Picture: Department of Fisheries

When two great white sharks were detected almost simultaneously by receivers off several Perth beaches, Department of Fisheries researchers suspected something was up.

The sharks, known as WA018 and WA020, appeared at Floreat and Scarborough one day and again at Ocean Reef days later.

Great white lurked off Perth beaches for a week | FULL COVERAGE

"What scientists found at each of these locations was unusually dense schools of baitfish, which had in turn attracted larger fish, sea lions and seabirds, all natural food sources for white sharks," the department's principal research scientist Rory McAuley said.

"So these sharks actually alerted authorities to a transient ecological event that was likely to attract untagged as well as tagged sharks."

For many West Australians their knowledge of the State Government's shark monitoring network likely extends to its ability to alert swimmers when sharks are close to beaches. Few would realise, as they towel themselves dry and debate whether to wait for the danger to pass, they are witnessing just one aspect of what the network is intended to do.

Warning swimmers about sharks is a key part of the network but by no means its sole purpose.

Receivers are constantly gathering information about the behaviour, movement and habits of tagged sharks.

Two types of receivers are used - satellite-linked receivers that communicate information about shark movements within minutes and data-recording receivers on the ocean floor. The former are expensive ($20,000), difficult to maintain and not practical deeper than about 25m, while the latter are cheaper ($1700) and virtually maintenance free but are only retrieved to have their data analysed once a year.

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Tags offer more than warnings