From the wiki:
Quote:
Mooching is a legendary technique used by anglers across Vana'diel. It involves using live fish as bait to attract those more "finicky" big targets.
Notes:
This key item increases the amount of time you have to land your catch when fishing with Drill Calamary or Dwarf Pugil bait. It does not function with any other bait/lure. The special bait and the key item are intended to be used together to catch Gugrusaurus and Lik for the Indomitable Spirit quest, fish which normally only permit you a very short amount of time to catch them. This help a lot in fishing Matsya, since it stay on the line for a very short time.
Emphasis added. Selling for 200K today on Lakshmi.