ROTTNEST Island looks likely to become home to a breeding colony of New Zealand fur seals, raising fears that great white sharks will be attracted to the holiday spot.

While several dozen seals have long called Cathedral Rocks near Cape Vlamingh home, University of WA researcher Ana Hara says the seals could establish a permanent breeding colony there by as soon as next summer.

It has raised fears that the popular surfing spot at the west end of Rottnest could attract more great whites.

"The great white is their big predator so that could pose a risk," Rottnest Island Authority ranger Sarah Ellis-Stott said.

Rottnest police officer-in-charge Sgt Peter Bahan, who is also a keen surfer, admitted he no longer surfed the popular break called Cathedrals after a great white "popped up" next to him during a surf last year.

The surf break is less than 50m from the outcrop of rocks the seals inhabit.

"She was a big one," Sgt Bahan said of the shark.

"I won't surf there any more."

He said his was one of at least three confirmed great white sightings off Rottnest last year and a pod of five killer whales was also spotted in waters off the island.

There are 17 recorded NZ fur seal colonies in WA, all in waters off Esperance and Albany.

Ms Hara, who is doing a masters at the University of WA into the diet and distribution of the seals in WA waters, said they were establishing colonies farther north and increasing in numbers.

"It looks like there is now a colony at Bunker Bay (in Dunsborough) and I believe the next point is going to be a breeding colony at Cathedral Rocks on Rottnest Island," she said.

Ms Hara said there were between 10 and 80 seals around Cathedral Rocks at any one time and one animal showed signs of a shark bite.

Rottnest rangers Claire O'Callaghan and Ms Ellis-Stott were monitoring the number of seals and had swum with them. "They're amazing animals," Ms Ellis-Stott said.

"They're really curious and come right up and check you out.

"You often see them thermo-regulating, which actually looks like they're doing yoga."

A Rottnest Island Authority spokeswoman said the seals were an exciting development that would increase visitor appeal to the island.

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