Massey University researchers have taken tissue samples from three rare Gray's beaked whales found dead on Ruakaka beach in order to study their lifestyle.
Emma Beatson and Catherine Lea took tissue samples from the mammals to assess their lifestyle and contents from their stomach for dietary assessment.
The whales stranded last Wednesday and were buried nearby.
Karen Stockin, director of Coastal-Marine Research Group at the university's Institute of Natural and Mathematical Sciences, said the taking of tissue samples must not be confused with a necropsy or a post-mortem examination.
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She said the university was not asked by the Department of Conservation to conduct a necropsy.
"A full post-mortem wasn't done so it would be wrong for us to suggest what happened or how those whales died."
She confirmed the whales had digested prey items such as fish remains but no items such as plastics were detected in their stomachs.
The whales were discovered about 2km south of the Ruakaka Surf Lifesaving Club by a member of the public.
Two whales lay dead 10m apart while the third was discovered about 100m north.
All were male, measured between 4.5m and 5m long and each weighed at least one tonne.