To get the "Big Iron Fishing Pole" you need to go off the shore of Shadowprey Village in Desolace. Bring some water breath pots or spell or seal form or something and swim around opening the "Shellfish Traps". Chances are you will end up having to fight a 33-34th level crawfish that crawls out of the trap when you open it OR shellfish. A rare drop out of shellfish trap is the +20 pole your after.

Just got mine last night. When I was done I could turn in the shellfish at Shadowprey to complete the repeatable quest 9 (almost 10) times... Takes a little while sometimes.