Contrary to popular opinion, slavery was a significant factor in the local economies of the Caribbean, and appears to be something for the most part that pirates abhored, or else found little use for. While generally ships of the time were not operating with slaves, they were often found transporting them to either the colonies or back to Europe for huge profit. Captured ships that had a couple slaves for sale might see those slaves freed by the pirate crew and asked to join them. Some pirate vessels had upto 50% of the crew as ex slaves. Proper slave vessels that were captured by pirates might instead see the slaves left inchains and sold as a lot at a suitable port.
Slaves were worth 50 pound or so during this time, but not long before had reached about 100 pounds.
In the 1500's, escaped slaves were called Cimaroons, or Maroons by the English. On the Panama land mass they established three main towns in the late 1500's. They consisted of a large 8' ditch with a 10' mud wall behind that, with some 50 or so houses inside.