"I already saw the fin, and I knew it wasn't a porpoise," he told KHOU-TV. "I turn around to get out of there and that's when he grabbed me by the leg. And, I guess the only way to explain it would be like sandpaper, is what it felt like; just grabbed on, like gritty."
Bleeding heavily, Shelton managed to get away from the shark and back to shore where a friend flagged down a passing deputy.
The shark had bitten through Shelton's thigh to the muscle above his right knee, injuring a tendon in his leg during the attack, KHOU reported.
Shelton is now receiving treatment for the flesh-eating bacteria, which can lead to amputations and even death.
He has set up a GoFundMe page to help pay for his medical expenses.