Dr Andrew Jeffs, a marine scientist at the University of Auckland, said the mussels have died as a result of "heat stress" and warns they may disappear from the region altogether as global warming tightens its grip.
"Yes they've died as a result of the recent hot weather and midday low tides. High pressure systems bringing the hot weather also forces the tide out for longer exposing the mussels to longer periods of sunshine.
"The mussels die of heat stress. You imagine lying in the midday sun every day for four hours for the best part of a week. You'd be pretty sunburnt at the end of that," he said.
Furthermore, Jeffs said that Northlanders may not be able to enjoy the seafood delicacy in the future as global warming ramps up a gear.
"I hate to say it but we can expect to see more of this with climate change effects – especially in the North with warming temperatures. In many other countries we are seeing poleward movement of the distribution of species as they adjust to temperature increases associated with climate change. I expect we may see the same in New Zealand."
Jeffs says this has occurred previously.
"Two years ago the same thing was observed at Muriwai on the west coast, which I visited. The smell was atrocious, and a number of years ago most of the cockle and pipi population was cooked in the Whangateau Harbour during similar conditions."
"Warm water temperatures during the marine heatwave (hot seawater) a couple of years ago also stressed mussels on mussel farms and resulted in significant losses."
Ministry for Primary Industries (MPI) director of diagnostic and surveillance services Veronica Herrera said they are currently investigating the matter and urged the public not to eat mussels in areas where they are dead or dying.
"MPI's incursion investigators have been notified by a member of the public. We appreciate the public informing us when events like this occur because it helps us quickly get to the bottom of potential issues."
"We regularly test for biotoxins every two weeks. The next round of testing is due tomorrow. In the meantime we are requesting samples of the dead mussels which we will send to the animal health lab for testing, where we can try and determine the cause of death.
"From the last round of biotoxin testing, there was no evidence of bio toxins being the cause of this event."
"Green-lipped mussels are vulnerable to changes in their environment. This can be due to storm events, shifting sand, and high temperatures or heat stress. Our current understanding is that the overall ecosystem is still healthy."
Ferguson said despite MPI's calls for the public to refrain from eating the mussels he is aware that people are still going out there and collecting them.
"Honestly this is such a shame because even with the shoreline littered with hundreds of thousands of dead and dying mussels, people are still going there to pick the few survivors!"
"Most people would say something like 'oh they'll grow back' or 'there's heaps there' but I personally think that at times like this, we should wake up and start respecting these places and paying attention to what is happening before we lose our taonga for good.
"I'm afraid for the future of our sacred mussel rock which has supplied our people for decades, maybe even centuries and I am heartbroken to see it in such a terrible state. I also fear that our next generation is going to miss out. That's what hurts me the most."
