In the last year or so saltwater crocs have become a popular underwater photography subject, with shots being published regularly in dive magazines (see Issue 1 of Scuba Diving Through The Lens) and winning competitions.
But photographers, be warned, these crocs hold the crown for hardest bit in the animal kingdom. According to a recent study by paleobiologist (yeah, I had to look it up too), saltwater crocs bite down with 3,700 PSI. In contrast, if you were to bite into your regulator if, say a saltwater croc came up to underwater, it would due probably be with around 200 psi.
It should be noted that our other photo friendly friends, great whites could rival the reptiles, as a computer study estimated a that a large great white could bite down with 4,000 psi, but it's never been actually tested.
More info on National Geographic.
Canon 15mm f2.8 Fisheye
Canon 5D Mark III
Sea & Sea YS-D1