle water-pressure disturbances created by their movement.
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Why Are Silent Whales Difficult to Detect?
Most whale monitoring today relies on Passive Acoustic Monitoring (PAM), which depends entirely on whale vocalizations.
The challenge is that whales do not sing all the time. While feeding, diving, or migrating, they may remain silent for extended periods. During these quiet intervals, conventional acoustic monitoring systems often fail to detect their presence.
According to lead author Robin André Rørstadbotnen, this limitation motivated the research team to develop a method that does not depend on whale calls. By detecting the hydrodynamic pressure generated by a whale’s body as it swims, the system can monitor whales even when they remain completely silent.
The findings were published in the journal Proceedings of the National Academy of Sciences (PNAS) in a paper titled Detecting Silent Whales Using Seabed Fiber-Optic Cables, June 2026.
The research was conducted by Robin André Rørstadbotnen and Martin Landrø of the Norwegian University of Science and Technology (NTNU).
The researchers used a 260-kilometer submarine fiber-optic cable connecting Longyearbyen and Ny-Ålesund in the Svalbard archipelago in the Arctic.
Before testing the method on whales, the team first validated it using ships whose locations, sizes, and speeds were known through the Automatic Identification System (AIS). These vessel data allowed the researchers to develop a mathematical model linking hydrodynamic pressure to the signals recorded by the fiber-optic cable.
Once validated, the model was applied to identify signals generated by blue whales.
Robin André Rørstadbotnen explained that, in addition to recording whale vocalizations, the DAS system could also detect the hydrodynamic pressure produced by whales as they swim. Martin Landrø said the technology opens new possibilities for monitoring whales that previously remained undetectable while silent.
Whales Can Be Tracked Even When They Stop Singing
One of the study’s most compelling observations occurred when the researchers monitored a blue whale that was initially vocalizing near the ocean surface.
As the whale began to dive and stopped singing, its acoustic signal disappeared. At the same time, however, the DAS system continued tracking the animal by recording the hydrodynamic signal generated by its movement through the water.
The finding demonstrates that whales can still be monitored beneath the ocean surface even when they are completely silent.
The researchers estimated that the whale was swimming at speeds of approximately 2 to 4 meters per second, while its hydrodynamic signal remained detectable when the animal was about 40 meters from the fiber-optic cable buried on the seafloor.
How Could Fiber-Optic Cables Benefit Whale Conservation?
The ability to detect silent whales could create new opportunities for marine mammal conservation.
Scientists have long struggled to estimate whale populations and migration patterns because these animals spend much of their lives underwater. By utilizing the extensive global network of submarine fiber-optic cables already installed across the oceans, whales could be monitored without capturing them or attaching tracking devices.
The technology could also complement existing monitoring systems. Whale vocalizations could continue to be detected when animals are near the surface, while DAS would allow scientists to follow their movements after they dive and stop calling by sensing the hydrodynamic disturbances produced by their bodies.
In the future, this technology could potentially be integrated with ship navigation systems, providing early warnings when whales are present near shipping lanes. Such a system could help reduce collisions between ships and whales.
Why Are Whales Frequently Struck by Ships and Entangled in Fishing Gear?
The new technology comes at a time when whale populations continue to face numerous human-related threats.
One of the leading causes of whale mortality is ship strikes. In many regions, whale migration routes overlap with busy international shipping lanes. When whales surface to breathe—especially at night or during poor weather—the risk of being struck by fast-moving vessels increases significantly.
Along the east coast of North America, several humpback whales have died in recent years following suspected vessel collisions. Similar incidents have also occurred in California’s San Francisco Bay, one of the world’s busiest maritime corridors.
Whales also frequently become entangled in fishing gear such as crab trap lines and gillnets. Entangled animals can suffer severe injuries, lose their ability to swim effectively, or even drown if they cannot reach the surface to breathe.
Another growing threat is underwater noise generated by commercial shipping, offshore energy development, and marine infrastructure projects. This noise pollution can interfere with whale communication, navigation, and feeding behavior.
In addition, mass whale strandings continue to occur in countries including New Zealand and Australia. Although the causes vary, scientists believe that a combination of natural factors and human activities contributes to many of these events.
By detecting whales even when they are silent and diving near the seafloor, submarine fiber-optic cable networks could eventually serve as an early warning system to reduce ship strikes while also providing scientists with an unprecedented tool for studying whale behavior in their natural habitat.
Infrastructure originally built to connect people through the internet may soon become one of the most valuable tools for protecting the largest mammals on Earth. (Wage Erlangga)
