SkyTruth Data Analysis Aids Fishing Slavery Investigation

Through careful monitoring of satellite-derived vessel location data from a six-month period, we were able to help the AP target a satellite image showing a transshipment at sea. Many of the fishing vessels we are interested in are exempt from broadcasting their location via AIS (Automatic Identification System), but because they stay at sea for months at a time, fishing vessels must offload their catch to refrigerated cargo ships (also known as “reefers”) like the Silver Sea 2. Large reefers like the Silver Sea 2, however, are required to broadcast their location, giving us a way to catch a glimpse of the shadowy world of transshipments at sea.

In April 2015 we observed the Silver Sea 2 briefly stop in Daru, Papua New Guinea before transiting to and lingering for three weeks in a region of Papua New Guinea’s Exclusive Economic Zone (EEZ) known as the Dog Leg. During this time, the reefer stopped broadcasting its location and was presumably receiving shipments of seafood from trawlers operating in the area. On May 17, the Silver Sea 2 turned its AIS transponder back on and headed west, destined for Indonesia and Thailand. Looking back in time, we found evidence of two other Silver Sea reefers making this exact same circuit. Armed with intelligence that revealed a predictable pattern about these rendezvous, our team was as confident as we could be that we might just be able to get a satellite snapshot of the “Dark Fleet” that was supplying the Silver Sea reefers.

Collecting a high-resolution satellite image of a moving target (such as a fishing boat with nets or lines in the water) is extremely difficult, and to our knowledge, has never been intentionally done by anyone in the public sector. Transshipments, however, are another story. Reefers are stationary for hours or days at a time while they receive catch from vessels in the area. There is still a chance clouds could obscure the target or no vessels are tied up at the exact moment the satellite flies overhead, but the chances of success are better.

On July 13th we notified the AP that the Silver Sea 2 was returning to PNG following the same pattern we observed in April. Another Thai reefer, the Sea Network, was also anchored offshore in this coastal transshipment area, so with two reefers likely transshiping catch in the area, now was time to try. Then on July 14, Digital Globe’s WorldView-3 satellite collected a high-resolution image of the Silver Sea 2 apparently engaged in a transshipment with two vessels believed to be part of the slave fleet previously operating out of Benjina, Indonesia.

60-day track of the Silver Sea 2, as of August 7, 2015. Image Credit: ShipView from ExactEarth. 

The Silver Sea 2 is now well under way toward Thailand, but news of this transshipment being spotted by satellite appears to have prompted authorities step up their efforts. Another Thai cargo ship, the Blissful Reefer, has been detained and eight more fishermen have been freed from purported slavery at sea.