More than 250 whales that stranded on the Chatham Islands on 7 October, 2022 died or had to be euthanised. Photo: Supplied / Tamzin Henderson
Warning: Some readers may find the pictures in this story distressing.
The second mass stranding of pilot whales at the Chatham Islands in less than a week is being described as unbelievable by the mayor.
About 250 pilot whales stranded on Chatham Island on Friday and an estimated 250 more beached about 4km south on Pitt Island yesterday.
The last beaching of this scale occurred in Farewell Spit, the South Island, in 2017, when an estimated 600 to 700 whales were stranded.
Chatham Islands Mayor Monique Croon said every stranding was distressing.
"It's a bit of a shock and I think people are feeling pretty sad about the huge amount of loss, which is actually unusual and we're aware they're happen regularly but to have two massive strandings like this is a little bit unbelievable."
More than 250 whales that stranded on the Chatham Islands on 7 October, 2022 died or had to be euthanised. Photo: Supplied / Tamzin Henderson
Whale Rescue co-founder Ingrid Visser said despite the frequency of whale strandings in New Zealand, there was still little data on what caused the animals to beach.
"I think it's an absolute tragedy that we've got these sorts of events going on and New Zealand has had a long history of whale strandings and yet we still don't know why and we don't even know the basics about these animals.
"We've got so many scenarios where we've had mass strandings of pilot whales here in New Zealand and yet just basic fundamental research hasn't even been done on what sort of groups we've got involved, like are they all related, or just even that simple stuff."
More than 250 whales that stranded on the Chatham Islands on 7 October, 2022 died or had to be euthanised. Photo: Supplied / Tamzin Henderson
Auckland University marine ecology and conservation biology professor Rochelle Constantine said the whales were often multiple different lineages, not all directly related, in these mass strandings.
"Within the stranding events, you'll often get a mixture of calves not next to their mothers, they may be some considerable distance away down the beach. So we know there can be a lot of confusion and a lot of mixing going on at these strandings."
Large changes in temperature and the amount of food in the water are often associated with mass stranding events.
More than 250 whales that stranded on the Chatham Islands on 7 October, 2022 died or had to be euthanised. Photo: Supplied / Tamzin Henderson
Dr Constantine said it could be one reason why these large scale events occurred.
"It may be these big events that we're seeing could be associated with one of these anomalies high -productivity events, so the whales are aggregating in a different way or going to different places to make the most of plentiful food supplies."
Department of Conservation (DOC) spokesperson Dave Lundquist said this could happen at any time.
"Most summers, we tend to have one [mass stranding]. Although we've had a handful of summers in recent years where there were no mass strandings at all, but there's no discernible pattern to that unfortunately."
More than 250 whales that stranded on the Chatham Islands on 7 October, 2022 died or had to be euthanised. Photo: Supplied / Tamzin Henderson
When strandings occur on the Chatham Islands, whales are not actively refloated due to the risk of shark attacks to people as well as to the whales themselves.
Therefore, whales which stranded and did not die had to be euthanised.
DOC said their bodies would be left to decompose where they washed up.
Pilot whales are not considered to be a threatened species under New Zealand's classification.
"We believe it is large and robust population that even when these unfortunate events happen, they're not expected to have any significant impact on the species in our waters," Lundquist said.