Exploration Mysteries: The Third Dive

A renowned environmentalist. A mysterious death. A tainted investigation. And a journalist determined to get to the bottom of it all.

In January 2017, an environmentalist famous for bringing the plight of sharks to global attention drowned. His death simultaneously shook the marine world and the Florida Keys community. The investigation was marred by coverups and intense media scrutiny. Negligence was allegedly to blame. Lawsuits followed.

But for Robert Osborne, too many questions were left unanswered. The Canadian journalist spent two years investigating the mysterious drowning.

Rob Stewart. Photo: Richard Shotwell


Stewart catapulted to fame in 2006 with the release of his debut film, Sharkwater. The documentary spent four years investigating the shark fin industry. The film won numerous awards prompted many countries to ban shark fin soup in restaurants.

Stewart had a lengthy history of diving. He first took up underwater photography, then scuba diving. His first career opportunity came when his wealthy parents purchased Canadian Wildlife magazine and gave him the role of chief photographer.

Despite his privileged upbringing and the nepotism with which he acquired his job, he was hardworking, committed, and passionate. He wanted the world to understand the beauty of the ocean and to look after it. More, he wanted humans to be accountable for the damage they were causing to a creature which the ocean relies heavily on for a healthy ecosystem: sharks.

After Sharkwater, he filmed Revolution, which covered the topic of environmental collapse. It was the highest-grossing Canadian documentary of 2013. By this point, Stewart was well-known around the world. His 2012 biography, Save The Humans, details the importance he places on sharks.

His next project was a sequel to Sharkwater. In it, he wanted to capture up-close some of the rarest species on the planet. Stewart felt that if the world could learn about sharks, they would be more interested in making positive daily choices that would have a lasting impact on the marine environment.

Stewart threw high levels of enthusiasm and energy into everything he did. For his latest film, he was eager to capture the endangered smalltooth sawfish, a member of the elasmobranch family, to which sharks belong.

Queen of Nassau lies on the ocean floor off the Florida Keys. Rob Stewart was eager to dive to the wreck so he could film an endangered shark cousin, the smalltooth sawfish.


Stewart knew that this rare species could be found around a sunken wreck called the Queen of Nassau in the Florida Keys. However, the ship, which sunk in 1926 under peculiar circumstances, lies 70m down, too deep for conventional scuba gear. He’d need a rebreather system to reach it.

Rebreathers are technical to use and require a great deal of knowledge because they involve mixing gases and recycling the gas that a diver has already expelled. Oxygen is added throughout the dive into the mixture, and the carbon dioxide is chemically removed.

This allows a diver to stay underwater longer than with scuba. Since rebreathers don’t expel bubbles, a diver also avoids disturbing marine life. Intent on filming, Stewart could use it to get close to a sawfish without scaring it away.

Stewart and his diving buddy, Brock Cahill, headed to the Florida Keys and connected with the company Add Helium, which specializes in rebreathers. Under the tutelage of Add Helium owner Peter Sotis, Stewart and Cahill underwent a rebreather training program.

They didn’t complete the required training hours, because Stewart was keen to get to the wreck as soon as possible. Sotis knew the wreck well, so Stewart enlisted his services to reach it.

On January 31, Sotis, his wife Claudia, their skipper Dave Wilkerson, his mate Bobby Steele, Cahill, and Stewart set off on Sotis’ 30-foot boat, the Pisces, to the Queen of Nassau‘s location. That day, Sotis and Stewart completed two dives to the wreck but didn’t manage to get any sawfish footage. Deciding to call it a day, he and Sotis then went on a third dive to retrieve the Pisces’  floating anchor.

After fetching the anchor, both men surfaced. Sotis immediately showed unusual behavior after being pulled on board. Stewart never made it that far: He vanished after reaching the surface and before boarding the boat.

The rebreather is a specialized piece of equipment that lets divers go deeper and not disturb marine life.


It didn’t take long for the “missing person” to make headlines. Since rebreathers are such a complex piece of equipment, it was quickly assumed that the accident occurred because of a faulty rebreather, with Sotis at fault.

Three days after Stewart disappeared, his body was found at the bottom of the ocean, right beneath where the Pisces had been positioned during the final dive.

When Osborne first read the story in the media, he immediately saw holes. The award-winning investigative Canadian journalist also happened to be a diver. So, when he was reading diving explanations that didn’t make sense, he decided to look into the incident himself.

Osborne understood that the best way to uncover what caused Stewart’s death would be to understand the Florida Keys, rebreathers, and most importantly, to speak to the people who were with Stewart the day he disappeared.

Sotis was forthcoming in Osborne’s investigation. He’d taken a lot of heat from the media and saw talking to Osborne as a chance to clear his name, or at least to share his side of the story. He invited Osborne to Add Helium to participate in a rebreather course held by his lead instructor.

