The governments of Tonga and the Cook Islands have condemned the illegal use of their flags after reports that at least 29 vessels were flying their identities to evade international sanctions.
Maritime analysts say most of the vessels are crude oil tankers operating between Iran and China. According to Mark Douglas, maritime domain analyst at Starboard Maritime Intelligence in New Zealand, these tankers load Iranian crude in the Persian Gulf, carry out ship-to-ship transfers and other maneuvers to obscure the oil’s origin, then discharge cargo in China.
Under maritime practice, ships broadcast unique identifiers via the Automatic Identification System (AIS), which helps authorities track vessels and reduces collision risk. Douglas said 21 of the 29 tankers using Tongan or Cook Islands flags are subject to sanctions and two are transmitting invalid AIS numbers, complicating checks on their sanction status. Crews can also switch off AIS transmissions entirely, effectively making ships invisible; North Korea has used that tactic to dodge UN sanctions.
In late January, Amnesty International reported that Myanmar’s military junta had been acquiring aviation fuel via “ghost ships” that either flew other nations’ flags or had turned off tracking systems.
Western governments have responded more aggressively. The US has stepped up maritime controls and seized several ships; on January 20, US forces boarded the Liberian-flagged Motor Vessel Sagitta in the Caribbean. French authorities recently detained the Russian tanker Grinch, which had left Murmansk in early January flying the Comoros flag.
Tonga and the Cook Islands notified the International Maritime Organization and publicly declared that the vessels were not legitimately flagged. The Cook Islands government moved to create a Vessel Verification Portal to improve transparency and access to vessel information after reports—later found inaccurate—that the tanker Bertha had been pictured flying its flag off Venezuela. Tongan authorities issued a statement saying any foreign vessel transmitting under the Tongan flag was doing so fraudulently, noting Tonga closed its international ship registry in 2002 and no longer registers foreign vessels on international voyages.
“Shadow fleet” operators also tamper with a ship’s Maritime Mobile Service Identity (MMSI) by altering the first three digits that indicate national registration, effectively changing a vessel’s reported nationality. Douglas said such frauds should be uncovered during port inspections, but these tankers often avoid entering ports or call at ports where documentation is unlikely to be rigorously checked.
Paul Chamberlain, a visiting research fellow at the National Institute for Defense Studies in Tokyo, said action against shadow fleets is overdue. He noted the practice surged in 2022 as networks were developed to evade sanctions and warned of the environmental and safety risks, saying it is only a matter of time before a major incident occurs—whether from explosion or poor seamanship. Chamberlain urged Tonga and the Cook Islands to raise diplomatic objections to deter misuse of their flags and encouraged capable states to enforce maritime law against shadow fleet vessels. He added that regional powers, potentially including China, should remind nations of their responsibilities under the law of the sea.
Edited by: Darko Janjevic