High-tech buoys with underwater microphones could save sperm whales from ship collisions
A computational technique offers the power to track whales in real time—a potential boon in the quest to save whales from ship strikes.
This article was originally featured on Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.
In the Mediterranean Sea, a prototype whale detection system can use the clicks of a sperm whale to pinpoint its location in three-dimensional space with an accuracy of 30 to 40 meters—only a body length or two for these 16-meter-long whales. In tests using both artificial pings and the sounds emanating from real sperm whales, researchers showed that the system can provide enough notice for a nearby ship to change direction or slow down when a whale is in its path.
The system was developed by a team of biological and computational researchers based in Greece. Led by Emmanuel Skarsoulis, research director of Greece’s Foundation for Research and Technology–Hellas, the team has dubbed their new tool the System for the Avoidance of Ship-Strikes with Endangered Whales (SAvEWhales). The name is a reflection of the researchers’ hope that, if implemented, their system could cut down on the leading cause of mortality for endangered sperm whales in the Mediterranean—ship strikes.
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SAvEWhales’ design is fairly simple. Near the Hellenic Trench, a five-kilometer-deep underwater canyon south of Crete, Greece, Skarsoulis’s team moored three buoys in a triangle one to two kilometers apart. Dangling from each buoy on a 100-meter line was a hydrophone to detect underwater sound.
These three hydrophones picked up each time a nearby sperm whale clicked, which they do to locate prey. Skarsoulis and his colleagues developed a computer program to compare how long it took the sound to arrive at each hydrophone, giving them a way to triangulate the whale’s position. But SAvEWhales’ secret weapon means it can do far more than just locate a whale on a grid.
While using boat-towed hydrophones to listen to sperm whales in previous work, one member of the team, Alexandros Frantzis, noticed that each sperm whale click he heard seemed to repeat, like a ghostly echo of itself. It wasn’t until Frantzis, the research director of the Pelagos Cetacean Research Institute in Greece, discussed the problem with Skarsoulis that they found an explanation: the second click was the sperm whale’s call bouncing off the surface of the ocean.
By harnessing these reflections, the scientists built their algorithm to calculate the depth of the clicking whale. The deeper a whale is when it clicks, the longer the gap will be between when the original click and the reflection arrive at the hydrophone. Using the information from both clicks, the SAvEWhales system can detect a whale at up to 900 meters depth within 10 kilometers of the buoys. And by running the same calculations each time a whale clicks nearby, the scientists can actively track whales as they swim. In the future, they could even use this system to warn ships that a whale is about to surface nearby and potentially avert a collision.
Experts see SAvEWhales as a useful addition to a growing field of passive whale-monitoring systems. Christopher Clark, a bioacoustician at Cornell University in New York, who led the effort to establish the Boston Harbor buoy network that automatically detects the calls of endangered North Atlantic right whales, applauds the novelty of getting near-real-time information that ships could use on the spot. He also emphasizes that observations of sperm whales are few and far between in the Mediterranean, adding value to the system.
Despite its promise, it may be some time before SAvEWhales, or something like it, can be in permanent use. So far, the system has only undergone a two-year pilot test, and Skarsoulis and his colleagues have already identified a few obstacles to expanding it to a full-time monitoring system. These include analytical challenges, such as the difficulty of differentiating individual whales when a group is traveling together. There are also logistical barriers involved in maintaining an at-sea system, which faces constant wear and tear from salt, sun, and storms. In fact, fishermen who happened to be nearby watched the first two SAvEWhales buoys that were deployed disappear underwater, dragged down by strong currents during a hurricane. Skarsoulis hopes that one day the system could be a permanent cabled observatory.
There are also limits, however, on how broadly applicable such a system could be. The surface reflection analysis that makes SAvEWhales so powerful can’t be used for whales that communicate through song rather than clicks, such as fin whales, which are also endangered in the Mediterranean.
There’s one last obstacle that is unique to current times. After the project’s initial prototype period, Skarsoulis, on February 23, submitted a proposal to the Greek Ministry for Environment and Energy to operate a single buoy off Crete so that his team could monitor how many sperm whales passed through the area. The next day, Russia invaded Ukraine, kicking off an international energy crisis.
It’s “important to note it was the Ministry for Environment and Energy,” Skarsoulis emphasizes, wryly suggesting that enthusiasm for detecting whales might get in the way of oil exploration. He has not heard back about his proposal since.
Yet such monitoring is urgently needed in the Mediterranean Sea, says Nino Pierantonio, a whale researcher with the Tethys Research Institute in Milan, Italy. Ship strikes are responsible for more than half of all sperm whale deaths in the area. Additionally, because Mediterranean sperm whales are genetically distinct from those in the North Atlantic, this population is especially vulnerable.
Pierantonio notes that the risk is particularly high around the Hellenic Trench, a place rich in marine life and a sperm whale hotspot. The area is favored by groups of sperm whale mothers with calves, which spend much more time at the surface.
Pierantonio says other efforts to reduce ship strikes, such as requiring boats to slow down in whale hotspots and shifting shipping lanes, will also be essential tools in protecting the Mediterranean’s endangered sperm whales. “When rerouting and reducing speed is not an option, we need another way to alert vessels of the presence of whales,” he adds.