Mid-June is normally the peak time for giant Australian cuttlefish to gather near Whyalla in South Australia's Spencer Gulf, with thousands—sometimes hundreds of thousands—arriving to breed in the shallows. This globally unique phenomenon is celebrated locally as 'Cuttlefest'. But this year, only a few dozen have turned up, sparking concern among locals and marine scientists.
Algal Bloom Blamed for Low Numbers
Associate Professor Zoe Doubleday, a marine ecologist at Adelaide University, says the meagre turnout is 'something we haven't seen before'. While the exact cause is uncertain, she believes 'on the balance of probabilities it is likely to do with the [algal] bloom'. This could be due to direct exposure to the toxic algae or a decline in the cuttlefish's food source.
Australia's first bloom of toxic Karenia cristata algae began in March last year and is still present along the South Australian coastline, including parts of Spencer Gulf. It is the largest and most destructive algal bloom in the nation's history. 'We know the effect of Karenia on cephalopods is swift and fatal,' Doubleday says, who is researching the bloom's impact on cuttlefish, squid, octopus, and nautiluses.
Latest testing results show elevated levels of Karenia algae at eight of 32 testing sites on the southern Eyre Peninsula and southern Spencer Gulf, with the highest concentration of 432,899 cells per litre at Proper Bay. The government considers levels above 10,000 per litre as 'elevated', with higher counts suggesting a bloom could be under way.
Dive Shop Reports Skittish Cuttlefish
Manny Katz from the Whyalla Dive Shop says normally by this point in the season, with water temperatures dipping below 17°C, there should be thousands of cephalopods along the entire Cuttlefish Coast. Instead, divers have observed a 'couple of dozen hanging around, at a couple of different spots – that's pretty much it'. The animals that had turned up were 'extremely skittish' and hiding underneath rocks.
'We're at this point where, the longer time goes by, the more we're worried about it,' Katz says. 'The cuttlefish should be here by now.' The business turned away $50,000 worth of bookings for the June long weekend when the cuttlefish failed to show. But the greater fear is the risk of losing the aggregation entirely. 'This is a world-renowned dive site. A natural phenomenon that we get to experience. And to not have that is really sad,' Katz says. 'From an environmental point of view, this is catastrophic.'
Economic and Heritage Impact
Cuttlefish numbers have varied year-to-year since surveys began in 1998, from a low of 13,500 in 2013 to 247,000 in 2020. Last year, nearly $10 million was spent locally during Whyalla's winter celebration 'Cuttlefest'. Festivities were under way this year, but 'unfortunately the special guests for the celebration weren't there – our cuttlefish', Whyalla Mayor Phill Stone said in an update.
The giant Australian cuttlefish are the largest in the world. The breeding event is so exceptional that the stretch of coastline 15 km north-east of Whyalla was added to the National Heritage List in 2023.
Government Monitoring and Future Outlook
Formal surveys will be conducted in coming weeks. A spokesperson for the state's Department of Primary Industries says government researchers are 'anecdotally receiving reports that population numbers of giant Australian cuttlefish in northern Spencer Gulf seem relatively low'. The spokesperson notes that cuttlefish numbers and timing can vary: 'While the peak of the spawning normally occurs in June it has been known to spread into July depending on the year.'
Doubleday says there is still uncertainty about how exposed cuttlefish hatchlings or adults have been to the bloom, but she is concerned about the dramatic decline. 'We'll probably need to wait to see what the numbers are,' she says. 'I think the next two weeks will be really telling.'
