I used to be a commercial diver.
This one day, on a job with my brother, we were taking turns (Easy Boys! My brother!) working a piling; at the end of his down time, he comes onto the boat and says he thinks he saw a shark swim by (we are in southern New England, not far at all from Martha's Vineyard, where Jaws was filmed and there are some large sharks around these parts, including Great Whites). He then spent the next one- half hour convincing me (but really himself) that it was not a shark, if it was, it was not a big shark, etc., etc.. A little funny, a little sad and frankly a little off- putting, all at once.
We did carry bang sticks, and while they are extremely effective against any size shark, it is unlikely any diver but especially a commercial diver (dark dives, limited to no visibility, usually facing down, working, etc.) would ever have a chance to use one on a shark before the shark already had the diver.
But the bright side is that sharks usually bite and then spit divers back out. It appears they do not like the taste of our suits. So it really all comes down to how bit the shark is and how large that first taste is as to how much damage the diver suffers.
Personally, I would be far, far more cautious about diving in a lot of other places than here including southern US waters, Australian waters, etc.
But look at the bright side: virtually no one ever gets shot underwater and the odds of getting hit by, say, a drunken driver go WAY down so there are those plusses.....
Brian
Ever since Jaws, I've never gone over ankle deep in any natural body of water.