Scientists and divers have called on the South Australian government to release official cuttlefish population estimates amid fears of a “catastrophic” decline, after a dive survey counted only 44 individuals.
Each year, tens to hundreds of thousands of giant Australian cuttlefish assemble off the coast of Whyalla, in the upper Spencer Gulf, to breed – the only place globally where cuttlefish gather en masse.
In surveys dating back to 1998, populations ranged from a low of 13,500 in 2013 to a high of 247,000 in 2020. More than 63,000 were recorded in 2025.
Numbers this year were widely expected to be the lowest on record, after the devastating effects of the toxic algal bloom on the state’s marine environment.
The team of four divers from ecological not-for-profit Eyrelab, who surveyed the coastline in July, also counted only 440 eggs where there would normally be millions.
“This is by far the lowest abundance that we’ve had on record,” said Manny Katz, diver and Eyrelab director, who added that the few dozen cuttlefish they saw were “not out and about – they’re hiding”.
Stefan Andrews, a marine biologist from the Great Southern Reef Foundation, called for the state government to release the official figures.
“It’s clear that it’s going to be bad news,” he said. “People need to know just how bad the situation is.
“Let’s see it, and not sit on it too long because the clock is actually ticking.”
The historically low numbers led tourism and dive operators in Whyalla to cancel their cuttlefish season in June. On 1 July, the state government introduced temporary restrictions on recreational activities such as swimming and snorkelling, to minimise disturbance to breeding cuttlefish and help protect their eggs and hatchlings.
At a press conference on 30 June, Prof Mike Steer, the SA Research and Development Institute’s executive director, said “less than 50 animals” had been observed earlier in the season. Those were “raw counts”, he said, with further monitoring and analysis required before providing a population estimate.
A state government spokesperson said surveys had now been completed, and 2026 estimates would be released after review.
“Cuttlefish numbers naturally rise and fall from year to year”, driven by environmental conditions, the spokesperson said. “The algal bloom reached the giant Australian cuttlefish breeding site at Point Lowly in upper Spencer Gulf and, while it appears likely the algal bloom has impacted cuttlefish numbers, researchers are working to determine whether this contributed to the reduced population.”
Assoc Prof Zoe Doubleday, a cuttlefish and octopus expert at Adelaide University, said the bloom may have killed cuttlefish directly or changed the availability of their food supply – or their predators’ food supply.
Cuttlefish live short lives and adults usually die after breeding, making the population heavily dependent on the success of each breeding season.
Australia’s first bloom of toxic Karenia cristata algae, which began in March last year, is still present along parts of the South Australian coastline. It is the largest and most destructive algal bloom in the nation’s history.
The latest testing results show elevated levels of Karenia algae at seven of 32 testing sites on the Eyre peninsula, and two of 19 sites on the Yorke peninsula.
Andrews said the federal government should also assess listing the species as threatened under the Environment Protection and Biodiversity Conservation Act, given the “catastrophic decline” in numbers.
While giant cuttlefish were found along the Australian coast, the animals in the upper Spencer Gulf were genetically distinct, he said. In addition to their globally unique aggregation, the animals displayed distinct behaviours, such as female mimicry – “males pretending to be female, to get up close to the other females so then they can sneak mate with them”.
