The annual gathering of giant Australian cuttlefish in the upper Spencer Gulf, a globally unique biological phenomenon that typically draws thousands of visitors to the town of Whyalla, has seen a collapse in numbers. Following a record-breaking toxic algal bloom that has impacted South Australia’s coast since March 2025, recent monitoring has revealed a harrowing decline in the species. During a dive survey conducted this past July, researchers identified only 44 individuals, marking the lowest turnout since population monitoring began in 1998.
The July 2026 survey recorded only 44 giant Australian cuttlefish and 440 eggs, a stark contrast to the 63,000 cuttlefish counted in 2025.
The presence of Karenia cristata, a toxic alga responsible for the largest and most destructive bloom in the nation’s history, is widely suspected as a primary driver of this decline. Marine experts suggest that the bloom may have caused direct mortality among the cephalopods or disrupted the delicate balance of their food chain. Because giant Australian cuttlefish possess short life cycles and rely on successful, consecutive annual breeding seasons, the absence of this year’s generation has left scientists and local dive operators fearing the potential for a catastrophic and permanent collapse of the population.
A Plea for Transparency and Protection
In response to the dire observations, tourism operators in Whyalla made the difficult decision to cancel the 2026 season. On July 1, the South Australian state government implemented temporary recreational restrictions on swimming and snorkeling in the area to provide the remaining wildlife with much-needed refuge from human disturbance. While surveys have been completed, officials maintain that formal population estimates are still undergoing rigorous analysis and have yet to be released. Researchers involved in the monitoring efforts, including teams from the South Australian Research and Development Institute (SARDI) and the University of Adelaide, are continuing to evaluate the extent to which the ongoing algal bloom contributed to this season's results.
As stakeholders await official data, the urgency of the situation cannot be overstated. The Whyalla breeding site, which gained National Heritage status in 2023, remains a critical piece of Australia’s marine identity. Whether this cycle represents a temporary, environmentally driven “bust” phase or a more permanent loss remains a point of deep concern for the conservation community.
Read the full original reporting at The Guardian →
Image: Tim Binns from Tomahawk, Australia (BY-SA 2.0)
Image: A giant Australian cuttlefish exhibiting its unique color-changing abilities on the seabed.