South Australia’s bloom left at least 8,250 sharks and rays dead. Can populations rebuild?

The Great Southern Reef Foundation publicised the findings on October 15, 2026. ABC South Australia’s November 2 account adds interviews and a species breakdown to that picture. These are losses accumulated during the bloom, not a newly discovered, single mass-death incident. The foundation’s minimum of 8,250 and ABC’s rounded figure of more than 8,200 describe the same tally, not separate waves of mortality.⁠8⁠1

Marine ecologist Janine Baker led the report, drawing on the South Australian Marine Mortality Events 2025–26 project on iNaturalist. People recorded dead marine animals, many after their bodies washed ashore. The reported losses fall heavily on familiar sharks and rays that live on or near the sea floor.⁠2⁠8⁠1

The tally is substantial, but it is not a census of every affected population. Animals that died unseen or went unreported are missing. The foundation says the actual toll is likely higher; there is no verified statistical estimate of how much higher. The species totals above are those reported by ABC from the foundation’s compilation, rather than an independent recount of the underlying records.⁠1⁠8

Nor does the tally mean that thousands of animals were individually tested and confirmed to have died from algal toxins. It documents deaths in bloom-affected waters. That distinction does not diminish the disaster, but it sets an important boundary around what the count itself establishes.⁠8

Huveneers, director of Flinders University’s Marine and Coastal Research Consortium, gave that assessment to ABC. “Probably” matters: this is an expert judgement about the event’s possible historical scale, not an independently established world record. The report warns that some local populations may have collapsed. It does not establish that every affected species has disappeared, or that any species is extinct.⁠1

A second warning comes not from carcasses but from animals researchers knew before the bloom. Huveneers’s research concerns metropolitan populations of Port Jackson sharks and fiddler rays. He told ABC: “Out of the more than 150 sharks and rays we tagged before the bloom, 12 months later none have returned.”⁠1

That absence is alarming without being a death certificate for every tagged animal. They could have died, moved elsewhere or gone undetected. The account does not provide the monitoring coverage, detection probabilities or movement histories needed to distinguish those possibilities. Treating all the missing animals as confirmed deaths would turn a serious warning into a conclusion the evidence cannot yet carry.

Concern about reproduction also predates the latest tally. On February 16, 2026, ABC reported that researchers investigating an apparent disappearance of Port Jackson sharks had found no eggs in the recent breeding season. That raised another question about the local population’s future; it did not settle the animals’ fate.⁠17

The bloom’s reach makes these local absences more consequential. After initially affecting the Fleurieu Peninsula near Adelaide, it extended to Yorke Peninsula, Kangaroo Island, Gulf St Vincent and parts of Spencer Gulf. This was not damage confined to one beach or one dive site.⁠5

Scientific work describes a complex bloom that included the brevetoxin-producing alga Karenia cristata. A 2026 mini-review in Microbiology Australia reports that toxin analyses found brevetoxin forms not previously reported in Australian harmful algal blooms. It also examines possible bacterial and viral influences on bloom dynamics. Those influences remain subjects of investigation, not established explanations for the shark and ray tally.⁠10⁠18

Most affected species have ranges extending into waters untouched by the bloom. Those populations offer a possible source of returning animals. The calculation is harsher for species with naturally low numbers or small ranges that overlap strongly with the affected area: they have fewer places from which to return.⁠1

The pygmy thornback skate illustrates that vulnerability. Diver David Muirhead, who says he has completed around 2,000 dives in South Australian waters, photographed one off Edithburgh Jetty early in the bloom. He had never seen one before. The skate is exceptionally rarely encountered, with many sightings occurring when fishing trawlers bring one up, and its small range lies mostly within affected South Australian waters.⁠1

Muirhead feared he might have witnessed the end of a species. Scientists have not confirmed that outcome. His encounter instead exposes a fundamental difficulty: assessing a disaster’s impact on an animal for which even experienced observers have little baseline information. Huveneers warned ABC that species with low abundance or restricted ranges overlapping the bloom could face “some level of extinction”—a warning about risk, not a finding that extinction has occurred.⁠1

There is a related gap in formal protection. Neither the pygmy thornback skate nor the coastal stingaree is federally listed as threatened under Australia’s Environment Protection and Biodiversity Conservation Act. The coastal stingaree is considered endangered by the International Union for Conservation of Nature. These are different assessment systems; the absence of a federal listing does not overturn the international assessment.⁠1

The federal environment department told ABC that its 2026 assessment cycle specifically invited nominations concerning species and ecological communities at risk from the bloom. No nominations were received for these two species. Anyone can nominate a native species, but the process requires scientific evidence, and insufficient population information has impeded assessment.⁠1

The federal system has no “data deficient” threatened-species category. Where there is too little evidence to assess a species against the criteria, it is found ineligible. That is a failure to establish eligibility on the available information—not a finding that the species is safe. The animals hardest to study can therefore also be the hardest to assess for protection.⁠13

There are reasons for cautious hope. Muirhead reports seeing many common bony fish and marine invertebrates recovering. But he recalled only one ray since the bloom, swimming under the steps at Second Valley. That is one experienced diver’s observation, not a systematic population survey. Other reports of returning stingrays likewise do not establish restored numbers or breeding populations.⁠1⁠15

Even successful recolonisation would not necessarily mean a quick recovery. Sharks and rays generally mature slowly, reproduce infrequently and have small litters, Huveneers explained. Animals moving in from unaffected waters could become visible well before local populations regain their former abundance.⁠1

The next meaningful test is therefore bigger than whether someone photographs another ray. Sustained monitoring needs to establish which animals remain or return, whether they reproduce, and whether their numbers rebuild. For the rarest species, it must also fill the information gap that has complicated assessment for protection. The documented dead establish the scale of the loss; sightings alone cannot yet establish the scale of recovery.