Or you can be sneaky. Put out some irresistable, yet covert job offers for pirates in the necessary ports, and see where the applications come from.

Or put a "Report a Pirate" bounty and crowdsource it.

but how do you confirm the validity of the reports

There are two types of reports, fraudulent ones and real ones. The fraudulent ones will come from everywhere, while the real reports come only from pirate infested harbors. Therefore just subtract the mean report density and what remains should be random fluctuations around zero plus the real reports. So if a harbor has more than some threshold of reports, then it is pirate invested.

At this point in the discussion, you could probably correlate it with the number of the letters "R" in the reports. Because we all know that it's the pirates' favorite letter.

Arrrrgh you would think so, but no, it's the C.

Ah, laughed out loud for this string of comments. Great job, all. And not a verge "combo breaker"-comment in sight.

Mechanical turrk?

Just send in 100 journalists and 99 of them will come back.