Bite marks left in the surfboard of a man mauled by a shark near Esperance show he was most likely attacked by a single great white shark, the Department of Fisheries principal shark scientist has said.

But tests on two white sharks caught and killed hours after the attack have failed to confirm if either was involved.

Sean Pollard, 23, lost an arm and his other hand in the attack at Kelpids Beach, Wylie Bay, on Thursday morning.

Scientist Rory McAuley said: "Those bites were very, very similar to bites I've seen a number of times before that we've confirmed were from white sharks," he said.

"Also given the location, and what I understand are the nature of Mr Pollard's injuries, I conclude that it was most likely a white shark that bit him."

He also said the stomachs of the two sharks captured when authorities set drum lines off the beach were completely empty except for a piece of bait.

"That result means it's inconclusive whether either of these sharks were involved in the attack on Thursday," Dr McAuley said.

"There are a number of explanations for why nothing was in the stomach contents.

"Either they hadn't eaten anything for some time before capture or it's not uncommon for sharks to regurgitate stomach content when they are captured, particularly when they are captured on hooks."

Dr McCauley said one of the sharks had an internal acoustic transmitter which was recovered during the examination.

"Unfortunately we don't have receivers in the vicinity of the incident on Thursday so we won't know whether the tagged shark was involved in the incident," he said.

Mr Pollard reportedly told authorities he believed he had been attacked by two bronze whalers but Dr McAuley dismissed that possibility.

"The white sharks commonly have a bronze colouration dorsally and they can be mistaken for bronze whalers quite easily," he said.

"My opinion from the evidence I've seen is that one white shark was involved."

Fishers staff abused after sharks killed

Fisheries staff received abusive phone calls after the two sharks were caught and killed.

One staff member was so concerned that she made a complaint to police and decided not to stay at her home on Friday night.

WA Premier Colin Barnett has said some "so-called conservationists" had engaged in intimidating behaviour.

Mr Barnett said the WA Government and the Fisheries Department were acting in the interests of public safety and threats against people who were simply doing their job would be reported to police.

WA's Opposition Leader Mark McGowan said there was no point in killing the sharks.

"They've culled sharks and found they didn't have any evidence of any attack inside their stomaches so I don't see any point in doing that," he said.

The department has issued a warning to water users after a series of shark sightings along the Perth coast.

Water users between Ocean Reef and Port Beach in particular have been urged to exercise additional caution.

All water users have been told to stay informed of the latest detection and sighting information via the Surf Life Saving twitter account, report any shark sightings to water police and adhere to beach closures.