Snapper caught in Otago, tropical species making New Zealand home and mussels shrinking due to more acidic waters - these are all climate change impacts, and all happening now.

But according to a new report, Climate-related risk scenarios for the 2050s, they are only a tiny snippet of climate-induced changes expected in the marine space over the next few decades.

Prepared for the Aotearoa Circle - made up of industry, iwi and government bodies focused on sustainable development - the report says there will be both physical risks - including warming seas and acidification threatening fish stocks; and transition risks - such as changes to energy use and supply, artificial intelligence and "green" fishing vessels, and increasing societal demands.

And industry leaders say now is the time for collaboration to both cut emissions and to ensure the impacts are minimised, even proposing a Ministry for Oceans be established.

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Since the late 1800s the planet's average surface temperature has risen by about
1.1C, with most of this warming in the past 35 years, and the past five years being the hottest years in history.

Sanford CEO Volker Kuntzsch is calling for New Zealand to develop an oceans strategy, overseen by a Ministry for Oceans, to adapt to climate changes. Photo / Supplied
Sanford CEO Volker Kuntzsch is calling for New Zealand to develop an oceans strategy, overseen by a Ministry for Oceans, to adapt to climate changes. Photo / Supplied

Oceans are taking the brunt of this warming, since 1970 absorbing over 90 per cent of excess heat trapped in the climate system.

The KPMG report looks at two scenarios for the year 2050: mako, where the world fails to curb greenhouse gas emissions; and kahawai, one where it achieves the aims of the 2050 Paris Agreement, keeping warming under 2C by 2100.

Under mako - named after the fast, aggressive and unpredictable shark - global warming is on course to exceed 4C by 2100, resulting in major oceanic changes due to increasing acidity and changes in temperature and currents.

By 2050, this would see commercially valuable species like hoki migrating south and becoming uncommercial to fish.

Meanwhile warm-water species from the tropics could begin intermittently migrating south with marine heat-wave events, altering the composition of marine food webs.

Traditionally-prized New Zealand species such as snapper and kingfish could migrate in greater numbers to the coastal waters of the South Island.

Māko scenario data. Image / Aotearoa Circle
Māko scenario data. Image / Aotearoa Circle

Some North Island QMA fishers could suffer financial losses due to a collapse in quota value of these species, but could be awarded quota for warm water species as compensation.

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However, the volatility in abundance and distribution of wild fish due to changing currents, amid increasing global socioeconomic pressures, could see fisheries governance overwhelmed, and collapse of global fish stocks.

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These pressures could also put strains on Crown and iwi relations, the authors said.

A higher emissions scenario could also spell disaster for farmed shellfish - such as mussels, with potential for a 150 per cent increase in acidity, severely affecting growth rates and productivity.

Māko 2050. Image / Aotearoa Circle
Māko 2050. Image / Aotearoa Circle

More variable sea temperatures would also make aquaculture unviable closer to shore, and need to be shifted further offshore into deeper waters, raising costs.

Under kahawai - a species known to collaborate to avoid danger, and punch above their weight - while the world avoids the worst physical impacts it still faces a range of transition-related challenges including energy use and societal and cultural expectations.

While globally species abundance could drop by around 10 per cent, New Zealand was placed to fare much better than most.

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Advances in technology and science would further enhance the understanding of species and habitats, leading to more sustainable fishing.

By 2050 report authors envision potential for "green" fishing vessels, not only reducing energy use but using enhanced technology and even AI-driven robotics to target species and eliminate bycatch.

Kahawai 2050. Image / Aotearoa Circle
Kahawai 2050. Image / Aotearoa Circle

Sanford CEO Volker Kuntzsch said from a marine perspective, climate change was the country's biggest natural capital challenge.

"Water temperatures are rising and the weather is more unpredictable.

"Algal blooms result from changes in nutrients in the water column driven by changing rainfall patterns on land, and warmer waters affect our aquaculture operations.

"Rising water temperatures are already creating shifts in the distribution of fish species and marine mammals around our coastlines."

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To address what was ahead, collaboration was key.

Kuntzsch called for an oceans strategy/policy for New Zealand, ideally to be administered by a Ministry for Oceans.

Kahawai scenario data. Image / Aotearoa Circle
Kahawai scenario data. Image / Aotearoa Circle

"There's no common approach to treating our big blue backyard in a way that respects kaitiakitanga or our collective future.

"An oceans policy should consider our ecosystem across all impacts, from the mountain to the sea.

"We need a holistic approach that adds up to an outcome that every New Zealander should be able to buy into."

This would enable sustainable relationships around the farming the most "environmentally-friendly protein", while restoring the environment.

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Examples included immediately promoting aquaculture, to a national focus on seaweed identifying appropriate farming regions and methods to innovating farming technology and products like high value algae oil extracts or pharmaceuticals.

"Add seaweed's potential to sequester carbon to the mix and we have a species that provides a convincing basis for a large scale multi-stakeholder project that would have benefits for the environment, the economy and the people."