Since 2014 a small group of environmentalists has been using satellites to track fishing vessels across the world’s oceans, alerting authorities when boats appear to violate protected marine areas. Now these watchdogs are opening their system to the public with an online mapping tool called Global Fishing Watch—and they are inviting anyone who can to put eyes on rogue fishers. Actor Leonardo DiCaprio, a longtime environmental activist, was set to formally unveil the tool on Thursday at a conference in Washington, D.C., organized by the U.S. State Department.

The project emerged from the Economist World Ocean Summit in 2014, when Paul Woods, chief technology officer of the tech-environmentalist group SkyTruth, met with Jacqueline Savitz, vice president for U.S. Oceans at the nonprofit organization Oceana, and Brian Sullivan, program manager of Google Earth Outreach. All three had been thinking about how to expose the global fishing fleet to public oversight, and in a conversation they sketched out a system to do just that. Within nine months they unveiled a working prototype. Two and a half years and 200 beta testers later, the system is being opened to everyone as a free service.

The hope, according to Savitz, is that governments and activists will use Global Fishing Watch to help improve the enforcement of fishing regulations—by seafood suppliers and customers to verify that fish are being caught sustainably; by fishing companies to demonstrate that they are complying with the rules; and by fisheries scientists to improve their estimates of fishing intensity and the effectiveness of fishery management programs.

Watch the world’s fishing boats in this new mapping tool called Global Fishing Watch. Each glowing dot indicates fishing activity, as identified by radio signals from ships. Thin blue lines indicate each country’s exclusive economic zone, and red patches denote protected areas. Activists hope this platform will help governments enforce fishing regulations.

The public monitoring system collects ship positions using digital Automatic Identification System (AIS) radio signals sent by large ships—not just fishing vessels but also cargo ships, cruise ships and others—primarily as a collision-avoidance measure. Those signals get picked up by spacecraft and terrestrial antennas operated by the satellite company Orbcomm and others, and accumulate in a database.

SkyTruth teamed up with engineers at Google to develop an algorithm that uses the speed, headings and other aspects of a ship’s motion to identify whether it is fishing or not. Vessels thought to be fishing are then cross-referenced to registries that can reveal their size, ownership and country of origin. As of last week, Woods says, the database includes 63,698 unique fishing vessels spending a total of about 14.5 million days at sea since 2012. On any given day Global Fishing Watch is tracking 10,000 to 20,000 fishing boats. Now nine terabytes and growing, the database tracks the movements of such ships from January 2012 onward. “We are adding about 22 million AIS messages per day,” Woods says. (Ship positions are delayed by 72 hours so as not to compete with Orbcomm’s sale of real-time data.)

Global Fishing Watch uses Google Earth Engine to display all of this information on an interactive map, which also shows the boundaries of marine protected areas and the exclusive economic zones that extend 320 kilometers off nations’ coasts. The system runs on more than 200 computing cores at Google’s cloud-computing centers around the globe, according to Woods.

Reining in the Rogues

The monitoring system is an example of an emerging trend in environmentalism: using remote surveillance technologies—once available only to governments or large corporations—to combat polluters and the illegal exploitation of natural resources. For example, Google previously joined forces with the World Resources Institute to create the Global Forest Watch system for monitoring illegal logging. Working with the nonprofit Environmental Defense Fund, Google is using methane sensors on its street view cars to map natural gas leaks in cities such as Boston and Dallas. Other conservation groups have started using drones to deter poaching of elephants and rhinos in Africa, to monitor orangutan habitat in Sumatra and to count populations of penguins and other seabirds on remote Australian islands. And Saildrone, a company in Oakland, Calif., has deployed autonomous sailboats that can remain at sea for months to collect data on fish abundance.

Trevor Branch, an associate professor of aquatic and fishery sciences at the University of Washington who is not involved in Global Fishing Watch, says the initiative is “absolutely very useful” to researchers trying to measure the scope of illegal, unreported and unregulated (IUU) fishing, which accounts for as much as 30 percent of the global catch. “But is very hard to get a handle on,” Branch adds.

Some fisheries managers and fishers themselves are welcoming the public oversight. “American fisheries are among the most sustainable—and regulated—in the world,” says Tim Sloane, executive director of the Pacific Coast Federation of Fishermen's Associations. “IUU fishing undercuts the steps American fishermen have taken to ensure that our fisheries are as healthy as they are.” Global Fishing Watch, he says, “could be a very useful tool for international fisheries managers to root out the IUU fishing operations that aren't playing by any rules.”

According to Oceana, the government of Indonesia has promised to take steps to ensure that all of the AIS-enabled fishing vessels that it has registered can be tracked on the monitoring platform. That step is important because AIS is not tamper-proof. Savitz says that Global Fishing Watch was instrumental last year in forcing a fishing company to pay $2 million to the government of Kiribati, an island nation in the South Pacific, when one of its boats was caught fishing in a protected area. “Trust me, with million-dollar fines on the line, ships determined to fish illegally will find a way to turn AIS off,” Branch says.

Another major limitation, Branch adds, is that “this system won’t tell us anything about recreational fishing boats or someone with a small outboard motor fishing around a coral reef around Kenya.” Such small-boat fishing, invisible to the AIS satellites, probably accounts for a majority of the fish taken in the coastal waters that fall within nations’ exclusive economic zones, he says.

On Alert

Savitz says that Global Fishing Watch plans to soon add features that will allow users to select regions of interest, such as a particular marine reserve or a section of coastline, and to receive automated alerts from the system when fishing activity is detected there. “We are also going to build a feature so that users can create a fleet themselves by selecting particular ships,” she says. “An insurance company, for example, might be interested in monitoring just those vessels it insures. Others might want to keep tabs on ships that have been placed on blacklists” because of previous regulatory violations.

Developers at Google and SkyTruth, meanwhile, are working to create a more sophisticated algorithm that can flag vessels if they appear to fish legally within a country’s exclusive economic zone but then dash outside of it repeatedly before finally returning to port. “This kind of behavior suggests they might be dumping their fish onto refrigerated transport vessels to get around their quotas, which is illegal,” Savitz says. “It could also indicate trafficking in drugs or people.”