These Islands do have pirates on them but can have quite a varying amount. These islands vary in sizes from tiny to huge, and also based on the factor of it's size- whether if it's huts there or not. Islands like these have a chance of having a repairable Old Pirate Ship next to the island, as an indicator that the pirates there are stranded.There are usually 1-3 Campfires that spawn on these islands. Each fire place is guarded by pirates of different types, such as common Pirates, pirate cartographers and pirate captains. Rarely, a chest can be found away from pirate camps which requires a bronze chest key to open, which is commonly dropped by pirates.
Pirate camp islands can be spotted far away, as smoke from campfires are indicating pirates on that particular island. The more campfires, the more pirates.