March 08, 2019

Skylight perspective: Transshipments as an indicator for suspect maritime activity

Dr. Mark Powell, Senior Researcher

Transshipments on our oceans

Our oceans are a vital component of a healthy planetary ecosystem, the source of food for billions of people and home to hundreds of thousands of marine species. At the same time, the oceans are under significant pressure from illicit activities, including illegal fishing. Weak to non-existent information and monitoring provide opportunities for illegal acts to take place without detection. Even where coastal nations attempt to patrol their waters and stop illicit activity, under international law vessels can hide behind “flags of convenience” that grant jurisdiction over vessels to governments willing to look the other way. (1) Amidst all this activity, transshipments, when ocean-going vessels rendezvous at sea to transfer cargo, can be a key facilitator of illicit maritime activity.

Transshipping can be used for legitimate purposes such as improving the efficiency of ocean transport. Fishing vessels, for example, use transshipments to support fishing operations by allowing fishing vessels to offload catch on fishing grounds and avoiding lengthy transits to distant ports.

But transshipments also have a darker side. The practice can be used to avoid inspection or escape sanctions or tariffs by making it difficult to identify the source of cargo on a vessel. Even better for illegal activity, transshipments are difficult to monitor, regulate, and enforce because they can take place at sea where there is little or no scrutiny. To make the challenge more difficult, vessels engaged in illicit transshipments can escape oversight by going “dark”— turning off automatic identification system (AIS) transmitters that reveal location. This leaves agencies at a significant disadvantage in tracking or prosecuting suspected illegal transshipments.

The impact of illegal transshipments

Why do transshipments matter? There are economic, ecological, and geostrategic reasons for monitoring transshipments closely to reduce illegal activity at sea, including:

Ocean health is vital to human health: Roughly one billion people rely on fish as their primary source of animal protein, and an estimated 880 million people rely on it for their livelihoods. Additionally, the estimated $23 billion annual value of illegal fish catch costs nations significantly in lost commercial and tax revenue. (2)

Illegal fishing is a massive drain on ocean resources: Illegal fishing, estimated to represent 20 percent of all catch worldwide, places massive pressure on ocean ecosystems. (3)

Geopolitical tension increases with low visibility into maritime activity: Conflict over fishing grounds exist in many places, such as in Southeast Asia where tensions are escalating in a region that many see as on the verge of serious armed conflict.

With this in mind, it is important to understand that undetected transshipments can mask illegal fishing by allowing fishing vessels to escape oversight. (4) At sea transshipment allows vessels that fish illegally to avoid port inspections and can be used to sell illegal catch into legitimate supply chains. (5) Vessels that receive transshipments of fish at sea typically aggregate catch from a number of fishing vessels and then transit to ports where the fish cargo is sold. By aggregating catch, fish carrier vessels make it difficult to detect illegally-caught fish during port inspection. Due to transshipment’s central role as a facilitator of illegal fishing and other crimes, some jurisdictions have banned or tightly regulated transshipments of fish to prevent fish laundering, and some researchers have even concluded that a ban on transshipment is likely necessary to end illegal fishing. (6) Developing the ability to detect transshipments of fish as they are occurring would allow managers to target suspicious vessels for inspection and potential enforcement with greater accuracy and increase the likelihood of effective interdiction.

Transshipments and other illegal activity

Fishing vessels have also been linked to many kinds of illicit activity beyond illegal fishing, and there are a number of reasons why fishing vessels can be a platform of choice for non-fishing crimes. (7) One reason is the status of fishing fleets as the least-regulated vessels at sea. For example, fishing vessels are exempt from the requirement that vessels larger than 300 tons use AIS to transmit identity and location. Fishing vessels are also a choice for criminal activity, because fishing vessels can escape scrutiny for loitering behavior typical of fishing – behavior that would be suspicious for other types of vessels that typically transit at cruising speed while at sea. (8) Finally, fishermen may resort to illicit activities when their primary source of income – fishing – is threatened by overfishing. Such an illegal fishing crisis has been cited as a cause of the outbreak of piracy in Somalia and helped explain why a fishing vessel seized in March 2016 off the coast of Oman was found to have approximately $2 million worth of arms hidden under fishing nets. (9)

Emerging monitoring and analysis tools can be used to analyze transshipments of drugs and weapons in non-fishing vessels, as well as instances of forced labor – when transshipments allow vessels to avoid port calls where imprisoned crew may escape or attract attention.

