Yep that is exactly what I meant, thanks for providing a background source.

I refuse to believe that AIS is the only way ships are being tracked. I think it's probably more likely that nobody is using their military intelligence to track fishing boats.

There's over 100k merchant sea vessels, and that does not include ships that nominally aren't supposed to be on high seas either. It's simply infeasible to do so, unless you're stacking high definition cameras with high precision accuracy control onto Starlink satellites.

Balloons? You only need to track sea cables. I am not sure how it would be helpful though. You could drag an anchor for miles behind a ship.