Most dive guidebooks speak of preventive measures to guard against encounters of the 3rd Kind (if you liked that phrase from the UFO movies) with sharks. Here is a list, from my memory.
1) Spend as little time on the surface of the ocean as possible. The overwhelming proportion of shark attacks occur at the surface.
2) Avoid swimming or diving in murky, low vis water. The shark's multiple senses of target location favor the animal over you when you cannot see through the water.
3) Avoid splashing when you are at the surface. This sound carries far underwater and seems to stimulate attention from sharks.
4) Avoid swimming at dusk or at night, when sharks predominately feed.
5) Avoid trailing a stringer of speared fish, which has the greatest potential of attracting sharks from a great distance down current.
6) Avoid locations that are teeming with pinnipeds, which attract permanent shark colonies.
7) Avoid locations that are near steep, deep underwater drop-offs.
8) Do not scuba or freedive solo. Always dive with a buddy or even better with a larger group of divers.
Then there is the list of what to do if you see a shark. Here it is, from my memory.
a) Keep the shark in your view.
b) Stay close to the bottom of the ocean.
c) Get behind rocks.
d) Wait a few moments for the shark to leave the area and stay calm, getting control of your breathing.
e) Swim back to shore or back to the anchor line of the boat slowly and calmly, keeping the shark in your view as you go.
f) Ascend the anchor line slowly and calmly, looking in all directions as you ascend.
g) Do not dart immediately to the surface.
My own experience with reef sharks in the waters of the Fiji Islands is that sharks either seem to be afraid of a large group of scuba divers and the sharks flee, or else the sharks totally ignor scuba divers altogether, especially if the sharks are resting on the bottom of the ocean.
My own experience with smaller dogfish and blue sharks in California waters is that they are curious animals that will dart around divers but will keep their distance at the same time.
The local news in California seems to report shark sightings at certain pinniped beaches like Stinson in Marin County regularly, and occasional shark attacks on surf boards all up and down the Northern and Central California coastline.
It has been over 10 years since I can remember a scuba diver being bitten by a shark in California. He saw the shark at depth, at a location that was near a steep, deep underwater drop-off, then he hurried to his anchor line and ascended it rapidly. He was diving with an underwater scooter. He was bitten on the way up the anchor line. There were harbor seal colonies nearby.
About the same time, a freediver was bit in approximately the same location as the previous diver had been, also near the same deep, steep underwater drop-off and seal colonies.
Both these individual divers were diving solo at the time.
The most gruesome shark attacks that I have read about occurred in Australia, at the Great Barrier Reef boat diving sites. I have not heard about anthing like that anywhere here in California.
In the local lore of diving author Bruce Watkins, the large GWS (sharks) that populate the Farallon Islands west of San Francisco annually migrate towards the California coast and then southward to warmer waters in a large circle that takes them on to Hawaii and then back to the Farralons.
We also know from marine biology studies that larger territorial sharks tend to drive off smaller, younger sharks, and this stage of maturing may give cause to migrations of smaller GWS seasonally as well.
GWS sightings seem to me to be equally infrequent all along the California coast.
The most recent sightings have been San Onofre (near San Clemente) and Morro Bay (near San Luis Obispo). But prior to this, a surfer's board was bitten at Davenport (near Half Moon Bay) earlier this year. Stinson Beach (in Marin County) got its share of shark alerts this year as usual. A few years ago, a lone surfer was bitten along the Sonoma Coast. Several years ago, a solo freediver was bitten at South Russian Gulch, near Jenner.
There is a pattern for California shark attacks. The pattern is irregular and infrequent. The pattern is mostly at the surface. The pattern is with mostly SOLO swimmers, surfers, or divers.
So if you dive with a buddy, just like the YMCA and Red Cross told you to always do in their version of Rule #1, and avoid long surface swims, statistically there should be no problem with sharks.
It is statistically highly unlikely that you will ever encounter a GWS. You are probably more likely to encounter aliens from outer space than a GWS. You are definitely more likely to have a traffic accident on the way to a scuba diving site than to ever see a GWS. In the early morning hours of the day, a deer is the most likely animal to hurt you, in a collision with a car, rather than is a GWS.
Having said all that, I believe that everyone who has ever been bitten by a shark has violated one of the several above-stated avoidance rules. So if you do not completely trust the statistics, then follow the rules for avoidance listed above and you should be fine.
