Scientists have detected blue fins using underwater fiber optics

Undersea fiber optic cables can be used not only to transmit data, but also to detect large marine mammals moving in sea and ocean waters. Scientists used the cable arranged off the coast of Spitsbergen to record signals indicating the presence of blue fins also when animals did not make any sounds.

How fiber optic detects silent fin

Passive acoustic monitoring of whales is primarily based on recording the sounds they make. When the animal does not vocalise, in other words it does not make voices or other sounds for communication, this method does not provide a signal to confirm its presence.

Researchers used a system of distributed DAS acoustic measurements. In this technology, fiber in the underwater telecommunications cable acts as a distributed network of distortion sensors. Scientists They did not limit the analysis to vocalisation, but also sought low frequency signals caused by pressure changes and water movement around the moving animal.

The flowing fin moves large water masses, creating a hydrodynamic pressure field reaching the bottom. It causes small deformations of sediments that are transferred to the buried cable and can be recorded by the DAS system. There is no need for an acoustic signal from an animal.

Research off the coast of Spitsbergen

The experiment started in 2022 and the collection used in the study included data recorded in different periods until September 2025. Measurements were carried out using offshore telecommunications cables connecting Longyearbyen and Ny-Ålesund to Spitsbergen, the largest island of the Norwegian archipelago of Svalbard in the Arctic. Cables are arranged in soft sediments, up to about 2 metres below the bottom surface.

Scientists first analysed signals from four ships of different sizes. Their location, course and speed could be checked on the basis of the AIS automatic identification system data. This allowed to assess how the size of the object and its distance from the cable affect the power of the recorded signal.

The model was then used for signals attributed to blue fins. The changes caused by the movement of water were also seen in fragments of the record in which no vocalisation was recorded. The AIS data did not indicate at that time the presence of ships which could be responsible for the recorded signals.

Range remains limited

The most important limitation of the method is a small detection distance. In the case of blue whales, the range was estimated at about 30-40 m. For a passenger ship 150 m long, the signal was recorded at a distance of up to 550 m from the cable, at a sea depth of 413 m.

The presence of fins was not confirmed by visual observations, transmitters or other independent methods. The interpretation adopted by the researchers was supported by signal characteristics, pre-recorded vocalisations and lack of movement of ships that could explain the resulting disturbances. However, this was not a direct observation of animals.

The model used requires further refinement. Some of the calculations pointed to the unrealistic length of the animals detected, which shows that at this stage the method does not yet allow to accurately determine their size.

Complementary monitoring of whales

The method will not replace hydrophones, observations from ships and aircraft or animal marking. However, it can supplement the way whales are monitored so far, allowing their movement to be recorded during periods when they do not make sounds.

Its advantage is the possibility of using existing offshore telecommunications cables. The signal reading device can be located on land so that additional point sensors do not need to be deployed in the sea. Technology can be particularly useful in Arctic areas where regular animal observation is difficult.

Scientific article was released online on 23 June 2026 in the journal "Proceedings of the National Academy of Sciences". The journal number in which the study was published is dated to 30 June 2026.

Source: Procedures of the National Academy of Sciences