The slaying came as mauled Tasmanian tourist Justine Barwick's husband said she was awake, improving and communicating through smiles and a thumbs-up to family.

It is unlikely experts will ever be able to confirm whether any of the killed sharks were responsible for biting and critically injuring the 46-year-old or Melbourne girl Hannah Papps, 12, within 24 hours of each other.

Three tiger sharks, one 3.3 metres long, another 2.2 metres and the third 2.6 metres long, were caught in drum lines and killed by officers from the shark control program on Saturday.

The fourth shark carcass would be taken further out to sea for disposal, a Fisheries Queensland spokesman said late Sunday afternoon.

The 3.7-metre long shark "would pose a serious threat to people swimming in the Cid Harbour waters", the spokesman said, confirming three drum lines would remain in place throughout the week.

"The intention is to remove large dangerous sharks from the area and reduce the risk to people," he said.

"Clearly there are a significant number of active sharks in local waters and people are urged not to swim."

The third shark was not shot like the previous two, but killed in a "quick and humane" procedure involving a spike being inserted through the animal's brain, the spokesman said.

The first three sharks' stomach contents were examined, as per normal procedure, but the spokesman said it was unlikely fisheries officers would find evidence to confirm whether any of those sharks were responsible for biting the tourists.

The spokesman said it was believed the two shark encounters were "test bites" and it was unlikely the sharks responsible would have ingested much, if any, any human flesh.

He also said sharks regurgitated much of what they ate and agreed the chances of finding definitive evidence within any of the sharks were "remote".

"The point of what we're doing is to remove big and dangerous shark from the immediate area, and reduce the level of risk," the Fisheries spokesman said.

"The fact we got three sharks in the drum lines in a day shows the level of shark activity in the area."

The rollout of the baited drum lines and shooting of sharks was announced in response to the two near-fatal attacks on Wednesday and Thursday afternoon in Cid Habour.

Melbourne schoolgirl Hannah Papps remained in a critical but stable condition in the Lady Cilento Children's Hospital on Sunday after being given life-saving first aid on a boat.

Tasmanian tourist Justine Barwick remained in a stable condition in the ICU at the Royal Brisbane and Women's Hospital on Sunday after being mauled in the 24 hours prior to Hannah's attack.

Ms Barwick's husband, Craig, issued a statement on Sunday afternoon saying his wife was off ventilation after her marathon intensive surgery to repair nerves, ligaments, muscles and skin on her leg.

"This morning Justine is conscious and no longer being ventilated, she is communicating using thumbs up, nodding and best of all smiling," he said.

Mr Barwick earlier said the surgeons had done "an amazing job" and praised Queensland Health and the intensive care unit at the Royal Brisbane and Women's Hospital.

Ms Barwick's daughter Sarah has stayed in Hobart and was waiting for her mother's condition to improve before flying to Brisbane to be with her.

“Kate and I are relieved to hear the improvement in Mum’s condition and I am looking forward to seeing her," Sarah said.

Mr Barwick said it was believed Ms Barwick would stay in Brisbane for two or three weeks recovery after her future move out of intensive care, then return to Tasmania for more rehabilitation.

Catching two sharks on the one line was "unusual", according to the department, which said the hooks would remain in place over the next week and reviewed regularly.

"The use of drum lines removes large dangerous sharks from a specific area and reduces the risk to people," the department said.

The Fisheries Queensland advice to swimmers was to go into the water in patrolled areas, never swim alone and not to swim near schools of fish.

The department also advised against swimming in murky water and to never swim after dusk, at night or before dawn.

Bond University associate professor of environmental science Dr Daryl McPhee said there was "no easy solution" to these situations.

"I reviewed all of the shark deterrents for New South Wales a couple of years ago," he said.

"There was no easy solution, no off-the-shelf solution for all situations."

Dr McPhee said two shark attacks in 24 hours was unusual but not unheard of, and did not believe the same shark was responsible for both attacks.

"Most sharks eat a range of prey. They don’t get a taste for humans or anything like that," he said.

- with Luke Sayer and AAP