Never, ever pull a wobbegong's tail.

While this may be sound advice when dealing with any shark, the normally docile wobbegongs have the unique ability to turn around and bite their own tail. And woe betide if your fingers are attached to it.

If harassed, they are likely to respond, Macquarie University professor of marine biology Rob Harcourt, said on Friday as five young wobbegongs were released off Manly as part of a project to unlock some of the mysteries of shark behaviour.

"They do have a very strong bite," he said as the tagged sharks swam off. "So pulling the tail is a very bad idea."

Children looked on excitedly as a Macquarie University researcher waded knee deep into the water to release the copper-spotted sharks off Shelly Beach in northern Sydney.

Prof Harcourt, who is overseeing the project, says the research has two aims - to restock depleted shark numbers and monitor the adaptation of captive sharks in the wild.

"The catch rate (for wobbegongs) has halved over a 10-year period," he said. "This brought about concern in NSW about whether or not numbers have fallen."

For the survey, the wobbegongs have acoustic tags sewn into their abdominal cavities, with the ceramic devices roughly the size of a small finger emitting a unique signal.

These signals will be picked up by the Australian Acoustic Tagging and Monitoring system, which has receivers placed all over Australia.

"The system allows researchers to monitor the movements of sharks," said Prof Harcourt.

It also allows researchers to see if sharks are protected within Sydney's Cabbage Tree Bay Aquatic Reserve off Manly, where they have been released.

"If they stay in one area then it means that aquatic reserves like this one might be an effective means of protecting them," said Prof Harcourt.

The first release of 10 wobbegongs in the reserve last September provided encouraging results, Prof Harcourt said.

"Four of those sharks are still being protected here in the reserve."

He said the released sharks were showing similar behaviour to wild animals.

"One of the many problems of releasing any animal from captivity into the wild is that it has to learn hunting behaviour and hiding from predators - it might be very vulnerable and it might die."

Wobbegong is a Aboriginal word meaning "beard", referring to the shaggy growths around the sharks' mouths.

While the juvenile sharks released on Friday measured just 50cm, they can grow up to three metres in length and are generally found in shallow water feeding on a diet of squid, yellow tail, octopus and crab.

Despite the wobbegongs' tail-twisting trick, Prof Harcourt said beachgoers had little to fear about the sharks.