A commercial shark-dive client has been missing since Sunday, July 13, when the U.S. Coast Guard received a distress call at 8 p.m. The diver, identified as John E. Petty, 63, was aboard controversial shark-dive outfitter Jim Abernethy’s yacht Shear Water.

On Saturday, Petty boarded the boat along with eight other divers and four crew in Palm Beach, Florida, for an eight-night expedition to Tiger Beach, a 20-foot-deep site about 20 miles off Grand Bahama’s West End. Their goal was to dive with a resident population of tiger sharks that hang out in the area.

For now, it’s hard to say what happened, but the most immediate possibility is that Petty got disoriented or accidentally swam into a swift current and was swept away before anybody noticed he was gone.

“It was a night dive, so getting lost is an option, as is unintentionally swimming out to the Gulf Stream and being caught in the current,” says Andy Dehart, shark adviser for the Discovery Channel and longtime Tiger Beach diver. Dehart also thinks a medical emergency, such as a heart attack, is a possibility.

In 2003, two divers off the Great Barrier Reef were left behind by a dive boat after the captain miscounted his passengers. That episode became the basis for the film Open Water, a true-life horror film chronicling the divers’ long drift to a slow death.

Though Abernethy wasn’t answering his phone on Tuesday, one of his instructors was available. “The exact location where we dive varies,” says April Mai, a boat captain and dive master for the outfitter. “It depends on currents and where the best action is.”

Typical shark-diving protocol is to keep the motor idling while tossing chum and fish blood overboard until shadows appear below. Unlike many shark-diving outfits, Abernethy’s Scuba Adventures doesn’t use cages and advertises this trip as only for divers with advanced open-water training. According to scuba certifying agency PADI, Petty received his advanced open-water certification earlier this month.

Abernethy has come under fire from the dive community in the past for promoting dangerous dives with shark species known to pose a threat to humans. Tiger sharks account for a large percentage of the relatively small number of shark attacks on people each year. Abernethy lost a diver to a shark attack in 2008 and has himself been bitten.

For now, information about Petty’s disappearance is slim. After fielding the distress call Sunday night, the Coast Guard, operating out of Miami, deployed an immediate air-and-sea search operation consisting of a cutter, a fixed-wing aircraft, and a helicopter. The only clues found so far don’t lend much hope.

“They found the mask and camera on the seafloor one nautical mile from where the incident was called in,” says Mark Barney, a spokesman for the Coast Guard.

Still, Petty Officer Jon-Paul Rios remains hopeful. “I can’t say how long we will be searching. It could be one more day, or it could be a week.”