A May 2025 underwater survey at Hall Bank Reef off Port Beach in North Fremantle documented bleached, fragmented coral and reduced coral cover in the area scanned. The survey team and a local report described the imagery as showing a stark decline, but the published accounts do not quantify the loss or show that the scanned area represents the whole reef.
What the underwater survey found
Advanced Navigation and marine consultancy O2 Marine surveyed Hall Bank Reef, a nearshore reef off Port Beach/Fremantle in Western Australia, in May 2025. PerthNow reported that the resulting imagery and 3D seabed model showed a barren-looking seabed and lifeless coral. Dr Alec McGregor, Advanced Navigation’s senior AI engineer, described a dramatic reduction in coral cover in the area scanned. PerthNow’s report, published 5 June 2025, and Advanced Navigation’s survey account, published 3 June 2025, also describe bleaching and fragmentation.
These are observations from a visual survey, not a published measurement of coral loss across Hall Bank. The reports do not provide a percentage, a numerical baseline, or evidence that the sampled area represents the entire reef. “Lifeless” is headline-style language for what the images appeared to show in the area examined, not proof that every part of Hall Bank is devoid of living coral.
How the Hydrus survey worked
According to Advanced Navigation, three Hydrus autonomous underwater vehicles followed coordinated transects at the site. They collected georeferenced high-resolution imagery and 4K video, which were used to assemble a 3D digital model of the seabed. PerthNow described Hydrus as a 7 kg robot; that is a reported product specification, not an independent measurement from the survey.
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Georeferenced imagery can connect visual observations to locations and make a site easier to revisit. In this case, however, the public reports do not include the full sampling design, underlying dataset, or independent validation. The published material therefore supports a concerning local visual finding, but not a reef-wide estimate or a comparison proving that this method is more accurate or sensitive than other monitoring approaches.
What the reports do—and do not—establish
- Established: Survey participants and PerthNow described bleaching, fragmentation, and reduced coral cover in the scanned area.
- Not established: The proportion of Hall Bank’s coral that was lost, how conditions compare with a measured historical baseline, or whether the images represent the full reef.
- Cause not established: Advanced Navigation discussed bleaching and marine heatwaves more broadly, but the reports do not provide a Hall Bank temperature measurement or demonstrate what caused the observed condition at this site.
Advanced Navigation’s account referred to marine heatwave conditions affecting other reef regions, including Ningaloo and the Great Barrier Reef. That broader context should not be mistaken for site-specific evidence about Hall Bank.
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Why repeat mapping could matter
Dr McGregor said repeat surveys every 6 to 12 months could help track change and the effects of conservation work. That interval is his suggested approach, not a validated standard for all reefs. Repeating a survey could make change easier to assess if coverage and methods are sufficiently consistent; the reports do not provide a published repeat-survey result for Hall Bank.
The survey’s 3D model and mapped imagery offer a record of what the team observed in May 2025. Whether that record can support robust change estimates depends on comparable future coverage and transparent validation—details not established in the published accounts.
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