South Australia’s Giant Cuttlefish Mating Season Plummets to Record Low

Every winter, a stretch of the South Australian coast hosts the world’s largest mating event for giant cuttlefish.

In certain years, hundreds of thousands of these unique marine species, endemic to Australia, gather along the Cuttlefish Coast for their annual mating season, bringing their colorful, shape-shifting forms to the shallow waters and drawing thousands of eager divers.

However, this year recorded the lowest turnout in history, raising fears of a “catastrophic decline” in the species.

Official figures released this month estimate that merely 1,811 cuttlefish appeared to mate this year, down from 63,000 last year—a staggering 97% decrease.

The state government attributes the sharp decline to a toxic algal bloom that has ravaged the coastline for over 18 months.

The dismal numbers have also triggered calls for the species to be listed as endangered.

Adult cuttlefish typically die after breeding, making each mating season critical for the species’ survival. However, in recent months, only 440 eggs have been counted instead of the millions typically laid.

Manny Katz, 28, was one of four divers who spent hours along the coast last month observing the annual breeding event after being tasked by South Australia’s Department of Environment and Water (DEW).

“Because there have been so few cuttlefish, DEW believed it was worth going out to assess how many eggs currently exist around the coastline to understand what the population will be next year.”

Over two days in July, his team conducted eight one-hour dives, exploring the undersides of rocky reefs to count the eggs.

“Along the eight kilometres (five miles) of coastline, there would normally be millions of eggs,” he noted, as each female can lay dozens of eggs and tens of thousands usually turn up to breed.

“[We] essentially looked under every single rock we could find and only discovered about 440 eggs.”

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