Navigating unsurveyed waters led to an amazing discovery
An indigo circle stains the otherwise clear, turquoise waters, with the horizon line melting into the swirling blue hues of the Coral Sea.
These blots of deep blue are dotted at various locations around Cockatoo reef, south east of the Whitsunday Coast.
Daydream Island Living Reef manager and marine biologist Johnny Gaskell said it was one of about seven he had spotted.
From above, the contrasting hues are striking and below the surface, a whole other world exist. Mr Gaskell said swimming inside these holes, the water was perfectly still, which was unusual in a marine environment.
"It's very rare to get into any marine environment that doesn't move at all. It's like everything has frozen,” he said.
Mr Gaskell said since his last expedition to a blue hole about a year ago, he had spotted six more of the deep blue blots on google maps.
His latest quest included the exploration of five more holes - the first time two of the voids were explored was by scientists in the 70s.
Cockatoo reef is part of the remote Pompey Complex, about 250 km south east off the Whitsunday Coast.
Mr Gaskell said the currents out in the hard-line reefs were 'formidable' as huge tides roared through the reef channels - most of the area is uncharted, and he spent nearly 14 hours navigating through reef fringed avenues.
"The navigation charts don't have any detail and most of the reefs don't even have names, they just have reference numbers,” he said.
Once again, google maps were his guide, and the expedition could only be undertaken during a neap tide - a tide just after the first or third quarters of the moon when there is least difference between high and low water.
His favourite hole was teeming with sharks. Mr Gaskell described the moment the boat crossed into the lagoon, about 10 sharks came up to the boat before swimming away again.
Once underneath the surface Mr Gaskell said there were about 30-40 sharks swimming around the lagoon, as well as turtles - "You can't really beat that,” he said.
"We think the sharks use the hole as a haven during the day when the sunlight is out, and are likely to leave the hole at dawn and dusk to hunt.”
Interestingly, the hole that is home to the sharks had the least coral cover, and Mr Gaskell said he wasn't sure why that was.
One hole was 78 metres deep, and Mr Gaskell describes the depths within as "fascinating”.
The furthest south of the five holes he explored, inside the hole is bright fan-like coral known as 'gorgonian coral' - each gorgonian is actually a colony of thousands of tiny coral polyps.
"The important thing we've learnt is we've found 100 per cent coral cover and at multiple locations; these reefs down there are regarded as the key source reefs of the Great Barrier Reef,” he said.
Mr Gaskell explained because of the location, these corals are among the most important for repopulating the reef during spawning, as the position of the corals has the spawn in the best location to travel to other parts of the reef.
"Not knowing what you're going to find is what drives these trips - the randomly picking sports on google maps and then just going there to get in, with no preconceived idea of what you're going to find when you jump in.”
"That's about as exciting as exploration can be.”
Since Cyclone Debbie ravaged the reef almost three years ago, Mr Gaskell has spent hours poring over maps, trying to find coral colonies that managed to escape the wrath of the cyclone.
"For most people, viewing a blue hole from the sky, seeing a perfect blue circle - it's just an amazing sight.
"It's such an obscure thing to see in nature, it's so unusual that a perfect circle can form like that.”