Deadliest Catch

The Deadliest Catch is a repeatable quest in Fallout 4: Far Harbor.

Quick walkthrough

 * Accept settler's proposal to hunt the giant hermit crab
 * Follow settler to location
 * Kill the hermit crab found at that location

Detailed walkthrough
You can get this quest from any settler at your settlements. While in the settlement, you will be approached by a random settler who informs you that a giant hermit crab has been spotted in the area and they'd like your help killing it. If you accept, the settler will then lead you to one of the five locations on the island where a hermit crab can spawn.

Upon reaching the location, you will need to find and kill a leveled hermit crab. The crab stays hidden in its "shell" (a ruined bus or trailer), but can still be targeted in VATS.