Transparency of Transshipment: Using Satellite Data to Reveal Meet-ups on the High Seas

Photo by: Francisco Blaha

New study reveals global footprint of support vessels involved in rendezvous at sea


Every day thousands of fishing vessels roam the world’s ocean, combing the most lucrative fisheries for catch to bring back to market. Some of these vessels don’t return to port for several months. Thanks to a practice known as transshipment—the transfer of catch between vessels—fishers can stay at sea for months at a time without ever having to take a costly and time-consuming trip back to port to offload catch. 

Transshipment at sea relies on two types of vessels: refrigerated cargo ships, or carriers, that take on fresh catch from fishing vessels and transport it back to port for processing; and bunker vessels, which are large tankers used to refuel fishing vessels so they can avoid transiting back to port and the crew can continue fishing. 

While transshipment and bunkering facilitate high seas fishing, allowing fishing efforts to be carried out uninterrupted, these activities can contribute to illegal, unreported and unregulated fishing and can also open the door for other transnational crimes. Limitations in effective monitoring have led to unscrupulous practices such as the manipulation or omission of data related to fishing practices and even incidences of forced labor, as it enables captains to keep their crew at sea for months—even years—at a time.  

To better understand this complex network of support vessels, Global Fishing Watch applied its machine learning technology to analyze billions of global position system (GPS) data points broadcast by fishing, carrier and bunker vessels from 2012-2019. By studying their positions and behaviors, we were able to identify when and where these vessels met up at sea. 

In our recently published report, “Revealing the Supply Chain at Sea: A Global Analysis of Transshipment and Bunker Vessels,” we built the first ever public database of support vessels made up of 1,350 carriers and 963 bunker vessels. Using automatic identification system, or AIS, data we pinpointed over 24,000 carrier encounters and 14,000 bunker encounters to see what happens when these vessels meet up with ships from the world’s long-distance fishing fleets. 

But the most interesting part of our findings lies in what we didn’t see. 

Monitoring the unseen

We documented more than 157,000 loitering events involving carrier and bunker vessels—a situation whereby a support vessel moves in a manner that suggests they are meeting or moving alongside a fishing vessel at sea. Yet when we checked the AIS data, sometimes no such neighboring vessel could be found. The result is the appearance of a supply vessel moving slowly as if to bunker or transship, but no other vessel ever comes into the picture.

AIS was originally implemented as a collision-avoidance mechanism and is mandated in vessels that are 300 GT or more. Most carrier and bunker vessels are outfitted with high-quality AIS devices which, due to stricter regulations, are rarely turned off. This makes them “visible” on the Global Fishing Watch map. Fishing vessels are not subject to the same regulations and are not always outfitted with AIS, hindering our ability to see them or publicly monitor their movements. And while the number of carrier loitering events unmatched to an encounter has declined in recent years, suggesting the potential for greater AIS adoption in many fishing fleets, it still piques our interest when these unmatched events occur. Although complications in reception can sometimes explain an absence of AIS data transmission, we believe the particular encounters within our study were simply the vessel’s failure to broadcast its position—be it a harmless coincidence or a more calculated decision. 

Carrier loitering may serve to identify regions in which dark vessels—vessels not transmitting on AIS—continue to operate and where greater transparency is still needed. Some carriers work with one specific vessel type, such as longliners. Harnessing this information in our work going forward, we hope to be able to identify the location and activity of dark vessels by determining the specific location of carriers engaged in loitering events with no other visible vessel. We plan on investigating this concept further towards our overarching goal to create a more comprehensive view of human activity at sea. 

Risk of forced labor

We also compared transshipment and bunkering activity with a new labor model that was recently published by the University of California, Santa Barbara, which reveals the risk of human rights violations in the world’s fishing fleet. Research from this study produced a model based on remote sensing data which shows that as much as half of the world’s pelagic longline fleet has an elevated risk of harboring forced labor. By analyzing information from the forced labor model across data from our new report, we found that almost every longliner engaged in a transshipment event had a high risk of forced labor. Startling as these results may be, we recognize that they are based on an initial proof-of-concept. Over the next two years, we will continue our work with research partners to further analyze the scale and level of this risk that is highlighted by this report. 

More information, more application

In the world of transshipment, the information we don’t know far outweighs the information we do know. Establishing clear rules for transshipment is critical to ensuring a legal and verifiable seafood supply chain and to mitigating the risk of illegal activities taking place. To do that, effective monitoring and controls are needed, and that’s only possible with transparency of information. 

Our work continues, and in the coming year, we hope to broaden the scope of our research to better understand the global network of transshipment. An analysis of this social network—a kind-of Facebook for fisheries—will allow us to build a more comprehensive network structure to represent vessels and examine the way they interact. This will help us identify key characteristics of networks that include high-risk vessels and eventually reveal and interpret the structures that are fueling illicit activities worldwide. Do these communities differ in size or complexity, or do similar members play critical roles, such as carriers or ports that connect separate distinct clusters? By identifying the central members of the social network—the members that play the greatest role in setting the structure—we can try to determine how the system might shift in response to external forces like environmental, policy or regulatory changes.

We are looking forward to drilling down on this information, linking networks to fishing effort footprints, and also scaling up existing efforts to connect vessel networks to beneficial owners, recruitment agencies or insurance providers. Greater transparency into the network of support can identify areas of greatest concern or those with the greatest opportunity, and this can then help inform management and enforcement responses, as well as assess how controls are being implemented. 

An analysis of this social network—a kind-of Facebook for fisheries—will allow us to build a more comprehensive network structure to represent vessels and examine the way they interact.

The path towards transparency

Transshipment and bunkering help underpin the economic viability of the world’s distant water fishing fleets and are an integral part of the seafood supply chain. But these activities need to be carried out fairly and in a manner that does not imperil fisheries or enable illegal activity. Our findings are just an initial slice of information that can be extracted from the dataset we studied. We hope others will use this work to build on our findings, which is why we make the data behind this report—and others—publicly available.

Global Fishing Watch will continue to harness innovative technology, research and science to support the transparent, legal and verifiable practice of transshipment. By providing detailed information on this activity, we hope studies like this serve as a vital step towards equity and sustainability across the commercial fishing industry. 

Nate Miller is a senior data scientist at Global Fishing Watch. 

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