Whales in the high Arctic can be listened to using underwater fibre optic cables

In a first of its kind approach, scientists have used existing underwater fibre optic cables to eavesdrop on whales in the high Arctic. This is a method that no one has tried before and it adds yet another tool to scientists’ arsenal alongside satellite tracking, aerial surveys, sightings and individual hydrophones to listen for whale calls.

The technique, called Distributed Acoustic Sensing, or DAS, uses an instrument called an interrogator to tap into a fibre optic system, turning unused, extra fibres 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 forage during the summer.

According to researchers, the other types of whale monitoring that rely on sound often only provide single or a few points of location information from a hydrophone. Point locations provide limited coverage of an area, and of course aren’t evenly spread across all oceans, which can make it challenging for researchers to study migratory routes, for example.

In contrast, DAS not only allows researchers to detect whale vocalizations, they can use the fibre network to locate where the whales are in both space and time, with an unprecedented spatial resolution.

The technology also allows researchers to “hear” other sounds carried through the water, from large tropical storms to earthquakes to ships passing by, said Martin Landrø, an NTNU geophysicist who was a co-author of the paper. Landrø is also head of the Centre for Geophysical Forecasting, a Centre for Research-based Innovation funded by the Research Council of Norway.

We detected at least four or five different large storms that occurred and we could go back to the meteorological data and identify them by name.

The researchers worked with Sikt, the Norwegian Agency for Shared Services in Education and Research, which provided access to 250 km of fibre optic cable in Svalbard, buried on the seabed between the archipelago’s main town, Longyearbyen, and Ny-Ålesund, a research settlement on a peninsula to the northwest. The cable goes from a sheltered fjord, called Isfjorden, and out into the open ocean, where 120 km of the cable was used as a hydrophonic array.

The research group also included Alcatel Submarine Networks Norway, which provided the interrogators — the instruments that allowed the group to tap into the Sikt fibre optic cable.

Two researchers travelled to Longyearbyen in June 2020, at the beginning of the COVID-19 pandemic, and were able to use the interrogator for 40 days, listening along the length of the 120 km long cable.

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