Mr Irwin, 44, was killed last week when his heart was pierced by a stingray barb while he was snorkelling off Port Douglas.
Since his death authorities say as many as 10 stingrays have been found dead on Queensland beaches.
Two stingrays were found today at Deception Bay, north of Brisbane, with their tails cut off, while up to eight stingrays were found in similar circumstances yesterday on Dundowran Beach, near Hervey Bay.
Department of Primary Industries and Fisheries (DPIF) biologist Wayne Sumpton examined the stingrays at Deception Bay and said it was not known how they were caught and whether the two incidents were connected to the death of Mr Irwin.
But Wildlife Warrior executive director Michael Hornby, a friend of Mr Irwin, said the killings could be in retaliation to his death – behaviour which flew in the face of everything the Crocodile Hunter believed in.
“We just want to make it very clear that we will not accept and not stand for anyone who's taken a form of retribution. That's the last thing Steve would want,” he said.
“Stingrays are beautiful creatures and play an important role for the environment.
“I hope everyone understands we have to protect wildlife now more than ever. This is what Steve was all about.”
Dr Sumpton said there had been reports of similar incidents in the past after fishermen had inadvertently caught stingrays and cut off the tails so they were not stung.
But such incidents were not common, he said.
“We don't condone the practice,” he said.
Instead, fishers should simply cut their line and allow the ray to swim away, he said.
DPIF general manager of animal welfare Rick Symons said staff were still investigating and offenders could be prosecuted under the Queensland Animal Care and Protection Act if evidence of cruelty was found.
The public are encouraged to report any further finds to the department, Dr Symons said.