Death of sharks on Adelaide beaches remains a mystery as algae bloom plagues sea life

7NEWS

14-05-2025

Researchers have been left scratching their heads at autopsy results from recent shark deaths on South Australian coastlines.
Sharks that washed ashore in recent weeks have been taken by the Department of Primary Industry and Regions (PIRSA) officials to be examined and determine their cause of deaths.
Autopsies have been done on both a great white shark that washed ashore on Henley Beach and another found at Port Willinga.
But the research returned 'inconclusive' results.
Since March, a toxic algae bloom has been appearing along South Australian coastlines and causing sealife to wash up on beaches.
The micro-algae karenia mikimotoi is causing the seafoam along and murky water across South Australia's Fleurieu Peninsula.
The foam — likened by some to the froth on a milkshake — and its effects were first noticed by surfers at Waitpinga, about 100km from Adelaide, on March 15.
The EPA reported the algae has since been found on beaches from Cape Jervis to Encounter Bay.
A spokesperson from PIRSA said research will continue into the loss of sea life.
'Researchers from the South Australian Research and Development Institute (SARDI), the research division of PIRSA, are continuing to investigate into the series of deaths of sharks around the South Australian coastline,' they told 7NEWS.
'A necropsy was performed on the White Shark retrieved from Henley Beach on 5 May 2025 but unfortunately, there were no conclusive histological findings to explain what caused its death.
'Extensive analysis and necropsies were also conducted on two White Sharks found by members of the public at Port Willunga and Port Moorowie last month, but unfortunately due to the age of the biological samples available a definitive cause of death was unable to be determined.
'The samples of all carcasses collected to date will be used for future scientific studies and help to improve our understanding of the White Shark population in South Australia.'
Beachgoers and swimmers along the Southern Coast are being reminded to stay clear of water that may be discoloured or have the foam present.
If any contact is made, people are advised to wash themselves in fresh water.
Human exposure, including through breathing in algae particles, can cause respiratory and eye irritation or skin rashes in some people, while ingestion could cause stomach upsets or flu-like symptoms.
PIRSA would also like to inform the public that sharks sighted more than 500 metres from shore and greater than three metres in length can also be reported via the 24-hour Fishwatch Hotline on 1800 065 522 or via the shark sighting report form.
If a shark is spotted within 500 metres of shore or presents an immediate threat to humans, police should be contacted.