Several people were in the water diving for lobsters, he said, because it was opening season for catching the crustaceans.
Lifeguards had been on duty due to two nearby events, and Giles said the response to the attack was "very short".
Speaking to CBS, Giles added: "We are working closely as a unified command with the California State Parks, California Fish and Game, San Diego County Sheriff's Department, City of Solana Beach and the City of Carlsbad to ensure public safety".
Three Good Samaritans rescued the boy and rushed him back to shore in a kayak, Encinitas lifeguard Capt. Larry Giles told reporters at a news briefing.
Emergency responders arrived, and the boy was flown by helicopter to the trauma center.
Kayaker Chad Hammel told how the boy cried out "I got bit".
Hammel says he heard screaming and then realised the boy was yelling, "I got bit!"
Fortnite Season 6 Brings Adorable Pets
In Shadow form, you'll also be able to run faster, jump higher, avoid fall damage and even pass through walls and ceilings. And then there's the new Shadow Stones - they are scattered throughout the map , letting you go completely invisible.
"He was conscious, he was above water, and the bystanders were able to get him up on the beach. and he was talking all the way to when he was being transported", the lifeguard said.
Hammel also said he couldn't have helped the teen without the help of his friends and the dozens of others on the beach.
'His whole clavicle was ripped open, ' Hammel continued.
Since the incident, there hasn't been any shark activity, according to Giles.
Witnesses estimated the shark was about 3.3m long, but the type was not known.
Beaches in the area were closed, and will remain so for at least 48 hours.