Large tides could be a factor behind a string of whale strandings, and so could climate change.
But at this stage, they remain a mystery - even to the experts.
Fifty pilot whales died after a stranding at Chatham Islands on Friday, and another had to be euthanised. One-hundred and forty-five whales perished earlier this week on Stewart Island, and another 11 died in Northland.
Floppy Halliday from Whale Rescue says bad spring weather doesn't help the situation.
"Everything's unpredictable and quite changeable - you've got wind directions coming from all over the place, your ocean's building up in all sorts of funny places."
She says it's hard to pinpoint the cause.
"Ultimately, none of us have the answers. I'm not sure that there is any particular one answer that can go with any of this."
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Dr Karin Stockin from Massey University says they're looking for a common thread.
"We imagine that some of those stranding records are likely linked to changes in water temperature being different, and that driving [whales] ashore, and bringing in of course marine mammal predators, coming closer to shore, as well."
Ms Halliday says water temperatures can have an impact - the ocean's absorption of heat is responsible for much of the recent rise in global temperatures.
"It may create different feeding situations for some of these animals, it's all basically guesswork - there's probably a whole host of different factors that come together and create half of these problems."
Dr Stockin says the public needs to call in the experts if they find beached whales.
"The recent context of the pygmy killer whales, I understand that some members of the public - in their very best efforts and intentions - spent nearly three hours trying to refloat those animals before the appropriate authorities were notified."
Marine mammal strandings are a relatively common occurrence in New Zealand. The Department of Conservation responds to about 85 incidents a year - mostly single-animal strandings.