Port Jackson sharks fall prey to algal bloom, SA ecologists fear

Shark population may have fallen prey to algal bloom, SA ecologists fearBy Lincoln RothallCBy Che ChorleyTopic:Oceans4m ago4 minutes agoSun 15 Feb 2026 at 7:31pmEcologists are concerned by the apparent disappearance of Port Jackson sharks from Adelaide waters. (Supplied: Carl Charter)In short:Researchers investigating the apparent disappearance of Port Jackson sharks from Adelaide metro waters say they have failed to find a single egg from the recent breeding season.One ecologist says it's unclear whether the algal bloom has killed the entire local population, or simply driven them away.What's next?The Department of Environment and Water has spoken of repopulating areas decimated by the bloom, but it's not clear if that option's being considered for Port Jackson sharks.abc.net.au/news/port-jackson-shark-populations-algal-bloom-impact/106335834Link copiedShareShare articleSouth Australia's algal bloom could be responsible for pushing a local population of sharks to the brink of collapse, some researchers say.Port Jackson sharks have all but disappeared from Adelaide metro waters and researchers have failed to find a single egg from the recent breeding season.Waters off Christies Beach once teemed with Port Jackson sharks. (ABC News: Lincoln Rothall)The small sharks grow up to about one-and-a-half metres and are harmless to humans.Before the bloom, snorkellers and swimmers could see masses of them in the shallow reefs just metres off Christies Beach.A dead Port Jackson shark washed up on Aldinga Beach in June 2025. (ABC News: Olivia Mason)It is a sad reality for Flinders University shark ecologist Charlie Huveneers as he emerges from the water after another fruitless search."We've been studying Port Jackson sharks here for many years," he said."Normally we would see 20 to 30. Today we haven't seen any."Professor Huveneers has tagged 71 Port Jackson sharks for tracking purposes, but hasn't detected a single one since July.Professor Huveneers has been tracking the drop in numbers along the coast. (ABC News: Lincoln Rothall)He also has concerns for the next generation of the much-loved local population."Normally at this time of year you would see fresh eggs that the Port Jackson sharks have recently laid," he said."This year, we haven't been able to find one of those fresh eggs."Professor Huveneers at Christies Beach. (ABC News: Lincoln Rothall)Researchers are also searching for the sharks further out to sea.PhD candidate Chloe Roberts is using baited lines to see how many have survived and says the difference from before the bloom is stark.Chloe Roberts, pictured here with a fiddler ray, is concerned about the scarcity of the Port Jackson sharks in waters off Christies Beach. (ABC News: Lincoln Rothall)"Last year when we would go out fishing we would catch more animals than we could process," she said."We would catch up to 20 in a day."On the day the ABC joined them, they only caught and tagged two fiddler rays.Chloe Roberts sets a fiddler ray free in the water. (ABC News: Lincoln Rothall)After days of searching all along the metro coastline, they have only found a single Port Jackson shark.Since the start of the bloom, citizen science website iNaturalist has recorded more than 700 dead Port Jackson sharks washed up on South Australia's beaches.Professor Huveneers said it was unclear whether the algal bloom had killed the entire local population, or simply driven them away.Professor Huveneers during a dive at Christies Beach. (ABC News: Lincoln Rothall)Either way, it's a blow to the ecosystem and the local community."It might be that this local population is gone and might not come back — meaning, all the locals and tourists won't have the opportunity to interact with one of the many friendly species of shark," he said.Thankfully, there are healthy Port Jackson populations in other parts of the state.An overhead view of the reef off Christies Beach. (ABC News: Lincoln Rothall)Repopulating areas decimated by the bloom was one of the options being considered, the Department of Environment and Water's director of conservation and wildlife Lisien Loan told ABC Radio Mornings."Some of our programs are looking at where we might be able to move species or translocate species if we need to in order to help fast-track the recovery," she said.However, the department hasn't confirmed if this is an option being considered for Port Jackson sharks.Posted 4m ago4 minutes agoSun 15 Feb 2026 at 7:31pmShare optionsCopy linkFacebookX (formerly Twitter)PromotionTop StoriesLiberals considering ban on some foreign citizens under tougher immigration stanceTopic:Liberal Party of Australia