THE first shark has been caught and shot dead under Colin Barnett's controversial shark-kill policy.

It happened before 8am this morning, less than 24 hours after drum lines and baited hooks were set off Old Dunsborough in the South-West as part of the WA Government's "shark mitigation program".

The fisherman contracted to set and monitor the drum lines was back on the water at 6am this morning to check the nine drum lines and their baits.

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He discovered one had successfully hooked a large shark and the animal was reportedly shot four times before being towed "well out" to sea.

The species of shark has not been confirmed, but there was reportedly confusion over whether it was a tiger or bull shark.

Sharks under 3m are to be released if possible and those over 3m are destroyed.

At 2.45pm today, there were no reports of any more sharks being caught and killed.

Conservationists and green groups including the Animal Rescue Team immediately denounced the shark kill and labelled it a "slaughter".

By 4.15pm yesterday, nine drum lines had been set 1km offshore from Old Dunsborough and Castle Rock at Cape Naturaliste.

The drum lines were attached to the ocean floor by anchor and connected to buoys and baited hooks designed to snare big sharks.

Within a couple of hours, PerthNow in a nearby boat watched as a very big ray investigated one baited hook.

Under his contract with the State Government, the professional fisherman who set the drum lines must now monitor the coast 12 hours a day between 6am and 6pm, rebaiting the hooks and waiting for a catch.

Yesterday's start came amid strong protests from green groups and activists who were in Dunsborough but did not interfere with the operation.

Amy-Lea Wilkins, spokeswoman for conservation group Animal Rescue Team, said she had a team of 22 volunteers in Dunsborough, including a vet and a marine biologist who would enter the water with diving gear to free hooked sharks as well as by-catch, such as dolphins, turtles and rays.

"We don't want any marine life dying and we'll do our best to save any animals that are caught, including sharks," Ms Wilkins said.

Anti-cull campaigner Simon Peterffy, who has formed a "marine response unit'', yesterday pledged: "We'll be stopping the hunt, we will be neutralising these drums and we'll be doing rescues of dolphins and other by-catch.''

In his only interview from the back of his boat, the fisherman - whom PerthNow has decided not to name - said he used mackerel to bait the "very large" hooks but from next week he would be using "really good bait", salmon from South Australia.

He said Water Police and Fisheries officers were on standby to protect him against protesters "but only if necessary, and so far it hasn't been necessary".

"We are worried about what they might do, what they might throw at us or the extreme things they might do," he said.

The fisherman said the drum lines "might make the beaches safer".

"But I'm more interested in the research we can contribute to," he said.

The fisherman, a South-West resident for 40 years, said he was "spooked" by the spate of shark attacks and the anecdotal increase in great white numbers.

If he caught a shark over 3m, he said: "We'll destroy it. We will shoot it and take it well offshore and dispose of it. We will puncture the gut cavity so the lice can get in."

He said by-catch would be unlikely because of the large size of the hooks used.

"We're targeting large sharks, the big ones. I doubt we'll catch anything else," he said.

Sharks under 3m would be released.

"We'll have to be very careful and we're still developing a procedure. We'll have to grab them and we've got a mesh glove for that. You don't want to put your hand down its mouth, that's for sure," he said.

"We're dealing with a wild animal that I have every respect for, and I really mean that, I have every respect for these animals and I take that very seriously."

Earlier threats from activists prompted some fishermen who had tendered for the Perth contracts to pull out.

As a result, Fisheries Department staff will now bait and monitor hooks off the five locations near metropolitan beaches.

More anti-cull rallies are planned for Saturday, including another one at Cottesloe.

Organiser Natalie Banks, hopes for an even bigger crowd than the 4500 who attended the first rally earlier this month.

"We know that the majority of people are frustrated with this initiative," she said.

Premier Colin Barnett has not responded to an invitation to attend.

Great whites are protected but Federal Environment Minister Greg Hunt this week granted the State Government a temporary exemption from national environment laws.