I read the novel Jaws years ago and man-o-man what a difference between it and the movie. Let's see if I can remember the differences.
1. After Chief Brody hires the shark expert Hooper to study the shark, Mrs. Brody, who is dissatisfied with her life, takes the sharkologist to a local motel and does the nasty with him.
2. After fisherman Quint is hired to kill the shark, he, Chief Brody and shark expert Hooper make multiple trips out into the sea to get the shark. (In the movie, they just make one long trip in search of the shark.)
3. After they find the shark, Hooper goes down in his shark tank and the shark proceeds to rip the cage open and then it eats Hooper. (Of course, he survived in the movie.)
4. When the shark causes the boat to begin to sink, Quint manages to harpoon it a number of times, but then his foot gets caught in the rope and when the shark dives into the deep, Quint is taken with him and drowns.
5. In the movie, Chief Brody was able to get the shark to explode, but in the book, the shark flopped its way up the sinking boat, eager to get a bellyful of the chief, but sadly (sad because I was rooting for the shark) it died from the effects of Quint's harpoon strikes, and Brody was able to paddle his way back to shore.
6. I imagine there are more differences that I can't remember. My god, I read that book back in 1975, not too long after the movie came out.