Great white shark numbers may be rising

Great white shark numbers could be on the rise, but there's no evidence to suggest bull shark numbers around Sydney have increased, authorities say.

The analysis comes in the wake of two shark attacks and amid speculation they could be linked to a growth in shark numbers as a result of shark fishing bans.

A navy diver and a surfer are recovering in hospital from separate shark attacks in Sydney Harbour and Bondi Beach last week. A bull shark was believed to be responsible the attack in Sydney harbour.

In the same week, shark fishermen reached their yearly limit of 60 tonnes due to new fishing quotas imposed by the state government which run until July.

NSW Primary Industries and Fisheries Minister Ian Macdonald refused to lift a ban on shark fishing quotas on Sunday, dismissing suggestions there was a link between the attacks and the government's quotas.

"Any connection between the attacks last week in Sydney Harbour (and at Bondi Beach) and the quotas for the shark catching industry in NSW is completely erroneous. It is a lie, it's false and it's mischievous and misleading," Mr Macdonald told reporters.

"The plain fact of the matter is the quotas of 60 tonnes per annum ... is set scientifically."

The NSW Fisheries chief scientist Steve Keneally said about five per cent of dangerous sharks were caught as part of the quota, but there was no evidence to show that bull shark numbers had grown.

"I think that we've probably reached a point where we'll get the odd attack every now and again, which is what we're seeing these days," Mr Keneally told reporters.

"Once every few years we might see an attack like we have seen recently, but there's no thought that we're suddenly going to get more attacks in Sydney Harbour or anywhere off our coast."

He said warmer water temperature at this time of the year was a big factor, with baitfish, tailor and kingfish attracting sharks.

"The numbers haven't gone up, but there's some small evidence to suggest that white pointer sharks are starting to increase after protection internationally of them about 10 or 12 years ago."

Mr Macdonald said the government would not review shark fishing quotas unless the science directed them to do so.

"These incidents are more related to the fact that Sydney Harbour now has much larger volumes of fish, and therefore shark, due to the ban on commercial fishing."

However, he said a review of the state's shark meshing program was underway.

Environmentalist and Clean Up Australia founder Ian Kiernan said fish numbers were increasing with the ban on fishing in Sydney Harbour.

"Sharks have always been here, you've only got to go back to the Aboriginal history of the colony," Mr Kiernan said.

"It is their territory."