Skills in multiplayer Stardew have two variations:
- Skills that affect selling price apply to all players, as long as the player with that skill is online.
- Skills that affect gameplay in some other way apply only to that player.
When a player places a crab cage with either the Luremaster or the Mariner skill, the effect is tied to that cage. That means that the abilities will remain so long as that cage remains there, even if another player collects from it.
However, if another player breaks the crab cage and replaces it, it will no longer have the effect from the skill.