The previous quest is completed once you've found the Fisherman on a jungle island. Talk to him to start the quest:
Ask about the key
Lenvell sent you, did he? Ah, you must be after the key. And here I thought this was just a chance meeting. Well at any rate, I've hidden it somewhere, and only I know of its location. I suppose if Lenvell wants you to have the key, then it must be pretty important…
Alright, I tell you what. I'll give you the location of the key, but you've got to do something for me first. Have you seen these poachers roaming this island? They carry with them a special lure that could be very useful to me as a fisherman. Unfortunately I've tried to offer them money for the lure, but they will not sell it.
Obtain that lure and bring it back to me. Once this is done, I'll give you the location of the key.
Head into the jungle and find some poachers. Kill a few until you find the Poachers Lure, then return it to the fisherman to complete the quest. He will give you the Strange Compass and will say the following:
I've hidden the key in a stump on an island. The compass I gave you will be useless to you until you get to the island, but once you are there, the compass will point you toward the stump.
Now, be on your way! I've got some fishing to do. Oh, and you can find the location of the island at [location].