The difficulty of detecting illicit transshipments and dark vessels

What makes illegal transshipment detection so difficult? To begin, even where governments have laws that limit transshipments and maintain active monitoring and surveillance programs, two ships meeting at sea for a transshipment can escape detection simply because the presence of two vessels near each other is not unusual enough, by itself, to attract attention. Because of this, vessels routinely transship with impunity in violation of regulations on where transshipments can occur and requirements for advance notice, the presence of observers, or other forms of oversight.

Identifying transshipments is even more difficult for those vessels that are “dark”—undetectable with AIS because of equipment issues or because AIS is turned off. Figure 1 below shows that 60 percent of AIS-transmitting fish carrier vessels are dark occasionally, transmitting an AIS signal less than once per day on average. Further, 25 percent are frequently dark, transmitting an AIS signal less than once every two days. (frequency < 0.5 transmissions per day). This means that many transshipment vessels have periods of time of 1 day or longer when they are not transmitting AIS. To help meet this identification challenge, technologies have begun to focus on identifying “one-sided” transshipments – instances where a dark vessel meets a vessel transmitting AIS and the event is detected by analysis of the transmitting vessel’s movements. Another approach is to detect when vessels go dark and use an AIS turn-off event as a possible indication of suspicious intent - and target those vessels for more in-depth monitoring and analysis. While vessels may turn off AIS for legitimate reasons, such as avoiding piracy, fishery managers are often suspicious of vessels that turn off AIS transmissions to avoid observation in typical fishing areas.

AIS Frequency

Figure 1: AIS transmission frequency (transmissions per day) by fish carrier vessels. Vessels that transmit AIS singals once per day or more are shown as “1”.

Transshipments by dark vessels can be detected with satellite Synthetic Aperture Radar (SAR) (see figure 2 below) or electro-optical imagery (EO) (see figure 3 below) if target locations are known. Indicators of potential transshipment hotspots include activity patterns of vessels transmitting AIS, locations where vessels routinely turn off AIS signals, and supply chain analysis that reveals gaps in transparency where illicit activities are suspected.

Detecting dark vessels that are not transmitting AIS, however, requires advanced data collection, integration, and analysis. Constructing and deploying a full intelligence suite to support this effort traditionally requires long-term investments of human and capital resources, and even then analysis may take too long to be useful. Fortunately new capabilities are emerging to reduce costs, speed up analysis, and support advanced maritime awareness that detects transshipments as they occur (see Solutions below).


Figure 2: Potential transshipment by two dark vessels detected with SAR.

Transship Fig 3

Figure 3: A transshipment that was detected automatically with AIS activity data (left), and the same transshipment captured in an EO image (right).

Value of real-time analysis and transshipment alerts

Better monitoring and control of transshipments can help governments detect illicit activity at sea. Tools and approaches that identify transshipments and alert relevant authorities can improve available information and allow governments to focus resources on the most important investigative opportunities. This is possible because transport steps represent a “chokepoint” - a step where a broad-based activity is restricted to a much smaller number of channels. Using illegal fishing as an example, there are many fewer fish carrier vessels worldwide (about 3,000 to 4,000) compared to the 400,000 industrial fishing vessels. (10) Monitoring suspicious transshipments of fish can provide insight by focusing analysis on a relatively small number of transshipment vessels as an entry point into identifying networks of suspicious vessels.

To be truly useful, however, transshipment identification must take place in real-time. Delays of even a few hours because of lack of data or the need for human analysis can render information useless for enforcement purposes. As described below, our solution meets this need, identifying transshipments as they are happening and alerting users in real-time, allowing customers to make informed asset allocation and investigation decisions.

Our Solution: Skylight

Skylight has developed a leading maritime information system that provides unique automated global alerts of ongoing transshipments in real-time. We’ve brought together AIS vessel tracking, satellite imagery for dark vessel detection, and algorithms produced by machine learning to identify transshipments and produce alerts in real-time to enhance understanding of maritime activities.

Industry leading database

To help detect and analyze transshipments of illegally-caught fish, we have compiled an industry-leading database that includes most of the world’s industrial fishing and fish carrier vessels - over 700,000 in total . This database includes information on vessel type, history, ownership, licensing, and other key characteristics. We add to this information on movements of vessels at sea using commercially available, real-time data from AIS that includes information on vessel identity and location. With approximately 200,000 fishing vessels (about half of the world’s industrial fishing vessels) broadcasting AIS signals at least once per day, this addition makes Skylight's information sources even stronger.

Machine Learning Driven Transshipment Analysis

We combine this AIS data with our proprietary fish carrier vessel database and apply machine learning to analyze rendezvous events and determine the likelihood of a transshipment. Taking one sample set as an example, our database includes 2,113 vessels identified as potential fish carrier vessels that have transmitted AIS between January and October 2018. In practice, we can identify where most of these vessels are operating using AIS; applying our proprietary algorithms, we can then determine what percentage of rendezvous were suspicious.

