Keep blasting them out of the water. They aren't frustrated fisherman, they're armed criminals. Haven't seen a political banner on any of the pirates' boats, so they aren't doing this out of protest. They are motivated by the same greed and malice as the guy who robs a convenience store, and then shoots the clerk for no reason. When liquor store clerks started shooting back, the robbers stopped trying to rob liquor stores because it became too dangerous to continue doing so... Shooting back works.