Divers off a Queensland beach found themselves among 70 grey nurse sharks last week, but the phenomenon was not evidence of a recovery in the population of the critically endangered fish, an expert says.

The large school was witnessed by divers at Wolf Rock at Rainbow Beach, a "standout" figure, Queensland Parks and Wildlife Service senior conservation officer Carley Kilpatrick said.

Ms Kilpatrick has been diving at the protected site since 2001 and said the last "standout" was in June 2007, when there were 40 sharks in one field of view.

There are about 2000 grey nurse sharks left along the entire east coast, Ms Kilpatrick said, and Wolf Rock was one of possibly two gestation sites for the population.

Grey nurse sharks use the site for nine to 12 months during their gestation period before the move south to pup.

"There is the potential that every mature pregnant female grey nurse shark, when it reproduces, which is every two years, is actually using Wolf Rock, which could be between 300 and 600 sharks," Ms Kilpatrick said.

"The improvement in biodiversity and biomass that has occurred over this time has really started to show in the last five years and this year is a standout compared to what I have seen there previously.

"In 2001, that is when the Queensland government first started looking at Queensland for its importance to grey nurse shark populations and it was then that Wolf Rock was identified as a critical grey nurse shark aggregation site," Ms Kilpatrick said.

"In 2003 it was protected from fishing and in 2006 diving was managed."

Ms Kilpatrick said despite the recent influx of grey nurse sharks at the site, it was not an indication that the population was increasing.

"We can't yet say the grey nurse shark population has increased, that is because we do not have baseline numbers of what they were when they were decimated and the numbers were first known to be in trouble in 2001," she said.

"We need about 10 years of data to show the population is increasing.

"Unfortunately whether it is due to ignorance or a lack of understanding of the impacts, we do still see people fishing within the Wolf Rock protected area.

"Accidental capture of pregnant females, if a hook was swallowed, it has a high chance of causing that shark to die and would have a major impact on the population's recovery."

Wolf Rock Dive co-owner and marine biologist Alex Heathcote regularly takes groups out to see pregnant grey nurse sharks at the site and said it was hard to describe seeing so many sharks in the one space.

"A lot of breeds of sharks are solitary animals," he said.

"How else do you describe it, it is a once-in-a-lifetime experience for a lot of people and we get to do it every day."

Mr Heathcote said the number of females was a "promising sign" but their slow reproductive rate meant it would take a "long time for their numbers to increase".

"They can take up to 15 years to reach sexual maturity and only breed about once every two years," he said.