New Zealand's commercial fishing industry will have to adapt, or risk decline as ocean temperatures warm, a leading marine scientist says.
Cliff Law of the National Institute of Water and Atmospheric (NIWA) Research published a paper in December, which shows that by the end of the century an area of ocean which currently provides 60 percent of the country's commercial fish catch could be in trouble.
Mr Law said sea temperatures were pegged to rise 2.5 degrees, which would affect the the Chatham Rise - an ocean plateau stretching 1000km east of New Zealand.
The area is known as one of New Zealand's most productive and important fishing grounds. Another vulnerable area is the sub-Antarctic waters south of New Zealand, which is also home to some commercial fisheries.
The details were contained in the preliminary study commissioned by the Ministry of Business Innovation and Employment as part of a wider look at the impacts of climate change on land and sea.
"The models are suggesting we're seeing a significant reduction in nutrients in those areas, and that will mean less of this phytoplankton growth - basically less input to the food web and potentially a decline in the fisheries in that area," Mr Law said.
Sea temperature rises of up to six degrees this summer had well exceeded the long-term view of a 2.5 degree shift by the century's end, he said.
The flip-side of warming seas was the possible arrival of new fish species.
The Federation of Commercial Fisherman said that was proving to be a positive trend in many inshore fisheries, judging by the increased volumes of albacore tuna migrating down the West Coast, and the presence of john dory in numbers not normally seen throughout Tasman and Golden Bays, and even on the West Coast.
Federation president Doug Saunders-Loder said there was no question change was happening, but it was not clear if it was linked to seasonal variations.
"This is not an unusual observation given the temporal variations that the industry has experienced over many years with changes from El Nino to La Nina weather patterns, but it is certainly noticeable that water temperatures have increased."
Sealord general manager of operations, Doug Paulin, said they had been working it into future planning.
"We're an inter-generational company, we're owned by iwi, so having a sustainable future and being able to catch fish for hundreds of years is of great importance."
The introduction of new species and the departure of current ones would mean changes to the quota management system and fisheries boundaries, Mr Paulin said.
He said Sealord wanted the government to use NIWA's study as the basis for further research.
Cliff Law said rapid warming of the ocean near Tasmania was an indication of how the water around New Zealand could change. He said increased ocean acidification could also have serious consequences for the likes of the paua industry.
The Paua Industry Council said that was already happening.
"Over the last 15 years we've seen a dramatic die off of macrocystis pyrifera - the big, long seaweed which is what paua live on. So already it's been well documented in the top of the South Island and into Tory Channel," council chief executive Jeremy Cooper said.
A bigger problem would be if the water column down to 10 metres, where paua usually grow, warmed dramatically, Mr Cooper said.