The shark at minute 5:30 is "squealing in pain".
Sharks however have no sound producing organs. Only one shark, the Draughtsboard Shark in New Zealand has the ability to bark, which is actually a belch.
There is dialogue among the divers during the final underwater scene. There is no means for wireless verbal communication underwater.
When the main characters are at the beach for the surfing competition, and the sharks break through the net and start eating the surfers, the woman says "Oh my God!" without moving her lips.
During the attack where the surfers are killed there are several times when a shot of a surfer is shown and the 'attacking shark' can be seen just centimeters away under the water, immobile and obviously a prop.
During the surf competition, while Tom is swimming away from the sharks, the water is calm, suggesting this scene was shot in a lake or pool. You can see it again while Nick is swimming back to his jet swimmer.