After his training, Osborne sent Stewart’s dive computer and rebreather off to be tested. He wanted to rule out whether the gear itself had been faulty or his gases mixed incorrectly. On both accounts, the reports showed nothing out of the ordinary, except that Stewart and Sotis had resurfaced at more than twice the recommended speed.

Osborne was systematically eliminating every possible cause of drowning in the incident.

During his rebreather course at Add Helium, and with his previous expertise in diving, Osborne knew that the number of dives within a certain period, and the time at the surface between each dive, is crucial to the body’s ability to re-oxygenate appropriately. Basically, time and frequency affect how the body manages gas exchange.

On the day that Stewart drowned, he and Sotis had completed three dives, which is widely regarded as posing a high risk to a diver. So therein lay the question: Who suggested doing so many dives?

Stewart appeared to be the sort of character who took risks. On previous dives, he’d spotted sharks that he was so keen to film that he risked running out of oxygen in his scuba gear just to get the footage. His friends spoke of a man who “pushed the envelope” and didn’t worry about consequences. Passion and drive clearly ruled over fear. Certainly, these traits ring true when he was keen to get to the Queen of Nassau without first completing the recommended rebreather diving hours.

One small but important technical dispute is whether Sotis was enlisted as the instructor on this trip. If he was, then he should have been the last person to board the boat, and only after all his divers were already onboard. In this case, he had boarded while Stewart was still in the ocean.

Witness accounts of Sotis’s role and who led the expedition conflict, but Stewart’s character suggests that he was the kind of person who didn’t let others stop him when he had his mind fixed on something. He’d hired Sotis and the Pisces crew, but he was an experienced diver himself and possibly enlisted them for their navigational skills. The leadership of the expedition may not have been managed appropriately and whose responsibility it was to ensure that Stewart boarded remained in question.

Those on the boat recalled Sotis wanting to return to the water for the third dive to retrieve the anchor and Stewart offering to help him. One witness claims that Sotis said something about being able to go on his own but that he’d prefer it if someone came with him, which is when Stewart volunteered.

The only person who really knows who was responsible for the number and leadership of the dives has died. In this case, though, one key piece of evidence could help determine answers: Stewart and Sotis completed three identical dives which are recorded on their computers. In most dive incidents, it is rare to have identical dive computer records.

When Sotis boarded the Pisces, he was disoriented and passed out. His wife, a physician, immediately began working on his vital signs, removing his dry suit, giving him oxygen, and medically overseeing him.

When Stewart came to the surface, he gave the international diving signal of “ok” but he had the loop out of his mouth. Divers are trained never to remove the loop until on the boat. This is because water can enter, flooding the equipment and essentially turning the rebreather into a weight that pulls the diver to the bottom of the ocean. No one knows for sure why Stewart had removed the loop from his mouth.

Both Sotis and Stewart’s identical dives suggest that both divers suffered the same issue. Sotis’ disorientation was observed and offers insight into what was potentially happening to both men. However, he was on the boat while Stewart’s potentially identical dilemma transpired in the water.

Decompression Sickness (DCS) was ruled out initially in the case of Sotis because he didn’t need recompression therapy. However, once Osborne was able to effectively rule out all other possible causes, DCS remained the most likely reason that Sotis became unwell. Osborne reasoned that due to the oxygen Sotis gained quickly on the boat, he recovered without the need for therapy. Meanwhile, Stewart’s own disorientation most likely caused the loop to fall from his mouth.

It is possible that DCS in Stewart from resurfacing too quickly reduced muscular tension in his mouth so that the loop fell out. Then, as the rebreather filled with water, it pulled him to the bottom of the ocean, drowning him.

Osborne’s investigation unveiled that Sotis’ history of previous criminal behavior from more than 20 years earlier had formed a public opinion of him that led to negative speculation. In Osborne’s eyes, it wasn’t reasonable to paint a murky picture of a man from incidents that happened so long ago.

Osborne’s thorough research revealed how unique the Florida Keys diving community was. In fact, the community culture may have prevented the truth from being told.

In the Florida Keys, Osborne discovered, locals intensely stick together. They and their families have lived in the area for generations, and most of the community’s income comes from dive tourism. Locals are fiercely protective of one another, sticking together to ensure that no incriminating information circulates.

In the case of Stewart’s death, the protective behavior went as far as the sheriff who prevented the coroner from conducting his necessary inquiry. Evidence was allowed to contaminate and those who recovered Stewart’s body from the water had a conflict of interest.

While Osborne concluded that DCS was most likely the reason Stewart drowned, the Florida Keys community prevented fair and reasonable justice.