Out on the high seas, more than 200 miles from shore, seafood companies can operate with almost no oversight. These are ungoverned, international waters where it’s easier for companies to get away with overfishing and abuses like modern-day slavery.

Scientists using new hacks for old technology are slowly changing that.

Two decades ago, large vessels began carrying a little box that connects to what’s called the maritime Automatic Identification System (AIS). It sends out a radio signal with information about the ship, like an identifying number, and its size, course, and speed. That’s supposed to help ships avoid running into each other. It also helps authorities see where vessels are when they’re close to shore.

After the 9/11 attacks, AIS started getting more attention from the US government. It saw the tech as a way to keep an eye on potential threats to national security at sea. The US Coast Guard contracted the telecommunications company Orbcomm to launch satellites that could pick up on AIS signals from space. Meanwhile, the Norwegian government and the European Space Agency were developing similar technology. When the first AIS-enabled satellites were launched in 2008, that was a game-changer.

Now, satellites can pick up on a vessel’s AIS signals no matter where the ship is sailing. In 2014, environmental groups and Google partnered up to create a near real-time map that traces the movement of about 60,000 commercial fishing boats with AIS. The effort is called Global Fishing Watch.

The Verge spoke with Jennifer Jacquet and Gabrielle Carmine, two scientists on a mission to find out who’s doing what out on the open ocean. Check out the video above to see how they used AIS and some old-school sleuthing to spot corporate actors on the high seas.