Great whites near Perth beaches: monitoring, sightings and uncertainty

Three kinds of information, three meanings

When assessing a possible great white near Perth, distinguish a reported sighting, an acoustic tag detection, and a precautionary beach advisory. Western Australia’s SharkSmart service presents reported sightings separately from detections of tagged sharks. A reported animal is an observation submitted to authorities; a tag detection is a receiver registering a signal; an advisory is an authority response that can account for conditions beyond a confirmed shark encounter. [1][2][3]

The distinction matters because maps compress different evidence into symbols. Before interpreting one, check its legend and the time window. The official public map can be filtered for the previous 24 hours, seven days, or 30 days. A mark in one window does not mean the same thing as a mark in another, and a lack of marks does not certify that no shark is present. [1][2]

What an acoustic receiver actually hears

A tagged shark carries an acoustic transmitter that emits coded signals. When the animal comes within a receiver’s detection range, the receiver records the signal, allowing the network to register that tagged individual at that location. Perth metropolitan waters are among the areas served by the network. This is a useful way to document movements of animals that have tags and pass close enough to a receiver. [2]

The system does not detect every shark: untagged animals are silent to it, and tagged animals outside receiver range can go unrecorded. Water coverage is also incomplete. Therefore, “no recent detection” means no matching receiver record for a detectable tagged animal in that place and period—not proof of absence. A receiver record also does not, by itself, predict where the animal will go next. [2]

A study of white-shark movements from 2009 to 2016 described them as mostly uncoordinated, limiting encounter prediction. That finding is a constraint on forecasting, not evidence that movement data are useless: detections can inform authorities about tagged animals, while leaving substantial uncertainty about other sharks and future movements. [2]

Read the alert as a timeline

The SharkSmart Sorrento Beach page illustrates why the update time and the reason for advice matter. Its October 26, 2026 update said beaches had reopened after removal of a whale carcass, while retaining extra caution because of possible residual attraction. The prior closure followed a carcass report. The notice did not identify a white shark or establish that any shark had been sighted. [4]

This is a dated example, not a live statement about beach conditions now. Advisory pages can change, and even one page can record a closure followed by reopening with continuing caution. For a practical reading exercise, ask: What was observed? What action did authorities take? When was the advice updated? In this case, the reported carcass prompted precaution; it was not a shark sighting. [4]

Use current local instructions

Before entering the water, consult the latest official SharkSmart information and follow directions from authorities and beach managers. Decisions may take account of sightings, tag detections, weather, patrols, and other local conditions; no single mitigation guarantees safety. On arrival, pay attention to local signs and instructions. The official guidance also identifies BEN signs as a way to communicate an emergency location. [3]

In Western Australia, the cited official sources give Water Police’s shark-sighting report number as 08 9442 8600. For immediate beach decisions, use current local instructions rather than an old screenshot or a dated example. A notification, reopening, or map entry should be read in its own time and evidence category. [1][3]