This quest is not available in game.
Katoom the Angler at Revantusk Village in the Hinterlands wants you to kill Gammerita and retrieve Katoom's Best Lure from her corpse.
Katoom mentioned that Gammerita hangs out on the coast with the other turtles.
Yo! There be a turtle out there not like the others. She be the Gammerita, leader of the saltwater snapjaws - a downright dirty thievin' reptile.
Mon, she stole my best lure. Snapped it right off my line! Since then, the fish just aren't biting the same.
Find Gammerita and get my lure out of her stomach.