Trade the Pirate's Chart to the ??? in Valkurm Dunes on the Whitebone Sands (F-9).
A mysterious tarutaru will appear and start talking about fishing. Start fishing as soon as you can!
About 15 seconds after you trade the chart, the tarutaru will die, and three NMs will appear.
You can have three people total in the fight and once you start, the whole party will be under the effect of level restriction at 20. All buffs except for food will be canceled. Healing from outside party will also be disabled.
There's a limit of around 10 minutes in this fight. If you can't kill all three NMs within the time limit the message "Too much time has passed. The monster has lost interest." will appear and all remaining NMs will despawn.
If the battle is lost, a new chart will be needed to start the fight again.
Kill all three to have a Barnacled Box appear, with four items inside it.
The Goblin Bounty Hunter that roams the beach WILL attack the group that's trying to do this quest. They also have a short respawn time, so it's a good idea to have an outside member just to kill them for added safety.