I have never had problems with sharks. They just seems to glide on by. But Barracuda have worried me a few times. Example, my partner was going for the ladder to get out of the water when I saw this Barracuda coming up from below fast, heading right for her. I was about 15 ft down on the other side of the ladder so I could see it going for her.
Dunno why, but I started up on an intercept course and we both reached her fins about the same time. For some reason the Barracuda stopped about 6 feet in front of me (we were facing each other) and headed back down. Weird, it was like a missile that stopped and hung a left.
I don't mind swimming with sharks, but the Barracuda don't seem to friendly.
As for moray, they seems to take off when they see me. If I hold real still they come up and hover then move on. Never had a problem with them either.
Most of the problems I have seen is when people are looking at their console taking a compass heading. They then swim right into things, like Barracuda!!!
Pay attention to your surroundings and you'll live a lot longer=-)