Another survey has shown a slowing decline in the numbers of giant Australian cuttlefish in upper Spencer Gulf in South Australia.

Overall, the number of cuttlefish aggregating at Point Lowly near Whyalla to breed has fallen dramatically in recent times.

South Australian Fisheries Minister Gail Gago said the research made clear a decline was still happening, but the rate had slowed.

She conceded attempts to pinpoint the reason had been unsuccessful but said there was no evidence to suggest the decline was unnatural and numbers might simply be returning to normal levels.

"The numbers that we have that are the peak population numbers could have been at a natural extraordinary event," she said.

The minister said the Government would keep work with researchers to protect the remaining cuttlefish population.

The State and Federal Governments have spent more than $700,000 to try to find out what has been affecting the numbers.