Continue sailing until you find a MASSIVE flock of birds. Keep note, the birds can definitely be off the path, and most of the time they are, so make the effort to sail to any birds near your trade route. Once you arrive at the sunken ship, you’ll want to recover ALL the trade shipment resources you can, along with any other treasure, and finally the Revered Merchant Manifest, which (at level 5 Emissary) will sell for around 10,000 gold.