its not about hard power necessarily, but soft power. If the EU united politically and made these harassment attacks consequential then they would stop.
E.g. perhaps something along the lines of prison for captains who were 'derelict in duty', rewards to crews who grass and seizing ships that, by dragging anchors 'by accident', have proven themselves unseaworthy etc.
I believe something like this will happen, sooner or later. For now, it's not easily to organize as the crew can always use the excuse "oh, this was unintentional" but charging them with the cost of repair plus additional penalty could be a good starting point.
> but charging them with the cost of repair plus additional penalty could be a good starting point.
Good luck enforcing that. The "shadow fleet" ships all operate under flags of convenience and ownership is hidden behind layers upon layers of shell companies.