Terry Peake, who established the Shark Research Institute of Australia, said the number of reported close calls was increasing and it was ''only a matter of time'' before there were more attacks.

The news comes after reports of three shark attacks around Australia in the past two days.

But marine biologist Rachel Robbins, from the Fox Shark Research Foundation in South Australia, said the attacks were ''freak coincidences'' and there was no scientific evidence to suggest shark populations were increasing. ''We take counts every year. With the sharks that we see, we're not seeing any increase,'' Dr Robbins said.

''There's certainly no way that shark numbers will have suddenly increased since last year.''

Dr Robbins said sharks, particularly white pointer sharks, were slow to reproduce.

Sharks generally reproduced once every two years, they had to be 10 to 15 years old to reproduce, and they had small litter sizes.

She said it was vital to protect sharks.

''They're a keystone predator. If you remove a keystone predator, it's going to have a cascading effect on the whole ecosystem,'' she said.

Tasmania's Hannah Mighall, 13, is recovering in hospital after an estimated 5m great white latched on to her leg in the state's north-east on Sunday. She made it to shore with the help of her 33-year-old cousin after fighting off the shark. On the same day, a suspected bull shark ripped a 40cm tear in a 31-year-old male surfer's thigh on NSW's North Coast.

Yesterday morning, a man in his 20s was also bitten on the leg in Lake Illawarra, south of Wollongong.

Mr Peake said he believed shark populations had increased because of protection laws.

''[Attacks] will increase,'' he said.

Meanwhile, the Australian Shark Attack File, a shark attack database managed at Taronga Zoo in Sydney, contains records of 717 shark attacks on humans over 216 years - 193 were fatal.

File curator John West said sharks killed just one or two people a year in Australia and there were no signs this would increase.