A tagged white shark has been spotted off Manly Beach two days after surfer Mercury Psillakis was fatally mauled by a shark at nearby Dee Why.

A shark tag sensor went off at 10.51am on Monday at the North Steyne receiver, according to the Department of Primary Industries and Regional Development’s (DPIRD) Shark Smart service.

The beach alarm system was then activated at Manly.

The shark was originally tagged at Diggers Beach in Coffs Harbour in 2023 and was last seen on the Central Coast in June before being recorded on Sydney’s Northern Beaches today.

“At the time it was tagged, it was 2.03 metres total length,” a statement from DPI said.

Sydney's Manly Beach

Sydney’s Manly Beach on Saturday, when swimmers were ordered to leave the water after a shark attacked a man in Dee Why. (ABC News: Anton Rose)

“DPIRD shark scientists estimate the shark would now be approximately 2.5-2.7 metres in length.

“This is smaller than the estimated size of the White shark involved in Saturday’s incident at Dee Why.”

Northern Beaches Council has been contacted for comment.

The waters off Long Reef Beach at Dee Why where Mr Psillakis was surfing on Saturday was netted as part of the state-wide rollout on September 1.

Government experts have estimated the shark that attacked Mr Psillakis was between 3.4 metres and 3.6 metres.

A beach with few people on it, yellow signs advising beach closed.

The scene at Dee Why on Monday, following the 57-year-old’s death at the weekend.  (ABC News: Marcus Stimson)

Friends who were on the water at the time Mr Psillakis was attacked by the shark recalled how he saved several of his friends in his final moments.

“Merc spotted the shark early, informed the other surfers in the water to band together and to try and get back to shore safely,” professional surfer and family friend Toby Martin said.

Friend describes ‘heroic’ final act of surfer killed in shark attack

A childhood friend has described how Mercury Psillakis steered his friends to safety before being mauled by a shark at Sydney’s Northern Beaches.

Police said his body was retrieved a short time later and that he was missing “a number of limbs”.

The beach at Dee Why was subject to a 72-hour closure while beaches from Narrabeen to Manly were closed for 24 hours after the attack.

A state government plan to trial removing shark nets from one beach on the Northern Beaches has been put on hold in the aftermath of Mr Psillakis’ death at the weekend.

Waverley and Central Coast councils were also set to be part of the trial to begin this summer.