A Maritime Mystery: What Has Been Causing Ships To Sail In Circles?

Ghost ships appear to be sailing in large circles off the coast of San Francisco, giving off GPS signals, without the ships actually being anywhere near the area. Almost all ships are legally required to use an Automatic Identification System (AIS) to track their location in order to help avoid collisions with other ships and ensure international laws are observed. There are a number of possible explanations, but no clear answer as to what's causing the strange phenomenon. Bjorn Bergman of SkyTruth and Global Fishing Watch has identified nine boats broadcasting signals that suggest they were around Point Reyes, northwest of San Francisco, when they were actually thousands of miles away. Bergman said it could be related to some sort of malfunction with the GPS device, or it could be deliberate manipulation, but both theories come with problems. Bergman hopes to find out more about the AIS devices being used on the nine ships that appeared above Point Reyes. If they were made by the same manufacturer, that would be a link that he could investigate further. If, however, there's some sort of hacking or deliberate fraud being perpetuated, the investigation will go even deeper.