Hundreds of giant Australian cuttlefish have swum into breeding grounds at the top of Spencer Gulf in South Australia, reversing a worrying decline of recent years.

The population had been dwindling and local diver Tony Bramley says he had not been expecting to see any this season, based on that trend.

He says it has been warmer-than-usual weather for the start of the breeding season and more cuttlefish might arrive as temperatures drop.

Mr Bramley says he does not know where the cuttlefish have travelled from as there has been no sign of many gathering offshore in recent weeks.

Cuttlefish research efforts include: Monitoring breeding aggregation in northern Spencer Gulf to check numbers, water quality and state of habitat.

Monitoring breeding aggregation in northern Spencer Gulf to check numbers, water quality and state of habitat. Looking at potential alternative cuttlefish spawning areas in northern Spencer Gulf.

Looking at potential alternative cuttlefish spawning areas in northern Spencer Gulf. Determining the habitat preferred by cuttlefish when laying eggs, to aid research into artificial habitats which might promote breeding.

"It's just baffling to see that many cuttlefish after the year that we had last year," he said.

"I'm really at a loss to explain how they've recovered so quickly, I mean it's wonderful to see that.

"It just proves that, no matter what you think you might know, nature can always surprise you, because it's out of left field. I really didn't expect anything like what we saw."

Mr Bramley says cuttlefish numbers are better than they have been in the past three years but still low overall.

"Now to be fair we've only dived Black Point, so we haven't been through the rest of the aggregating sites."

Federal and state funding has supported research into cuttlefish breeding in northern Spencer Gulf since the decline in numbers was noted.