Fraser Island may be known for its dazzling Australian wildlife, but a chance encounter between a boatie and a whale shark has experts questioning where the giant fish came from.

Key points: A farmer out boating on Saturday night had a close encounter with a whale shark

A farmer out boating on Saturday night had a close encounter with a whale shark They were moored off Fraser Island when the estimated 8-metre long fish bumped the boat

They were moored off Fraser Island when the estimated 8-metre long fish bumped the boat Researchers are trying to find out why whale sharks are appearing on the east coast more frequently

Bundaberg farmer Danny Gapp had anchored his boat near Rooney Point, on the northern end of Fraser Island, on Saturday night when he spotted something swimming in the water.

He estimated the fish to be about a metre wide and up to eight metres long, and at one point he said it struck the bottom of his 18-metre boat.

"There were a couple of other boats there and we had our underwater lights on, because we like to look at the fish," he said.

"I saw this big shadow come up under the duckboard and it was trying to eat the little bait fish under the lights."

It was then that the boaties realised they were looking at a whale shark.

Whale sharks are being sighted more frequently on the east coast of Australia with researchers trying to ascertain why. ( Supplied: Leith Holtzman (file photo) )

"It disappeared and came back, and disappeared and came back, and then it bumped the back of the boat on the corner," Mr Gapp said.

"It must have bumped into us by accident. It touched the corner of the boat and made it rock, as if it was a small wave or something."

Mr Gapp said he did not realise theirs was a rare encounter until they came home and shared their photos with friends.

"It was pretty amazing, and we didn't at the time realise — otherwise we probably would have taken more photos," he said.

East coast sightings on the rise

University of Queensland researcher and whale shark expert, Brad Norman, said the gentle giants usually frequented the Ningaloo Reef off the coast of Western Australia.

"Whale sharks have been returning to that part of the world for many years now," he said.

Dr Norman said while the sighting off Fraser Island was unusual, whale sharks were becoming more frequently sighted on the east coast.

"It's really unusual [but] we're starting to receive reports of sightings on the east coast," he said.

"Particularly off Queensland, there have been a number of sightings each year.

The whale shark 'accidentally' bumped into Mr Gapp's boat near Fraser Island. ( Supplied: Judy Green )

"There were whale sharks up at Raine Island and further north of Cairns [and] now they might be coming down the coast."

Research has commenced to try to understand what might be attracting the world's largest fish species to the east coast of Australia.

"In December 2019 we started a research program on the whale sharks on the Great Barrier Reef," Dr Norman said.

"It was very much a pilot study, but we found a number of the sharks [and] we're planning on extending that program this year."

Finding food on the Great Barrier Reef

Dr Norman said whale sharks were in a constant search of food and that could be the reason for their migration.

"It's a little too early to say why numbers are starting to be seen over here more than they previously were," he said.

"They're coming up near the coastal shelf where there's greater concentration of prey, whether that's the top of the Great Barrier Reef, right down to Fraser Island... the food moves."

People are being encouraged to report any sightings of whale sharks to help understand the migratory nature of the species.

"They are an endangered species and it's really important to start documenting these interesting sightings," Dr Norman said.