LAKE ROTOMA, New Zealand — A riot of native plant life once covered the shallows of Lake Rotomā, one of the many bodies of water that speckle New Zealand’s upper North Island. At night, mottled green crayfish scuttled from the deep to graze beneath the fronds in such plentiful numbers that the local Māori tribe could gather a meal in a few minutes of wading.
These days, the lake bed is carpeted by an alien canopy. Sharply spiraled weeds, introduced by goldfish owners dumping unwanted tanks, form an impenetrable wall around the lake’s edge. Unable to push through it on their daily commute, the crayfish largely vanished.
Now, the local tribe, Te Arawa, and conservation agencies are racing to suppress the weed’s explosive growth as it chokes once-pristine aquatic ecosystems. At Lake Rotomā, the tribe found a surprising solution in a centuries-old tool — and added to a pitched debate about how ancestral Māori knowledge can complement conventional science.
Te Arawa, which has long used woven flax mats, known as uwhi, to cross water and gather food in shallow swamps, is employing modern diving technology to staple uwhi underwater where aquatic herbicide hasn’t worked or shouldn’t be sprayed. It has helped stop the weed’s growth and create new migration routes for the crayfish.
“This is a perfect example of combining mātauranga Māori” — traditional Māori knowledge — “and Western science,” said William Anaru, Te Arawa’s biosecurity manager.
The use of uwhi is an example of the growing prominence in Western societies of Indigenous knowledge systems, accumulated and handed down over centuries.
In Canada, a 2019 law requires the government to consider Indigenous knowledge in regulatory decisions. In New Zealand, researchers inspired by mātauranga have conducted studies on whether kauri forests are harmed by a lack of Māori prayer and on the use of crushed whalebone to treat fungal infections that are devastating native trees.
The phenomenon has proved contentious among academics unused to drawing on amorphous — and sometimes spiritual — knowledge systems. The resulting backlash has split New Zealand’s scientific community, attracted interventions from one of the world’s most prominent academics and prompted a discussion about what it means to “know” something at all.
According to Dan Hikuroa, a senior lecturer in Māori studies at the University of Auckland, mātauranga Māori “spans knowledge, culture, values and worldview.”
It includes everything from systematic observations about what plants grow best in certain areas or which stars to follow across vast oceans, to legends referring to certain rivers as the home of taniwha — unpredictable supernatural beings.
Such legends can be both literal and metaphorical, Dr. Hikuroa said. Understanding a river as the home of a taniwha, for example, helps describe its sinuous appearance and warn of its volatility or capacity to break its banks.
Additionally, mātauranga is not just a collection of knowledge, but also a philosophy underpinned by values like kaitiakitanga and manaakitanga — guardianship and hospitality.
Many of New Zealand’s more traditionally minded scientists, however, see the spiritual and moral aspects of mātauranga as contradictory to conventional science, which is supposed to be value-neutral and limited to knowledge that can be empirically proven.
That tension came to a head last year, when a collection of New Zealand’s top academics published an open letter in The Listener, a major national magazine. In it, they denounced proposed changes to the school curriculum that would “ensure parity” between mātauranga Māori and conventional science and teach that “science has been used to support the dominance of Eurocentric views.”
Kendall Clements, a marine biologist who signed the letter, said they were not trying to disrespect mātauranga, but to emphasize the differences between it and conventional science.
Mātauranga has the “seeds of science,” he said, “but to then say that mātauranga Māori is equivalent to science makes no sense, because there are a whole lot of elements that are not in science, like visions, prophecies and dance.”
Advocates of mātauranga say that misses the point. Dr. Hikuroa agreed that mātauranga is not the same as conventional science. But it is valuable, he said, because it provides alternative explanations about the world and encourages people to think differently.
“In trying to probe that difference, we may collectively come to a better understanding of a solution than if we drew on a single body of knowledge in isolation,” he said.
As an example, Dr. Hikuroa pointed to the construction of a state highway in the early 2000s. It was supposed to run through a swamp that local Māori said was inhabited by a tempestuous taniwha. Engineers had not identified any risks, but rerouted the road to address their concerns. A year later, a major flood hit the area. The redirected road was spared major damage.
A taniwha was the local tribe’s “way of codifying the observation made through years that this place floods from time to time,” Dr. Hikuroa said.
Skeptics, however, say that if the truth of the more spiritual aspects of mātauranga cannot be definitively proved, they cannot be called knowledge.
This tension between traditionally minded scientists and mātauranga advocates, brought to a boil by the open letter in The Listener, spiraled into a fiercely personal debate.
Advocates who had watched for years as scientists dismissed mātauranga as unquantifiable superstitions were sensitive to a perceived lack of respect from the letter’s signatories.
Some alleged that the letter was an example of white supremacy. Waikaremoana Waitoki, the president of the New Zealand Psychological Society, denounced the letter’s “racist tropes” and “moral panic.”
Others were frustrated that the letter’s authors had no expertise in mātauranga. Melanie Mark-Shadbolt, an environmental sociologist, said it was motivated by “a bit of fear” and “a lot of ignorance.”
The signatories, for their part, felt that their positions had been intentionally misconstrued. “I believe the vast majority of people who attacked our letter attacked a misrepresentation,” Dr. Clements said. “Some of that was absolutely deliberate.”
New Zealand’s prestigious Royal Society began investigating whether two of its fellows — the biochemist Garth Cooper and the philosopher Robert Nola — should face disciplinary action for signing the letter. The situation became more tense after the polarizing British biologist Richard Dawkins denounced the Royal Society’s investigation and described mātauranga as “not science and not true.”
The commotion quieted only recently, after the Royal Society dropped its investigation and Dr. Cooper and Dr. Nola chose to resign as fellows. Neither side is happy, but few have the energy to continue fighting.
Outside these ivory tower debates, however, the use of mātauranga carries on.
For Te Arawa, the melding of mātauranga with conventional science has proved successful. Amid the weedy jungle in Lake Rotomā’s shallows, an enormous clearing has emerged.
The tribe turned to uwhi after becoming disillusioned with burlap mats and herbicide, two alternatives that are costlier and involve imported materials that often draw suspicion from local people.
Cory O’Neill, Te Arawa’s lead diver, said that the uwhi placed by his team have been more effective than the burlap mats or ones made of rubber, which can be ripped from the lake bed by accumulated gas from degrading lake weed.
Even better, while the uwhi stops thick weeds, thin gaps in its weave allow more slender native plants to grow through and create new forests of their own. Now, for the first time in decades, crayfish in Lake Rotomā have a clear path to old feeding grounds among the plants they relied on for millenniums.
“We’ve essentially created new mātauranga,” Mr. O’Neill said before carefully tucking his dreadlocks beneath the cap of his wet suit and slipping into the lake. “And we’re going to use it to finish the last of the lake weed off.”