SCUBA diver Sue Newson is keeping a close eye on 13 Port Jackson shark eggs in Jervis Bay.
Thousands of them hatch every year but it is rare to see it happen.
She predicts they will hatch in the next couple of weeks.
“I’ve been watching this batch of eggs since March. Three hatched on Sunday and I expect the rest will hatch soon.
“Once they hatch they will head for a nursery area in the middle of the bay.”
Ms Newson, who owns a dive school, has been recording shark and shark egg numbers in Jervis Bay for 12 years.
Her observations are forming part of a theory that adult Port Jackson sharks enter Jervis Bay to lay eggs depending on water temperature and moon phases.
“Long-term data is what’s missing on these sharks, so I think having someone in the water on a regular basis is important,” she said.
“Now I know what’s normal out there and I now know when changes are happening.”
The corkscrew shape of the eggs allows them to become lodged in cracks in the rocks where they remain for the nine-month gestation period.
Ms Newson has seen Port Jackson sharks lay their eggs.
“The adult circles around a spot getting ready. Then it lays the egg and then it rests for about 30 minutes before leaving.”
Other sharks are known to prey on helpless baby sharks growing inside the eggs.
In the past Ms Newson has watched a shark unscrew one of the eggs from a crevice.
“I saw this shark, head down turning its body around to get the egg out,” she said.
Her years of data have been analysed by Macquarie University PhD student Nathan Bass.
Mr Bass is writing a thesis on Port Jackson aggregations in Jervis Bay.
He chose Jervis Bay because of the high number of sharks.
“They form aggregations along the coast but Jervis Bay seems to be the place,” he said.
“This is my third year working with them and we basically look at who hangs out with who.
“We tag them with a bunch of equipment and we’ve found they have their own group of friends, and the same ones come back to Jervis Bay and the same spot in the bay.”
Mr Bass said the diversity in the bay was incredible.
“There are so many species of sharks, rays and fish in the bay, it’s crazy.
“Sue’s very passionate about the sharks.
“One of my colleagues took that information and analysed it with water temperatures and moon phases.
“It seems their movement into the bay is related to water temperature and the moon phase.
“If we can prove it is linked to temperature and if the water stays warm for too long it’s going to shorten their breeding season.”
Mr Bass said in terms of the hatching, there were massive numbers of sharks that hatch each year.
However he said about 95 per cent of the eggs get eaten and of those sharks that hatch about 85 per cent of them are eaten.
“They still occur in massive numbers, we can see 200 sharks on a dive in the middle of the season,” he said.