The James Cook University research team had seen some sights tagging marine life off the Queensland coast, especially from tiger sharks.
They are known to eat anything - seabirds, tyres, license plates and even small TV screens.
"They're just a scavenger. I've seen videos of them eating a rock for no reason," marine biologist Nicolas Lubitz said.
Yet Dr Lubitz's JCU team was still stunned by what a three-metre tiger shark regurgitated as they wrangled it near Orpheus Island off the north Queensland coast.
"It was a fully intact echidna with all its spines and its legs," said Dr Lubitz, describing it as a "world-first discovery".
"It was a decent-sized tiger shark, but it wasn't massive. It's very rare that they throw up their food but sometimes when they get stressed they can.
"In this case, I think the echidna must have just felt a bit funny in its throat."
Tiger sharks are known to eat almost anything, even rocks. (Epa/AAP PHOTOS)
It quickly turned what had been a standard day of tagging marine life on its head.
"We were quite shocked at what we saw. We really didn't know what was going on," Dr Lubitz said.
"When it spat it out, I looked at it and remarked 'what the hell is that?'."
Dr Lubitz believed the unlucky echidna may have been snapped up attempting to swim from one island to another looking for food or a mate.
The echidna was still whole when it was regurgitated, suggesting it was a recent kill.
The tiger shark quickly recovered after clearing its throat and was fitted with an acoustic tracker before being released unharmed.
The May 2022 incident occurred during a four-year, state-wide, multi-agency research effort that is set to release its data.
The project has uncovered new information about the migration habits of shovelnose rays. (Supplied/AAP PHOTOS)
The project has to date tagged more than 800 marine animals with 10-year trackers from the Gold Coast up to the Torres Strait.
Researchers will be able to analyse migratory patterns of various species when full data downloads are made available later this year.
It has already revealed new information.
"We've picked up movements of species like shovelnose rays travelling from Townsville to the Sunshine Coast which people never thought were migratory at all," Dr Lubitz said.
But it seems few discoveries will match the surprise of the echidna incident - although another ill tiger shark came close during their research.
"It threw up a big piece of blubber and then a full vertebral column. I think it was a dugong calf it had a go at," Dr Lubitz said.
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