BOSTON -- The man bitten by a shark off Cape Cod this month said on Tuesday that he escaped by punching the powerful predator in the gills after it clamped down on his leg.

In his first interview since the Aug. 15 attack , William Lytton said he'd been swimming in about "8 to 10 feet" (2.4 to 3 metres) of water just a few yards from shore when he felt an incredible pain shoot through his left leg and quickly realized he was being attacked by a shark.

The 61-year-old neurologist from Scarsdale, New York, said he gave the animal a strong smack in the gills with his left hand, a move that likely saved his life but also resulted in some torn tendons. He now sports an arm cast as well as bandages and a brace around most of his left leg.

"I initially was terrified, but, really, there was no time to think," he said, recounting the ordeal following a physical therapy session at Spaulding Rehabilitation Hospital in Boston, where he's been since Sunday. "It doesn't feel like I did anything heroic. A lot of this was luck."

Lytton said he must have recalled from nature documentaries that the gills were one of the most vulnerable parts of the shark.

After the animal broke its grip, he took a few quick stokes back to shore, where he shouted for help. Lytton said he doesn't recall being too far out in the water, but police have said he was about 30 yards (27 metres) off Long Nook Beach in Truro, Massachusetts.

Beachgoers -- including off-duty nurses and other medical professionals -- helped stem the bleeding and carried him up the dunes to the beach parking lot as he started to lose consciousness from the blood loss, he recalled. Someone also alerted his wife, who had been on the beach with their two young daughters and family friends.

"The pain was really excruciating," Lytton said. "I remember the helicopter landing and then nothing for the next two days."

Lytton was airlifted to Tufts Medical Center in Boston where he said he was placed into a two-day coma, underwent six surgeries and had nearly 12 pints (6 litres) of blood pumped into him.

The professor at SUNY Downstate Medical Center in Brooklyn said he's grateful to be alive, but knows he has weeks more of rehab -- and at least one more surgery -- before he's back on his feet.

The shark, fortunately, missed critical nerves and veins and didn't leave major bone damage, though pieces of shark teeth were cleaned out of his wounds and his bandages cover "hundreds" of sutures used to stitch back together muscles and skin, Lytton said.

"It looks very artistic," he said diplomatically of his battle wounds.

Lytton was transferred on Sunday to Spaulding, a rehabilitation hospital where many of the most severely injured survivors of the 2013 Boston Marathon bombing were treated. He is expected to be there around two weeks before eventually returning to New York for possibly more rehab.

Lytton said he isn't in any rush to wade back into the ocean waters off Cape Cod, where he spends nearly every summer doing research. Truro was the site of the state's last shark attack in 2012; Massachusetts' last fatal attack was in 1936.

"It's kind of terrifying thinking about it," he said of ocean swimming. "I know it's not the best thing to say, but I didn't like sharks before, and like them even less now."

Lytton's wife, June, said she hopes the attack is a warning for others visiting Cape Cod -- particularly as the busy Labor Day weekend approaches -- to take shark safety seriously.

Shark sightings have continued to close Cape Cod beaches this week; one was even captured on video mere feet from shore.

"It's still not real to me," June Lytton said Tuesday standing at her husband's side. "It happened so close to shore. I never thought that could happen."

Lytton admits he didn't get a good look at the shark that bit him, but the "prime suspect" is likely a great white shark, said Greg Skomal, a shark expert with the state's Division of Marine Fisheries who hopes to examine Lytton's injuries soon.

"The most abundant type of sharks out where he was attacked are great whites," he said Wednesday. "Quite honestly, there are not a lot of options."