\The night beach picnic is entirely Steven Spielberg’s. In Peter Benchley’s novel, when Chrissie and a friend leave a house party and head for the beach for a swim, they stop to make love before Chrissie goes alone for her fateful meeting with the great white shark.
Spielberg uses a similar ploy in Jurassic Park: The Lost World, which opens with an afternoon picnic on an island off the coast of Costa Rica.
See Peter Benchley. Jaws. Garden City, NY: Doubleday & Co., 1974; Stephen Spielberg. Jaws (1975). The screenplay by Peter Benchley and Carl Gottlieb is based on Benchley’s 1974 novel.