A Norwegian research team used two submarine fibre-optic cables to record the sounds of fin whales, following them along the west coast of Svalbard for hours in near real time
Tracking whales in the vastness of the ocean is no easy feat. They can be anywhere and nowhere. Currently, fixed or mobile hydrophones, underwater microphones, are the most reliable and widely used method to locate whales. However, no network of hydrophones dense enough to follow whales exists. In most cases, data are only available at specific points, and most of the vast ocean habitat is not adequately covered.
Martin Landrø, head of the Centre for Geophysical Prediction at NTNU, a Norwegian technical university, and his team recently succeeded in tracking eight fin whales swimming along two parallel fibre-optic submarine cables off the west coast of Spitsbergen in near real time for over five hours. This was made possible by a relatively new technology, Distributed Acoustic Sensing, which has been used for some time in various fields for acoustic remote sensing, for example in earthquake seismology, geophysical exploration or oceanography.
“This work demonstrates how we were able to simultaneously locate and follow these whales over an 1,800km2 area — with relatively low infrastructure investment,” Mr Landrø said.
The two fibre-optic cables run along the west coast of Spitsbergen from Longyearbyen to Ny Ålesund (Illustration: Rørstadbotnen et al 2023)
DAS uses an instrument called an interrogator to send laser pulses into the fibre-optic cable and record the returning light pulses, turning the cables into a series of hydrophones.
Mr Landrø and his team conducted the first tests off Spitsbergen to explore how well DAS recorded underwater vibrations and sounds in June 2020 during the pandemic. They recorded for over 40 days and collected about 250 terabytes of data containing what they have identified as more than 800 whale songs and calls.
Building on this, the researchers expanded their ability to identify different whale species for the current study, published in Frontiers in Marine Science.
The two fibre-optic cables, which are about 250 kilometres long and run between Longyearbyen and Ny Ålesund, allowed the researchers to locate the whales with an accuracy of about 100 metres.
“This shows that the two fibre cables are a very effective means of monitoring whales in the Arctic,” Mr Landrø said.
The Arctic, especially the Svalbard region, is a popular destination for cruise ships and smaller expedition cruise ships. According to Visit Svalbard, which promotes tourism in the Norwegian-controlled territory, up to 75,000 visitors are expected around Svalbard alone this year. As sea ice recedes, shipping traffic of all sorts will continue to increase, including tankers, container ships and others. In addition, sea-ice retreat is tempting whales to increasingly stay in Arctic regions year-round. Both developments increase the risk of collision between whales and ships.
Using the existing global fibre-optic-cable network in conjunction with DAS for real-time tracking of whales can help reduce this risk, the researchers write in their study. “The capabilities demonstrated here establish the potential for a near-real-time whale tracking capability that could be applied anywhere in the world where there are whales and fibre-optic cables. Coupled with ship detection, using a similar approach … a real-time collision-avoidance system could be developed to reduce ship strikes.”
The development comes as Nordic research institutions are seeking to create a fibre-optic cable system called PolarConnect that would link Europe, Asia and North America, creating a shorter route through the Arctic Ocean. Such an initiative “would open up much larger areas for us to track the movements of whales in the Arctic”, Mr Landrø said.
Julia Hager, PolarJournal
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