Being that I'm a canyoneer, and not having had too many shark encounters in the desert lately, I spoke with Lifeguard Lt. Andy Lerum. He works for the city of San Diego and gave me some good pointers on surfing safety in shark country.
Regarding how to avoid sharks, the key is keeping your eyes open for telltale signs in the water where you are heading. The day I spoke with Lt. Lerum, he said they had a surfer report a shark sighting after he had spotted its telltale dorsal fin. Also, talk to the locals, fishermen, and lifeguards before heading out as they are tuned into what is happening on a daily basis.
Like most predators, dawn or dusk is when most sharks are on the prowl so you may reduce your chances of an encounter by hitting the surf in the afternoon.
You can increase your safety by going out in a group versus surfing solo as sharks often hunt creatures that are alone. And if you have any recent cuts or open sores, then stick to skateboarding that day as sharks can sense blood in the water from a great distance.
If you are attacked while surfing, then fight back. Lt. Lerum said that the eyes, gills, and snout are more vulnerable than other parts of the shark's body. Like most two-legged or four-legged predators, sharks are looking for an easy victim not an aggressive fighter.
As far as finding shark-free zones to surf in Californiagood luck. Talk to Pacific fishermen and they will tell you that sharks are more common in coastal waters than you'd think. Again, the key is awareness and talking to the locals to find out where the sightings have been occurring.