TORONTO — The parents of award-winning Canadian filmmaker Rob Stewart, an environmental activist campaigning to protect sharks, said on Thursday they hoped his experience in the water could help him survive after he disappeared off the Florida coast this week.

Stewart, 37, went missing on Tuesday after a deepwater dive to retrieve an anchor. His dive partner collapsed after returning to the boat, while Stewart, who signaled he was OK when he surfaced, later disappeared, his parents said.

"If anybody can survive in the water, it is him," Brian Stewart, his father said in a telephone interview, adding his son was "super fit" and a highly skilled scuba diver.

"A bunch of the people in the boat gave their attention to the guy who collapsed and a minute later they turned, and Rob was gone. They haven’t seen him since," he said.

At the time of the incident, Stewart was filming a documentary called Sharkwater: Extinction, which he was aiming to show at the Toronto International Film Festival later this year, his parents said.

The US Navy, US Customs and Border Protection, Florida wildlife officials, a county sheriff’s office and civilian volunteers have joined the Coast Guard in the search for Stewart, using ships, helicopters, airplanes, dive teams and sonar equipment, the Coast Guard said.

"We would not still be searching for him if we could not find him alive," said Petty Officer Eric Woodall, a Coast Guard spokesman.

Aerial and sea-based searches are planned for Friday if he is still missing.

His mother, Sandy Stewart, said support was pouring in from all over the world.

Rob Stewart’s 2006 documentary "Sharkwater" was aimed at exposing the shark hunting industry that was feeding demand for fins, a delicacy in Chinese cuisine.

The hunting has ravaged shark populations and the film was part of a campaign that helped persuade some governments to crack down on finning.

With finning, typically the fins are cut off and the live shark is tossed back into the sea. Unable to swim properly, the shark suffocates or is killed by predators.

Stewart said his new film was looking at other ways that as many as 80 million sharks were being harvested each year for items ranging from cosmetics to pet food.

"Sharks are sophisticated, intelligent and often shy creatures that aren’t interested in eating humans," he said in a video seeking funding for his new movie. — REUTERS