Those are the shipping lanes.
4 seconds sound clip from the Batman & Mr. Freeze: SubZero movie soundboard.
You can hear this line at 00:44:21 in the Blu-ray version of the movie.
Quote context
[...]
- That's a ship's foghorn. He's somewhere near the water.
- But the police have combed every inch of the coast.
- Listen to it again. There's something else in the background. I'll try to enhance it.
- Those are the shipping lanes.
- No wonder the police can't find him on the coast. He's 5 miles offshore in the middle of the ocean.
- There's an abandoned oil derrick out there.
- Miss Gordon, we're ready to begin.
- I'm afraid you have no choice.
[...]
Top rated lines from this movie
Actors: Kevin Conroy (Batman), Michael Ansara (Mr. Freeze), Mary Kay Bergman (Batgirl Barbara Gordon)
Matilda (1996) 
Easy Money (1983) 
Invincible Super Chan (1971) 
Immortal Combat (1994) 
The Pebble and the Penguin