The "dark fleet" of vessels operating off AIS is much bigger than usually conceived, particularly in some regions, according to a new study led by Global Fishing Watch.
AIS was intended as a safety tool, a way for vessels to automatically communicate the most important details of their movements to each other. Since it is an unencrypted VHF broadcast and is detectable by satellite, it has also evolved into a tracking tool, used every day by researchers, journalists, market analysts and businesses to follow ship movements. AIS is often treated as a reliable depiction of activity on the water - even though the signal can be turned off, falsified or lost in coastal clutter.
The new study - published Wednesday in the scientific community's premier journal, Nature - delineates the limits of AIS' capabilities. Global Fishing Watch's researchers found that about three quarters of all fishing activity and one quarter of all merchant traffic is invisible to satellite AIS tracking.
The study drew on modern satellite sensing systems (synthetic aperture radar and visual imaging) to create a dataset covering the busiest 15 percent of the ocean surface over a period of five years. Using machine learning, they created algorithms to identify fishing vessels, oil and gas vessels, merchant ships and oil platforms, with high accuracy (more than 90 percent for all classes).
The existence of "dark" shipping is well-known to security researchers, who are familiar with the methods that sanctions violators, smugglers and fishermen use to defeat surveillance - but the sheer scale of untracked activity in some regions may come as a surprise.
Among the unexpected findings, the researchers discovered that some of the highest fishing pressure in the world can be found off the Yellow Sea coast of North Korea. This extreme activity peaks during the month of May, the season when China's domestic fishing fleet is required to pause operations in neighboring Chinese waters.
The team also discovered a surprising amount of fishing activity in the world's flagship marine protected areas, including multiple vessels per week found operating in the Galapagos and the Great Barrier Reef.
"If the industrial fleets of the world knew they were being watched everywhere they went, all the time, by everyone in the world, they would break fewer laws. Governments must make sure their vessels are trackable so they can be held accountable," said Andrew Sharpless, CEO of Oceana and co-founder of Global Fishing Watch.
While Asia had by far the highest number of untracked vessels, and easily the most activity overall, the lowest rate of tracking in the world for fishing was North America. Just 17 percent of North American fishing vessel movements were publicly visible on AIS, confirming the sector's low utilization of the navigational-safety system.
