I assume you're talking about how the men Zaroff hunts find his island. The island is called "Ship Trap Island" for a reason. Zaroff sets a trap for the ships that pass near his island by making the crew of the ship think the lights Zaroff has set up are a channel through which the ship may pass safely. Instead, there are jagged rocks with sharp edges that can tear a ship to shreds. Other "prey" sometimes find the island when something goes wrong, and the sailors have no choice but to swim to the island, thinking they can save themselves.