Undersea Internet Cables Could Become a Global Whale-Watching Network

In a pioneering experiment published in 2022, scientists used an existing submarine telecommunications cable off Svalbard, Norway. They transformed a 120-kilometre stretch into approximately 30,000 sensing points, spaced just four metres apart. The system detected the low-frequency calls of blue and fin whales, animals whose vocalizations can travel enormous distances through seawater.

The team went beyond simple detection. Because sound reaches different sections of the cable at slightly different times, researchers used those delays to estimate where the calls originated — essentially triangulating the whales' positions.

A follow-up in 2023 pushed further. Using five hours of recordings from two Arctic cables, researchers identified 1,808 fin whale calls and tracked eight whales, including as many as four simultaneously. The animals could be detected as far as 9.4 kilometres from the cables, and the researchers demonstrated localization accuracy of roughly 100 metres. Two cables on the seabed reconstructed the movements of several enormous animals without deploying a single additional microphone.

Why does this matter now?

Marine mammals already navigate an increasingly industrialized ocean. Cargo ships cross migration routes, offshore wind farms are expanding, and oil exploration, construction and commercial shipping add noise to an environment where many animals depend on sound to communicate, navigate and find one another.

Ships pose a particularly direct threat: large whales can be seriously injured or killed in collisions with vessels. Bouffaut's review envisions a shipping corridor equipped with fibre-optic acoustic monitoring, in which software identifies a whale's call signature, estimates its position and sends an alert to operators, who could potentially take precautions. The system would not be perfect, but it could prove useful.

There are practical advantages as well. In many deployments the monitoring equipment can remain on land, eliminating the need to send boats out to recover underwater recorders or replace their batteries. Telecommunications companies have already installed extraordinary lengths of fibre across the world's oceans, and offshore energy operators already use fibre-optic systems to watch their own infrastructure for damage and security threats. Some cables could potentially perform both jobs at once.

What stands in the way?

The challenges remain considerable. The most immediate is data volume: depending on the recording settings, a single 50-kilometre DAS installation can generate several terabytes of data per day. Manual processing would be impractical, and while researchers are developing automated detection algorithms — including machine-learning systems that separate whale vocalizations from ship noise, earthquakes and other disturbances — there is still room for improvement.

Calibration presents another hurdle. Different cable designs and seabed conditions influence sensitivity, meaning a whale detected near one cable might go unnoticed near another. Nor is monitoring every cable as simple as plugging in a laser: some lack accessible fibres, while optical repeaters (amplifiers built into long cables) and other components can limit which sections can be observed. Large-scale deployment would require cooperation among researchers, telecommunications operators, regulators and offshore industries.

For decades, humans have laid cables across the ocean floor so that we could communicate with one another. Nobody thought about the whales — until the whales turned out to be audible all along.