What is behind a battle between ocean predators off the WA coast? Photo: Discovery Channel
What creature would be able to chase down and devour a 500 kilogram great white shark on the sea floor off Western Australia?
But as filmmakers David Riggs and Leighton De Barros began to investigate what dark fate could have befallen the ten-foot monster shark earlier this year, an even bigger mystery unfolded.
Why, once a year, does a rough, remote spot off the WA coast, just half a square kilometre in size, become the epicentre for a barely believable colosseum of battling marine life?
Killer whales by the dozen. Sperm whales. Giant squid. And masses of sharks, all fighting for food and supremacy.
Their resultant documentary, The Search for the Ocean's Super Predator will screen early in November, and aims to answer the question of what colossal creature killed the shark, how and why.
But as Riggs explains, the bigger mystery to arise out of the film is what is to become of the area where it happened, a marine "hotspot" known as the Bremer Canyon.
"It started as a film about the demise of a shark, and what could have done it - but it has opened up this huge other discovery," Riggs said.
"It is a multi-species seasonal bonanza, and it happens to be on what is now recognised as a major hydrocarbon resource.
"It is mind boggling."
As the film, to be screened on the ABC on November 3 uncovers, the area off Bremer Bay in WA's South West is home to a natural phenomenon involving a leak from massive hydrocarbon pocket under the seabed, which fuses with the surrounding water to create an ice-like reef known as methane hydrate.
This in turn sparks a food chain involving crustaceans releasing billions of nutrient-rich eggs into the desolate waters.
And that food source brings with it the ocean's big boys.
"On one particular day, over a four nautical mile period, we saw in excess of 100 killer whales - it was ridiculous," Riggs says.
"That is a lot of mouths to feed, so what the hell are they doing?"
To try to work that out, Riggs reached out to oil and gas company Arcadia Petroleum, which holds tenements that cover nearly 19,000 square kilometres in the area.
And the company was happy to hand over its survey findings.
"They supplied me with all their observations, and the observations correlated exactly with what I had observed over the last eight years. They referred to it as the 'hotspot'," Riggs revealed.
"So it definitely seems there is a link between these pressurised deep sea systems leaking, creating methane hydrate reef systems which creatures like."
That link was explored during a filming expedition involving a massive catamaran travelling 60 kilometre offshore, where footage was taken from inside an underwater canyon 4500 metres deep using camera gear requiring a cable spool weighing 3000 kilogram.
On board were marine ecologist Michelle Blewitt, great white expert Rachel Robbins, and Mark Norman, an expert on the hunting behaviour of the giant squid from the Melbourne Museum.
The footage that was beamed back left them all agog, despite their experience.
"You won't speak to anyone on that boat that was not flabbergasted by the intensity of life out there," Riggs said.
And having solved the original mystery of who killed the shark by the end of the film, Riggs and his collaborators are left with a bigger question.
What is to happen to the amazing summer phenomenon off WA's south-western coastline, given the uncertain future of the resources that lie below the seabed?
"It is effectively a balloon of hydrocarbon underneath the sea floor which is pressurised, and it is leaking. So what happens when you put a hole in that with an oil rig and depressurise it?" Riggs asked.
"Is that going to cause this [sea life phenomena] not to happen? And if that is the case is that something worth taking notice of?
"I would love in 20 years for my kids to be able to go and look at this spot. That is what this is all about."
* The Search for the Ocean's Super Predator will screen on ABC 1 at 7.30pm on November 3.