Girl's battle to stay alive at sea, treading water for hours off Auckland
An 8-year-old girl surviving in Manukau Harbour by treading water for hours is an "amazing" feat, a water safety expert said.
WaterSafe Auckland chief executive Jonathon Webber said anyone treading water in the harbour would have become quickly exhausted.
Auckland police said the girl and her still-missing 52-year-old father were reported missing from their 3.6 metre fishing dinghy on Wednesday afternoon.
"It's still an amazing feat for someone her age, especially if she wasn't wearing a lifejacket, but even if she was wearing a lifejacket, just floating for that period of time would have taken a great amount of energy," Webber said.
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Floating in seawater "the issue with smaller people is they have a bigger surface to mass ratio (more skin exposure) and a higher metabolic rate, their energy levels are depleted a lot sooner," Webber said.
Coastguard spokeswoman Georgie Smith said the girl treaded water for more than two hours on Wednesday afternoon.
By then winds had picked up to more than 25kmh.
Police told RNZ searchers heard the "cold, exhausted and slightly confused" girl's voice in the dark around 7pm and pulled her aboard.
The girl told rescuers she had became separated from her father about an hour earlier.
A rescue hovercraft from Auckland Airport whisked the "otherwise unharmed" girl ashore where she was taken to Middlemore Hospital by ambulance.
Despite Manukau Harbour's water temperature being around a relatively mild 20 degrees Celsius, stopping hypothermia remained a race against time, Webber said.
As a benchmark, Canadian research conducted in colder 6C waters still provided a useful guideline for how people afloat were affected.
"One of the rules used is the 1-10-1 rule, it's the starting point to understanding exposure.
"Basically, when you unexpectedly fall into the water most people hyperventilate and can swallow water, it's called the 'cold-shock response', it's the riskiest phase because you can't control hyperventilation - that's basically a minute.
"Then they talk about the next 10 minute phase of useful muscle function where you can do things like operate flare guns, blow whistles, put on lifejackets, after that your muscles start to cool.
"After that is the 1 hour [in which] the coldest water in the world will render you unconscious."
At this point wearing a lifejacket becomes essential for survival as it can hold an unconscious person's head above water, Webber said.
Although not an expert on the harbour's "massive" tidal movements, actually finding people adrift on the Manukau could take some time, he said.
The pair's dinghy was found adrift in the Papakura Channel, a Coastguard spokeswoman said.
Fortunately search and rescue authorities now have location-tailored drift prediction software that can help point rescuers in the right direction.
On Thursday morning the police launch Deodar and Eagle helicopter joined the resumed Coast Guard search for the still missing man.