Australia usually hosts the world's biggest cuttlefish mating event - not this year

Each winter, a particular section of the South Australian coastline becomes the site of the planet's most significant breeding gathering for giant cuttlefish.

In some years, hundreds of thousands of these distinctive Australian marine creatures converge on the Cuttlefish Coast for their annual reproductive cycle, showcasing their vibrant, adaptable forms in the shallow waters, which draws thousands of enthusiastic divers.

However, this year saw the lowest attendance ever recorded, raising alarms about a potential "catastrophic decline" in the species' numbers.

Official statistics released this month indicated that only 1,811 cuttlefish arrived to breed this year, a dramatic fall from 63,000 last year, representing a 97% reduction.

The state government has suggested that a poisonous algal bloom, which has affected the state's coastal areas for over 18 months, might be responsible for this sharp decrease.

The unusually low figures have also prompted calls for the species to be officially designated as endangered.

Mature cuttlefish typically perish after reproduction, making each breeding season vital for the species' survival; nevertheless, in recent months, only 440 eggs have been counted, a stark contrast to the millions usually deposited.

Manny Katz, aged 28, was among a team of four divers who spent numerous hours along the coast last month observing the annual breeding spectacle, having been assigned this task by South Australia's Department of Environment and Water (DEW).

Katz explained that due to the scarcity of cuttlefish, DEW considered it worthwhile to conduct an assessment of the current egg count along the coastline to anticipate the following year's population.

Over a two-day period in July, his team carried out eight one-hour dives, examining the undersides of rocky reefs to count the eggs.

He noted that along the eight-kilometre (five-mile) stretch of coastline, there would typically be millions of eggs, as each female can lay dozens and tens of thousands usually arrive to breed.

Katz stated that they had inspected almost every accessible rock and found only approximately 440 eggs.

Crucially, adult cuttlefish have a lifespan of only about 12 to 18 months, as Katz pointed out, meaning that the success of one breeding season directly influences the population for the subsequent year.

Katz expressed uncertainty about the population's ability to recover given the current situation of so few eggs along the coastline.

While it is currently too early to determine the long-term implications for the species, Katz predicted that they would have an answer within the next year or two regarding whether this year truly represents a catastrophic decline.

His team also monitored the number of adult cuttlefish during their dive survey, observing that the roughly dozen they encountered – instead of the expected tens of thousands – displayed unusual behaviour.

He observed that this year, the cuttlefish were very timid and sought refuge under rocks because with such low numbers present, they lacked the safety in numbers.

Katz mentioned that he was not surprised by the low numbers this winter, attributing it to the severe impact of the toxic algal bloom in South Australia since its initial detection in March of the previous year.