Angus said that meant necropsies to determine how they died were not possible.
"Standard samples were taken for scientific analysis but these are unlikely to reveal the cause of death.
"So, at this stage we don't know why the whales died and it is probable that we never will know for sure."
Some of the whales have been prepared for burial. Others, because of the rugged coastline, would be left for nature to take its course.
DoC said there had been 13 mass strandings of sperm whales since 1895. The largest was in 1974 in Muriwai when 74 sperm whales stranded.
No one knows why the whales strand.