Source: Earth Sciences New Zealand
A new report has outlined the likelihood of gradual long-term warming of the waters around New Zealand, and an increase in short-term heat events, under different greenhouse gas emission scenarios.
New Zealand’s ocean temperatures are rising and marine heatwaves – periods of unusually warm ocean temperatures which persist for five or more days – are becoming more frequent and severe, with implications for fisheries and marine ecosystems.
The report by Earth Sciences New Zealand (formerly NIWA) was completed on behalf of Fisheries New Zealand to analyse the regional impacts of long-term warming and temperature extremes on fish species around New Zealand.
Earth Sciences NZ physical oceanographer Dr Erik Behrens says along with the warming of the oceans, marine heatwaves are projected to increase.
“Seas are projected to get hottest around the North Island, and to become longer and more frequent around the South Island. This is in addition to the continued, slower, general warming of New Zealand’s waters,” said Dr Behrens.
Average sea surface temperatures around New Zealand have warmed between 0.2 to 0.3 degrees Celsius per decade from 1982 to 2022. Meanwhile, over those last 40 years, seafloor temperatures have warmed by about 0.1 degrees Celsius per decade.
The warming trends in coastal waters off eastern New Zealand are particularly pronounced, along with offshore waters in the Tasman Sea, and east of New Zealand over the Chatham Rise.
Dr Behrens says marine heatwaves could double in their intensity by the end of the century in high emissions scenarios compared to what we experience today.
“Some recent marine heatwaves have already exceeded historic baseline temperatures by 5 degrees Celsius. So, by the end of the century these could be exceeded by 10 degrees Celsius. Scientists worldwide are working to better understand the effects of marine heatwaves and warming ocean temperatures on the marine environment to prepare for the future,” he said.
Earth Sciences NZ Principal Scientist Dr Matt Dunn says further investigation is required to determine exactly how these changes will affect fisheries and fish species.
“We now know which regions are most likely to experience marine heatwaves and have an understanding of the fish and fisheries that may be impacted. However, further data is needed to confidently predict how the ecosystems will respond, and what specific threats or opportunities ocean warming may bring. Nevertheless, this study represents an important step toward building climate-aware and resilient fisheries for New Zealand,” said Dr Dunn.
Fisheries New Zealand’s Director Science & Information Simon Lawrence says the distribution of some species is changing, and this is expected to continue as our oceans get warmer.
“This research provides another piece in the climate change puzzle that will not only help inform fisheries management, but it also provides vital information for New Zealand’s fishing industry to be adaptable and more resilient to the changes warmer oceans bring,” said Mr Lawrence.
To support a more climate-aware and resilient fisheries, a team led by Earth Sciences New Zealand’s Dr Behrens has secured new funding from the MBIE Endeavour Fund to develop multi-month forecasts for marine heatwaves.
The project aims to provide an early warning system that will help marine industries, iwi, and regulators to anticipate and prepare for the impacts of approaching heatwaves in their planning and decision-making.
