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Elast year, Bjorn Bergman noticed something strange about a fishing boat off the coast of Mauritania.
Like other large ships in those waters, this trawler broadcasts Automatic Identification System (AIS) radio signals. AIS information contains a ship’s name, location, speed, and course—critical data to help nearby ships safely avoid each other. All large vessels are required by international law to use AIS for navigation, and the data is also useful for fisheries monitoring organizations.
But this trawler’s AIS feed is unique. Instead of showing a consistent track as it slowly laid its nets, the ship seemed to leap impossible distances in the blink of an eye. Here one second, miles away the next. “From looking at the data, they’re mixing up false and true tracks in a pretty confusing way,” said Bergman, an ocean analyst at SkyTruth, a non-profit that uses satellite technology to pursue environmental justice.
Bergman is still investigating the mystery of the teleporting trawler, but he suspects it may be the first hard evidence of something he’s long feared: the advent of sophisticated technology that allows unscrupulous vessels to carry out fishing which destroys the environment under the cover of digital alibis in that area. they are hundreds of miles away.
Whether or not they escape may come down to the systems Bergman and others are now building to stay one step ahead of rule-breaking ghost ships. “There are always challenges with some actors trying to hide what they’re doing,” said Jennifer Raynor, a natural resource economist at the University of Wisconsin-Madison. “But the more we know, the better we can do.”
The ship appears to jump impossible distances in the blink of an eye.
It’s no secret that the ocean is in crisis. Marine life is caught between climate change, acidification, and overfishing. More than one-third of the fish population is being caught at unsustainable levels—a number that has doubled since the 1980s—driving fishing vessels to travel farther, and increasingly bend or break rules to land their catch . As for the trawler in Mauritania, it probably hunts sardinella, a beautiful silvery species whose population has been overfished to the point of collapse; they are often processed into feed for aquaculture and livestock in Europe, the United States, and China.
Historically, there was little way to track those ships. Captain’s log books are unreliable; and putting government observers on every ship is unaffordable. (It can also be dangerous for observers.) That changed in the early 2000s with AIS, which broadcasts unencrypted radio signals that are easily recorded within a range of about 20 miles. Most moving ships send AIS chirps every few seconds.
Suddenly ships could be tracked—within a few miles of major ports and coasts, that is. The movement of ships in the open ocean remained a mystery. Conservationists trying to monitor unauthorized and illegal fishing in marine reserves and protected areas, often far from human infrastructure, still have a few ways to go. Then came the satellite revolution. Suddenly, cheap miniature satellites raised in large numbers into low Earth orbit opened up new ways of looking at the planet. Both companies that operate terrestrial AIS recorders realize that they can now track ships almost anywhere on Earth. And fisheries activists are right behind.
The most ambitious of these is Global Fishing Watch, founded in 2015 as a partnership between SkyTruth, the Oceana conservation nonprofit Oceana, and Google. Using satellite data, it began piecing together a truly global map of AIS tracks. “When the AIS data set first came out, there was no reason for captains to think that someone was watching them and they were just doing whatever they were doing,” Raynor said. “It’s transformative.”
Now the ships knew they had eyes on them—but they adapted. Using Global Fishing Watch data, Oceana described multiple cases of fishing vessels turning off their AIS, including two Spanish vessels that went dark in West Africa. Although ships are allowed to temporarily silence their AIS systems if they fear an attack, they have done so for several days over several months, with no record of where they might have gone. Oceana has also identified other vessels that are similarly turning off AIS near marine reserves in the Galapagos Islands and the Indian Ocean. Although not conclusive evidence of wrongdoing, it was highly suggestive—and led to fines for Spanish ships.
But what if instead of disappearing altogether, fishing vessels could fake their location so that it appeared they did not enter protected areas? In late 2022, Bergman released a Russian oil tanker that appeared to be sending false coordinates via AIS, presumably to conduct a sanctions-busting mid-ocean transfer of crude oil near Malta. While the AIS tracks showed the two tankers about 10 miles apart, in reality they were almost right next to each other.
The fictitious data marks a step change in how researchers can rely on AIS. “Having no data can in some cases be easier than having bad data,” Raynor said. If the ships just go dark, it’s a clear signal to activists that something is up. If they spoof their location instead, their activities can remain hidden in the ocean of data.
What if instead of disappearing completely, illegal fishing vessels could fake their location?
But Bergman was already one step ahead. In his work on oil tankers, Bergman noticed that fake AIS tracks often lacked the normal variations in course and speed of real voyages. They are also sometimes detected by satellites that cannot receive the signals if they are genuine. And his latest weapon against spoofers is the most powerful yet: the European Space Agency’s Sentinel-1 satellites. They circle the globe twice each week, using sophisticated radar systems to map vegetation, track sea ice, and, by chance, detect ships longer than about 65 feet By comparing Sentinel-1 images with AIS data, Bergman could work out the actual location of the oil tankers.
“This kind of subtle manipulation is interesting because it’s hard to detect and I think it goes almost unnoticed,” Bergman said. He identified similar spoofed AIS tanker tracks in the Mediterranean, Persian Gulf, and near Venezuela. He next automated the process, building a system that correlates vessel positions from the Sentinel-1 satellite with AIS data. This system flagged the trawler off Mauritania—and many others.
“There is clearly software proliferating to enable this deception,” he said. “And we see certain ships coming over and over again.”
In January, Global Fishing Watch and SkyTruth published a paper on Nature, with Raynor as a co-author, summarizing their work. The organizations estimate that around 75 percent of the world’s industrial fishing vessels are currently untracked in AIS databases, with the problem most pronounced near Africa and South Asia. About 25 percent of ships used to transport goods and fuel are also not monitored by the public. This is mostly due to AIS systems being turned off rather than being spoofed, but it shows the scale of the problem.
I asked Bergman if the AIS has now been hacked or if it can be salvaged. Like a Russian tanker in the Mediterranean, “it’s going in the same direction at the same time,” he said. There are technical solutions on the horizon that can authenticate AIS using cryptography “but you’re also talking about 200,000 ships around the world. That’s going to take a really long time to replace.”
In the meantime, Bergman and his satellites will continue to monitor the world’s oceans from the skies above. His next step was to incorporate high-resolution optical imagery from the European Sentinel-2 satellite; one of his first targets was the teleporting trawler in Mauritania.
This ability to bring more and smarter systems to bear keeps Raynor enthusiastic about the future of illegal fishing monitoring. “You can think of these technologies like pieces of Swiss cheese on top of each other,” he said. “Each one has holes—but the more pieces you put on top of each other, the more holes are covered.” 
Lead image: Illus_man / Shutterstock
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