Sea Trap is an item from Don't Starve: Shipwrecked DLC. It's a Nautical item used to catch Wobsters, but will not catch Bottlenosed Ballphins, Jellyfishes, or Dogfishes. It can be crafted at a Science Machine with 4 Palm Leaves, 2 Empty Bottles, and 1 Jellyfish.
Once set, Sea Traps can be baited with food, which are attractive to Wobsters. Baited or not, a Sea Trap will trigger once a Wobster moves close enough to it.