Statoil arranged a hackathon for this competition at my university (NTNU) where I asked this question. They said that AIS data makes the problem easier to solve

Statoil arranged a hackathon for this competition at my university (NTNU) where I asked this question. They said that AIS data makes the problem easier to solve, however in addition to not every ship having such a transponder, there are vessels where it is intentionally turned off due to for example illegal fishing or smuggling. When they are unable to identify an object using remote sensing they use airplanes to visually identify the object. More satellites and lower remote sensing costs have resulted in much more data being available, which is why they need to automate their analysis pipeline further.