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A 2026 study by Florida International University and Georgia Southern University researchers found that vessels disappearing from automatic identification system (AIS) tracking off West Africa do not go dark at random. Most dark journeys were concentrated among a small group of repeat vessels, especially around Gulf of Guinea waters and the outer edges of exclusive economic zones (EEZs). The patterns can help authorities target inspections, but an AIS gap or a flag of convenience is not, by itself, proof of illegal fishing.
The strongest finding: a small number of vessels account for most disappearances
The study, published in Applied Geography in 2026, examined more than 3,600 dark journeys over three years in waters off 23 West African countries. A dark journey is a period when a vessel’s AIS transmissions disappear and later resume. The gaps in the dataset lasted from hours to days and, in some cases, weeks.
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Eleven vessels accounted for 73% of all dark journeys recorded in the study. That concentration is important for enforcement agencies with limited patrol boats, aircraft and inspectors: they may be able to improve coverage by identifying chronic repeat offenders instead of attempting to board every vessel that experiences one tracking interruption.
| Study finding | What it indicates | Important qualification |
|---|---|---|
| More than 3,600 dark journeys | AIS visibility was interrupted repeatedly across the region during the three-year study period. | A gap records loss of tracking data, not confirmed fishing or criminal activity. |
| 11 vessels produced 73% of dark journeys | Dark activity was highly concentrated among repeat vessels. | The result supports prioritization, not automatic guilt. |
| 1,058 journeys involved convenience-flagged vessels | Flag status was associated with different dark-journey patterns. | Flags of convenience are legal, and the flag alone is not evidence of a violation. |
| Nearly twice as likely to start or end beyond an EEZ | Convenience-flagged vessels more often had dark-journey endpoints outside national maritime zones. | This is a statistical association from the dataset, not proof of intent. |
| About five times as many dark journeys per vessel | Convenience-flagged vessels averaged substantially more dark journeys than other vessels. | The average does not describe every vessel flying such a flag. |
What a “dark vessel” means in this study
Commercial vessels commonly use AIS to broadcast their identity, position, course and speed. Receivers on satellites and onshore infrastructure can use those transmissions to reconstruct a ship’s route. When transmissions stop and later resume, analysts can see a period of missing visibility. The researchers call that interval a “dark journey.”
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AIS can fail or be interrupted for legitimate reasons, including equipment faults, power problems, signal coverage limitations, maintenance, congestion or operational decisions. Some vessels may also be permitted or required to limit transmissions in particular circumstances. Consequently, a dark track is an observation about data availability rather than a direct observation of illegal fishing, transshipment or another crime.
Where the disappearances cluster
Gulf of Guinea concentration
The dark journeys were concentrated around the Gulf of Guinea, a heavily used maritime region bordered by multiple West African states. The area includes busy fishing grounds, shipping routes and jurisdictions with different monitoring resources and enforcement procedures.
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Outer edges of exclusive economic zones
Many dark journeys began or ended near the outer edges of EEZs. An EEZ generally extends up to 200 nautical miles from a coastal state’s baseline and gives that state rights over natural resources, including fisheries. It does not make the entire area equivalent to territorial waters, and enforcement authority can change as a vessel crosses into another country’s zone or into international waters.
That jurisdictional transition creates a practical enforcement challenge. Patrols may be less frequent near a boundary, agencies may need to coordinate across borders, and a vessel can move between areas with different reporting requirements. The study’s crime-science framework treats those locations as places where opportunity may be high and perceived detection risk lower.
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Why convenience flags drew attention
A flag of convenience is a legal registration arrangement in which a vessel is registered in a country different from the country associated with its owners or operations. The researchers did not claim that convenience flags are illegal. Their analysis found that convenience-flagged vessels were nearly twice as likely as other vessels to begin or end a dark journey beyond an EEZ and averaged about five times as many dark journeys per vessel.
Those figures make flag status useful as one risk indicator when combined with behavior and location. They do not justify stopping every vessel with such a flag. Stephen Pires, an associate chair in FIU’s Department of Criminology & Criminal Justice, put the enforcement principle this way: “You don’t need to track down and board every fishing vessel flying a flag of convenience or going dark.”
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How the researchers identified the pattern
Global Fishing Watch supplied publicly available vessel-tracking data. Stephen Pires and Emilie Christiansen of FIU, working with Dylan Spencer of Georgia Southern University, examined where dark journeys started and ended, how often individual hulls repeated the behavior and whether patterns differed by flag type.
They applied ideas from crime science, which studies how place, opportunity and guardianship influence where offenses may occur. In this application, repeated AIS loss near a boundary is treated as a pattern that can help allocate investigative resources, not as a finding that establishes a crime.
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What an AIS gap can—and cannot—show
- It can show: when a vessel stopped appearing in the available AIS record, where the last transmission occurred, where the next transmission appeared and whether the same vessel repeats the pattern.
- It can suggest: a higher-priority inspection when the gap repeatedly occurs near an EEZ boundary, coincides with other risk signals or is followed by an implausible route.
- It cannot establish on its own: that fishing occurred during the gap, that fish were caught illegally, that a ship-to-ship transfer happened or that the operator intended to evade authorities.
Emilie Christiansen said that a vessel that turns off AIS near an EEZ boundary, disappears for hours or days and resumes just outside the same boundary is “very suspicious.” She also qualified that interpretation as a potential indicator of illegal activity rather than conclusive proof.
How authorities could use the findings
The researchers’ proposals focus on concentrating scarce enforcement capacity and adding independent evidence before taking action.
- Rank repeat vessels first. Build a vessel-level history of AIS gaps and prioritize the chronic repeaters. In this study, 11 vessels represented most of the dark journeys.
- Set boundary-focused alerts. Use geofencing to flag AIS loss or reappearance near high-risk EEZ boundaries, protected areas and other designated zones.
- Combine signals. Compare AIS gaps with fishing authorizations, vessel identity records, port calls, catch documentation, ownership information and possible ship-to-ship encounters.
- Board and inspect proportionately. When several indicators align, inspectors can request logbooks and registration documents, verify the catch and investigate related concerns such as labor abuse or illicit cargo.
- Coordinate across jurisdictions. Share alerts and evidence with neighboring coastal states so a vessel cannot exploit an information gap at a maritime boundary.
Other measures mentioned by the researchers include vessel confiscation and insurance-related penalties. Those are proposed enforcement options; the report does not establish that each measure has been tested or will work equally well in every jurisdiction.
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Why the pattern matters beyond tracking
Illegal fishing is a major threat to ocean health, food security and coastal livelihoods. Better targeting could make inspections more efficient while reducing unnecessary boardings of vessels whose AIS interruptions have benign explanations. The study does not provide a causal estimate of how much illegal fishing would be prevented or a dollar value for the potential benefits.
The practical takeaway is narrower and more useful: authorities can treat repeated, boundary-adjacent dark journeys as a reason to ask better questions and gather more evidence. They should not treat a missing AIS signal, a convenience flag or a single unusual route as a verdict.
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