The detention of the Eagle S by Finland in Jan 2025, a “shadow fleet” tanker suspected of damaging the EstLink 2 power cable and several telecommunications cables in the Gulf of Finland, showed that shadow-fleet vessels can pose risks to safety and subsea infrastructure beyond sanctions evasion. Yet identifying a suspicious vessel is not the same as having the jurisdiction and evidence needed to act against it, as shown by the June 2026 interdiction of MV Smyrtos. (From: S. Rajaratnam School of International Studies, NTU Singapore)
The challenge is maritime governance. The shadow fleet exploits weak registration practices, opaque ownership, inadequate insurance and fragmented enforcement. Governments may have extensive maritime-domain awareness, but unless information supports lawful boarding, detention and prosecution, visibility has little effectThere is no universally accepted definition of the “shadow fleet“, sometimes referred to as the “dark fleet” or “ghost fleet”. These are generally ageing or poorly maintained vessels with opaque ownership, questionable insurance, and flagged under “flags of convenience”. They may carry sanctioned cargo, conduct deceptive ship-to-ship (STS) transfers, or manipulate Automatic Identification System (AIS) data to conceal their movements. Such practices are not new. They were used by apartheid-era South Africa to circumvent oil sanctions, later adopted by Iran and subsequently expanded by Russia on a massive scale.
The concern is no longer simply that these vessels transport sanctioned oil. These ageing tankers operate without recognised Protection and Indemnity insurance and deliberately manipulate their AIS to conceal their movements. This increases the risk of accidents and oil spills, leaving no credible mechanism to compensate coastal states or affected parties when an accident occurs. Commercial vessels may also become entangled in grey-zone activities, as recent cable-cutting incidents damaging undersea cables and energy infrastructure – including the Eagle S case – illustrate. Yet a vessel cannot be boarded or prosecuted merely because it appears on such a “Shadow Fleet” list.
The Jurisdictional Challenge
Most sanctions against Russian oil are unilateral or coalition-based rather than imposed by the United Nations Security Council (UNSC). Their enforcement therefore depends on the jurisdiction and domestic laws of participating states; they do not give every state a general right to enforce these sanctions at sea. The practical question is therefore: what legal mechanism/connection allows a state to move from suspicion to enforcement?
In the Smyrtos case, the British authorities stated that the vessel had lost its claimed Cameroonian registration and was sailing without a legitimate flag. That opened a right of visit under Article 110 of the United Nations Convention on the Law of the Sea (UNCLOS). UK authorities then relied on domestic sanctions law to charge the captain with allegedly transporting prohibited Russian oil. The case remains before the courts, but it shows the necessary sequence: verify identity, establish jurisdiction, board lawfully, gather evidence and prosecute under national law.
This distinction matters because most shadow-fleet vessels are not stateless. They are registered, at least formally, under a flag. Under UNCLOS Articles 91 and 94, every vessel must be flagged to a country with which it maintains a genuine link, and the flag state must exercise effective jurisdiction and control over ships flying its flag. Article 92 further provides that ships may not change nationality mid-voyage except where ownership or registry has genuinely changed. Where a flagged vessel breaches safety, registration or other applicable requirements, the flag state should investigate and, where its domestic law permits, prosecute or impose penalties. Detention by another state without a prosecutable offence may be challenged and is less effective than flag-state enforcement.
Falsified Identity as an Enforcement Opportunity
Fraudulent registration and falsified identity provide a second route to action. A vessel may display a terminated flag, use forged registry documents, transmit another ship’s identity, or materially falsify AIS particulars. In April 2026, IMO reported that 529 ships had falsely flown a state’s flag in the preceding year, affecting nearly 40 member states. Its new ship registration guidelines emphasise due diligence, ownership verification and checks on ship identity.
Authorities should therefore treat identity verification as an operational task, not an administrative afterthought. Claimed nationality should be checked promptly against the relevant registry and against IMO’s Global Integrated Shipping Information System (GISIS). Confirmation that a ship is not lawfully registered may support treating it as a vessel without nationality; falsified documents or AIS data may also trigger port-state measures, denial of services, or domestic offences where legislation provides. The key is to convert anomalies into admissible evidence and a clear enforcement basis.
Dealing with the Shadow Fleet
First, flag states must move beyond issuing registration certificates and require the ship owners to adhere to governance standards. They should verify ownership, monitor registry changes, investigate reported violations, and act decisively against masters, owners or managers who breach their laws. IMO audits, technical assistance, and scrutiny by port states, insurers and classification societies can reinforce this responsibility.
Second, states should establish rapid procedures to resolve vessel identity and jurisdiction, including cross-checking ship details against reliable national and international information sources such as GISIS. A falsely flagged or stateless vessel may confer a right of visit on warships under UNCLOS, creating an enforcement opportunity; subsequent detention or prosecution requires a legal basis. States, however, are not obliged to act. Broader international agreement on sanctions would strengthen the basis for action where domestic enforcement levers are in place.
Third, maritime authorities must work more closely with the private sector. Improved information sharing between enforcement agencies and the shipping industry would enhance the identification of suspicious activity. Trusted relationships and information exchange can help build a fuller picture before an incident occurs and lead to more effective coordinated action across jurisdictions, including evidence-sharing.
Conclusion
The shadow fleet is not a problem of insufficient detection, nor can unilateral sanctions alone provide universal authority at sea. Shadow fleet operators have exploited the gap between what states can detect and what they can lawfully enforce. Addressing this threat requires stronger maritime governance: responsible flag state control, a clear legal framework and closer cooperation amongst stakeholders.
*Nicholas Lim is a Senior Fellow at the Institute of Defence and Strategic Studies (IDSS) at the S. Rajaratnam School of International Studies (RSIS), Nanyang Technological University (NTU). He retired from the Republic of Singapore Navy after more than 30 years of service. Eric Ang is a PhD student at RSIS, a Chartered Marine Technologist (CMarTech) with the Institute of Marine Engineering, Science and Technology (IMarEST), and a Research Fellow with the Yokosuka Council on Asia Pacific Studies (YCAPS)
