Lunkers, Lunkers Everywhere

I sadly didn't finish this when it was easy by joining Lurker groups. =(

But now, I've found a "decent" way to complete the achievement.
By fishing in the small pond next to Loamm in Zaralek Cavern.
/way #2133 55.80, 57.65 Throw Here

Randomly, you will catch an [item=194701] and Massive Thresher will appear, and each of these spawns counts toward the achievement.

After fishing for 1h I was wondering why I wasn't getting any Lunkers. I realised I was cancelling the cast by casting again.
Use this macro to prevent that:
/cast [nochanneling] Fishing

After much confusion I finally figured out the difference between regular and Massive Lunkers. Whenever you fish up an [item=194701], you will start a cast called Looking for Lunkers that will be interrupted if you try to fish again. If you let the cast play out for long enough, you'll find a Lunker that will count for this achievement. Oddly enough, the lunkers I found were called Massive Threshers, but they don't actually count as a Massive Lunker. The Massive Lunkers are spawned by using 5 of the Ominous Conches at the Large Lunker Sighting area, but they will count for both this achievement and the We're Going to Need a Bigger Harpoon achievement. Also, you don't need to actually Harpoon or kill the Lunkers to get credit for either achievement.