20 Things You Didn't Know About Jaws 3D
3. Shark Biology 101: The Shark Is Too Big
Initially, the great white captured by Seaworld is pregnant. At the time, no great white had survived captivity, so naturally it dies, but not before giving birth to the real monster of the movie.
It's understandable that a sequel wants to up the ante a bit, so the killer shark is longer by ten feet (35) than that of the creature in Jaws (25, according to Quint). And that's just scientifically impossible. A baby great white is no bigger than a Chinook Salmon when born, posing threat to - at best - an infant or a puppy. And in captiviity, it's highly unlikely that it'd grow at the size and rate it does over the course of the film.
Alas, the shark is simply too big to be real. Throw in some ridiculously bad dry-for-wet shots and, as Michael J. Fox says in Back to the Future part 2, "Shark still looks fake."