I'm currently playing a marathas campaign, and didnt bother sending out trade fleets during the early stages, instead concentrating on taking out the mughals. While i was doing that i noticed that the AI factions have been giving the pirates a pretty comprehensive beating, to the extent that the pirates are a spent force, every ship they spawn gets taken out the turn after it appears.

So now i'm in the situation where most of the trade theatres are free of pirates, and there are still plenty of trade spots available as a result of inter-faction fighting. As i'm fairly isolated down in the indian subcontinent i'm not at war with anyone except the remnants of the mughal empire (and they dont have any fleets left, and no ports to build any ships with) i have a free reign to go out and start filling up those trade spots.