This is an Event Commodity, put in to be sold at the Shipyard and bought by the Fort.
FLHook detects the purchase and sale of the stuff, and if the amount being hauled does not change between purchase and sale, a bonus is paid out.
Assume you pick up, for example, 1000 units of stuff and sell 1000 units of it at Fort Albi. You will receive the regular trade profits as well as a bonus of 1500 per unit. The 1500 is paid out of FLHook generating money ex nihilo to reward peeps for hauling.
Side note: If a pirate demands you drop like 1 unit or so, that actually constitutes cheating. Just so you're aware.
Though if you're getting something like this, it means Skorak borked the event again.
