I'm not afraid of sharks I've been diving as long as I can remember and have ran into Mako's, Tigers and a small Great White. Theres a couple places you WON'T catch me in the water San Francisco Bay and Cape Town I have been to the Great Barrier and really wasn't aware of the danger until the guide spelled it out for me afterwards.

http://www.theglobeandmail.com/servlet/story/RTGAM.20041115.wshark1115/BNStory/Front/

Well I don't share your comfort level. I've had occasion to see them do some really unpredictable things and once they get into that crazed "I'm eatin" state nothing is safe. Twice in the Gulf of Mexico while doing salvage of structures that had burnt, we had huge numbers (hundreds) of sharks show up. It was if they were schooling and were drawn by the concussion of the explosives we were using. These are the typical Gulf shark - we called them Brown Sharks - they're in the Mako family, but I don't know what they're really called- the thing is there were so many. Continental Divers was working a couple of miles away and shut down because of all the sharks in the water so they were dispersed over a large area. I think this is the first time we started talking about having a union or something.
Nobody was attached, but all of the air hoses (these are made up from hydraulic hose) had leaks. Not that they actually bit the hoses (I think) but they never really close their mouths and the hose probably just got caught as they swam around. They did totally break a Chicago Pneumatic hose (21/2" 2 ply reinforced red rubber) we were using to run an airlift. That wasn't real encouraging.
Another time one morning as we ran down a buoy line we came upon a Hammerhead that was circling and biting at an orange Styrofoam buoy. When he heard the boat he darted away, but he was worked up and just couldn't control his urge. Came back and totally attached that buoy. Then as we got really close he left - but where'd he go? A few sighs and looks of "why do we do this s**t?" - good money! - hit the water and went to work.
I shoot Rattlesnakes.

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"The object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane."
Marcus Aurelius

The rule of thumb . . . where there are seals or sea lions, there's usually large predator sharks or killer whales. Then, add to the mix, humans wearing wet suits that make them look like . . . Although some of us wearing speedos would be quite repellant!

My guess would be because of the shark attacks we get in the area from time to time. (not meant to be sarcastic; it's really an issue) Besides, Bay water is coooooooold You can get hypothermia in June if you're not careful. One last thing...the Chinese freighters that frequent the Bay don't bother with pumping their sewage into treatment tanks before pumping it overboard. My old Scout boat is docked right next to a pier that Asian scrap-metal ships frequent...and you don't want to know what I've seen in the surrounding water when there's a ship in-port...