Use the [Horn of Poseidon] to summon and illuminate the fishes you attract. This will also activate an Ocean Scanner, pinpointing their heading and distance, while you extend or retract your line.

The Ocean Scanner will activate when you retract your line, pinpointing the heading and distance of nearby rare fish.

Protect your line from pulling back upon accidentally hitting a fish on the way down. You have a limit of two accidents without penalties per round, and can use the [Reel Stabilizer] to gain another two.

The ocean depths are very dark, drastically reducing your visibility. Use a [Lantern] to illuminate more of your surroundings here.