Giant Cuttlefish Breeding Numbers Crash in Australia, Raising Fears of Species Decline
South Australia: The world’s largest gathering of giant Australian cuttlefish has recorded its lowest numbers ever, sparking concerns among scientists and conservationists about the future of the unique marine species.
Every winter, hundreds of thousands of giant cuttlefish traditionally gather along South Australia’s Cuttlefish Coast for their annual breeding season. The spectacular underwater event attracts thousands of divers who come to witness the animals’ remarkable colour-changing displays and complex mating behaviour.
However, this year’s breeding season saw a dramatic collapse in numbers. Official estimates show that only 1,811 cuttlefish arrived to mate, compared with around 63,000 last year — representing a decline of approximately 97%.
Experts and environmental authorities believe a long-lasting toxic algal bloom affecting South Australia’s coastline may have contributed to the severe reduction in the population. The bloom has damaged marine ecosystems across the region for more than 18 months, raising concerns about its impact on various ocean species.
The sharp fall in breeding numbers has also led to calls for giant cuttlefish to receive stronger protection, including possible classification as an endangered species.
Scientists say the situation is particularly concerning because adult cuttlefish usually die after reproduction. This means each breeding season plays a vital role in maintaining future populations. Surveys conducted this year found only about 440 eggs, compared with the millions normally expected along the coastline.
Marine diver Manny Katz, who worked with South Australia’s Department of Environment and Water to assess the breeding population, described the findings as alarming. His team carried out eight one-hour dives over two days in July, searching rocky reefs across an eight-kilometre stretch of coastline for cuttlefish eggs.
Despite extensive efforts, divers found only a few hundred eggs in areas where millions would typically be present.
Katz explained that giant cuttlefish have a short lifespan of around 12 to 18 months, meaning the success of a single breeding season can determine the size of the population in the following year. The lack of eggs has created uncertainty about whether the population can recover naturally.
Environmental researchers warn that the decline highlights broader challenges facing marine ecosystems. Rising ocean pressures, pollution, climate impacts, and harmful algal events are increasingly threatening marine biodiversity worldwide.
Authorities and scientists will continue monitoring the Cuttlefish Coast in the coming months to understand the causes behind the collapse and determine what conservation measures may be needed to protect one of Australia’s most iconic underwater species.
