Several people were in the water diving for lobsters, he said, because it was opening season for catching the crustaceans.
"When the bystanders got there, he was conscious, he was above water... and he was talking all the way while he was being transported", Giles said.
Giles says the rescuers were an off-duty police officer, an off-duty and a third person who were also lobster diving.
Encinitas is about 25 miles north of San Diego.
A witness who knew the victim told Fox 5 that the youngster was on a lobster diving trip.
The 13-year-old endured traumatic injuries to his upper torso and was airlifted to Rady Children's Hospital. Three good Samaritans heard the boy's cries and assisted in bringing him ashore using a kayak, Giles said. He said he heard the boy screaming and then realized he had been bitten. Help, help, ' " Hammel said.
As the group paddled to shore, Hammel turned around to a terrifying sight: "Once we threw him up on the kayak and started heading in, that's when I looked back, and the shark was behind the kayak".
"Once we get him on the kayak, we could really see what happened, and his whole clavicle is ripped open".
A boy, 13, was diving for lobsters when he was attacked by a shark off the southern Californian coast.
Officials have closed off the beach for 48 hours and cancelled a surfing competition after the attack.
The boy underwent surgery but no other information about him, including his name, was released.
Since the incident, there hasn't been any shark activity, according to Giles.
The victim was attacked in about 9 feet of water and was approximately 150 yards offshore, Giles said.