Queensland researchers have spotted an unusually large group of manta rays in a feeding frenzy near Lady Elliot Island.

University of Queensland researcher Dr Kathy Townsend believes up to 150 manta rays were feeding in the area last month.

She said the phenomenon was a result of recent flooding in Bundaberg, with excess levels of water sending a surge of nutrients into the ocean, leading to a spike in plankton.

"To date that's the only one that we've recorded and we are able to directly associate with the flood events that were happening at the coastline," she said.

"When we first started this project back in the early 2000s it was estimated that there was probably only about 40 individual manta rays that could be regularly found around Lady Elliot Island.

Feeding stations: Manta rays spotted close in to Lady Elliot Island ( Photo courtesy of Project Manta )

"Since then we have discovered we currently have over 700 individuals that we have identified from that region as well as the rest of the east coast.

"[But] we've never seen anything to that extent; we certainly had ones of up to say 50 to 60 animals but have never seen the likes of having up to 150 animals.

"The rays are taking advantage of that large flush of nutrients but as soon as the plankton has gone they all sort of split up again they sort of meander off to where they all have to go to feed the rest of the time."

Dive instructor Chris Garraway says it was reassuring to see the animals were not forced away by the floods.

"It's quite unusual for this time of year to have so many individuals this far north they tend to migrate further south," he said.

"They always seem to know exactly where that plankton is the densest and they all sort of move to that point in the current and all start swimming in the same direction."

Manta rays, which can grow to a wingspan of more than five metres, have recently been listed as vulnerable to extinction.

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