Strife on the Ocean Waves

AIS Spoofing
AIS spoofing is a growing problem on the high seas. A new report by Global Fishing Watch discusses the extent of this problem and includes important recommendations for policy makers.

A new report highlights shortcomings in global maritime surveillance capabilities provided via the Automatic Identification System.

The International Maritime Organisation (IMO) mandates Automatic Identification System (AIS) transponders for all vessels displacing over 500 Gross Tonnage (GT). Vessels displacing over 300GT on international voyage are also obliged to use AIS alongside all passenger vessels. AIS transponders transmit details of a vessel’s identity, position, voyage and cargo. This information is sent across frequencies of 161.975 megahertz/MHz to 162.025MHz. AIS data can be overlaid onto a radar’s recognised maritime picture to populate this with vessel identification information. Usefully, AIS data can be shared across Ultra High Frequency (300MHz to three gigahertz) satellite links.

A recent study by Global Fishing Watch (GFW), a non-government organisation monitoring illegal activity on the high seas, highlighted how important AIS data has become in tracking suspect maritime activity. One revelation of GFW’s report concerns the lack of AIS data on certain vessel activities, notably fishing. IMO mandates “currently excludes fishing vessels unless the flag state decides to include fishing vessels in the (domestic AIS) requirement,” says David Kroodsma, GFW’s director of research and innovation. Unless the country where the vessel is registered requires AIS to be fitted, there is a chance it may not be.

The good news, according to GFW, is that the European Union and the United States now require some smaller-sized fishing vessels to transmit AIS when out of port. “Global Fishing Watch would like to see the rules requiring AIS on fishing vessels to be adopted more universally and to be harmonised so we can avoid a patchwork of different regulations governing the use of AIS on fishing vessels.”

“We see a lot of vessels between ten and 20 metres (33 and 66 feet/ft) in length, most of which are not required to broadcast their positions on AIS,” said Mr. Kroodsma. That said, some states may require these ships to transmit their position to government-owned vessel monitoring services. Another problem when tracking vessels with AIS is that the quality of the transmission in some regions may affect signal reception. For example, although AIS messages may be transmitted, they may not always be received by satellites because of poor coverage.


Some vessels deliberately switch off their AIS transponders. Deactivation may have an innocent explanation. A ship traversing pirate-infested waters may not want to advertise her presence to would-be hijackers. Given that AIS data is freely available online, this is an understandable concern. Other vessels deactivating their AIS transmissions maybe doing so for nefarious reasons: “Previous research, published in Science Advances, has shown that fishing vessels more often turn off their AIS when close to a country’s Exclusive Economic Zone (EEZ),” notes Mr. Kroodsma. Deactivating AIS transponders when a vessel is near an EEZ may indicate that she plans to covertly enter the EEZ for illegal fishing.

Another of GFW’s findings relates to voyages by vessels not transmitting AIS but carrying energy products: “Large transport and energy vessels are mostly broadcasting,” says Mr. Kroodsma. Nonetheless, some smaller vessels are not. Again, this could have an innocent explanation given that satellite reception for AIS signals can be poor in some areas. However, some of these vessels maybe engaged in illegal activity such as illicit oil trafficking. For example, both the Islamic Republic of Iran and Russia are under international sanctions regarding their oil exports.

While a lack of AIS transmission can be a cause of concern, so can the transmission of deliberately false AIS data. The GFW research showed that “a very small faction of vessels broadcast false AIS data.” False AIS data indicates that a vessel may be doing something she should not. GFW’s study employed satellite data to determine if AIS information was false as AIS transmissions are designed to be received by satellites. GFW used radar imagery provided by the European Space Agency’s (ESA’s) Sentinel-1 spacecraft. Sentinel-1 is equipped with a Synthetic Aperture Radar (SAR). The radar can detect ships and AIS transmissions from vessels can be overlaid onto this. If a ship is in the middle of the South China Sea, but her AIS data is saying she is in the North Sea this discrepancy could indicate that AIS data is being deliberately falsified.


One of GFW’s recommendations is to extend the mandate for AIS to equip smaller fishing vessels below the IMO’s stipulations. “Requiring AIS on fishing vessels improves safety and transparency within the fishing sector,” says Mr. Kroodsma. GFW’s report has been instructive in exposing gaps in global AIS maritime surveillance coverage which risks leaving suspect activities on the high seas unchecked. It is now up to governments and supranational organisations like the IMO to decide what actions they will take to this end.

by Dr. Thomas Withington