A new study has found sea temperatures in Hauraki Gulf have sharply increased in the past decade and warming was most apparent in the autumn and winter.
Sea surface monitoring at Leigh Marine Laboratory since 1967 has found 2022 was the warmest year on record, with heat wave conditions for 85 percent of the year.
A marine heat wave happens when the sea surface warms up for a prolonged period and owner of Auckland fishing charter business Hooked Up Charters, Laurie Powell, has noticed they're happening more and more.
"This year especially is I think the highest we've had on record which was just over 27 degrees on the way out [to sea], which is very warm," he said.
His observations are confirmed in a new study published in the New Zealand Journal of Marine and Freshwater Research which gathers almost 60 years of sea surface readings taken at Leigh Marine Laboratory.
It shows a steady and abnormal rise in temperature in the Hauraki Gulf.
University of Auckland marine scientist Andrew Jeffs said the study shows the pace of ocean warming is starting to really ramp up.
"There's been a real uptick in the number of heatwave events that were picked up for the Hauraki Gulf."
According to NIWA, marine heatwaves can disturb ecosystems and threaten fishing and aquaculture.
They cause penguins to starve as the fish they feed on move to deeper, cooler waters.
The study notes the sea surface temperature in Hauraki Gulf has been consistently and unusually warm for the last decade, with 2022 being the warmest in the 57-year record.
Boaties have also noticed the warmer water is stretching beyond summer.
"Going into autumn it doesn't drop away... you expect it to cool down in winter and it seems to be taking longer and those warmer temperatures are lasting longer into the year," Powell said.
And that's exactly what the study shows - an upward trend in autumn and winter, which can be damaging for cooler water species like sponges which don't get a respite.
"Once you raise the temperature up, they start getting stressed and animals start suffering," Jeffs said. "Animals and plants for that matter."
But higher temperatures benefit warmer water species, like the invasive pest seaweed caulerpa.
The ocean has long been absorbing human-made heat trapped in the atmosphere and the effects of that are now emerging.
