"I hope the cage is as strong as a it looks," says diver James Hay, before jumping into an aluminium frame to swim with the ocean's most feared predator, the great white shark.
Coming face-to-face with a powerful great white, which can measure up to six metres (20 feet) in length and has a reputation as a bloodthirsty man-eater, may be the stuff of nightmares for swimmers and surfers.
But for Andrew Fox, who guides shark expeditions off South Australia, it's a chance to explain why the awesome creatures don't deserve their "Jaws" reputation and are in fact under threat from overfishing.
"I think it's important to show these people that these sharks aren't the crazy man-killers that are often portrayed in a lot of the media," says Fox, who has been going out to observe the animals since he was seven.
"I think it's important that people see that these are magnificent animals."
About 300 species of shark inhabit Australia's 370,000 kilometre (229,400 mile) coastline, but only a handful are harmful to humans and attacks are very rare, says expert John West who has spent three decades studying the animals.
"We only have an average of one fatality a year and, putting that into perspective, we have about 80 drownings a year at our beaches," says West, who curates Australia's Shark Attack File.
But the public perception of great whites as killers is strong, leaving the animals as the sea's "least respected citizen", says writer Tim Winton, who has publicly campaigned for the preservation of the species.
"I think Australians in particular have a peculiar, pathological feeling about sharks. It's like mother's milk, the fear and loathing of sharks," he told national broadcaster ABC earlier this year.
"In the last few generations we've come a long way in terms of finding empathy for animals and an appreciation for nature, but the shark is still the last excuse for our barbarism."
Experts say shark populations are at risk of overfishing and this could have a major impact on delicate marine ecosystems, because removing the apex predators upsets the balance of undersea life.
The Australian Marine Conservation Society says an explosion in shark fishing means some 100 million are killed around the world each year, slashing numbers by some 90 percent.
"They can be caught on the high seas still so they will certainly be subject to fishing pressure out there, and the fins and the jaws in particular are very very valuable," says society campaigner Ben Birt.
In particular, an immense demand for shark fins, considered a delicacy in parts of Asia where they are used to make soup, is not only dramatically cutting numbers but condemning sharks to a cruel death.
The fins are often removed while the animal is still alive, before the shark is tossed back into the ocean, unable to swim.
"Can you imagine cutting the hind legs off a kangaroo and leaving it alive?" asks Winton.
Shark-finning is illegal in Australia, where great whites are a protected species, but the fish is as mysterious as it is feared. Plus little is known about the populations of other lesser known shark species.
Part of the work done by the Fox family, which runs Rodney Fox Shark Expeditions, is research. Andrew and his team use satellite tagging to track the sharks' movements.
Tagging recently revealed the epic journey of one shark from South Africa to Australia and back again - a round trip of more than 20,000 kilometres.
While some sharks are long-distance swimmers, others are so familiar to the Neptune Islands, some 70 kilometres off South Australia where they feed on a seal colony, staff have given them names such as Sylvia, Punk and Pip.
"The power of the great white shark is so great that once you see them first hand - they are so awesome - everyone goes away appreciating and admiring the sharks rather than being scared of them," says Andrew Fox.
Sharks are attracted to the cube-shaped aluminium diving cages, which measure about two metres across and can accommodate up to four divers, by big chunks of tuna thrown overboard on a line from the boat.
"It's quite a humbling and amazing feeling; I think any residual fear you might have had of sharks might just dissipate a little bit and you see them as this beautiful, big, graceful animal," says recent diver Catherine Leach.
"You don't necessarily see them as something that's going to tear you limb from limb."
Fellow diver Phil Donovan also described the four-day expedition as a learning experience.
"I didn't realise they had warmer blood than other fish, I didn't realise their eyes were blue and not a dead black that you see in documentaries; I didn't realise they travelled so far," he explains.
Businessman James Hay comes up for air, wanting more time with the sharks.
"Not scary but awesome I would say," he says, describing his first dive some 18 metres below the surface to view the animals. "And I'd love to do it again - as long as I'm in a cage!"