In the Mediterranean Sea, a prototype whale detection system can use a sperm whale’s clicks 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 whales. long . In tests using both artificial pings and sounds from real sperm whales, the researchers showed that the system can provide enough notice that a nearby vessel will change direction or slow down when a whale is on its way. path.
The system was developed by a team of biology and computer science researchers based in Greece. Led by Emmanuel Skarsoulis, research director of the Greek Foundation for Research and Technology – Hellas, the team dubbed their new tool the System to Avoid Collisions with Endangered Whales (SAvEWhales). The name reflects the researchers’ hope that, if implemented, their system could reduce the main killer of endangered sperm whales in the Mediterranean – ship strikes.
The design of SAvEWhales is quite simple. Near the Hellenic Trench, a five kilometer deep underwater canyon in southern Crete, Greece, Skarsoulis’ team moored three buoys in a triangle one to two kilometers apart. Suspended from each buoy in a 100 meter line was a hydrophone to detect underwater sounds.
These three hydrophones pick up every click of a nearby sperm whale, which they do to locate prey. Skarsoulis and his colleagues developed a computer program to compare the time it took for sound to arrive at each hydrophone, giving them a way to triangulate the position of the whale. But SAvEWhales’ secret weapon means it can do more than just locate a whale on a grid.
While using hydrophones towed by boats to listen to sperm whales in previous work, team member Alexandros Frantzis noticed that every sperm whale click he heard seemed to repeat itself, like a ghostly echo of himself. It wasn’t until Frantzis, the research director of the Pelagos Cetacean Research Institute in Greece, discussed the problem with Skarsoulis that they came up with an explanation: the second click was the call of the sperm whale bouncing off the surface of the ocean.
By exploiting these reflections, the scientists built their algorithm to calculate the depth of the whale’s rattle. The deeper a whale is when it clicks, the longer the gap will be between when the original click and the reflection arrives at the hydrophone. Using the information from the two clicks, the SAvEWhales system can detect a whale up to 900 meters deep within 10 kilometers of the buoys. And by running the same calculations each time a whale clicks nearby, 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 avoid 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 efforts to establish the Boston Harbor array of buoys that automatically detect the calls of endangered North Atlantic right whales, applauds the novelty to obtain near real-time information that ships could use on the spot. He also points out that sperm whale sightings are rare in the Mediterranean, which adds value to the system.
Despite its promise, it may be some time before SAvEWhales, or something like it, can be used permanently. So far, the system has only undergone a two-year pilot test, and Skarsoulis and his colleagues have already identified some obstacles to expanding it into a full-time monitoring system. These include analytical challenges, such as the difficulty of differentiating between individual whales when a group travels together. There are also logistical barriers involved in maintaining a system at sea, which faces constant wear and tear from salt, sun and storms. In fact, nearby fishermen saw the first two deployed SAvEWhales buoys disappear under water, swept away by strong currents during a hurricane. Skarsoulis hopes that one day the system could be a permanent wired observatory.
However, there are also limits to the scope of application of such a system. The surface reflection analysis that makes SAvEWhales so powerful cannot be used for whales that communicate through song rather than clicks, such as fin whales, which are also endangered in the Mediterranean.
There is one final hurdle that is unique to the current era. After the project’s initial prototype period, Skarsoulis on February 23 submitted a proposal to the Greek Ministry of Environment and Energy to operate a unique buoy off Crete so that his team could monitor the number of sperm whales crossing the area. The next day, Russia invaded Ukraine, triggering an international energy crisis.
It is “important to note that it was the Ministry of the Environment and energySkarsoulis points out, wryly suggesting that enthusiasm for whale-spotting could hamper oil exploration. He has not heard of her proposal since.
Yet such monitoring is urgently needed in the Mediterranean Sea, says Nino Pierantonio, a whale researcher at the Tethys Research Institute in Milan, Italy. Ship strikes are responsible for more than half of all sperm whale deaths in the region. Moreover, as Mediterranean sperm whales are genetically distinct from those of the North Atlantic, this population is particularly vulnerable.
Pierantonio notes that the risk is particularly high around the Hellenic Trench, a place rich in marine life and a hotspot for sperm whales. The area is favored by groups of mother sperm whales with their young, which spend much more time on the surface.
Pierantonio says other efforts to reduce ship strikes, such as forcing boats to slow down in whale hotspots and changing shipping lanes, will also be key tools to protect the Mediterranean’s endangered sperm whales. . “When re-routing and speed reduction is not an option, we need another way to alert ships to the presence of whales,” he adds.
This article is from Hakai Magazine, an online publication on science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.
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