Biologists believe the shark that killed a surfer at a Sydney beach on Saturday is a great white up to 3.6 metres long.

Mercury Psillakis, 57, was taken by a shark at Long Reef Beach in Dee Why and is believed to have lost multiple limbs in the attack.

Fellow surfers say he spotted the predator and began warning those around him, but was unable to save himself.

New measures are being taken in response to the fatal attack.

“On Saturday, Sunday, and Monday, the DPIRD contractor added two more SMART drumlines between Dee Why and Long Reef, supplementing the three that are deployed daily off Dee Why throughout the year,” according to the DPIRD statement.

“Surf Life Saving NSW have also deployed drones in the area again today, plus helicopter surveillance.”

The Northern Beaches Council also declared the temporary closure of these two popular beaches, following the NSW Government Shark Smart app’s report of a “tagged shark spotted near” the beaches.

This marks the fourth beach to be closed in the area, with Dee Why Beach and Long Reef Beach also remaining closed after Saturday’s attack.

In addition to the beach closures, a planned trial to take down shark nets from Sydney beaches was paused yesterday.