Strandings are common along Māhia Beach, with sick whales often beaching themselves.
Const. Prentice said a witness told him the shark was more than five metres long and had gone for the head of the whale.
“When the mother pygmy whale, which is about three metres long was being refloated, in belly-button deep water, a large shark — probably a great white — has come along and hit the whale and then taken the carcass out to sea.”
One person was in the water and was “miraculously” not injured, he said.
“I am told when the shark hit the whale the first time it was like lightning . . . it came out of the water and took its whole head off.
“The water was red and about 30 seconds later the shark came back and hit the whole thing and took it out to sea — there is not an ounce of remains left.
“There are not many sharks that can do that.”
Const. Prentice said there had been no sightings of the shark since the incident but warned anyone going into the water to take extreme care.
Ruawharo Marae kaitiaki Aaron Raureti did not witness the attack but helped after the mother’s calf was euthanised and frozen by first responders Grace Ormond and Te Hau Spark.
Mr Raureti said strandings had become “more than frequent” and warmer sea temperatures played a role.
“The most common thing with the recent strandings is with the water temperature. It is so high at the moment.
Mr Raureti said strandings had included species rarely seen in this part of the world.
Since October of last year a sperm whale, a pod of 40 false killer whales, a striped dolphin and the pygmy sperm whales had stranded at Māhia. When whales stranded, people needed to stay out of the water and, in this case, follow a rāhui, which had been extended to March after the January stranding.
“It is important as we monitor the decomposition process. We have dragged the ones that we could out of the water, out of the tidal zone, and we are letting nature take its course.”
Mr Raureti said the heads of the false killer whales were taken for customary purposes, while other parts were used for scientific study.
“The science stuff is in the testing of the blubber. It’s also in the tongue to test for diseases and that tells us what has been in their diet . . . or what’s not been in their diet for the last six months.”
Project Jonah marine mammal charity general manager Daren Grover was aware Māhia was a hotspot for whale strandings and said it was normal behaviour for sharks to prey on sick animals.
“Sharks are opportunistic predators, and whales can be predated on by sharks. Pygmy sperm whales are very small — under four metres long.”
There were underlying reasons that brought whales ashore, while the geographical formation of Māhia and historical migration knowledge may have played a role, he said.
“Māhia used to be an island, and there was a channel that passed through from the shallow bay to the south, and over time that has silted up.”
Less than 20km offshore the ocean was more than 1000m deep, and where it becomes shallow provided a perfect environment for plankton, he said.
Sick whales would often strand themselves as a way of taking their last breaths without the effort required to resurface from the water.
Mr Grover said the best practice in a stranding was to call the Department of Conservation or Project Jonah to get advice on how to help the animals.
