The last thing a group of scientists busy tagging marine animals along the coast of north Queensland expected to see was a shark regurgitate a fully intact echidna – but that is exactly what happened.

In what is believed to be a world-first, researchers from James Cook University, including former PhD student Dr Nicolas Lubitz, were tagging marine wildlife off the coast of Orpheus Island between Townsville and Lucinda in May 2022.

Until that point it was a pretty “standard day” for the group of scientists, who had already tagged hundreds of marine animals before the tiger shark they had wrangled vomited a whole, dead echidna, leaving the group “stunned”.

“My theory is the echidna was swimming from one island to another [via a narrow channel], probably looking for food or for mates, and just got unlucky and got snapped by a big tiger shark,” Lubitz said.

“I would be very surprised if that has ever been recorded before … I don’t think it’s too common that they would feed on echidnas.”

As part of his PhD, Lubitz has been tracking the movement and behaviour of large sharks around the coast, looking for connections between food availability and climate change.

He believes the shark could have digested the echidna if given the chance – spikes and all – but says it likely threw it up as a “stress response” to being wrangled and tagged.

The fact the echidna was still intact with no signs of digestion showed it was swallowed “maybe an hour or two” earlier, Lubitz said.

Tiger sharks can grow up to six metres in length and are responsible for the second largest number of recorded attacks on humans, after the great white. They have dark, vertical stripes on their sides and back, and are scavengers by nature, feeding in shallow water.

While tiger sharks are known to feast on human rubbish, the echidna seems to be a first.

Lubitz said tiger sharks had serrated teeth, and whether they would chew their prey or swallow it whole depended on its size.

“A big tiger shark would definitely just swallow an echidna whole,” he said. “They can crack a turtles shell and just cut off a slice of a turtle with their teeth.”

The researcher, who works for the Biopixel Oceans Foundation, said tiger sharks were an “opportunistic predator” that would “eat whatever they think they can overpower or whatever thing they think is nutritious”.

The sharks will visit temperate waters seasonally and are known to frequent waters in south western Western Australia, around the tropical north and down the east coast until the southern coast of New South Wales.

Last year the group caught a different tiger shark, which also regurgitated its food – some blubber and a fully intact vertebrae, meaning it had recently fed on a dugong calf.

While tiger sharks were known to hunt dugongs, they “really don’t throw up their food that often”, Lubitz said.

The echidna incident showed a connection between terrestrial and marine food webs, he said – and “we don’t really understand what the overlap” between the two is yet.