Sea temperatures rise as marine heatwave hits lower South Island


A severe marine heatwave is affecting the lower South Island, with sea temperatures expected to peak in the coming days.

MetService oceanographer Dr Joao de Souza said sea surface temperatures were rising rapidly along the West Coast of the South Island, in Fiordland, around Stewart Island and towards the Otago Peninsula.

Temperatures off the West Coast today were forecast to reach 4.7C above average for this time of year.

"We have seen these really large anomalies, temperatures way above average. It is peaking now in Stewart Island, but over the next seven days we will see it peak in Fiordland.

"Then, surface temperatures are forecast to reach 18.C, compared to the 13.5C average - a difference of almost 5C."

The warmer water is good news for holidaymakers, but will cause problems for marine life and also result in more rainfall on land.

Last summer, Fiordland experienced a marine heatwave that resulted in kelp dying and sea sponges being bleached, while the aquaculture industry around the country experienced negative effects.

Those marine heatwaves were now being tracked as part of the Moana Project, funded by the Ministry Business Innovation and Employment and led by Metservice. It utilises sensors in partnership with the fishing industry.

"Every time a fisherman drops some gear in the water that has one of our sensors attached to it, it returns observations so we know not only what is happening at the surface, but also what is happening below the surface," said de Souza.

The project is forecasting marine heatwaves around the country in a bid to predict how things will change, and where, in the near future.

"The ocean is warming. It has been warming at an accelerated rate since 2010/2012 and marine heatwaves are becoming more frequent and long-lasting."

The project aims to monitor and investigate the cause of marine heatwaves, as well as the effect on marine species.

De Souza said the Bay of Plenty experienced the longest marine heatwave in New Zealand, beginning in November 2021 and lasting for a year.

The seven-day forecasted sea surface temperatures and how they differ from the 25-year average for New Zealand's ocean can be explored on MetService's marine forecasting website SwellMap.