Concerns are growing over the local giant cuttlefish population as low numbers are being reported this breeding season after disappointing numbers last year.
Upper Spencer Gulf Marine Park Local Advisory Group representative Alan Hall believes a number of causes need to be explored to determine what is affecting cuttlefish numbers.
With more than 40 years' experience observing cuttlefish numbers, Mr Hall said Whyalla was not always blessed with the massive congregation that has been seen in recent years.
"In the '70s there were cuttlefish here but in no way near the numbers seen in recent times," Mr Hall said.
"The cuttlefish numbers were kept in check by schools of snapper and also what locals called black fish."
"The water used to turn red with snapper feeding on cuttlefish along the Lowly peninsula.
Mr Hall said when the snapper were cleaned out by heavy commercial activity and the blackfish disappeared, cuttlefish numbers then bloomed.
In the late '80s, the commercial sector then took advantage of the situation and fished the cuttlefish, establishing markets in Asia for the product.
Mr Hall said when this commercial fishing was put to an end, against popular belief and rumours there was still a good breeding population of cuttlefish at this time.
"There was a good population for a period of two years after the commercials were stopped from fishing for them," Mr Hall said.
The next threat to the cuttlefish was the arrival of the kingfish farms in Fitzgerald Bay which Mr Hall said saw escaped kingfish enter waters.
"Many observations were made of the escapees feeding on cuttlefish and also foraging in crevices and under rocks for what I believe to be cuttlefish eggs," Mr Hall said.
"Thus begun the decline of the cuttlefish numbers and it has continued ever since."
With last season's cuttlefish numbers very low and this year also appearing to be low, Mr Hall said he has made a number of observations as to why the local population is declining.
"Despite popular belief that Whyalla has the only breeding congregation of cuttlefish another breeding aggregation occurs at Point Riley at Wallaroo although much smaller," Mr Hall said.
"All appears to be normal over there, so the question must be asked what is happening here and why are cuttlefish deserting the Lowly peninsula?"
Mr Hall said potential causes include nearby army explosives exercises, more kingfish farm escapees then originally estimated, high levels of chlorophyll A off Fitzgerald Bay due to fish farms, small colonies of seals or possibly diving activities.
"I now also believe diving activities have a major part to play," Mr Hall said.
"This is something the cuttlefish have never had to put up with until recent times.
"Perhaps diving should be curtailed during the breeding season?"
Mr Hall said Adelaide anglers are reporting good catches of cuttlefish which is unusual for those waters as well as Arno Bay charter operations reporting cuttlefish catches well above normal.
"Robin Sharp at Port Augusta is telling me that they are now catching cuttlefish at Port Augusta, something which has never happened before," Mr Hall said.
"This makes a mockery of the experts who tells us that they need a specific temperature and salt content in the water.
"Water at Port Augusta is considerably warmer than Whyalla and their salt level also rates a lot higher than Whyalla."
Mr Hall said the cuttlefish populations at Arno Bay and Port Augusta need to be looked at to see if they belong to the Whyalla congregation.