Bonito usually show up when water temperatures rise above 70 degrees, they migrate up from Mexico. Buy a copy of Western Outdoor News, a So. Cal. fishing and hunting newspaper, then read the saltwater section, you will see where the bonito are being caught. Either take your boat there or wait until they come to your area.
Say they have been caught in your area, launch your boat and get yourself a scoop of live bait. Now go looking for birds, if you cannot find any birdpiles look for an area where birds are sitting on the water, the more birds the better. Birds don’t just hang out for no apparent reason, if they are there in numbers, there is food nearby and soon predatory fish will chase them to the roof ( surface )
If the water is less than 100 ft deep, you can drop live bait down to the bottom where you may catch halibut or sand bass, or, you may just want to cast 2 oz. chrome crocodile spoon made by Lur Jensen. This spoon will catch almost all of So. Cal’s game fish including all the tuna. If the tuna are the larger grade you may want to upgrade to a 4 or 5 oz spoon.
When I am prospecting for bonito, I usually cast the “croc” out as far as I can towards where the birds are sitting, then with the reel in gear I let it sink on a tight line till it hits the bottom. Sometimes you get hit on the sink sometimes when you are reeling in the lure, in any case as soon as someone gets a fish a hand full of chunks and a few live bait should be thrown in the water behind the boat.
If the fish is a bonito his friends are usually right behind him, as soon as you see it is a bonito, throw a hand full of live chum behind the boat. If his friends are near they will usually start crashing the chum, grab your fly rod and cast a fly to the crashing fish, usually the hookup is instant. I keep throwing 5 or 6 chums per minute until the school leaves or stops crashing the chum. Then I start casting the crocs again until I get a hookup or 20 minutes goes by, then I start looking for a new group of birds. And start the whole process again.