This will be inherently inaccurate because data was based on public AIS signal, but ships are turning off their AIS to avoid detection.
> In an attempt to evade detection, many ships appear to be deliberately switching off their tracking system - known as AIS (Automatic Identification System).
https://www.bbc.com/news/articles/c4geg0eeyjeo
> In an attempt to evade detection, many ships appear to be deliberately switching off their tracking system - known as AIS (Automatic Identification System). https://www.bbc.com/news/articles/c4geg0eeyjeo