This response might be laughed off, but I'm not kidding. My relatively short time in the underwater realm has lead me to conclude that fish are psychic. I don't think they can pick up on the actual words in your mind (i.e. fish don't speak English), but they nonetheless seem receptive to motive, feeling, emotion etc. I think the best way to avoid a shark attack would be to put out a vibe of "I'm just a guy scuba diving, I don't want any trouble" or something along those lines. Semi-example: Have you ever had the experience where you're not in a bad mood, but then your girlfriend/wife says: "why are you in such a bad mood" and you say "I'm not in a bad mood." Then she says "fine, if you don't wanna talk about it..." then you say "I'M NOT IN A BAD MOOD!" And, Goddamit, now you ARE in a bad mood. She was so convinced that you were in a bad mood that she actually created a bad mood within you even though there wasn't one before. I think a shark can be triggered in a similar way; albeit non-verbally. Just the mere act of you thinking that this creature is vicious, bloodthirsty, something to fear tremendously, etc. can make the shark act in a way it would not have acted had you just been cool, impressed, etc. (this kinda explains how that guy on '60 minutes' could safely swim with Great Whites...he puts out the right sorts of mental vibes, the sharks pick up on them, and no sort of violent reaction is triggered in the sharks).