A marine heatwave which has kept New Zealand’s oceans much warmer than usual is expected to stick around for the rest of summer.
NIWA meteorologist Ben Noll said there’s been unprecedented temperature increases across December.
“We've seen some of the warmest ocean temperatures in the last four decades around New Zealand over the last month”.
While the temperature increases have been felt across the entire country, the North Island has seen the biggest increases.
On the west coast of the North Island, the water temperature was between 18-21C, up 2.51C on usual.
In the north the water was between 20-23C, that’s up 2.31C.
A marine heatwave is an extended period of extremely warm ocean temperatures. The water needs to be in the top 10 per cent of previously recorded temperatures for five days straight.
Noll said this marine heatwave is similar to that of summer 2017-2018, but may last longer.
“We do expect that it will continue over the next couple of weeks and perhaps the next month or two into the February time frame. So all up we could be looking at about three months potentially of marine heatwave conditions”.
He said in some cases areas are around 4C hotter, with the hottest being 24C so far this summer.
Toby Wild, who owns Moana Stand Up Paddleboard in Nelson, said the difference this summer has been obvious.
“The feedback from a lot of the sea swimmers, a lot of the surfers, paddle boarders around here, is that they're jumping in and going for a swim and staying in longer way earlier than they normally would. So it's definitely warmer.”
The warm water is expected to attract rarer species of fish and keen anglers happy this summer. But in the long run marine heatwaves can have a negative impact on fish stocks and be devastating for marine ecosystems.
Robert Smith, who lectures in marine science at Otago University, said of particular concern in New Zealand will be mussels and pāua which rely on cooler climates.
“Over time increased exposure to extreme temperatures may lead to irreversible loss of habitat and also important species”.
Experts say it’s expected that marine heatwaves like this will become more common due to climate change.