Do pirate ships eventually despawn or must they be sunk for a chance for a merchant ship?

[Tanivar]

Been hunting ships the past week and can no longer find merchants around Tokuno Isles. Something change?

 

[Acid Rain]

I always thought merchant ships spawned independently of pirate ships.
I believe pirate ship do not despawn under normal means (ie, they must be scuttled/sunk/destroyed before new ones spawn).

Maybe try another location? Maybe you skeered em off ! I've found them in the northern waters of Tram often.