Satellite analytics and proprietary analysis for dark-ship detection

Skylight leverages best-in-class satellite technology including electro-optical (EO) and synthetic aperture radar (SAR) imaging to detect dark vessels that are not transmitting AIS and help address some of the challenges they present referenced above. We are working to couple this technology with one-sided rendezvous detection to help better identify suspicious activity for investigation.

We’re also building on the traditional transshipments indicators mentioned at the beginning of this paper - activity patterns of vessels transmitting AIS, locations where vessels routinely turn off AIS signals, and supply chain analysis that reveals gaps in AIS transmission where illicit activities are suspected - to better identify locations of suspected transshipments.

One specific analysis method we deploy is a network analysis map - using transshipments to identify vessels of interest for additional investigation. An example of this is illustrated below in a network analysis of transshipments between fishing vessels and fish carriers (Figure 4). The network shows transshipments as a line between two circles with the circles representing the two interacting vessels and the line representing the transshipment. The network on the right shows the circles colored according to vessel types and the highlighted cluster of fishing vessels connected to a fish carrier demonstrates the activity pattern of a fish carrier transshipping catch from a group of fishing vessels. The network on the left indicates which vessels are authorized to transship in this region. The refrigerated cargo ship highlighted is authorized to transship, but has transshipped with two fishing vessels that are not authorized to transship and appear to be implicated in unauthorized transshipments. Vessels that are linked to these three suspicious vessels are consequently classified as targets for further monitoring and analysis. We have constructed networks of this type using a wide range of information including vessel ownership, vessel history, and areas of operation.

Transshipment map

Figure 4: Transshipment networks for selected region. Circles represent vessels and lines represent transshipments between two vessels. Colors in left network image indicate whether vessels are authorized by the Western and Central Pacific Fisheries Commission (regional management body) to transship, while colors in right network image represent vessel type.

What’s Next

Continual enhancements to Skylight's databases, machine learning algorithms, and satellite analytics are planned throughout 2019 and beyond to enhance our transshipment and dark-ship detection capabilities. Our goal is to shine an increasingly bright light on transshipments so that illicit maritime activity can be detected by customer agencies and investigated by their governments.

All nations can derive value from Skylight’s transshipment detection capabilities and technology advances, particularly those in regions known as high traffic and/or suspicious ocean activity areas. With enhanced visibility into maritime activity, governments will be better able to monitor key behaviors such as fishing – leading to better protected oceans and stronger ecosystems for all to enjoy.

About Skylight

Skylight is part of Microsoft co-founder and technologist Paul G. Allen’s Seattle-based Vulcan Inc. At Skylight, we harness cutting edge satellite and machine learning technologies to enable maritime transparency for our customers.


  1. Vessels obtain a flag of convience that provides cover for illicit activity by registering a fishing vessel in a nation that provides little oversight of vessel operations. Under international law, the nation that provides a vessel’s flag has primary jurisdiction over the vessel. Vessels utilize flags of convenience to escape from laws or management requirements. Some nations provide registration — and a flag — based on a simple online transaction for a nominal fee.
  2. Estimating the Worldwide Extent of Illegal Fishing. Agnew, D. J., J. Pearce, G. Pramod, T. Peatman, R. Watson, J. R. Beddington, and T. J. Pitcher. PLOS One, Vol. 4, e4570. 2009. doi: 10.1371/journal.pone.0004570
  3. Ibid.
  4. Potential Ecological and Social Benefits of a Moratorium on Transshipment on the High Seas. C. Ewell, S. Culliss, Suzuki, M. Ediger, J Hocevar, D. Miller, and J. Jacquet. Marine Policy, Vol. 81, pp. 293-300.
  5. Global Hot Spots of Transshipment of Fish Catch at Sea. Boerder, K, N. A. Miller, and B. Worm. Science Advances, Vol. 4, No. 7, 2018, DOI: 10.1126/sciadv.aat7159; Global Study on Transshipment, FAO. June 2018.
  6. Ewell, et al., Marine Policy, 81, 293-300. 2017.
  7. Miller, et. all, 2018.
  8. Ibid.
  9. Transnational Organized Crime in the Fishing Industry. UN Office on Drugs and Crime, UNODC. 2011.
  10. Industrial = Motorized commercial fishing vessels longer than 12 meters. State of the world’s fisheries and aquaculture, 2018, UN Food and Agriculture Organization.

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