Continuity mistake: When the guy is standing on the beach in the opening scenes the sunset is covered by cloud. When seeing the sunset from the woman in the sea's perspective the sky is clear with no clouds.
Continuity mistake: When Jaws gets trapped between the cage and the boat the shark is really thrashing about. Cut to the surface and Brody is trying to free the cage - the surface of the water does not match the actions of the shark.
Continuity mistake: When Quint is up in the crow's nest, Brody tells him "Let Hooper take a turn" (regarding chumming the water). When Quint, while looking down at Brody, says "Hooper drives the boat, Chief", his right arm is across his body and looks to be resting on the safety railing of the crow's nest. When Brody looks up at Quint, his right arm is away from his body and is just holding onto the crow's nest railing with his hand.
Continuity mistake: As Brody flips through his shark book, he pauses to look at a photo of two fishermen and their catch. The photo is on the right page, but in the previous shot where we see Brody stop flipping through, there was no picture on the right page as seen in a reflection on his glasses, just words. (00:25:30)