Project Jonah wrote on its Facebook page:
Six whales had died overnight, upon arrival it was discovered a further six had died and within moments two more whales had passed. The remaining whales were showing physical signs of distress and the difficult decision was made to euthanise.
The explanation for whale strandings is not simple. While sick or injured whales beach themselves most often, whales have also washed ashore while chasing prey in shallow waters, or are swept onto beaches by strong currents and inclement weather.
The number of whales who have been found stranded in New Zealand is higher than anywhere else in the world, due to its extreme tides and wide-ranging coastlines. However, conservation groups have also made the rate of rescue success one of the highest in the world.
"Its worth remembering that any time the whales spend out of their natural environment is a highly stressful time for these beautiful animals," writes Project Jonah. "Once again, thank you to everyone who has been involved. A sad outcome after the successes of yesterday's efforts."