I'm not sure why, but I was under the impression that Peter Benchley's novel Jaws was really bad. It appears to have been a best seller when it debuted in 1973, but it has been swallowed up by the movie. Nobody talks about it much, but it's number 11 on Amazon's Kindle bestseller list for sea adventure books. Take from that statistic what you will. I checked out the top twenty of that list and was disappointed to find The Odyssey nowhere on it. It is dominated by someone named Clive Cussler.
Anyway...Benchley's book was pretty good. There's a whole lot about life in Amity, how the town is in trouble because of the lack of tourism, which leads everybody wanting the beaches open despite the shark. There's stuff about the mob, and Brody's tension with his wife. In short, the bulk of the book is about the effect of the shark on the town, not about the shark. That's not necessarily a bad thing, it's just not as good as the movie.
Also not as good as the movie: that part where Brody is dumping chum into the water and the shark comes right up to surprise him. It's precisely the same event in both mediums, but it's a whole lot more effective on film. Here it is in the book:
Brody's butt was sore from sitting on the hard transom, and his arm was growing weary from the dipping and emptying of the ladle. So he stood up, stretched, and facing off the stern, tried a new scooping motion with the ladle.
Suddenly he saw the monstrous head of the fish--not five feet away, so close he could reach over and touch it with the ladle--black eyes staring at him, silver-gray snout pointing at him, gaping jaw grinning at him. "Oh, God!" Brody said, wondering in his shock how long the fish had been there before he had stood up and turned around. "There he is!"
Compare that to this:
There really is no comparison. Everything in that scene adds to the tension, from the camera angles to the acting to the music. In the book, it's all very calm and matter-of-fact, exclamation points notwithstanding. And it's not very compelling. We don't need to read Brody's worry that the shark had been there for a while, but we do need to see his face after he notices the shark. And then there's the line. Not in the book. Is there a way to invoke that sense of shock using only words? It doesn't seem like it. There's no means of doing that, making people jump.
We can say that about every shark scene, I think. I've been a big fan of horror fiction since I was a teenager, but I am rarely scared or startled by what I read. The only book that ever really creeped me out was Salem's Lot, and staying up until the middle of the night to read it had a lot to do with it.
I seem to be digressing a lot here.
As with "You're gonna need a bigger boat," nearly everything great about the movie is original to it. The script puts that chum ladeling scene at the beginning of the trip out to the water to get the shark. Benchley puts it just a few pages from the end. The result is that we get our first good look at the shark with Brody, and feel his fear of it. It's a great move on the screenwriter's part (either Benchley or Carl Gottlieb).
If the book is better than I expected, the movie isn't as good as I remembered. There's an awkwardness to a lot of it, especially the sound editing. Some of it feels forced. The story has gotten some complaints about how unlikely it is that the town would still go to the beach with the threat, and I will say that the novel spends a lot of time making this plausible, giving the mayor motivation.
Still, everything having to do with tension, with the shark, works better on film. I think that's because of the documentary quality of the camera's presence. When writing, the limited nature of prose--describing one thing at a time as opposed to the encompassing nature of the visual image--really allows tension in certain ways. The camera can imbue any object with menace, find tension in the simplest things. Every time anyone's in the water we can feel the tension. David Lynch is a master of this technique.
But once the trio is on the water, the movie just works. That's all there is to it. Even the end, with Brody killing the shark, works despite the fact that it's not realistic. The novel just sort of fizzles out.