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. However, transshipment also obscures the seafood supply chain from hook to port and hobbles efforts to manage fisheries sustainably. To better understand transshipment, Global Fishing Watch applies its machine learning technology to analyze tens of millions of global position system (GPS) data points broadcast by fishing and carrier vessels every day. By studying their positions and behaviors, we are able to identify when and where these vessels meet up at sea.

Transparency in International Fisheries
Credit: Francisco Blaha

How it works

We identify fishing vessels and those capable of receiving transshipments—fish tenders, live fish carriers, factory processors and refrigerated cargo vessels which are collectively referred to as “transshipment vessels”—by using our comprehensive vessel identity database. The information in this database is routinely validated through manual review.

Next, using cloud computing, we process tens of billions of automatic identification system (AIS) signals to detect when transshipment vessels behave in ways that indicate potential transshipment activity. AIS data cannot confirm if goods or people are exchanged when vessels meet, but it can identify potential transshipment events at sea. We identify two types of such activity: two-vessel encounters and loitering events. The complete methods for identifying potential transshipment events at sea are described in our 2018 paper Identifying Global Patterns of Transshipment Behavior.

Transshipment at sea

Two-vessel encounters

Encounters represent locations where a fishing vessel and a neighboring vessel are continuously within 500 meters from one another for at least two hours and traveling at less than two knots, while at least 10 kilometers from an anchorage. 


When a carrier vessel meets with a fishing vessel at sea, they move slowly, sometimes motoring steadily into the waves or wind to facilitate an easier exchange. Because transshipment vessels are much larger than fishing vessels and are often subject to different regulations, almost all of them carry high-quality AIS devices, which are rarely turned off. Fishing vessels, in contrast, may not always be outfitted with AIS or have it turned on and, as a result, may not be visible in our AIS dataset. This results in the appearance of a transshipment vessel moving slowly as if to transship, but no other vessel is visible. To address this behavior, we developed two models to identify loitering at sea. All encounters also include a loitering event by a supply vessel. Loitering events that do not include an encounter in the AIS data may either be a transshipment event with a fishing vessel that is not broadcasting, or merely the transshipment vessel waiting until its next task.

Access the data

Our data on global transshipment activity covers over 1,300 carrier vessels dating back to 2012 and is available in several places on our website. It can be explored in near real-time using our map and, more specifically, our carrier vessel portal, which provides a valuable tool for managers that seek to verify transshipment activities, helping to reduce opportunities for unauthorized transfers of fish products and identify when such activity is not being adequately reported. The carrier vessel portal allows users to download data for specific regions and the complete dataset can be accessed on our data download portal. We have also produced several detailed reports on global transshipment activity and the underlying data for these reports can be found on our data download portal.

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