Aerial shark patrols of Perth beaches are set to resume this weekend amid a spike in detections along the metropolitan coast.

The seasonal helicopter patrols begin for the summer on Saturday, following a winter in which two people were killed by sharks off the Perth coast within a week.

Surfer Ben Gerring died in June after he was mauled by a shark near Mandurah, while diver Edith Collyer was killed by an attack off Mindarie one week later.

Authorities also recorded a significant increase in detections between Trigg and Cottesloe in the past day, with two white sharks detected a total of 38 times in that area within just 24 hours.

That prompted authorities to issue a shark warning, advising ocean users to take extra caution.

Ahead of the resumption of aerial patrols, Fisheries Minister Joe Francis said the state did what it could to safeguard ocean users but there was a limit to the level of protection that could be provided.

"Nobody can guarantee that all of the West Australian coastline is going to be safe from sharks," he said.

"We just can't guarantee perfect safety in the ocean but we are doing what we can."

Mr Francis said shark enclosures at Sorrento Beach and Quinns Rocks should be in place by Christmas.

He said the Government's chief information officer was also examining whether the state should install "clever buoys" — a locally developed technology which can detect both tagged and untagged sharks and send an alert to lifeguards.

"We will talk more about that in the coming month," Mr Francis said.

The Government's "imminent threat" policy, allowing it to destroy sharks deemed to pose a high risk, also remains in place and Premier Colin Barnett said the state needed to be "a little bit more aggressive" in the use of that.