California's spiny lobster season opened at 6 a.m. Saturday.
A witness who knew the victim told Fox 5 that the youngster was on a diving trip.
Mr Hammel and his companions brought the boy ashore, where they applied pressure to his injuries and beachgoers called for an ambulance. "He's in a panic and flops on my kayak and his whole clavicle and back is exposed, blood coming out filling up the kayak", explained Hammel.
"I tell him he's going to be fine, keep breathing, he stops screaming and it'll be okay. I yelled at everyone to get out of the water: 'There's a shark in the water!'"
"Sure enough I look back and the shark is following", said Hammel. "He didn't want to give up yet".More news: Zidane's surprising phone call to Man United coach Mourinho
Witnesses estimated the shark was about 11 feet (3.3 meters) long, but Giles says the species hasn't been determined.
Tim Fairbanks, director of pediatric surgery shared that at the family's request they won't be detailing what treatments were required.
The beach area from La Costa Avenue to Swami's Beach in Encinitas is closed for the next 48 hours. They plan to monitor the area for sharks via boat, helicopter and drones.
Another lifeguard, sheriff's deputies and paramedics rushed to the scene and the teen was quickly airlifted to the Rady Children's Hospital in San Diego, Capt. Larry Giles of Encinitas' Marine Safety Department said at a press conference.
Still, a number of attacks have occurred along the California coast over the years.More news: Some iPhone XS, iPhone XS Max users reporting charging issues
The victim was diving for lobsters with friends at the time of the attack. The man was several yards offshore at Pebble Beach when he was bitten in his right thigh. The 13-year-old male skin diver was pulled from the water by three people nearby who saw he was in trouble.
According to the LA Times, the boy, whose photo has been released without his name by family, was in the chilly Pacific off the coast of Encinitas outside San Diego when the unlikely attack occurred. The shark ripped muscle and flesh from her leg and briefly dragged the woman under the water.
The most recent fatal shark attack in the area was in 2008 when a swimmer was killed at Solana Beach.
Union-Tribune staff writers Greg Moran and Pauline Repard contributed to this report.More news: Sen. Lindsey Graham got really, really mad at the Kavanaugh hearing