TWO sharks have been caught on Perth's drum lines, which were deployed only hours ago to catch and kill big sharks off metropolitan beaches.

The first was a 1m tiger shark caught off Cottesloe, which was released by Fisheries Department officers because it was below the 3m catch limit. The second shark, a 2.6m tiger shark, was caught about 11.30am.

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Surf Life Saving WA has advised swimmers at Cottesloe to exercise caution after the second shark was released 1km from shore by Fisheries officers.

This afternoon, the Department of Fisheries issued a statement, saying undersize and non-target species sharks would be released further out to sea.

It read: "The Department of Fisheries has advised that where practicable, it will release any non-targeted species that is still alive further out to sea, having due regard to not compromising the survival of the shark and of remaining within state waters."

Fisheries officers set out from Fremantle early this morning to begin deploying drum lines and baited hooks 1km from shore.

Protesters including the "marine response unit" - a team of activists who say they are determined to stop the drum line operation - are now considering how they will respond.

Greens MLC Lynn MacLaren said the dropping of drum lines off popular Perth beaches this morning "goes completely against what the community wants and will be met with continuing resistance".

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Set to speak at the 5000 strong anti-shark cull rally tomorrow, Ms MacLaren said: "The Premier seems to have made this decision all by himself while disregarding overwhelming science and constituent concern.

Mr Barnett will still be able to hear the protests of 5000 Western Australians from Africa, where he has conveniently disappeared to while the metropolitan drum-lines are dropped."

"I wonder how safe South Fremantle beachgoers will feel knowing that there is a meat curtain in the form of baited hooks hanging 1km from their favourite beach, with a fisher waiting with a rifle," she said.

"From South Fremantle to Scarborough, Leighton Beach, Cottesloe and Scarborough we now have to witness the killing of an apex predator that maintains the balance of our oceans, the world is watching and this is an embarrassment to Western Australia".

It comes as an email bombardment began targeting every local MP in WA with no shark cull messages as the Conservation Council urges West Australians to "ramp up the pressure on their local Members of Parliament".

Since the introduction of the shark mitigation program earlier this month in the South-West, only one shark is known to have been caught and shot dead off Old Dunsborough.