Experts fear algal bloom to blame for disappearance of Whyalla's cuttlefish

Giant Australian cuttlefish in the waters of Stoney Point, near Whyalla, South Australia. (Supplied: Carl Charter)

The giant Australian cuttlefish annually return to the waters of the Upper Spencer Gulf, near Whyalla, in their tens of thousands for its breeding season. But this year, barely any have arrived.

Tourism operators, environmentalists and marine experts are worried the species has been devastated by the algal bloom.

The cause is as-yet undetermined, with PIRSA and South Australian Research and Development Institute investigating. A full population survey to be undertaken next week.

At this time of year, the waters of Whyalla are normally home to tens of thousands of giant Australian cuttlefish, but so far this winter, they haven't arrived in even close to those numbers.

Marine experts fear the harmful algal bloom has had a devastating impact on the species, which annually breeds in the Upper Spencer Gulf.

Owner of the Whyalla Dive Shop and Eyre Lab director Manny Katz said those thousands of cuttlefish "should" have arrived, with waters now within the temperature range for the species' breeding conditions, yet they're almost nowhere in sight.

Mr Katz says only a few dozen cuttlefish have been spotted so far. (Supplied: Manny Katz)

"We've seen maybe a couple dozen spread out across all of the different sites that we go to, across the 8 kilometres of coast," Mr Katz said.

"There's been maybe 25 to 30 that we've been able to spot. It's not great at the moment."

Fears for the Upper Spencer Gulf's cuttlefish population were raised last year during the height of South Australia's harmful algal bloom, with discussions on whether to relocate the species' hatchlings.

Those discussions culminated in a government investment of $700,000 to install a "bubble curtain", which was hoped would protect the species and its eggs.

With the bloom never arriving in the Upper Spencer Gulf, the curtain — which was hoped to form a shield around a specific part of the Upper Spencer Gulf — was never needed to be turned on. However, the population's migratory patterns take the species out of that protected area during warmer seasons.

Two male giant Australian cuttlefish. (South Australian Tourism Commission: AAP)

Mr Katz said they will not fully know how the tourism season will fare until temperatures drop further, but his business had thus far been postponing tours.

"If the cuttlefish don't rock up, there's not going to be a season."

Tony Bramley has been a scuba diver, environmentalist and tourism operator in the Upper Spencer Gulf for almost four decades