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The mass stranding is not unusual, as octupuses are "terminal spawners" and move to shallow waters when near death, Dr John Jillett said.
They live no more than two years, reproduce once and then die.
"Their dying off is quite normal, particularly in late autumn and early winter.
"They seem to be susceptible to frosts, but whether that is coincidental to them dying this time of year, I don't know," Dr Jillett, formerly of the University of Otago marine science department, said.
He said octopuses moved into shallow water near the end of their lives and often died on the shore.
Dr Jillett noticed four or five octopus carcasses at Macandrew Bay about a week ago.
Octopuses were increasingly being caught for food at the late stage of their lives, especially around Andersons Bay Inlet.
"That's why you don't see as many on the shore as you used to," he said.
Dr Jillett said the octopuses did not pose any danger to people or other animals.