Great white sharks feeding on whale carcass
The 16m whale's body washed up against the rocks on the north eastern tip of the island.
Great white sharks more than 6m long circled the area and had been feeding on the carcass.
Jess Condo, 34, of Penneshaw, said he saw about four great whites in the area yesterday morning.
"One big one was nearly as big as our (6.1m) boat," he said.
"They were circling around the whale.
"Then they came up to the side of the boat and brushed against it."
The SA Museum is expected to carry out DNA testing on the whale carcass to determine what type it is, how it died, and how long ago.
Joe Springall, 19, of Morphett Vale, said one of the sharks tried to attack his boat.
"All of a sudden this shark floated under the boat . . . he decided to have a go at the back of it," he said.
"He came up on the marlin board . . . and took a bite.
"Then it stuck its head up then went back under the boat."
Acting director of Fisheries Martin Smallridge has asked that people respect a 100m exclusion zone around the carcass.
"People's natural curiosity can turn to inappropriate behaviour, as was witnessed during similar previous events," he said.
"It is an offence under the Fisheries Act to interfere with a whale and this applies if the whale is dead or alive."
Mr Smallridge said fines of up to $100,000 or two years in prison could apply to anyone breaching the Act.
"It is also appropriate to remind the public that great white sharks are fully protected in SA," he said.